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Classifications

Harrison's Chapter

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Inheritance

1

Autosomal recessive inheritance HP:0000007

Disease requires two damaging DTYMK alleles. Of the three published families, one is a consanguineous Egyptian family with a homozygous missense allele, one is a non-consanguineous Dutch family with compound heterozygous missense alleles, and one is a Hong Kong family with two variants in trans; the fifth reported individual is homozygous. Carrier parents are clinically unaffected but have measurably reduced dTMPK activity in fibroblasts. Recurrence risk for siblings of a proband is 25 percent, and carrier testing plus genetic counselling are indicated for at-risk relatives.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:40696808 SUPPORT Human Clinical

"Childhood-onset neurodegeneration with progressive microcephaly (CONPM) is a rare autosomal recessive disorder caused by pathogenic variants in the DTYMK gene."

States the autosomal recessive mode of inheritance for the entity.

PMID:31271740 SUPPORT Human Clinical

"have been diagnosed to harbor two heterozygous variants in trans in the DTYMK gene of the thymidine biosynthesis pathway"

Documents the biallelic (two variants in trans) requirement in the first reported family.

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Mechanistic Hypotheses

2

Nuclear genome instability from dTTP depletion

dtymk-nuclear-genome-instability CANONICAL

Evidence balance 1 support

The accepted model. Loss of dTMPK collapses the dTTP pool, which impairs nuclear DNA replication, drives ribonucleotide misincorporation into genomic DNA, and leaves DNA damage unrepaired. Neurons and oligodendrocytes die by apoptosis and the brain atrophies postnatally. This model is supported by patient enzymology, patient fibroblast replication assays and an independent zebrafish knockout.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"we identified loss-of-function of DTYMK as the cause of a severe postnatal neurodegenerative disease and highlight the essential nature of dTTP synthesis in the maintenance of genome stability and neuronal survival"

The authors' own statement of the canonical model.

Mitochondrial DNA depletion

dtymk-mtdna-depletion ALTERNATIVE

Evidence balance 1 support 2 partial 2 refute

The original 2019 proposal was that DTYMK belongs to the mitochondrial DNA depletion syndrome gene set, on the basis of an in silico inference of mtDNA depletion in the more severely affected of two siblings. The 2022 study tested this directly in patient fibroblasts and found normal mtDNA copy number, no mtDNA deletions on long-range PCR, and normal respiratory chain complex I-V activities, alongside normal lactate and alanine in its own two individuals. The hypothesis is nevertheless kept as ALTERNATIVE rather than DEPRECATED for two reasons. First, the 2022 authors themselves state the caveat that fibroblast or blood mtDNA copy number is not representative of affected tissue and that they had no muscle biopsy. Second, and more substantively, the 2021 enzymology paper showed that in the same patient fibroblasts the loss of TMPK activity is COMPLETE in mitochondria and only near-complete in cytosol, which is a positive biochemical reason to keep a mitochondrial arm on the table.

This is the single most consequential disagreement in the DTYMK literature, and it matters for curation as well as for biology: the 2019 paper's title calls DTYMK a mitochondrial DNA depletion syndrome gene, so any curator reading titles alone would classify this disease into the wrong mechanism class. Conversely, a curator reading only the 2022 paper would discard the mitochondrial arm entirely and miss that DTYMK is a listed eligible genotype in an active deoxynucleoside trial for mitochondrial depletion disorders (clinicaltrials:NCT04802707, curated under treatments). The evidence list below deliberately carries the original claim, the original authors' own hedge, the disconfirming experiment with supports REFUTE, and the compartment finding that partially rehabilitates it, so the disagreement is visible in the data rather than resolved silently in prose. An earlier revision of this entry set this hypothesis to DEPRECATED. That was wrong, and specifically it was wrong because it had been written before PMID:34926941 was read. The status is corrected to ALTERNATIVE here.

Show evidence (5 references)

PMID:31271740 SUPPORT Computational

"Mitochondrial DNA depletion has been demonstrated in silico in the more severe sibling."

The original claim, and its own abstract makes clear the evidence was in silico rather than measured.

PMID:31271740 PARTIAL Human Clinical

"DTYMK may be the missing link in the mitochondrial nucleotide salvage pathway but further characterization and additional evidence would be needed."

The original authors' own hedge, which the later disconfirmation should be read against.

PMID:34918187 REFUTE In Vitro

"In conclusion, we find no significant indications of mitochondrial dysfunction in fibroblasts of individual I."

Direct experimental disconfirmation in patient-derived cells, covering mtDNA copy number, mtDNA integrity and respiratory chain function.

+ 2 more references

?

Discussions and Knowledge Gaps

3

Is DTYMK deficiency a mitochondrial DNA depletion syndrome, as its first description asserted, or a nuclear genome instability disorder?

CONTROVERSY OPEN dtymk-mtdna-controversy

PMID:31271740 titles DTYMK a novel gene for mitochondrial DNA depletion syndrome on the basis of an in silico inference. PMID:34918187 measured mtDNA copy number, mtDNA integrity and respiratory chain activity in patient fibroblasts and found all normal, and instead demonstrated a nuclear phenotype: impaired DNA replication, ribonucleotide misincorporation and a persistent DNA damage response. The question is not fully closed because the 2022 authors concede that fibroblast mtDNA copy number does not represent affected tissue and that muscle would be needed to settle it.

Proposed experiments

mtDNA copy number in affected tissue rather than fibroblasts

exp_dtymk_mtdna_affected_tissue

Measure mtDNA copy number in post-mortem brain and in skeletal muscle from an affected individual, the tissues in which depletion would actually matter. PMID:34918187 explicitly states that fibroblast and blood copy number is not representative and that muscle is required, so this is the experiment its own authors nominate.

Direct dNTP pool measurement in patient-derived neurons

exp_dtymk_dntp_pool_in_neurons

Quantify the dNTP pool, including dTTP, directly in patient-derived neurons or cerebral organoids. Existing measurements were made in fibroblasts and whole zebrafish larvae and were normal; the cell type that actually dies has never been assayed.

Show evidence (1 reference)

PMID:34918187 SUPPORT In Vitro

"Unfortunately, we do not have access to muscle tissue of the described individuals."

The 2022 authors state that the tissue in which mtDNA depletion could actually have been assessed was unavailable to them, which is why their negative fibroblast result does not formally close the question. Their fuller statement of the caveat, that fibroblast and blood copy number is not representative of affected tissue, is broken across a line-break hyphen in the cached PDF extraction and so is paraphrased in this discussion's rationale rather than quoted.

How much weight should the dtymk zebrafish eye phenotype carry for the human disease?

HUMAN MODEL MISMATCH OPEN dtymk-zebrafish-eye-mismatch

The dtymk knockout zebrafish has small, deformed eyes lacking four of the six retinal layers, plus absent Meckel's cartilage. Neither human individual had a structural eye abnormality; their visual deficit was central, and formal ophthalmologic examination in individual II was normal. The model reproduces the microcephaly, neuronal apoptosis and early lethality faithfully, so it is a good model of the neurodegeneration, but its ocular and craniofacial readouts should not be back-projected onto the human phenotype. This matters for curation because it would be easy to add microphthalmia and a jaw anomaly to the human entry on the strength of a persuasive figure.

Show evidence (2 references)

PMID:34918187 SUPPORT Model Organism

"A notable difference between the human phenotype and the dtymk-deficient zebrafish model is the degree in which eye development is affected."

The authors flag the human-model divergence themselves.

PMID:34918187 SUPPORT Human Clinical

"However, the eyes were morphologically normal in both individuals."

Establishes that the human eye is structurally normal, which is the basis for excluding the ocular terms from the phenotype list.

How is any cell viable when the only route to dTTP is blocked?

KNOWLEDGE GAP OPEN dtymk-viability-paradox

dTMPK sits downstream of the convergence of the de novo and salvage pathways, so a complete block should abolish dTTP entirely and be incompatible with life. Affected individuals nonetheless survived 18 and 32 months; patient fibroblasts still cycle and in one study proliferated at a normal rate; and measured dTTP levels in both patient fibroblasts and mutant zebrafish were normal. The primary authors call this remarkable without explaining it and state that a compensatory pathway remains to be proven. Two candidate explanations have been advanced and one has been excluded. CMPK2 (UMP-CMP kinase 2, sometimes called TMPK2) was considered and rejected by PMID:34918187 on the grounds that it cannot use dTMP as a substrate. An unidentified TMPK-like activity remains open: PMID:35346037 reports a TMPK-like enzyme in zebrafish at later developmental stages with similar biochemical properties to Dtymk but not recognised by the Dtymk antibody, and PMID:34926941 independently infers a hitherto unknown compensatory TMPK-like enzyme from the normal proliferation of patient fibroblasts. Whether a human counterpart exists is unknown. Resolving this would also explain why the brain is selectively vulnerable, since a compensating enzyme with restricted expression is one of the two hypotheses PMID:34918187 offers for the tissue selectivity.

Proposed experiments

Biochemical identification of the compensatory TMPK-like activity

exp_dtymk_identify_compensatory_tmpk

Identify the postulated compensatory TMPK-like activity in human tissue, and test whether its expression is low in forebrain-derived structures. A compensating enzyme with restricted expression is one of the two explanations PMID:34918187 offers for why the brain is selectively vulnerable, so this experiment would resolve the compensation gap and the tissue-selectivity question at once.

Ultrasensitive residual-activity assay of the patient alleles

exp_dtymk_residual_activity_ultrasensitive

Determine the residual catalytic activity of recombinant p.Pro81Leu and p.Asp128Asn dTMPK with an assay sensitive well below the 0.62 pmol/min/mg floor reported in patient fibroblasts, to test whether survival is explained by sub-detection-threshold residual activity rather than by a separate compensating enzyme.

Show evidence (3 references)

PMID:34918187 SUPPORT In Vitro

"Thus, a compensatory pathway for dTTP generation remains to be proven."

The primary authors state the gap directly, in the same paragraph in which they exclude CMPK2 as the candidate.

PMID:34926941 SUPPORT In Vitro

"surprisingly the proliferation rate of the patient-derived fibroblasts was normal, suggesting the existence of an alternative and hitherto unknown compensatory TMPK-like enzyme for dTTP synthesis"

An independent group reaches the same conclusion from a different observation, normal fibroblast proliferation despite absent enzyme activity.

PMID:35346037 SUPPORT Model Organism

"Furthermore, there is a novel TMPK-like enzyme expressed at later stages of development."

Identifies the candidate alternative activity that could in principle explain residual dTTP synthesis, in the zebrafish model.

⚙

Pathophysiology

9

Biallelic Damaging DTYMK Variants

The disorder is initiated by inheritance of two damaging DTYMK alleles. The published allelic spectrum is entirely missense: p.Pro81Leu (recurrent, seen homozygously in an Egyptian family and in a Mexican family and in trans in a Dutch family) and p.Asp128Asn. Neither residue lies in a named functional domain of dTMPK, yet fibroblasts from a compound heterozygote have almost no measurable enzyme activity, so these alleles behave functionally as severe hypomorphs or nulls.

DTYMK hgnc:3061

Downstream

Loss of dTMPK Homodimerization The missense substitutions destabilise the obligate homodimer.

Loss of dTMP Kinase Catalytic Activity The patient alleles leave the cell with almost no dTMP kinase activity.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"Here, we describe two unrelated children with bi-allelic variants in DTYMK, encoding dTMPK, which catalyzes the penultimate step in dTTP biosynthesis."

Establishes biallelic DTYMK alleles as the initiating lesion and names the enzymatic step affected.

PMID:40696808 SUPPORT Human Clinical

"Genetic analysis identified a homozygous missense variant in DTYMK (NM_012145.4:c.242C>T; p.Pro81Leu)."

Independent replication of the same recurrent missense allele in a third unrelated family.

Loss of dTMPK Homodimerization

Wild-type dTMPK works as a homodimer. None of the substituted residues contacts the substrate directly; instead each substitution destabilises the dimer, so the purified mutant proteins run as monomers with drastically reduced substrate affinity and catalytic efficiency. The mechanism of inactivation is therefore structural rather than active-site, which is why in silico substrate-contact reasoning called two of these alleles tolerated.

DTYMK hgnc:3061

protein homodimerization activity GO:0042803 ↓ DECREASED

Downstream

Loss of dTMP Kinase Catalytic Activity Monomeric dTMPK is catalytically crippled.

Show evidence (2 references)

PMID:34926941 SUPPORT In Vitro

"The wild-type TMPK mainly exists as a dimer with high substrate binding affinity"

Establishes that the functional form of the enzyme is a dimer, which is what the disease alleles disrupt.

PMID:34926941 SUPPORT In Vitro

"Based on the human TMPK structure, none of the mutated amino acids interacted directly with the substrates."

Confirms the substitutions act structurally rather than by blocking substrate binding, which is the distinguishing feature of this mechanism.

Loss of dTMP Kinase Catalytic Activity

dTMPK phosphorylates dTMP to dTDP. Because the de novo route (dUMP to dTMP via thymidylate synthase) and the salvage route (thymidine to dTMP via thymidine kinase) both converge on dTMP, dTMPK is the single obligatory enzyme downstream of that convergence and is therefore the bottleneck for the entire dTTP supply. In fibroblasts of the compound heterozygous individual, activity was 0.62 pmol/min/mg protein against 43.65 and 31.08 in the heterozygous mother and father respectively. The loss is not uniform across compartments: in patient fibroblasts carrying P81L and D128N, mitochondrial TMPK activity was completely absent while cytosolic activity was extremely low and unstable. That compartment asymmetry is the strongest remaining argument for a mitochondrial contribution to the phenotype.

DTYMK hgnc:3061

dTMP kinase activity GO:0004798 ↓ DECREASED

Downstream

Block of Canonical dTTP Biosynthetic Flux With the bottleneck enzyme inactive, neither the de novo nor the salvage route can deliver dTTP.

Show evidence (4 references)

PMID:34918187 SUPPORT Human Clinical

"This makes dTMPK the bottleneck for dTTP biosynthesis"

States why loss of this one enzyme cannot be bypassed by the alternative pathway.

PMID:34918187 SUPPORT In Vitro

"dTMPK enzyme activity of the individual is significantly lower than those of the parents"

Quantifies the enzymatic deficit in patient fibroblasts against heterozygous parental controls.

PMID:34926941 SUPPORT In Vitro

"the P81L and D128N mutations led to a complete loss of TMPK activity in mitochondria and extremely low and unstable TMPK activity in cytosol"

Establishes the compartment asymmetry of the enzymatic loss in patient fibroblasts: total in mitochondria, near-total in cytosol.

+ 1 more reference

Block of Canonical dTTP Biosynthetic Flux

dTTP is one of the four building blocks of DNA, and the canonical route to it is completely blocked. Crucially, this is a defect of FLUX, not a demonstrated depletion of the steady-state pool: measured dTTP nucleotide levels in patient fibroblasts and in mutant zebrafish resembled normal controls. The disorder is therefore best modelled as a demand-limited and possibly compartment-limited supply failure that manifests in cells with high replicative and repair demand, rather than as bulk pool depletion.

dTTP biosynthetic process GO:0006235 ↓ DECREASED

Downstream

Impaired DNA Replication and Reduced Cell Proliferation An inadequate dTTP supply stalls S-phase.

Elevated Ribonucleotide Incorporation into Genomic DNA Deoxynucleotide pool imbalance drives the replication machinery to misincorporate ribonucleotides in place of the scarce deoxynucleotide.

Show evidence (3 references)

PMID:34918187 SUPPORT Human Clinical

"This study shows that impairment of the biosynthesis of one of the building blocks of DNA, dTTP, causes a severe, early-onset neurodegenerative disease."

Names the restricted metabolite and asserts the causal link from its shortage to the disease.

PMID:40696808 SUPPORT Computational

"This variant is predicted to disrupt dTMP phosphorylation, a key step in the maintenance of dTTP pools required for genomic stability and neural function."

Independent report framing the same mechanism, although as a prediction rather than a measurement, which is why this item is classified as computational.

PMID:34918187 PARTIAL In Vitro

"dTTP nucleotide levels resemble those of normal controls"

Measured steady-state dTTP was normal in both patient fibroblasts and mutant zebrafish. Curated as PARTIAL rather than REFUTE: what this measurement refutes is POOL depletion, which is not what this node claims. The node deliberately claims a block of FLUX, and a normal steady-state pool is compatible with reduced flux through the canonical route. The item is kept attached here because it constrains the node's meaning and is the reason the node is named for flux rather than for a restricted pool, but it neither confirms nor contradicts the flux claim itself.

Impaired DNA Replication and Reduced Cell Proliferation

Patient fibroblasts show a collapse in the S-phase fraction, from about 24 percent and 16 percent in the heterozygous mother and father to 2.8 percent in the affected individual. In dtymk mutant zebrafish the number of proliferating cells in the forebrain, the structure homologous to the human cerebral cortex, is significantly reduced.

DNA replication GO:0006260 ↓ DECREASED

Downstream

Apoptotic Loss of Neurons and Oligodendrocytes Cells that cannot complete replication or repair are removed by apoptosis.

Show evidence (1 reference)

PMID:34918187 SUPPORT In Vitro

"In contrast, the fraction of S-phase cells in individual I fibroblasts was only 2.8%."

Quantifies the replication defect in patient-derived cells against parental controls measured in the same experiment.

Elevated Ribonucleotide Incorporation into Genomic DNA

Genomic DNA from dtymk mutant zebrafish is markedly more sensitive to alkaline hydrolysis, indicating elevated ribonucleotide content, and behaves on alkaline gels like DNA from Rnaseh2-null mice, the canonical ribonucleotide-excision-repair-deficient model. Ribonucleotides in DNA carry a reactive 2'-hydroxyl, which makes the backbone fragile.

Downstream

Genome Instability and Abnormal DNA Damage Response Ribonucleotides in the genome make DNA fragile and provoke a persistent DNA damage response.

Show evidence (1 reference)

PMID:34918187 SUPPORT Model Organism

"An increase of ribonucleotide incorporation in the genome as well as impaired responses to DNA damage were observed in dtymk mutant zebrafish, providing novel pathophysiological insights."

The primary observation of ribonucleotide misincorporation and abnormal DNA damage signalling in the model.

Genome Instability and Abnormal DNA Damage Response

dtymk mutant zebrafish irradiated with UV retain high levels of gammaH2AX 24 hours later, consistent with unrepaired DNA breaks. Essentially every DNA repair pathway involves repair-associated DNA synthesis, which the dTTP shortage also constrains.

DNA repair GO:0006281 ↓ DECREASED

Downstream

Apoptotic Loss of Neurons and Oligodendrocytes Unrepaired genomic damage in post-mitotic and differentiating neural cells triggers apoptosis.

Show evidence (1 reference)

PMID:34918187 SUPPORT Model Organism

"The effects of DTYMK deficiency on the process of DNA damage signaling was evaluated in vivo."

Establishes that DNA damage signalling was directly assayed in vivo in the dtymk model, which is the experiment underpinning this node. The authors' one-sentence conclusion from that experiment is split across an interposed figure caption in the cached PDF extraction and cannot be quoted contiguously, so the setup sentence is quoted and the result is stated in this node's description instead.

Apoptotic Loss of Neurons and Oligodendrocytes

Post-mortem neuropathology in individual I showed massive neuronal dropout across essentially the whole brain, astrogliosis, loss of oligodendrocytes with caspase-3-positive apoptotic profiles, ameboid microglial activation and a paucity of myelin, together with neuronal loss in the granular and Purkinje cell layers of a cerebellum that had looked normal on MRI. dtymk mutant zebrafish show the same signature of neuronal apoptosis.

neuron CL:0000540 ↓ DECREASED oligodendrocyte CL:0000128 ↓ DECREASED astrocyte CL:0000127 ↑ INCREASED microglial cell CL:0000129 ↑ INCREASED

apoptotic process GO:0006915 ↑ INCREASED

Downstream

Progressive Postnatal Cerebral and Basal Ganglia Atrophy Cumulative loss of neurons and oligodendrocytes produces the shrinking brain seen on serial imaging.

Show evidence (3 references)

PMID:34918187 SUPPORT Human Clinical

"Brain pathology confirmed massive neuronal dropout in virtually the entire brain, sparing the brain stem."

Human autopsy evidence of the cellular lesion and its anatomical distribution.

PMID:34918187 SUPPORT Model Organism

"implicate neuronal apoptosis as one of the hallmarks of this disease."

The authors' conclusion, drawn jointly from the human autopsy and the zebrafish model, that apoptosis is the mode of neuronal loss.

PMID:34918187 SUPPORT Model Organism

"In addition, we generated dtymk mutant zebrafish that replicate this phenotype of microcephaly, neuronal cell death and early lethality."

Cross-species replication of the neuronal death phenotype.

Progressive Postnatal Cerebral and Basal Ganglia Atrophy

The structural lesion is postnatal and progressive rather than a malformation. Individual I had a near-normal fetal head circumference and only slight underdevelopment of the caudate and frontal cortex at three weeks, then dramatic hemispheric atrophy with ventricular enlargement by six months. The thalamus, brainstem and cerebellum look normal on MRI even when the hemispheres and basal ganglia are devastated, although microscopy shows the cerebellum is not truly spared.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"growth retardation, puffy body, seizures, failure to reach developmental milestones, microcephaly and severe, progressive atrophy of the cerebral hemispheres and basal ganglia"

Lists the features that emerged postnatally in both individuals, including the progressive nature of the atrophy.

PMID:34918187 SUPPORT Human Clinical

"as well as the cerebral atrophy that only sets in postnatally"

States explicitly that the atrophy is postnatal, which is what makes this a neurodegenerative rather than a malformative disorder.

✶

Histopathology

4

Global neuronal loss with sparing of dentate nucleus and brainstem

Autopsy of individual I in PMID:34918187 showed severe atrophy of the neocortex, cerebral white matter and basal ganglia with massive neuronal dropout, while the brainstem, cerebellar dentate nucleus and the gross size of the cerebellum were preserved. The sparing pattern is the diagnostically informative part: this is not a uniform encephaloclastic process but a selective one that leaves specific structures intact, matching the imaging observation that brainstem and cerebellum look comparatively normal on MRI.

Show evidence (3 references)

PMID:34918187 SUPPORT Human Clinical

"Gross neuropathological examination showed severe atrophy of the neocortex,"

Opening of the gross neuropathology description. The sentence continues "cerebral white matter and basal ganglia", which cannot be quoted contiguously because the cached PDF extraction breaks "matter" across a line.

PMID:34918187 SUPPORT Human Clinical

"with normal size of brainstem and cerebellum"

The gross sparing of brainstem and cerebellum, in the same sentence.

PMID:34918187 SUPPORT Human Clinical

"only sparing the dentate nucleus and brain stem."

The authors' own summary of the sparing pattern. The clause preceding this one is not quoted because the extraction breaks "massive" across a line.

Anisomorphic astrogliosis of the cerebral cortex

The cortex of individual I showed intense anisomorphic astrogliosis with only a minimal degree of vascular proliferation, and reactive gliosis was also present in the neostriatum and thalamus alongside neuronal loss.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"intense anisomorphic astrogliosis"

The cortical gliosis finding.

PMID:34918187 SUPPORT Human Clinical

"show loss of neurons and reactive gliosis."

The same reaction in the neostriatum and thalamus.

Oligodendrocyte loss by apoptosis with paucity of myelin

Deep periventricular white matter showed loss of oligodendrocytes with moderate microglial activation; the more peripheral hemispheric white matter showed massive ameboid microglial activation, lack of myelin and loss of oligodendrocytes by apoptosis, with paucity of myelin throughout the hemispheres and capsules. Caspase-3 was among the stains used. This is the histological evidence that the oligodendroglial arm of the disease is apoptotic rather than purely hypomyelinating.

Show evidence (3 references)

PMID:34918187 SUPPORT Human Clinical

"and loss of oligodendrocytes by apoptosis"

The apoptotic mechanism of oligodendrocyte loss.

PMID:34918187 SUPPORT Human Clinical

"spheric white matter shows massive activation of microglia with ameboid morphology"

The microglial reaction in peripheral white matter. The quote starts mid-word because the cached PDF extraction breaks "hemispheric" across a line immediately before it.

PMID:34918187 SUPPORT Human Clinical

"show paucity of myelin throughout the cerebral hemispheres and capsules"

The myelin deficit, on whole mounts of the cerebral hemispheres.

Cerebellar granular and Purkinje cell layer neuronal loss

Microscopy of a cerebellum that was of normal gross size, and that had looked normal on MRI, nevertheless showed loss of neurons in the granular and Purkinje cell layers with a moderate Bergmann glial reaction. The cerebellum is therefore involved microscopically even where imaging and gross examination suggest it is spared, which is a caution against reading normal cerebellar imaging as normal cerebellum.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"shows loss of neurons in the granular and Purkinje cell layer"

The cerebellar microscopic finding.

⬡

Pathograph

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●

Phenotypes

18

Blood 1

Hypochromic Microcytic Anemia Hypochromic microcytic anemia HP:0004840

No frequency band. Documented in 1 of the 5 published individuals. It is worth flagging rather than dropping because normocytic anaemia is part of DEE50, the CAD-related dTTP-pathway disorder that PMID:34918187 names as a comparator, so haematological involvement may be a shared consequence of constrained nucleotide supply in an erythroid lineage. That connection is a hypothesis, not something either paper asserts.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"Microcytic hypochromic anemia and elevated liver enzymes"

The Table 1 "Other findings" row for individual II, naming both the anaemia and its microcytic hypochromic character.

PMID:34918187 SUPPORT Human Clinical

"Severe anemia was detected and treated by blood transfusion."

Documents the clinical severity of the anaemia in individual II at 7 months.

Genitourinary 2

Micropenis Micropenis HP:0000054

No frequency band. Documented in 1 of the 5 published individuals, who is also one of only two reported males with a described genital examination. Whether this is part of the disorder or an incidental finding is not established by a single case.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"Micropenis and undescended testis"

The Table 1 "Other findings" row for individual II.

Cryptorchidism Cryptorchidism HP:0000028

Laterality: BILATERAL

No frequency band. Documented in 1 of the 5 published individuals. Same caveat as micropenis: a single observation cannot separate a disease feature from an incidental one.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"Micropenis and undescended testis"

The Table 1 "Other findings" row for individual II; the bilaterality is stated in the body text.

Metabolism 1

Elevated Circulating Hepatic Transaminase Concentration Elevated circulating hepatic transaminase concentration HP:0002910

No frequency band. Documented in 1 of the 5 published individuals.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"hematological indices and liver enzymes at different occasions"

Records that liver enzymes in individual II were measured repeatedly on different occasions, which is what establishes the abnormality as persistent rather than a single reading. The Table 1 row quoted on the anaemia phenotype states the result itself, that the liver enzymes were elevated.

Musculoskeletal 3

Hypotonia Hypotonia HP:0001252

Onset: CONGENITAL

No frequency band. Hypotonia is documented in 2/2 individuals in PMID:31271740 and in 1/2 in PMID:34918187 (individual II is described as having good head control and increased distal tone rather than hypotonia), and is not mentioned in PMID:40696808, whose case has hypertonia. Combining these into a single band would obscure that the tone abnormality changes character over the course of the illness.

Show evidence (2 references)

PMID:31271740 SUPPORT Human Clinical

"Two siblings of a quartet family, presenting with hypotonia, microcephaly and severe intellectual disability"

Documents hypotonia as a presenting feature in both siblings of the first reported family.

PMID:34918187 SUPPORT Human Clinical

"The girl was hypotonic at birth but developed spasticity with opisthotonus within 1 year of age."

Documents congenital hypotonia in individual I and its evolution into spasticity, which is the reason no single tone band is asserted.

Spasticity Spasticity HP:0001257

No frequency band. Pyramidal hypertonia is documented in 2/2 in PMID:34918187 and 1/1 in PMID:40696808, but the descriptors differ (spasticity with opisthotonus, distal hypertonia with clonus, unqualified hypertonia) and PMID:31271740 describes hypotonia instead. Rather than force a band across heterogeneous descriptions of tone, both spasticity and hypotonia are curated as unbanded features of a biphasic course.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"The girl was hypotonic at birth but developed spasticity with opisthotonus within 1 year of age."

Documents the emergence of spasticity in individual I.

PMID:34918187 SUPPORT Human Clinical

"Tendon reflexes were increased, with bilateral clonus and positive Babiniski signs."

Documents the pyramidal signs accompanying the hypertonia in individual II. The misspelling of Babinski is present in the source and is preserved so the quote stays verbatim.

Opisthotonus Opisthotonus HP:0002179

No frequency band. Documented in 1 of the 5 published individuals.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"The girl was hypotonic at birth but developed spasticity with opisthotonus within 1 year of age."

Documents opisthotonus in individual I.

Nervous System 5

Absent Neurodevelopmental Progress VERY_FREQUENT Global developmental delay HP:0001263

Severity: PROFOUND

Derivation: 2/2 in PMID:34918187 (Table 1 row "Development No developmental progress No developmental progress"), 2/2 in PMID:31271740 (severe intellectual disability in both siblings) and 1/1 in PMID:40696808 (progressive neurodevelopmental regression), which resolves to 5/5 of the five published individuals and therefore the VERY_FREQUENT band. The underlying descriptions are not identical - the PMID:31271740 siblings are characterised as intellectually disabled rather than as having made no progress at all - so this band asserts severe global impairment of development, not literally zero milestones in all five.

Show evidence (3 references)

PMID:34918187 SUPPORT Human Clinical

"No neurodevelopmental milestones were achieved."

Documents the complete absence of developmental progress in individual I.

PMID:34918187 SUPPORT Human Clinical

"He made almost no developmental progress: he did not roll over, sit, vocalize, or smile."

Documents the same in individual II, with the specific milestones enumerated.

PMID:31271740 SUPPORT Human Clinical

"Two siblings of a quartet family, presenting with hypotonia, microcephaly and severe intellectual disability"

Documents severe intellectual disability in the first reported family.

Developmental Regression Developmental regression HP:0002376

Course: PROGRESSIVE

No frequency band is asserted. Regression is explicitly described only in PMID:40696808. In the two individuals of PMID:34918187 no milestone was ever gained, so there was nothing to regress from, and PMID:31271740 does not describe the developmental trajectory of its siblings. A denominator for regression therefore does not exist across the published series.

Show evidence (1 reference)

PMID:40696808 SUPPORT Human Clinical

"A 2-year-old male with progressive neurodevelopmental regression presented with severe microcephaly, epilepsy, hypertonia, and cortical and cerebellar atrophy."

Documents regression as the presenting problem in the fifth reported case.

Cerebral Atrophy VERY_FREQUENT Cerebral atrophy HP:0002059

Course: PROGRESSIVE

Derivation: 2/2 in PMID:34918187 and 1/1 in PMID:40696808, which resolves to 3/3 and therefore the VERY_FREQUENT band. The denominator here is the three individuals with published neuroimaging, not the whole series of five; the two siblings of PMID:31271740 have no imaging described in the abstract that is cached for this entry, so they are excluded from this denominator rather than counted as negative.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"Brain MRI at 6 months of age showed dramatic atrophy of the cerebral hemispheres with severe enlargement of the lateral ventricles and subarachnoid spaces"

Documents the hemispheric atrophy and its imaging correlates in individual I at 6 months.

PMID:40696808 SUPPORT Human Clinical

"This ultra-rare condition is characterized by progressive neurological regression, epilepsy, severe microcephaly, and global cerebral atrophy."

Names global cerebral atrophy as a defining feature of the entity.

Cerebellar Atrophy Cerebellar atrophy HP:0001272

No frequency band is asserted, and this is the one phenotype in the entry where the sources genuinely disagree. Radiological cerebellar atrophy is reported in 1 of the 3 imaged individuals (PMID:40696808), while PMID:34918187 explicitly describes the cerebellum as appearing normal on MRI in its two individuals - yet reports histological cerebellar neuronal loss in the one individual who came to autopsy. The term is retained because the histology and the third case both point to real cerebellar pathology, but a band would misrepresent a 1/3 imaging finding.

Show evidence (2 references)

PMID:40696808 SUPPORT Human Clinical

"A 2-year-old male with progressive neurodevelopmental regression presented with severe microcephaly, epilepsy, hypertonia, and cortical and cerebellar atrophy."

Documents radiological cerebellar atrophy in the fifth reported case.

PMID:34918187 PARTIAL Human Clinical

"Brain stem and cerebellum appeared normal"

The Table 1 entry for individual I states the cerebellum appeared normal on MRI, which is why this phenotype is curated as partially supported rather than as an established feature.

Seizure VERY_FREQUENT Seizure HP:0001250

Temporal: RECURRENT Onset: INFANTILE; 0.5-2.0y

Derivation: 2/2 in PMID:34918187 (Table 1 row "Seizures Recurrent febrile seizures myoclonic jerks") and 1/1 in PMID:40696808, which resolves to 3/3 and therefore the VERY_FREQUENT band. The denominator is the three individuals whose seizure status is reported; PMID:31271740 does not mention seizures in either direction for its two siblings, so they are excluded rather than counted as unaffected.

Show evidence (3 references)

PMID:34918187 SUPPORT Human Clinical

"She developed recurrent febrile seizures with flat trace EEG at 6 months of age which were successfully treated with phenobarbital."

Documents seizure onset, semiology, EEG and response to treatment in individual I.

PMID:34918187 SUPPORT Human Clinical

"He developed severe myoclonic jerks at 15 months of age, which were treated with carbamazepine."

Documents seizure onset and treatment in individual II.

PMID:40696808 SUPPORT Human Clinical

"A 2-year-old male with progressive neurodevelopmental regression presented with severe microcephaly, epilepsy, hypertonia, and cortical and cerebellar atrophy."

Documents epilepsy in the fifth reported case.

Growth 1

Failure to Thrive VERY_FREQUENT Failure to thrive HP:0001508

Derivation: 2/2 in PMID:34918187 (both the abstract sentence naming growth retardation for "the affected children" and the Table 1 weight and height SD scores for each individual). The denominator here is only the two individuals of that one series; PMID:31271740 and PMID:40696808 do not report anthropometry in the cached abstracts. A 2/2 denominator is thin, and the band is asserted only because the same paper states the feature for both children in a summary sentence as well as in the table. Readers wanting a five-case denominator will not find one.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"The affected children show severe microcephaly and growth retardation with minimal neurodevelopment."

States growth retardation for both affected children of this series.

PMID:34918187 SUPPORT Human Clinical

"Because of poor feeding, she was readmitted to the hospital on the 3rd day."

Documents the feeding difficulty that opened the growth failure in individual I, in the first week of life.

Other 5

Progressive Microcephaly VERY_FREQUENT Progressive microcephaly HP:0000253

Course: PROGRESSIVE

Derivation: 2/2 in PMID:31271740 (microcephaly named for both siblings in the abstract), 2/2 in PMID:34918187 (Table 1 row "Microcephaly Yes Yes") and 1/1 in PMID:40696808, which resolves to 5/5 of the five published individuals, that is 100 percent and therefore the VERY_FREQUENT band of 80-100 percent. The denominator of five is the entire published series.

Show evidence (4 references)

PMID:34918187 SUPPORT Human Clinical

"The affected children show severe microcephaly and growth retardation with minimal neurodevelopment."

Documents severe microcephaly in both individuals of this series.

PMID:34918187 SUPPORT Human Clinical

"She developed severe microcephaly with a very puffy appearance"

Documents that the severe microcephaly in individual I DEVELOPED after birth rather than being present at birth, which is what distinguishes this from primary microcephaly. The adjacent sentence stating that head circumference and height progressively deviated from the centiles is broken across a line-break hyphen in the cached PDF extraction and is therefore not quoted.

PMID:31271740 SUPPORT Human Clinical

"Two siblings of a quartet family, presenting with hypotonia, microcephaly and severe intellectual disability"

Independent documentation of microcephaly in the first reported family.

+ 1 more reference

Small Basal Ganglia Small basal ganglia HP:0012697

No frequency band is asserted. The finding is documented in both individuals of PMID:34918187, but PMID:40696808 reports cortical and cerebellar atrophy without specifying the basal ganglia, so the denominator across the imaged cases is not clean.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"Brain imaging revealed severe cerebral atrophy and disappearance of the basal ganglia."

Documents the basal ganglia involvement as a distinct imaging feature in both individuals of this series.

PMID:34918187 SUPPORT Human Clinical

"The basal nuclei were small, but visible, while the thalamus appeared to have a normal size."

Documents the same finding in individual II and records the sparing of the thalamus that distinguishes this pattern.

Myoclonic Seizure Myoclonic seizure HP:0032794

No frequency band. Myoclonic semiology is documented in 1 of the 5 published individuals; the other individual with characterised seizures had febrile seizures instead, so the two documented semiologies differ and no dominant seizure type can be asserted.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"He developed severe myoclonic jerks at 15 months of age, which were treated with carbamazepine."

Documents the myoclonic semiology and its age of onset.

Cerebral Visual Impairment Cerebral visual impairment HP:0100704

No frequency band. Documented in 2/2 individuals in PMID:34918187 but not addressed in PMID:31271740 or in the PMID:40696808 abstract. A denominator of two out of a series of five is too thin to band. Curated as HP:0100704 Cerebral visual impairment rather than the more general HP:0000505 Visual impairment. The specific term is what the two curated snippets actually support taken together: absent visual tracking with morphologically normal eyes and a normal ophthalmologic examination is a central rather than an ocular deficit. HP:0100704 is also the term used in the HPO annotation set for OMIM:619847. No imaging of the optic radiations or visual cortex, and no VEP, is reported in any cached reference, so the localisation rests on the exclusion of an ocular cause rather than on a positive cortical finding.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"Vision No tracking of objects, only light/dark No tracking of objects"

The Table 1 vision row records absent visual tracking in both individuals. The run-on wording is an artefact of the two-column table being extracted as one line, and is quoted verbatim rather than tidied.

PMID:34918187 PARTIAL Human Clinical

"However, the eyes were morphologically normal in both individuals."

Establishes that the visual deficit is central rather than structural, which is why the ocular terms used in the zebrafish model are not curated as human phenotypes here.

Neuronal Loss in Central Nervous System Neuronal loss in central nervous system HP:0002529

No frequency band. Neuropathology is available for exactly one of the five published individuals, so there is no denominator at all. This phenotype is included because it is the histological substrate of the imaging finding, not because it is known to be universal.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"Brain pathology confirmed massive neuronal dropout in virtually the entire brain, sparing the brain stem."

Direct autopsy documentation of the neuronal loss and its distribution.

🧬

Genetic Associations

1

DTYMK

Gene: DTYMK hgnc:3061 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:34918187 SUPPORT Human Clinical

"we identified loss-of-function of DTYMK as the cause of a severe postnatal neurodegenerative disease and highlight the essential nature of dTTP synthesis in the maintenance of genome stability and neuronal survival"

The definitive gene-disease statement, supported in the same paper by patient enzymology and an independent animal model.

PMID:31271740 SUPPORT Human Clinical

"have been diagnosed to harbor two heterozygous variants in trans in the DTYMK gene of the thymidine biosynthesis pathway"

The first report implicating DTYMK in human disease, in an independent family.

PMID:38621447 SUPPORT Model Organism

"Dtymk-/- mice were confirmed to be embryonic lethal before E12.5, and Dtymk+/- mice on all three experimental diets did not show the presence of open neural tube defects, spina bifida or exencephaly."

Establishes recessive essentiality rather than haploinsufficiency: total loss is embryonic lethal, one copy is enough. This is consistent with the human disease being caused by hypomorphic biallelic missense alleles rather than by biallelic nulls, and with the unaffected status of carrier parents.

💊

Medical Actions

6

Supportive and symptomatic management

Category: Therapeutic Action: supportive care Ontology label: Supportive Care NCIT:C15747

No disease-modifying therapy exists and none has been trialled. All reported management has been symptomatic and is curated as separate atomic entries below: anti-seizure pharmacotherapy, nasogastric tube feeding, and blood transfusion for the anaemia in individual II, with genetic counselling recorded as a non-therapeutic action. Both individuals with reported outcomes nonetheless died in early childhood after intercurrent infection.

Show evidence (1 reference)

PMID:40696808 SUPPORT Human Clinical

"Further functional studies are needed to elucidate the mechanisms linking DTYMK dysfunction to neurodegeneration."

The most recent report still frames the mechanism as incompletely understood, which is the state of play that precludes any targeted therapy.

Anti-seizure pharmacotherapy

Category: Therapeutic Action: anti-seizure pharmacotherapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: phenobarbital CHEBI:8069 carbamazepine CHEBI:3387

Both individuals in PMID:34918187 received an anti-seizure drug: individual I was treated with phenobarbital for recurrent febrile seizures at 6 months, reported as successful, and individual II was treated with carbamazepine for severe myoclonic jerks at 15 months, with no response stated. These are the only two anti-seizure agents named anywhere in the DTYMK literature and the phenobarbital response is the only treatment response reported for this disease.

Target Phenotypes: Seizure HP:0001250 Myoclonic seizure HP:0032794

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"She developed recurrent febrile seizures with flat trace EEG at 6 months of age which were successfully treated with phenobarbital."

Documents symptomatic anti-seizure treatment and its effect in individual I. It is the only treatment response reported anywhere in this literature.

PMID:34918187 PARTIAL Human Clinical

"He developed severe myoclonic jerks at 15 months of age, which were treated with carbamazepine."

Documents carbamazepine use for individual II's myoclonic seizures. Curated as PARTIAL because the sentence records only that the drug was given; unlike the phenobarbital sentence it makes no claim about seizure control, so it supports the intervention but not any efficacy.

Nasogastric tube feeding

Category: Therapeutic Action: nasogastric tube feeding Ontology label: Enteral Tube Feeding NCIT:C93322

Individual I of PMID:34918187 required nasogastric tube feeding for the early feeding failure and tolerated it well. This is the only nutritional intervention reported in the DTYMK literature.

Target Phenotypes: Failure to thrive HP:0001508

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"Nutrition with naso-gastric tube was needed and well tolerated."

Documents the feeding intervention used for the early feeding failure.

Blood transfusion for anaemia

Category: Therapeutic Action: blood transfusion Ontology label: Blood Transfusion NCIT:C15192

Individual II of PMID:34918187 was admitted at 7 months with fever and vomiting, was found to have severe anaemia, and was treated with blood transfusion. Repeated later testing continued to show microcytic hypochromic anaemia, so the transfusion addressed an episode rather than the underlying haematological abnormality.

Target Phenotypes: Hypochromic microcytic anemia HP:0004840

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"Severe anemia was detected and treated by blood transfusion."

Documents the transfusion given to individual II.

Genetic counselling

Category: Counseling / Informational Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Individual II of PMID:34918187 was referred for genetic counselling at 30 months of age, which is how the diagnosis was pursued. Counselling is relevant to this disorder because it is autosomal recessive with a 25 per cent recurrence risk for siblings, and because both reported families were consanguineous.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"At 30 months of age, the boy was referred for genetic counseling."

Documents that genetic counselling was part of this individual's care pathway. It is the only mention of counselling in the DTYMK literature.

Deoxycytidine plus deoxythymidine substrate-enhancement therapy (investigational)

Category: Therapeutic Action: deoxynucleoside substrate-enhancement pharmacotherapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: deoxycytidine CHEBI:15698 thymidine CHEBI:17748

An open-label phase II trial of oral deoxycytidine plus deoxythymidine for mitochondrial DNA depletion disorders lists DTYMK among its eligible genotypes. This is the only interventional study anywhere that names DTYMK. No result specific to a DTYMK-mutant participant has been published, and no DTYMK patient is known to have been enrolled.

Show evidence (1 reference)

clinicaltrials:NCT04802707 PARTIAL Human Clinical

"The subjects included are children (0-18Y), with positive MDS diagnosis and express mutations in one of the following genes: POLG, POLG2, C10orf2, RRM2B, MPV17, SUCLA2, SUCLG1, FBXL4, DTYMK."

Documents that DTYMK is an eligible genotype for this deoxynucleoside trial. Curated as PARTIAL because eligibility is not efficacy and the trial's mitochondrial rationale is itself contested for this gene.

🔬

Biochemical Markers

2

Deficient dTMPK activity in cultured fibroblasts (ABNORMAL)

Context: An in vitro dTMPK assay on cultured skin fibroblasts from family I of PMID:34918187 gave 0.62 pmol/min/mg protein in the affected individual against 43.65 in the heterozygous mother and 31.08 in the heterozygous father, that is roughly 1.4 to 2.0 per cent of parental activity. The same assay in the zebrafish model gave 1.80 pmol/min/mg in mutant larvae against 38.55 in siblings and 41.43 in unrelated wildtype larvae.

Pathograph Readouts

Readout Of Loss of dTMP Kinase Catalytic Activity Negative Diagnostic

The assay is a direct measurement of the enzymatic step the disease abolishes, so a near-zero value in a biallelic individual with clearly detectable activity in both carriers is the functional confirmation of a candidate genotype.

Show evidence (5 references)

PMID:34918187 SUPPORT In Vitro

"In fibroblasts of the parents, dTMPK activity was readily detectable."

Establishes the carrier baseline against which the affected value is interpreted.

PMID:34918187 SUPPORT In Vitro

"In the mother, an activity of 43.65 pmol/min/mg protein"

The maternal carrier value.

PMID:34918187 SUPPORT In Vitro

"whereas the cells of the father showed lower activity: 31.08 pmol/min/mg protein."

The paternal carrier value.

+ 2 more references

Normal routine metabolic work-up (NORMAL)

Context: A normal biochemical screen is diagnostically load-bearing in this disorder rather than merely unremarkable. Glucose, lactate, ammonia, biotinidase, creatine kinase, acylcarnitines, amino acids, very long-chain fatty acids and urinary organic acids were all normal in individual II of PMID:34918187, and extensive metabolic investigation in individual I was likewise unrevealing. The corollary is that no first-line metabolic panel will raise this diagnosis and that a normal screen does not exclude it.

Pathograph Readouts

Readout Of Block of Canonical dTTP Biosynthetic Flux Present Absent Diagnostic

Read together with the separately curated finding that steady-state dTTP pools are normal, the normal metabolic screen is what forces the mechanistic claim to be about FLUX rather than about a measurable metabolite abnormality. There is no analyte to test for.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"Metabolic work-up including glucose, lactate, ammonia, biotinidase, creatine kinase, acylcarnitines, amino acids, very long-chain fatty acids and urinary organic acids profile were all normal."

The itemised normal panel in individual II.

PMID:34918187 SUPPORT Human Clinical

"Extensive metabolic investigations were performed"

Documents that biochemical investigation was undertaken in individual I and did not make the diagnosis.

🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from DTYMK-Related Neurodegeneration:

Aicardi-Goutieres syndrome MONDO:0018866

Overlapping Features The closest clinical and mechanistic mimic, and the comparison the primary paper itself draws. AGS also presents with progressive microcephaly, psychomotor retardation, white matter destruction, brain atrophy and death in early childhood, and at the mechanistic level both disorders are characterised by elevated ribonucleotide incorporation into genomic DNA - in AGS because RNase H2 cannot excise them, in DTYMK deficiency because the dTTP shortage causes them to be inserted in the first place.

Distinguishing Features

Molecular: AGS is genetically heterogeneous (RNASEH2A/B/C, TREX1, SAMHD1, ADAR, IFIH1 and others) and is a type 1 interferonopathy; DTYMK deficiency is a single-gene nucleotide-biosynthesis defect with no interferon signature reported.
Imaging and laboratory: intracranial calcification and CSF lymphocytosis are characteristic of AGS and are not reported in DTYMK deficiency. Systemic features of AGS such as thrombocytopenia and hepatosplenomegaly are also absent.
Directionality of the ribonucleotide defect: in AGS, ribonucleotides accumulate because ribonucleotide excision repair fails. In DTYMK deficiency they accumulate because the replication machinery substitutes them for the missing deoxynucleotide. The shared readout has opposite upstream causes.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"White matter destruction and brain atrophy are shared phenotypic features of AGS and DTYMK deficiency."

The primary paper's own statement of the clinical overlap that makes AGS the leading differential.

PMID:34918187 SUPPORT Human Clinical

"at the mechanistic level, AGS and DTYMK deficiency are similar as both are characterized by elevated ribonucleotide incorporation in the genome"

Establishes the shared mechanistic readout, which is why the two are confusable at the level of pathophysiology and not only at the bedside.

CAD-related developmental and epileptic encephalopathy 50 Not Yet Curated MONDO:0014647

Overlapping Features The other neurodegenerative disorder of the dTTP pathway, caused by biallelic CAD variants (HGNC:1424, verified by OAK on MONDO:0014647). CAD performs the first steps of de novo pyrimidine synthesis, several enzymatic steps upstream of dTMPK. Like DTYMK deficiency it is autosomal recessive, progressive, neurodegenerative, and begins in the first months or years of life with early-onset seizures and developmental regression; it also features anaemia.

Distinguishing Features

Molecular: CAD (HGNC:1424, MONDO:0014647) versus DTYMK (HGNC:3061, MONDO:0859241). Different genes, different MONDO entities.
Position in the pathway: CAD acts at the entry to de novo pyrimidine synthesis, so its loss can in principle be bypassed by the salvage pathway. DTYMK sits downstream of the point where de novo and salvage converge, so its loss cannot be bypassed at all. This is the reason uridine supplementation is a rational therapy in CAD deficiency and is not one here.
Anaemia type: DEE50 features normocytic anaemia, whereas the one DTYMK individual with anaemia had microcytic hypochromic indices.

Show evidence (1 reference)

PMID:34918187 SUPPORT Human Clinical

"Another human neurodegenerative disease, linked to dTTP metabolism and caused by pathogenic variants in CAD"

The primary paper names the CAD disorder as the comparator within the same metabolic pathway.

TYMP-related mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) Not Yet Curated MONDO:0011283

Overlapping Features The third dTTP-pathway disorder named by the primary paper, caused by biallelic TYMP variants (HGNC:3148, verified by OAK on MONDO:0011283). Thymidine phosphorylase loss causes thymidine and dTTP to ACCUMULATE, which produces a dNTP pool imbalance and mtDNA depletion. This is the mirror image of DTYMK deficiency, where dTTP is depleted.

Distinguishing Features

Molecular: TYMP (HGNC:3148, MONDO:0011283) versus DTYMK (HGNC:3061, MONDO:0859241).
Direction of the metabolic lesion: thymidine and dTTP accumulate in MNGIE and are depleted in DTYMK deficiency, so plasma thymidine and deoxyuridine are diagnostically elevated in MNGIE and are not a feature here.
Clinical: MNGIE is a multisystem disorder dominated by gastrointestinal dysmotility, cachexia, ptosis and ophthalmoplegia, peripheral neuropathy and leukoencephalopathy, typically with onset in the second or third decade. DTYMK deficiency is an infantile brain-restricted degeneration with no gastrointestinal or neuromuscular signature reported.

Show evidence (2 references)

PMID:34918187 SUPPORT Human Clinical

"Thymidine phosphorylase (TP) deficiency causes MNGIE"

The primary paper names MNGIE as the thymidine-pathway comparator.

PMID:34918187 SUPPORT Human Clinical

"When accumulation of dTTP occurs, dNTP pool imbalance is promoted, leading to mtDNA depletion"

States the accumulation-driven mechanism of MNGIE, which is the opposite of the depletion-driven mechanism curated for DTYMK deficiency.

Autosomal recessive primary microcephaly (MCPH) MONDO:0016660

Overlapping Features The differential that the disease name itself is built to exclude. Both are autosomal recessive, both present with severe microcephaly and profound developmental impairment in a consanguineous family, and both will be referred for exome sequencing on that basis. MCPH is a neurodevelopmental disorder in which the brain is small from the outset because too few neurons were generated; DTYMK deficiency is a neurodegenerative disorder in which a near-normal head circumference at birth is followed by destruction of brain already built.

Distinguishing Features

Timing: MCPH is primary or congenital microcephaly, present at birth by definition. In DTYMK deficiency head circumference is at or near the normal range at birth and then falls away from the centiles, reaching minus 7.6 SD at 9 months in individual I and minus 7.4 SD at 26 months in individual II (see the Progressive Microcephaly phenotype, where those figures are evidenced). This is the single most discriminating feature and is why the disorder is named for PROGRESSIVE microcephaly.
Trajectory: MCPH is classified as a neurodevelopmental disorder, not a degenerative one. DTYMK deficiency is degenerative - progressive neurodevelopmental regression is documented in the fifth reported case (PMID:40696808) and both individuals with reported outcomes died in early childhood. Note the honest limit here: in the two individuals of PMID:34918187 no milestone was ever gained, so regression could not be observed in them; the degenerative character in those two rests on serial imaging and on autopsy, not on skill loss. See the Developmental Regression phenotype, which records the same limitation.
Imaging: what separates the two is SERIAL imaging, not a single scan. DTYMK deficiency shows a near-normal or only mildly abnormal neonatal scan followed within months by severe hemispheric and basal ganglia atrophy with ventricular and subarachnoid enlargement (see the brain-MRI diagnosis entry). A single small-brain scan in a microcephalic infant does not discriminate; two scans months apart do. No cached reference in this entry describes MCPH imaging, so no positive imaging claim is made about MCPH here.
Molecular: MCPH is caused by variants in centrosomal and mitotic-spindle genes such as ASPM, WDR62 and MCPH1 (MONDO:0016660), whereas DTYMK deficiency is a nucleotide-biosynthesis defect (MONDO:0859241).

Show evidence (2 references)

PMID:35111754 SUPPORT Other

"Autosomal recessive primary microcephaly (MCPH) is the prototype of isolated primary (congenital) microcephaly, affecting predominantly the cerebral cortex."

Establishes that MCPH is congenital microcephaly, which is the axis on which it separates from a disorder whose head circumference is near normal at birth. Tagged OTHER because the source is a narrative review rather than a primary human observation.

PMID:35111754 SUPPORT Other

"MCPH is a group of rare heterogeneous neurodevelopmental disorders characterized by intellectual disability"

Classifies MCPH as neurodevelopmental rather than neurodegenerative, the second half of the contrast.

🔬

Clinical Trials

1

NCT04802707 PHASE_II

Open-label, monocentre, single-arm phase II study of combination oral deoxycytidine and deoxythymidine in children aged 0-18 years with mitochondrial DNA depletion syndrome. DTYMK is named in the eligible-genotype list alongside POLG, POLG2, C10orf2, RRM2B, MPV17, SUCLA2, SUCLG1 and FBXL4. This is the only interventional study anywhere that names DTYMK. No result specific to a DTYMK-mutant participant has been published and no DTYMK patient is known to have been enrolled.

Target Phenotypes: Absent neurodevelopmental progress HP:0001263

Show evidence (2 references)

clinicaltrials:NCT04802707 PARTIAL Human Clinical

"The subjects included are children (0-18Y), with positive MDS diagnosis and express mutations in one of the following genes: POLG, POLG2, C10orf2, RRM2B, MPV17, SUCLA2, SUCLG1, FBXL4, DTYMK."

Documents DTYMK as an eligible genotype. PARTIAL because eligibility is not efficacy, and because the trial's mitochondrial rationale is itself contested for this gene.

clinicaltrials:NCT04802707 SUPPORT Human Clinical

"In this phase II Trial a mix of Deoxynucleosides Pyrimidine (Deoxycytidine dC and Deoxythymidine dT) will be used as early treatment of MDS."

States the intervention and the phase.

{ }

Source YAML

click to show

name: DTYMK-Related Neurodegeneration
creation_date: "2026-08-01T00:00:00Z"
category: Mendelian
description: >-
  Childhood-onset neurodegeneration with progressive microcephaly (CONPM,
  MIM 619847) is an ultra-rare autosomal recessive disorder caused by biallelic
  variants in DTYMK, which encodes deoxythymidylate kinase (dTMPK, also called
  thymidylate kinase or TMPK). dTMPK catalyses the phosphorylation of dTMP to
  dTDP, the penultimate step in dTTP biosynthesis and the single point at which
  the de novo and salvage routes to dTTP converge, which makes the enzyme the
  bottleneck of the whole pathway. Affected children are born without
  malformations and with a head circumference in or near the normal range, then
  fail to make any developmental progress, develop severe and progressively
  worsening microcephaly, seizures, growth failure and a movement disorder that
  evolves from neonatal hypotonia to spasticity, and show dramatic postnatal
  atrophy of the cerebral hemispheres and basal ganglia while the brainstem is
  relatively spared. Death has occurred in the second or third year of life in
  the individuals with reported outcomes. The proximate mechanism is restriction
  of the dTTP pool available for nuclear DNA replication and repair, with
  consequent impaired DNA replication, elevated ribonucleotide misincorporation
  into genomic DNA, an abnormal DNA damage response, and apoptotic loss of
  neurons and oligodendrocytes.
notes: >-
  Named-entity-confusion guardrail. This entry is anchored strictly on
  MONDO:0859241 / OMIM:619847 / DTYMK (HGNC:3061). The anchor was confirmed
  before any curation by running `uv run runoak -i sqlite:obo:mondo relationships
  --direction up MONDO:0859241` and reading the returned line
  `MONDO:0859241 RO:0004003 HGNC:3061 ... DTYMK`, and by
  `uv run runoak -i sqlite:obo:mondo mappings MONDO:0859241`, which returns
  OMIM:619847, UMLS:C5676972, MEDGEN:1801540 and GARD:0027309 and no ORPHA code.
  Every DTYMK-disease source cited here names DTYMK or its zebrafish orthologue
  `dtymk` in its title. There is one deliberate exception, added on review:
  PMID:35111754, an autosomal-recessive-primary-microcephaly review, is cited
  ONLY in the MCPH differential-diagnosis entry and only for statements about
  MCPH. It makes no claim about DTYMK and is not evidence for anything in this
  entry other than the comparator.

  The dominant confusable literature for this gene is oncology, not another
  Mendelian disorder. A PubMed search for `DTYMK[tiab] OR dTMPK[tiab] OR
  "thymidylate kinase"[tiab]` run on 2026-08-01 returns a set in which the great
  majority of recent records are cancer-biology or antimicrobial
  drug-design papers in which DTYMK is OVEREXPRESSED and its INHIBITION is the
  proposed therapy - the mechanistic opposite of this recessive
  loss-of-function disorder. None of those papers is cited here, and no
  DTYMK inhibitor is curated as a treatment. Restricting that search to
  clinical terms and reading the titles leaves only four papers that concern
  human DTYMK disease or its animal model: PMID:31271740, PMID:34918187,
  PMID:35346037 and PMID:40696808. All four are cited. To the best of this
  search, that is the entire disease literature.

  Contrast entities were each verified with OAK rather than typed from memory.
  Aicardi-Goutieres syndrome is MONDO:0018866 (label confirmed by
  `runoak -i sqlite:obo:mondo relationships --direction up MONDO:0018866`, which
  also shows it is a type 1 interferonopathy of childhood and a leukodystrophy).
  The MNGIE differential is bound to MONDO:0011283 `mitochondrial DNA depletion
  syndrome 1`, whose OAK relationships include `RO:0004003 HGNC:3148 ! TYMP`;
  the parent grouping term MONDO:0017575 carries no gene relation, so the
  gene-bearing child term was used. The CAD differential is bound to
  MONDO:0014647 `developmental and epileptic encephalopathy, 50`, whose OAK
  relationships include `RO:0004003 HGNC:1424 ! CAD`. The entry's own MONDO
  superclass, MONDO:0024237 `inherited neurodegenerative disorder`, is
  deliberately NOT listed as a differential.

  Onset discipline. The disease label says "childhood-onset", but the HPO
  CHILDHOOD onset category (HP:0011463) is bounded at 1 to 5 years and the
  reported ages do not fit it. In PMID:34918187 individual I was hypotonic at
  birth, needed nasogastric feeding from day 3, and had seizures at 6 months;
  individual II had a head noted to be small at birth and no visual tracking in
  the first months of life. Structured onset is therefore recorded as INFANTILE
  where a first-year age is documented, and the disease-name mismatch is called
  out rather than propagated. The one individual who does fit a childhood-onset
  description is the 2-year-old in PMID:40696808, and only because that is the
  age at ascertainment, not the age at onset.

  Frequency discipline. Only five affected individuals have been published: two
  siblings in PMID:31271740, two unrelated children in PMID:34918187, and one
  child in PMID:40696808 (which states its case is the fifth reported). Bands
  are asserted only for features documented in every individual for whom the
  feature is reported, and every band carries its explicit numerator and
  denominator in the phenotype's `notes:`. Where the denominator is a subset
  (for example only the three individuals with published neuroimaging), that
  subset is named. Features seen in a single individual - the anaemia and raised
  transaminases, the micropenis and undescended testes - carry no band at all,
  because 1 of 5 on a total series of five is not a frequency estimate.

  GeneReviews. No GeneReviews chapter exists. Three PubMed E-utilities searches
  were run on 2026-08-01 and all three returned zero results: `DTYMK
  GeneReviews[All Fields]`, `thymidylate kinase GeneReviews[All Fields]` and
  `childhood-onset neurodegeneration with progressive microcephaly
  GeneReviews[All Fields]`.

  Structured sources unavailable, and in this case also absent upstream. Two
  things were checked rather than assumed. (1) Orphanet: EBI OLS4 searches of
  ORDO for `DTYMK` and for `childhood-onset neurodegeneration with progressive
  microcephaly` were run on 2026-08-01 and both returned `numFound: 0`, and
  MONDO:0859241 itself carries no ORPHA cross-reference. There is therefore no
  ORPHA code to cite, not merely an uncachable one. Independently,
  `data/orphadata/` in this working tree contains only a MANIFEST.yaml stub with
  no bulk data and the sha256 refresh is a known blocker (#7234, #7539, #7199,
  #7522), so no ORPHA record could have been generated regardless. (2) ClinGen:
  `data/clingen/` likewise contains only a MANIFEST.yaml stub, and a request to
  `https://search.clinicalgenome.org/api/curations/gene/DTYMK` on 2026-08-01
  returned an HTML page rather than a curation record, so no ClinGen
  gene-disease validity, dosage or actionability assertion could be retrieved or
  cited. The gene-disease relationship is supported here entirely by primary
  literature. This is a genuine gap, not a claim that no ClinGen curation exists.

  Full text versus abstract. PMID:34918187 and PMID:35346037 are cached as
  open-access full text, so several snippets in this entry are taken from their
  bodies (the clinical descriptions of individuals I and II, Table 1 rows, the
  enzyme-activity and EdU results, and the discussion paragraphs on
  Aicardi-Goutieres syndrome, MNGIE and DEE50) rather than from their abstracts.
  Snippets from PMID:31271740, PMID:34926941, PMID:38621447 and PMID:40696808
  are abstract-only, because those are abstract-only caches; the full-text
  fetch for PMID:34926941 and PMID:38621447 returned HTTP 403. A few snippets
  from the PMID:34918187 full text begin or end mid-word, because the cached
  PDF extraction hyphenates across line breaks; those are quoted exactly as
  cached and the truncation is flagged in the relevant explanation rather than
  silently repaired.

  Deep research provenance. `just research-disorder claude_code
  DTYMK-Related_Neurodegeneration` was run on 2026-08-01 (928 seconds, 5 web
  searches, 61 turns, 21 citations, models claude-haiku-4-5 and
  claude-opus-5[1m]); the report is at
  research/DTYMK-Related_Neurodegeneration-deep-research-claude_code.md. Its NEC
  profile was checked before use: DTYMK occurs 102 times with word-boundary
  matching against a next-highest of 5 (TK2), and every hit read in context
  refers to the gene. Three of the report's findings materially corrected an
  earlier draft of this entry and are worth naming, because each was an error
  the draft would have shipped. (1) The draft marked the dTTP chemical as
  DECREASED; the report pointed to a full-text passage showing measured dTTP
  levels are NORMAL, so the node was reframed as a block of flux. (2) The draft
  marked the mtDNA-depletion hypothesis DEPRECATED; the report surfaced
  PMID:34926941, which shows mitochondrial TMPK activity loss is complete, so
  the status was corrected to ALTERNATIVE. (3) The draft asserted in a treatment
  note that no source proposes nucleoside supplementation; the report identified
  clinicaltrials:NCT04802707, which lists DTYMK as an eligible genotype, so that
  false-absence claim was removed and the trial is now curated with its
  mechanistic caveat.

  Report content deliberately NOT curated. The report states elevated lactate
  (2/2) and hyperalaninemia (1/2) in the PMID:31271740 siblings, and gives
  prenatal details (breech presentation, small for gestational age) and a
  laryngomalacia mention. None of these appears in any cached reference
  available here, so none is curated. It also proposes a specific variant
  pairing for the PMID:31271740 siblings and a ClinVar coordinate for the
  frameshift allele; both are flagged in the report itself as requiring
  verification against a full text that was not obtained, and both are recorded
  in this entry as explicitly uncurated inferences rather than as facts. Kinetic
  constants from Table 2 of PMID:34926941 are not curated because only the
  abstract is cached. The report's suggested gnomAD constraint metrics were not
  retrievable in its own session and are not asserted here.

  Review response (PR #7783, 2026-08-01). Changes made in response to review, so
  the record shows what moved and what did not. (1) The single bundled
  "Supportive and symptomatic management" treatment was split into five atomic
  entries - the umbrella, anti-seizure pharmacotherapy, nasogastric tube
  feeding, blood transfusion and genetic counselling - and every one now carries
  an NCIT `treatment_term` verified with OAK and confirmed reachable from
  NCIT:C25218, with CHEBI therapeutic agents on the two drug entries. (2) The
  visual-impairment phenotype was retermed from HP:0000505 to HP:0100704
  Cerebral visual impairment, which is what the existing snippets actually
  support. (3) A `biochemical:` section now carries the fibroblast dTMPK numbers
  and the diagnostically load-bearing NORMAL metabolic screen; a
  `histopathology:` section carries the autopsy findings including the sparing
  pattern; a `clinical_trials:` entry makes NCT04802707 queryable as a trial.
  (4) An MCPH differential was added. (5) Three evidence classifications were
  corrected: the zebrafish paper's background sentence about human microcephaly
  is now OTHER rather than HUMAN_CLINICAL; the normal-dTTP measurement on the
  flux node is now PARTIAL rather than REFUTE, because it refutes pool depletion
  and the node claims a flux block; and an explanation that said the causal link
  was "curated as PROBABLE" - a value that is not in the enum - was rewritten to
  name the actual value.

  Declined on review, with reasons. No "multidisciplinary supportive/palliative
  care" treatment entry was created: literal case-insensitive searches for
  `supportiv`, `palliat`, `symptomatic`, `multidisciplinary`, `no cure`, `no
  specific`, `no effective` and `no disease-modif` across the four cached
  disease references on 2026-08-01 returned zero hits, so there is no quotable
  basis for one, and inventing it would be exactly the unsourced padding this
  entry has otherwise avoided. Nutritional-support and deoxynucleoside entries
  were NOT bound to NCIT:C15433 Nutritional Support as the research artefact
  suggested: NCIT:C93322 Enteral Tube Feeding is more specific and matches the
  quoted route, and the deoxynucleoside trial is pharmacotherapy rather than
  nutrition. No frequency band was added anywhere in the new sections;
  neuropathology exists for one of five individuals and the enzyme assay for one
  family, so no denominator supports a band.
disease_term:
  preferred_term: childhood-onset neurodegeneration with progressive microcephaly
  term:
    id: MONDO:0859241
    label: neurodegeneration, childhood-onset, with progressive microcephaly
parents:
- Inherited Neurodegenerative Disorder
- Inborn Error of Pyrimidine Metabolism
synonyms:
- CONPM
- childhood-onset neurodegeneration with progressive microcephaly
- DTYMK deficiency
- deoxythymidylate kinase deficiency
- thymidylate kinase (dTMPK) deficiency
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    notes: >-
      The clinical burden is almost entirely neurological: progressive
      microcephaly, absent neurodevelopment, seizures, spasticity and
      radiologically and pathologically confirmed cerebral and basal ganglia
      atrophy.
    evidence:
    - reference: PMID:40696808
      reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This ultra-rare condition is characterized by progressive neurological
        regression, epilepsy, severe microcephaly, and global cerebral atrophy.
      explanation: >-
        States in one sentence that the defining features of the disorder are
        neurological, supporting a neurologic chapter assignment.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    notes: >-
      A monogenic autosomal recessive Mendelian disorder identified and
      diagnosed by exome sequencing.
    evidence:
    - reference: PMID:40696808
      reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Childhood-onset neurodegeneration with progressive microcephaly (CONPM)
        is a rare autosomal recessive disorder caused by pathogenic variants in
        the DTYMK gene.
      explanation: >-
        Names the entity, its autosomal recessive Mendelian basis and its causal
        gene in a single sentence.
  icimd_category:
  - classification_value: pyrimidine_metabolism
    notes: >-
      dTMP and dTTP are pyrimidine deoxynucleotides, and dTMPK acts on the dTMP
      to dTDP step, so the defect sits in pyrimidine nucleotide metabolism. This
      matches the way MONDO classifies the two other dTTP-pathway disorders that
      PMID:34918187 uses as comparators: both MONDO:0011283 (TYMP, MNGIE) and
      MONDO:0014647 (CAD, DEE50) are subclasses of MONDO:0019238 `inborn
      disorder of pyrimidine metabolism`. MONDO:0859241 itself is not currently
      placed under that grouping term, so this classification is a curatorial
      judgement rather than an inherited MONDO assertion.
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This makes dTMPK the bottleneck for dTTP biosynthesis
      explanation: >-
        Places the enzymatic defect squarely in the biosynthesis of a pyrimidine
        deoxynucleotide triphosphate.
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Disease requires two damaging DTYMK alleles. Of the three published
    families, one is a consanguineous Egyptian family with a homozygous
    missense allele, one is a non-consanguineous Dutch family with compound
    heterozygous missense alleles, and one is a Hong Kong family with two
    variants in trans; the fifth reported individual is homozygous. Carrier
    parents are clinically unaffected but have measurably reduced dTMPK
    activity in fibroblasts. Recurrence risk for siblings of a proband is 25
    percent, and carrier testing plus genetic counselling are indicated for
    at-risk relatives.
  evidence:
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Childhood-onset neurodegeneration with progressive microcephaly (CONPM) is
      a rare autosomal recessive disorder caused by pathogenic variants in the
      DTYMK gene.
    explanation: >-
      States the autosomal recessive mode of inheritance for the entity.
  - reference: PMID:31271740
    reference_title: "Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      have been diagnosed to harbor two heterozygous variants in trans in the
      DTYMK gene of the thymidine biosynthesis pathway
    explanation: >-
      Documents the biallelic (two variants in trans) requirement in the first
      reported family.
prevalence:
- population: Worldwide reported literature
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population-based prevalence study exists and no Orphanet prevalence class
    is available to adopt, because no ORPHA entity for this disorder exists (EBI
    OLS4 ORDO searches for `DTYMK` and for the disease name both returned
    numFound 0 on 2026-08-01, and MONDO:0859241 carries no ORPHA
    cross-reference). The published case count is therefore the only defensible
    measure. PMID:40696808, published in 2025, states that only four cases had
    been reported before its own, which it describes as the fifth. Those four
    resolve to the two siblings of PMID:31271740 and the two unrelated children
    of PMID:34918187, giving a cumulative published total of five individuals
    worldwide. That count places the disorder in the ultra-rare tier. Note that
    the five-case total is the arithmetic of adding the earlier series to the
    2025 report; the number five is stated by PMID:40696808, but the
    attribution of the earlier four to those two specific papers is a curatorial
    reconciliation, not a statement read off that paper.
  evidence:
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Only four cases have been reported in the literature to date.
    explanation: >-
      Gives the published worldwide case count immediately before this paper's
      own case, supporting an ultra-rare classification based on cases in the
      literature.
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This paper's objective is to describe the fifth globally reported case of
      CONPM and the first documented in a Mexican patient
    explanation: >-
      Establishes the cumulative total of five published individuals and the
      paper's own position in that series.
pathophysiology:
- name: Biallelic Damaging DTYMK Variants
  biological_scale: MOLECULAR
  description: >-
    The disorder is initiated by inheritance of two damaging DTYMK alleles. The
    published allelic spectrum is entirely missense: p.Pro81Leu (recurrent, seen
    homozygously in an Egyptian family and in a Mexican family and in trans in a
    Dutch family) and p.Asp128Asn. Neither residue lies in a named functional
    domain of dTMPK, yet fibroblasts from a compound heterozygote have almost no
    measurable enzyme activity, so these alleles behave functionally as severe
    hypomorphs or nulls.
  genes:
  - preferred_term: DTYMK
    term:
      id: hgnc:3061
      label: DTYMK
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we describe two unrelated children with bi-allelic variants in
      DTYMK, encoding dTMPK, which catalyzes the penultimate step in dTTP
      biosynthesis.
    explanation: >-
      Establishes biallelic DTYMK alleles as the initiating lesion and names the
      enzymatic step affected.
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genetic analysis identified a homozygous missense variant in DTYMK
      (NM_012145.4:c.242C>T; p.Pro81Leu).
    explanation: >-
      Independent replication of the same recurrent missense allele in a third
      unrelated family.
  downstream:
  - target: Loss of dTMPK Homodimerization
    description: >-
      The missense substitutions destabilise the obligate homodimer.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34926941
      reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        In contrast, all mutants were present as monomers with dramatically
        reduced substrate binding affinity and catalytic efficiencies.
      explanation: >-
        Establishes the specific structural mechanism by which the patient
        alleles inactivate the enzyme.
  - target: Loss of dTMP Kinase Catalytic Activity
    description: >-
      The patient alleles leave the cell with almost no dTMP kinase activity.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        In cells of affected individuals, dTMPK enzyme activity was minimal,
        along with impaired DNA replication.
      explanation: >-
        Directly links the patient genotype to loss of the enzyme activity in
        patient-derived cells.
- name: Loss of dTMPK Homodimerization
  biological_scale: MOLECULAR
  description: >-
    Wild-type dTMPK works as a homodimer. None of the substituted residues
    contacts the substrate directly; instead each substitution destabilises the
    dimer, so the purified mutant proteins run as monomers with drastically
    reduced substrate affinity and catalytic efficiency. The mechanism of
    inactivation is therefore structural rather than active-site, which is why
    in silico substrate-contact reasoning called two of these alleles tolerated.
  genes:
  - preferred_term: DTYMK
    term:
      id: hgnc:3061
      label: DTYMK
  molecular_functions:
  - preferred_term: protein homodimerization activity
    term:
      id: GO:0042803
      label: protein homodimerization activity
    modifier: DECREASED
  evidence:
  - reference: PMID:34926941
    reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The wild-type TMPK mainly exists as a dimer with high substrate binding
      affinity
    explanation: >-
      Establishes that the functional form of the enzyme is a dimer, which is
      what the disease alleles disrupt.
  - reference: PMID:34926941
    reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Based on the human TMPK structure, none of the mutated amino acids
      interacted directly with the substrates.
    explanation: >-
      Confirms the substitutions act structurally rather than by blocking
      substrate binding, which is the distinguishing feature of this mechanism.
  downstream:
  - target: Loss of dTMP Kinase Catalytic Activity
    description: >-
      Monomeric dTMPK is catalytically crippled.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34926941
      reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        TMPK mutations identified in patients represent loss of function
        mutations
      explanation: >-
        The authors' summary of the functional consequence of the dimerization
        defect.
- name: Loss of dTMP Kinase Catalytic Activity
  biological_scale: MOLECULAR
  description: >-
    dTMPK phosphorylates dTMP to dTDP. Because the de novo route (dUMP to dTMP
    via thymidylate synthase) and the salvage route (thymidine to dTMP via
    thymidine kinase) both converge on dTMP, dTMPK is the single obligatory
    enzyme downstream of that convergence and is therefore the bottleneck for
    the entire dTTP supply. In fibroblasts of the compound heterozygous
    individual, activity was 0.62 pmol/min/mg protein against 43.65 and 31.08 in
    the heterozygous mother and father respectively. The loss is not uniform
    across compartments: in patient fibroblasts carrying P81L and D128N,
    mitochondrial TMPK activity was completely absent while cytosolic activity
    was extremely low and unstable. That compartment asymmetry is the strongest
    remaining argument for a mitochondrial contribution to the phenotype.
  genes:
  - preferred_term: DTYMK
    term:
      id: hgnc:3061
      label: DTYMK
  molecular_functions:
  - preferred_term: dTMP kinase activity
    term:
      id: GO:0004798
      label: dTMP kinase activity
    modifier: DECREASED
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This makes dTMPK the bottleneck for dTTP biosynthesis
    explanation: >-
      States why loss of this one enzyme cannot be bypassed by the alternative
      pathway.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      dTMPK enzyme activity of the individual is significantly lower than those
      of the parents
    explanation: >-
      Quantifies the enzymatic deficit in patient fibroblasts against
      heterozygous parental controls.
  - reference: PMID:34926941
    reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      the P81L and D128N mutations led to a complete loss of TMPK activity in
      mitochondria and extremely low and unstable TMPK activity in cytosol
    explanation: >-
      Establishes the compartment asymmetry of the enzymatic loss in patient
      fibroblasts: total in mitochondria, near-total in cytosol.
  - reference: PMID:35346037
    reference_title: "Differential expression of enzymes in thymidylate biosynthesis in zebrafish at different developmental stages: implications for dtymk mutation-caused neurodegenerative disorders."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: >-
      TMPK and TK activities are prominent in the cytosol of embryos, larvae and
      adult fish and brain contains the highest TMPK activity.
    explanation: >-
      In zebrafish, brain carries the highest tissue level of this enzyme
      activity. This is curated as PARTIAL rather than SUPPORT because
      PMID:34918187 argues the opposite for human, stating that a restricted
      expression pattern of DTYMK is unlikely to explain the brain selectivity
      since DTYMK is expressed in all human tissues. The two statements are not
      strictly contradictory - highest activity is not the same as restricted
      expression, and one is fish and one is human - but the human paper's
      position should govern, so this is not used to assert a
      tissue-expression explanation for the human phenotype.
  downstream:
  - target: Block of Canonical dTTP Biosynthetic Flux
    description: >-
      With the bottleneck enzyme inactive, neither the de novo nor the salvage
      route can deliver dTTP.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        since the metabolic pathway for dTTP synthesis is completely blocked
      explanation: >-
        States that the consequence of the enzyme defect is a complete block of
        the dTTP biosynthetic pathway.
- name: Block of Canonical dTTP Biosynthetic Flux
  biological_scale: MOLECULAR
  description: >-
    dTTP is one of the four building blocks of DNA, and the canonical route to
    it is completely blocked. Crucially, this is a defect of FLUX, not a
    demonstrated depletion of the steady-state pool: measured dTTP nucleotide
    levels in patient fibroblasts and in mutant zebrafish resembled normal
    controls. The disorder is therefore best modelled as a demand-limited and
    possibly compartment-limited supply failure that manifests in cells with
    high replicative and repair demand, rather than as bulk pool depletion.
  biological_processes:
  - preferred_term: dTTP biosynthetic process
    term:
      id: GO:0006235
      label: dTTP biosynthetic process
    modifier: DECREASED
  chemical_entities:
  - preferred_term: dTTP
    term:
      id: CHEBI:18077
      label: dTTP
  notes: >-
    The dTTP chemical is deliberately listed WITHOUT a DECREASED modifier. An
    earlier draft of this entry marked it DECREASED, which the sources do not
    support: PMID:34918187 reports that dTTP nucleotide levels in both the
    fibroblast and zebrafish models resemble those of normal controls. Only the
    biosynthetic PROCESS carries a DECREASED modifier. The practical corollary
    is that a normal dNTP panel on fibroblasts does not exclude this diagnosis.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study shows that impairment of the biosynthesis of one of the
      building blocks of DNA, dTTP, causes a severe, early-onset
      neurodegenerative disease.
    explanation: >-
      Names the restricted metabolite and asserts the causal link from its
      shortage to the disease.
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      This variant is predicted to disrupt dTMP phosphorylation, a key step in
      the maintenance of dTTP pools required for genomic stability and neural
      function.
    explanation: >-
      Independent report framing the same mechanism, although as a prediction
      rather than a measurement, which is why this item is classified as
      computational.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: >-
      dTTP nucleotide levels resemble those of normal controls
    explanation: >-
      Measured steady-state dTTP was normal in both patient fibroblasts and
      mutant zebrafish. Curated as PARTIAL rather than REFUTE: what this
      measurement refutes is POOL depletion, which is not what this node claims.
      The node deliberately claims a block of FLUX, and a normal steady-state
      pool is compatible with reduced flux through the canonical route. The item
      is kept attached here because it constrains the node's meaning and is the
      reason the node is named for flux rather than for a restricted pool, but
      it neither confirms nor contradicts the flux claim itself.
  downstream:
  - target: Impaired DNA Replication and Reduced Cell Proliferation
    description: >-
      An inadequate dTTP supply stalls S-phase.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        These results show that DNA replication is impaired in fibroblasts of
        affected individuals.
      explanation: >-
        Direct experimental demonstration in patient cells that the metabolic
        block translates into a replication defect.
  - target: Elevated Ribonucleotide Incorporation into Genomic DNA
    description: >-
      Deoxynucleotide pool imbalance drives the replication machinery to
      misincorporate ribonucleotides in place of the scarce deoxynucleotide.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        An increase of ribonucleotide incorporation in the genome as well as
        impaired responses to DNA damage were observed in dtymk mutant
        zebrafish, providing novel pathophysiological insights.
      explanation: >-
        Establishes ribonucleotide misincorporation as a measured consequence of
        the metabolic block, in the animal model.
- name: Impaired DNA Replication and Reduced Cell Proliferation
  biological_scale: CELLULAR
  description: >-
    Patient fibroblasts show a collapse in the S-phase fraction, from about 24
    percent and 16 percent in the heterozygous mother and father to 2.8 percent
    in the affected individual. In dtymk mutant zebrafish the number of
    proliferating cells in the forebrain, the structure homologous to the human
    cerebral cortex, is significantly reduced.
  biological_processes:
  - preferred_term: DNA replication
    term:
      id: GO:0006260
      label: DNA replication
    modifier: DECREASED
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In contrast, the fraction of S-phase cells in individual I fibroblasts was
      only 2.8%.
    explanation: >-
      Quantifies the replication defect in patient-derived cells against
      parental controls measured in the same experiment.
  downstream:
  - target: Apoptotic Loss of Neurons and Oligodendrocytes
    description: >-
      Cells that cannot complete replication or repair are removed by apoptosis.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        have significantly more apoptotic cells in the forebrain
      explanation: >-
        TUNEL quantification in dtymk mutant zebrafish forebrain links the
        proliferative defect to apoptotic cell death in the affected structure.
- name: Elevated Ribonucleotide Incorporation into Genomic DNA
  biological_scale: MOLECULAR
  description: >-
    Genomic DNA from dtymk mutant zebrafish is markedly more sensitive to
    alkaline hydrolysis, indicating elevated ribonucleotide content, and behaves
    on alkaline gels like DNA from Rnaseh2-null mice, the canonical
    ribonucleotide-excision-repair-deficient model. Ribonucleotides in DNA carry
    a reactive 2'-hydroxyl, which makes the backbone fragile.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      An increase of ribonucleotide incorporation in the genome as well as
      impaired responses to DNA damage were observed in dtymk mutant zebrafish,
      providing novel pathophysiological insights.
    explanation: >-
      The primary observation of ribonucleotide misincorporation and abnormal
      DNA damage signalling in the model.
  downstream:
  - target: Genome Instability and Abnormal DNA Damage Response
    description: >-
      Ribonucleotides in the genome make DNA fragile and provoke a persistent
      DNA damage response.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        An increase of ribonucleotide incorporation in the genome as well as
        impaired responses to DNA damage were observed in dtymk mutant
        zebrafish
      explanation: >-
        Couples the two observations in one sentence: ribonucleotide
        misincorporation and an impaired DNA damage response occur together in
        the model. The authors elsewhere state the causal direction more
        strongly, but that sentence is broken across a line-break hyphen in the
        cached PDF extraction and is not quotable verbatim, so the weaker
        co-occurrence statement is used here instead.
- name: Genome Instability and Abnormal DNA Damage Response
  biological_scale: MOLECULAR
  description: >-
    dtymk mutant zebrafish irradiated with UV retain high levels of gammaH2AX
    24 hours later, consistent with unrepaired DNA breaks. Essentially every DNA
    repair pathway involves repair-associated DNA synthesis, which the dTTP
    shortage also constrains.
  biological_processes:
  - preferred_term: DNA repair
    term:
      id: GO:0006281
      label: DNA repair
    modifier: DECREASED
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The effects of DTYMK deficiency on the process of DNA damage signaling
      was evaluated in vivo.
    explanation: >-
      Establishes that DNA damage signalling was directly assayed in vivo in the
      dtymk model, which is the experiment underpinning this node. The authors'
      one-sentence conclusion from that experiment is split across an
      interposed figure caption in the cached PDF extraction and cannot be
      quoted contiguously, so the setup sentence is quoted and the result is
      stated in this node's description instead.
  downstream:
  - target: Apoptotic Loss of Neurons and Oligodendrocytes
    description: >-
      Unrepaired genomic damage in post-mitotic and differentiating neural cells
      triggers apoptosis.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        we identified loss-of-function of DTYMK as the cause of a severe
        postnatal neurodegenerative disease and highlight the essential nature
        of dTTP synthesis in the maintenance of genome stability and neuronal
        survival
      explanation: >-
        The authors' summary statement linking genome stability to neuronal
        survival. The link is curated as INDIRECT_UNKNOWN_INTERMEDIATES rather
        than DIRECT because no experiment in either paper shows that blocking
        the damage response rescues the neurons, so the intervening steps
        between damage signalling and cell death are not identified here.
- name: Apoptotic Loss of Neurons and Oligodendrocytes
  biological_scale: CELLULAR
  description: >-
    Post-mortem neuropathology in individual I showed massive neuronal dropout
    across essentially the whole brain, astrogliosis, loss of oligodendrocytes
    with caspase-3-positive apoptotic profiles, ameboid microglial activation and
    a paucity of myelin, together with neuronal loss in the granular and Purkinje
    cell layers of a cerebellum that had looked normal on MRI. dtymk mutant
    zebrafish show the same signature of neuronal apoptosis.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
    modifier: DECREASED
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
    modifier: DECREASED
  - preferred_term: astrocyte
    term:
      id: CL:0000127
      label: astrocyte
    modifier: INCREASED
  - preferred_term: microglial cell
    term:
      id: CL:0000129
      label: microglial cell
    modifier: INCREASED
  biological_processes:
  - preferred_term: apoptotic process
    term:
      id: GO:0006915
      label: apoptotic process
    modifier: INCREASED
  notes: >-
    The astrocyte and microglial modifiers are INCREASED because the pathology
    describes reactive astrogliosis and massive ameboid microglial activation,
    that is a reactive increase, not a primary proliferation defect in those
    lineages. Only the neuron and oligodendrocyte populations are lost.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain pathology confirmed massive neuronal dropout in virtually the entire
      brain, sparing the brain stem.
    explanation: >-
      Human autopsy evidence of the cellular lesion and its anatomical
      distribution.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      implicate neuronal apoptosis as one of the hallmarks of this disease.
    explanation: >-
      The authors' conclusion, drawn jointly from the human autopsy and the
      zebrafish model, that apoptosis is the mode of neuronal loss.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In addition, we generated dtymk mutant zebrafish that replicate this
      phenotype of microcephaly, neuronal cell death and early lethality.
    explanation: >-
      Cross-species replication of the neuronal death phenotype.
  downstream:
  - target: Progressive Postnatal Cerebral and Basal Ganglia Atrophy
    description: >-
      Cumulative loss of neurons and oligodendrocytes produces the shrinking
      brain seen on serial imaging.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Brain imaging revealed severe cerebral atrophy and disappearance of the
        basal ganglia.
      explanation: >-
        The imaging counterpart of the cellular loss documented at autopsy.
- name: Progressive Postnatal Cerebral and Basal Ganglia Atrophy
  biological_scale: TISSUE
  description: >-
    The structural lesion is postnatal and progressive rather than a
    malformation. Individual I had a near-normal fetal head circumference and
    only slight underdevelopment of the caudate and frontal cortex at three
    weeks, then dramatic hemispheric atrophy with ventricular enlargement by six
    months. The thalamus, brainstem and cerebellum look normal on MRI even when
    the hemispheres and basal ganglia are devastated, although microscopy shows
    the cerebellum is not truly spared.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      growth retardation, puffy body, seizures, failure to reach developmental
      milestones, microcephaly and severe, progressive atrophy of the cerebral
      hemispheres and basal ganglia
    explanation: >-
      Lists the features that emerged postnatally in both individuals, including
      the progressive nature of the atrophy.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      as well as the cerebral atrophy that only sets in postnatally
    explanation: >-
      States explicitly that the atrophy is postnatal, which is what makes this a
      neurodegenerative rather than a malformative disorder.
phenotypes:
- name: Progressive Microcephaly
  category: Neurologic
  description: >-
    Head circumference is at or near the normal range at birth and then falls
    away from the centiles, reaching minus 7.6 SD at 9 months in individual I
    and minus 7.4 SD at 26 months in individual II. This is postnatal failure of
    brain growth superimposed on active atrophy, not primary microcephaly.
  frequency: VERY_FREQUENT
  notes: >-
    Derivation: 2/2 in PMID:31271740 (microcephaly named for both siblings in
    the abstract), 2/2 in PMID:34918187 (Table 1 row "Microcephaly Yes Yes") and
    1/1 in PMID:40696808, which resolves to 5/5 of the five published
    individuals, that is 100 percent and therefore the VERY_FREQUENT band of
    80-100 percent. The denominator of five is the entire published series.
  phenotype_term:
    preferred_term: Progressive microcephaly
    term:
      id: HP:0000253
      label: Progressive microcephaly
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The affected children show severe microcephaly and growth retardation with
      minimal neurodevelopment.
    explanation: >-
      Documents severe microcephaly in both individuals of this series.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      She developed severe microcephaly with a very puffy appearance
    explanation: >-
      Documents that the severe microcephaly in individual I DEVELOPED after
      birth rather than being present at birth, which is what distinguishes this
      from primary microcephaly. The adjacent sentence stating that head
      circumference and height progressively deviated from the centiles is
      broken across a line-break hyphen in the cached PDF extraction and is
      therefore not quoted.
  - reference: PMID:31271740
    reference_title: "Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two siblings of a quartet family, presenting with hypotonia, microcephaly
      and severe intellectual disability
    explanation: >-
      Independent documentation of microcephaly in the first reported family.
  - reference: PMID:35346037
    reference_title: "Differential expression of enzymes in thymidylate biosynthesis in zebrafish at different developmental stages: implications for dtymk mutation-caused neurodegenerative disorders."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      For instance, mutations in DTYMK, the gene coding for thymidylate kinase
      (TMPK), cause severe microcephaly in human.
    explanation: >-
      Third-party restatement of microcephaly as the cardinal human phenotype of
      DTYMK mutation. Classified OTHER, not HUMAN_CLINICAL: this sentence is a
      literature restatement in the introduction of a zebrafish paper, so it is
      neither a primary human observation nor that paper's own model data. It
      is retained because independent restatement is worth recording, but it
      carries no observational weight of its own.
- name: Absent Neurodevelopmental Progress
  category: Neurologic
  description: >-
    No developmental milestone is achieved. Neither individual in PMID:34918187
    rolled over, sat, vocalised or smiled, and neither ever made eye contact.
    The first-reported siblings are described as having severe intellectual
    disability.
  frequency: VERY_FREQUENT
  notes: >-
    Derivation: 2/2 in PMID:34918187 (Table 1 row "Development No developmental
    progress No developmental progress"), 2/2 in PMID:31271740 (severe
    intellectual disability in both siblings) and 1/1 in PMID:40696808
    (progressive neurodevelopmental regression), which resolves to 5/5 of the
    five published individuals and therefore the VERY_FREQUENT band. The
    underlying descriptions are not identical - the PMID:31271740 siblings are
    characterised as intellectually disabled rather than as having made no
    progress at all - so this band asserts severe global impairment of
    development, not literally zero milestones in all five.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
    severity: PROFOUND
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      No neurodevelopmental milestones were achieved.
    explanation: >-
      Documents the complete absence of developmental progress in individual I.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      He made almost no developmental progress: he did not roll over, sit,
      vocalize, or smile.
    explanation: >-
      Documents the same in individual II, with the specific milestones
      enumerated.
  - reference: PMID:31271740
    reference_title: "Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two siblings of a quartet family, presenting with hypotonia, microcephaly
      and severe intellectual disability
    explanation: >-
      Documents severe intellectual disability in the first reported family.
- name: Developmental Regression
  category: Neurologic
  description: >-
    The disorder is degenerative rather than static. The Mexican case is
    described as presenting with progressive neurodevelopmental regression, and
    the reviews of the entity describe progressive neurological regression as a
    defining feature.
  notes: >-
    No frequency band is asserted. Regression is explicitly described only in
    PMID:40696808. In the two individuals of PMID:34918187 no milestone was ever
    gained, so there was nothing to regress from, and PMID:31271740 does not
    describe the developmental trajectory of its siblings. A denominator for
    regression therefore does not exist across the published series.
  phenotype_term:
    preferred_term: Developmental regression
    term:
      id: HP:0002376
      label: Developmental regression
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 2-year-old male with progressive neurodevelopmental regression presented
      with severe microcephaly, epilepsy, hypertonia, and cortical and
      cerebellar atrophy.
    explanation: >-
      Documents regression as the presenting problem in the fifth reported case.
- name: Cerebral Atrophy
  category: Neurologic
  description: >-
    Severe, progressive, postnatal atrophy of the cerebral hemispheres with
    enlargement of the lateral ventricles and subarachnoid spaces. Autopsy in
    individual I confirmed atrophy of neocortex and cerebral white matter.
  frequency: VERY_FREQUENT
  notes: >-
    Derivation: 2/2 in PMID:34918187 and 1/1 in PMID:40696808, which resolves to
    3/3 and therefore the VERY_FREQUENT band. The denominator here is the three
    individuals with published neuroimaging, not the whole series of five; the
    two siblings of PMID:31271740 have no imaging described in the abstract that
    is cached for this entry, so they are excluded from this denominator rather
    than counted as negative.
  phenotype_term:
    preferred_term: Cerebral atrophy
    term:
      id: HP:0002059
      label: Cerebral atrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain MRI at 6 months of age showed dramatic atrophy of the cerebral
      hemispheres with severe enlargement of the lateral ventricles and
      subarachnoid spaces
    explanation: >-
      Documents the hemispheric atrophy and its imaging correlates in individual
      I at 6 months.
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This ultra-rare condition is characterized by progressive neurological
      regression, epilepsy, severe microcephaly, and global cerebral atrophy.
    explanation: >-
      Names global cerebral atrophy as a defining feature of the entity.
- name: Small Basal Ganglia
  category: Neurologic
  description: >-
    The basal ganglia are disproportionately affected. Individual I showed
    severe underdevelopment of the putamen at three weeks and effective
    disappearance of the basal ganglia by six months; in individual II the basal
    nuclei were small but still visible at two years. The thalamus is spared on
    imaging in both.
  notes: >-
    No frequency band is asserted. The finding is documented in both individuals
    of PMID:34918187, but PMID:40696808 reports cortical and cerebellar atrophy
    without specifying the basal ganglia, so the denominator across the imaged
    cases is not clean.
  phenotype_term:
    preferred_term: Small basal ganglia
    term:
      id: HP:0012697
      label: Small basal ganglia
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain imaging revealed severe cerebral atrophy and disappearance of the
      basal ganglia.
    explanation: >-
      Documents the basal ganglia involvement as a distinct imaging feature in
      both individuals of this series.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The basal nuclei were small, but visible, while the thalamus appeared to
      have a normal size.
    explanation: >-
      Documents the same finding in individual II and records the sparing of the
      thalamus that distinguishes this pattern.
- name: Cerebellar Atrophy
  category: Neurologic
  description: >-
    Cerebellar involvement is discordant between imaging and pathology. In
    PMID:34918187 the cerebellum looked normal on MRI in both individuals, but
    microscopy in individual I showed loss of neurons in the granular and
    Purkinje cell layers. PMID:40696808 reports cerebellar atrophy on imaging.
  notes: >-
    No frequency band is asserted, and this is the one phenotype in the entry
    where the sources genuinely disagree. Radiological cerebellar atrophy is
    reported in 1 of the 3 imaged individuals (PMID:40696808), while
    PMID:34918187 explicitly describes the cerebellum as appearing normal on MRI
    in its two individuals - yet reports histological cerebellar neuronal loss
    in the one individual who came to autopsy. The term is retained because the
    histology and the third case both point to real cerebellar pathology, but a
    band would misrepresent a 1/3 imaging finding.
  phenotype_term:
    preferred_term: Cerebellar atrophy
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  evidence:
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 2-year-old male with progressive neurodevelopmental regression presented
      with severe microcephaly, epilepsy, hypertonia, and cortical and
      cerebellar atrophy.
    explanation: >-
      Documents radiological cerebellar atrophy in the fifth reported case.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain stem and cerebellum appeared normal
    explanation: >-
      The Table 1 entry for individual I states the cerebellum appeared normal
      on MRI, which is why this phenotype is curated as partially supported
      rather than as an established feature.
- name: Seizure
  category: Neurologic
  description: >-
    Seizures begin in the first two years. Individual I had recurrent febrile
    seizures from 6 months with a flat-trace EEG, controlled with phenobarbital;
    individual II had severe myoclonic jerks from 15 months with a slow EEG
    background and occasional sharp waves, treated with carbamazepine; the
    Mexican case had epilepsy.
  frequency: VERY_FREQUENT
  notes: >-
    Derivation: 2/2 in PMID:34918187 (Table 1 row "Seizures Recurrent febrile
    seizures myoclonic jerks") and 1/1 in PMID:40696808, which resolves to 3/3
    and therefore the VERY_FREQUENT band. The denominator is the three
    individuals whose seizure status is reported; PMID:31271740 does not mention
    seizures in either direction for its two siblings, so they are excluded
    rather than counted as unaffected.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
    temporality: RECURRENT
    onset:
      onset_category: INFANTILE
      min_age_years: 0.5
      max_age_years: 2.0
      notes: >-
        Ages at first documented seizure: 6 months (individual I,
        PMID:34918187), 15 months (individual II, PMID:34918187). The
        PMID:40696808 case had epilepsy at ascertainment aged 2 years but the
        age at first seizure is not stated in the abstract, so 2.0 years is an
        upper bound on ascertainment, not a reported onset age. INFANTILE
        (HP:0003593, 28 days to 1 year) is chosen because the earliest and
        best-documented onset falls in that window; the 15-month onset in
        individual II strictly falls in the CHILDHOOD band.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      She developed recurrent febrile seizures with flat trace EEG at 6 months
      of age which were successfully treated with phenobarbital.
    explanation: >-
      Documents seizure onset, semiology, EEG and response to treatment in
      individual I.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      He developed severe myoclonic jerks at 15 months of age, which were
      treated with carbamazepine.
    explanation: >-
      Documents seizure onset and treatment in individual II.
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A 2-year-old male with progressive neurodevelopmental regression presented
      with severe microcephaly, epilepsy, hypertonia, and cortical and
      cerebellar atrophy.
    explanation: >-
      Documents epilepsy in the fifth reported case.
- name: Myoclonic Seizure
  category: Neurologic
  description: >-
    Severe myoclonic jerks were the seizure type in individual II of
    PMID:34918187, beginning at 15 months.
  notes: >-
    No frequency band. Myoclonic semiology is documented in 1 of the 5 published
    individuals; the other individual with characterised seizures had febrile
    seizures instead, so the two documented semiologies differ and no dominant
    seizure type can be asserted.
  phenotype_term:
    preferred_term: Myoclonic seizure
    term:
      id: HP:0032794
      label: Myoclonic seizure
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      He developed severe myoclonic jerks at 15 months of age, which were
      treated with carbamazepine.
    explanation: >-
      Documents the myoclonic semiology and its age of onset.
- name: Hypotonia
  category: Neurologic
  description: >-
    Central hypotonia is present early. Individual I of PMID:34918187 was
    hypotonic at birth before evolving into spasticity, and hypotonia is the
    first feature named for both siblings in PMID:31271740.
  notes: >-
    No frequency band. Hypotonia is documented in 2/2 individuals in
    PMID:31271740 and in 1/2 in PMID:34918187 (individual II is described as
    having good head control and increased distal tone rather than hypotonia),
    and is not mentioned in PMID:40696808, whose case has hypertonia. Combining
    these into a single band would obscure that the tone abnormality changes
    character over the course of the illness.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
    onset:
      onset_category: CONGENITAL
      notes: >-
        Individual I of PMID:34918187 is stated to have been hypotonic at birth,
        which is congenital onset (HP:0003577) for this feature specifically.
        The onset of hypotonia in the PMID:31271740 siblings is not stated.
  evidence:
  - reference: PMID:31271740
    reference_title: "Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two siblings of a quartet family, presenting with hypotonia, microcephaly
      and severe intellectual disability
    explanation: >-
      Documents hypotonia as a presenting feature in both siblings of the first
      reported family.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The girl was hypotonic at birth but developed spasticity with opisthotonus
      within 1 year of age.
    explanation: >-
      Documents congenital hypotonia in individual I and its evolution into
      spasticity, which is the reason no single tone band is asserted.
- name: Spasticity
  category: Neurologic
  description: >-
    Tone increases over the first years. Individual I developed spasticity with
    opisthotonus within the first year; individual II had increased distal tone
    in arms and legs with brisk reflexes, bilateral clonus and extensor plantar
    responses; the Mexican case had hypertonia.
  notes: >-
    No frequency band. Pyramidal hypertonia is documented in 2/2 in
    PMID:34918187 and 1/1 in PMID:40696808, but the descriptors differ
    (spasticity with opisthotonus, distal hypertonia with clonus, unqualified
    hypertonia) and PMID:31271740 describes hypotonia instead. Rather than force
    a band across heterogeneous descriptions of tone, both spasticity and
    hypotonia are curated as unbanded features of a biphasic course.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The girl was hypotonic at birth but developed spasticity with opisthotonus
      within 1 year of age.
    explanation: >-
      Documents the emergence of spasticity in individual I.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Tendon reflexes were increased, with bilateral clonus and positive
      Babiniski signs.
    explanation: >-
      Documents the pyramidal signs accompanying the hypertonia in individual II.
      The misspelling of Babinski is present in the source and is preserved so
      the quote stays verbatim.
- name: Opisthotonus
  category: Neurologic
  description: >-
    Individual I of PMID:34918187 developed opisthotonic posturing together with
    spasticity within the first year of life.
  notes: >-
    No frequency band. Documented in 1 of the 5 published individuals.
  phenotype_term:
    preferred_term: Opisthotonus
    term:
      id: HP:0002179
      label: Opisthotonus
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The girl was hypotonic at birth but developed spasticity with opisthotonus
      within 1 year of age.
    explanation: >-
      Documents opisthotonus in individual I.
- name: Cerebral Visual Impairment
  category: Neurologic
  description: >-
    Neither individual in PMID:34918187 tracked objects; individual I was
    thought able to distinguish only light from dark. The eyes were
    morphologically normal and formal ophthalmologic examination in individual
    II was normal, so this is cortical or central visual impairment rather than
    an ocular abnormality.
  notes: >-
    No frequency band. Documented in 2/2 individuals in PMID:34918187 but not
    addressed in PMID:31271740 or in the PMID:40696808 abstract. A denominator
    of two out of a series of five is too thin to band.

    Curated as HP:0100704 Cerebral visual impairment rather than the more
    general HP:0000505 Visual impairment. The specific term is what the two
    curated snippets actually support taken together: absent visual tracking
    with morphologically normal eyes and a normal ophthalmologic examination is
    a central rather than an ocular deficit. HP:0100704 is also the term used in
    the HPO annotation set for OMIM:619847. No imaging of the optic radiations
    or visual cortex, and no VEP, is reported in any cached reference, so the
    localisation rests on the exclusion of an ocular cause rather than on a
    positive cortical finding.
  phenotype_term:
    preferred_term: Cerebral visual impairment
    term:
      id: HP:0100704
      label: Cerebral visual impairment
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Vision No tracking of objects, only light/dark No tracking of objects
    explanation: >-
      The Table 1 vision row records absent visual tracking in both individuals.
      The run-on wording is an artefact of the two-column table being extracted
      as one line, and is quoted verbatim rather than tidied.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      However, the eyes were morphologically normal in both individuals.
    explanation: >-
      Establishes that the visual deficit is central rather than structural,
      which is why the ocular terms used in the zebrafish model are not curated
      as human phenotypes here.
- name: Failure to Thrive
  category: Growth
  description: >-
    Growth failure affects weight and length as well as head circumference.
    Individual I never achieved normal growth despite nasogastric feeding from
    the third day of life and was minus 6.5 SD for height at 16 months;
    individual II was minus 4.0 SD for weight and minus 5.4 SD for height at
    26-30 months.
  frequency: VERY_FREQUENT
  notes: >-
    Derivation: 2/2 in PMID:34918187 (both the abstract sentence naming growth
    retardation for "the affected children" and the Table 1 weight and height SD
    scores for each individual). The denominator here is only the two
    individuals of that one series; PMID:31271740 and PMID:40696808 do not
    report anthropometry in the cached abstracts. A 2/2 denominator is thin, and
    the band is asserted only because the same paper states the feature for both
    children in a summary sentence as well as in the table. Readers wanting a
    five-case denominator will not find one.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The affected children show severe microcephaly and growth retardation with
      minimal neurodevelopment.
    explanation: >-
      States growth retardation for both affected children of this series.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Because of poor feeding, she was readmitted to the hospital on the 3rd
      day.
    explanation: >-
      Documents the feeding difficulty that opened the growth failure in
      individual I, in the first week of life.
- name: Hypochromic Microcytic Anemia
  category: Hematologic
  description: >-
    Individual II of PMID:34918187 required transfusion for severe anaemia at 7
    months and thereafter showed persistent microcytic hypochromic indices on
    repeated testing. Anaemia was not reported in individual I.
  notes: >-
    No frequency band. Documented in 1 of the 5 published individuals. It is
    worth flagging rather than dropping because normocytic anaemia is part of
    DEE50, the CAD-related dTTP-pathway disorder that PMID:34918187 names as a
    comparator, so haematological involvement may be a shared consequence of
    constrained nucleotide supply in an erythroid lineage. That connection is a
    hypothesis, not something either paper asserts.
  phenotype_term:
    preferred_term: Hypochromic microcytic anemia
    term:
      id: HP:0004840
      label: Hypochromic microcytic anemia
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Microcytic hypochromic anemia and elevated liver enzymes
    explanation: >-
      The Table 1 "Other findings" row for individual II, naming both the
      anaemia and its microcytic hypochromic character.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Severe anemia was detected and treated by blood transfusion.
    explanation: >-
      Documents the clinical severity of the anaemia in individual II at 7
      months.
- name: Elevated Circulating Hepatic Transaminase Concentration
  category: Gastrointestinal
  description: >-
    Repeated liver enzyme testing in individual II of PMID:34918187 was
    persistently abnormal. No structural liver disease was described and
    post-mortem examination of the internal organs in individual I was normal.
  notes: >-
    No frequency band. Documented in 1 of the 5 published individuals.
  phenotype_term:
    preferred_term: Elevated circulating hepatic transaminase concentration
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      hematological indices and liver enzymes at different occasions
    explanation: >-
      Records that liver enzymes in individual II were measured repeatedly on
      different occasions, which is what establishes the abnormality as
      persistent rather than a single reading. The Table 1 row quoted on the
      anaemia phenotype states the result itself, that the liver enzymes were
      elevated.
- name: Micropenis
  category: Genitourinary
  description: >-
    Individual II of PMID:34918187 had a micropenis alongside bilateral
    undescended testes.
  notes: >-
    No frequency band. Documented in 1 of the 5 published individuals, who is
    also one of only two reported males with a described genital examination.
    Whether this is part of the disorder or an incidental finding is not
    established by a single case.
  phenotype_term:
    preferred_term: Micropenis
    term:
      id: HP:0000054
      label: Micropenis
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Micropenis and undescended testis
    explanation: >-
      The Table 1 "Other findings" row for individual II.
- name: Cryptorchidism
  category: Genitourinary
  description: >-
    Bilateral undescended testes in individual II of PMID:34918187.
  notes: >-
    No frequency band. Documented in 1 of the 5 published individuals. Same
    caveat as micropenis: a single observation cannot separate a disease feature
    from an incidental one.
  phenotype_term:
    preferred_term: Cryptorchidism
    term:
      id: HP:0000028
      label: Cryptorchidism
    laterality: BILATERAL
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Micropenis and undescended testis
    explanation: >-
      The Table 1 "Other findings" row for individual II; the bilaterality is
      stated in the body text.
- name: Neuronal Loss in Central Nervous System
  category: Neurologic
  description: >-
    Autopsy in individual I of PMID:34918187 showed massive loss of neurons
    including cortical pyramidal cells, with anisomorphic astrogliosis, loss of
    oligodendrocytes by apoptosis, ameboid microglial activation, a paucity of
    myelin, and neuronal loss in the neostriatum, thalamus and cerebellar
    granular and Purkinje cell layers.
  notes: >-
    No frequency band. Neuropathology is available for exactly one of the five
    published individuals, so there is no denominator at all. This phenotype is
    included because it is the histological substrate of the imaging finding,
    not because it is known to be universal.
  phenotype_term:
    preferred_term: Neuronal loss in central nervous system
    term:
      id: HP:0002529
      label: Neuronal loss in central nervous system
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain pathology confirmed massive neuronal dropout in virtually the entire
      brain, sparing the brain stem.
    explanation: >-
      Direct autopsy documentation of the neuronal loss and its distribution.
progression:
- phase: Neonatal and early infantile presentation
  age_range: Birth to about 3 months
  notes: >-
    Head circumference is at or near the normal range at birth and there are no
    dysmorphic features. What is present instead is nonspecific: hypotonia,
    feeding failure requiring nasogastric support, and absent visual tracking.
    A neonatal MRI may show only slight underdevelopment of the caudate and
    frontal cortex, so this phase is easily mistaken for a static
    encephalopathy.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At birth, no apparent dysmorphic features were observed in both children.
    explanation: >-
      Establishes the unremarkable appearance at birth that makes early
      recognition difficult.
- phase: Infantile decline
  age_range: About 3 months to 2 years
  notes: >-
    The features that define the disorder all emerge in this window: head
    circumference falls away from the centiles toward minus 7 SD, tone converts
    from hypotonia to spasticity, seizures begin, no developmental milestone is
    gained, and serial imaging shows the cerebral hemispheres and basal ganglia
    atrophying. This is the phase in which the disorder becomes recognisably
    neurodegenerative rather than static.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      growth retardation, puffy body, seizures, failure to reach developmental
      milestones, microcephaly and severe, progressive atrophy of the cerebral
      hemispheres and basal ganglia
    explanation: >-
      Lists the features that became apparent after birth in both individuals of
      the founding series.
- phase: Terminal
  age_range: Second to third year of life in the individuals with reported outcomes
  notes: >-
    Both individuals in PMID:34918187 died after an intercurrent respiratory
    illness: individual I at 18 months from cardiopulmonary arrest during a
    respiratory illness, and individual II at 32 months from pneumonia followed
    by coma.

    Mortality is deliberately NOT carried as a phenotype frequency band. Outcome
    is reported for only 2 of the 5 published individuals, both fatal; the
    PMID:40696808 case was alive at report and PMID:31271740 states no outcome,
    so a mortality proportion cannot be computed. Separately, HP:0003819 "Death
    in childhood" sits under Clinical modifier rather than Phenotypic
    abnormality and is therefore not a valid phenotype_term in this schema, so
    this progression record is the correct home for the observation. The same
    reasoning and the same HPO limitation are recorded in
    SNIP1-Related_Neurodevelopmental_Disorder.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Died at age 18 months Died at age 32 months
    explanation: >-
      The Table 1 outcome row for the two individuals. The run-on wording is an
      artefact of the two-column table being extracted as a single line.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At the age of 32 months, the boy developed a pneumonia followed by coma
      and death.
    explanation: >-
      Documents the terminal event in individual II.
genetic:
- name: DTYMK
  gene_term:
    preferred_term: DTYMK
    term:
      id: hgnc:3061
      label: DTYMK
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    DTYMK sits at chromosome 2q37.3 and encodes dTMPK (deoxythymidylate kinase,
    thymidylate kinase, TMPK), a 212-residue cytosolic nucleoside monophosphate
    kinase. PMID:34918187 identifies its P-loop motif at residues 13-21, a
    DR(Y/H) motif at residues 96-98 and a LID domain at residues 135-150.
    Notably, neither disease variant lies within any of these named domains,
    which the authors state explicitly, so the near-total loss of activity in
    patient fibroblasts is not explained by direct disruption of a catalytic
    motif. Gene identity was verified against the MONDO gene-association
    relation `RO:0004003 HGNC:3061 ! DTYMK` on MONDO:0859241.

    A separate transcript-level point worth recording: PMID:34918187 uses
    NM_012145.3 and PMID:40696808 uses NM_012145.4 for the same c.242C>T
    p.Pro81Leu allele. The version differs, the variant does not.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified loss-of-function of DTYMK as the cause of a severe
      postnatal neurodegenerative disease and highlight the essential nature of
      dTTP synthesis in the maintenance of genome stability and neuronal
      survival
    explanation: >-
      The definitive gene-disease statement, supported in the same paper by
      patient enzymology and an independent animal model.
  - reference: PMID:31271740
    reference_title: "Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      have been diagnosed to harbor two heterozygous variants in trans in the
      DTYMK gene of the thymidine biosynthesis pathway
    explanation: >-
      The first report implicating DTYMK in human disease, in an independent
      family.
  - reference: PMID:38621447
    reference_title: "DTYMK is an essential gene in mice and heterozygosity does not cause neural tube defects."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Dtymk-/- mice were confirmed to be embryonic lethal before E12.5, and
      Dtymk+/- mice on all three experimental diets did not show the presence of
      open neural tube defects, spina bifida or exencephaly.
    explanation: >-
      Establishes recessive essentiality rather than haploinsufficiency: total
      loss is embryonic lethal, one copy is enough. This is consistent with the
      human disease being caused by hypomorphic biallelic missense alleles
      rather than by biallelic nulls, and with the unaffected status of carrier
      parents.
  variants:
  - name: NM_012145.3:c.242C>T (p.Pro81Leu)
    type: MISSENSE
    clinical_significance: PATHOGENIC
    description: >-
      The recurrent allele. Homozygous in the Egyptian individual II of
      PMID:34918187 and in the Mexican case of PMID:40696808, and inherited from
      the father in the compound heterozygous Dutch individual I. It substitutes
      a moderately conserved amino acid at a highly conserved nucleotide (phyloP
      5.29). In silico prediction is discordant: SIFT called it tolerated,
      PolyPhen-2 possibly damaging, MutationTaster disease-causing. In gnomAD as
      accessed by PMID:34918187 in May 2021 it appeared once, heterozygous only.
      The functional evidence, not the prediction, is what establishes
      pathogenicity.
    evidence:
    - reference: PMID:40696808
      reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Genetic analysis identified a homozygous missense variant in DTYMK
        (NM_012145.4:c.242C>T; p.Pro81Leu).
      explanation: >-
        Names the allele in its homozygous state in the third independent
        family.
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Variant, protein Maternal: p.Asp128Asn; Paternal: p.Pro81Leu p.Pro81Leu
      explanation: >-
        The Table 1 protein-variant row, showing p.Pro81Leu as the paternal
        allele in individual I and homozygous in individual II. The run-on
        wording is an artefact of two-column table extraction.
  - name: NM_012145.3:c.382G>A (p.Asp128Asn)
    type: MISSENSE
    clinical_significance: PATHOGENIC
    description: >-
      The maternal allele in the compound heterozygous Dutch individual I of
      PMID:34918187. It changes an amino acid conserved as far as Saccharomyces
      cerevisiae at a highly conserved nucleotide (phyloP 5.61). SIFT called it
      tolerated; MutationTaster and PolyPhen-2 called it disease-causing and
      probably damaging. Reported four times in gnomAD as accessed in May 2021,
      never homozygous.
    evidence:
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Variant, protein Maternal: p.Asp128Asn; Paternal: p.Pro81Leu p.Pro81Leu
      explanation: >-
        The Table 1 protein-variant row identifying p.Asp128Asn as the maternal
        allele in individual I.
    - reference: PMID:34918187
      reference_title: "DTYMK is essential for genome integrity and neuronal survival."
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: >-
        This variant is known to gnomAD and appears 4 times with a MAF of
        0.00001591, but only in a heterozygous state
      explanation: >-
        Documents the population-frequency argument for pathogenicity: the
        allele is vanishingly rare and has never been observed homozygous, which
        is the expectation for a recessive disease allele. The parallel
        conservation argument (the residue is conserved as far as Saccharomyces
        cerevisiae) is stated in this variant's description but is not quoted,
        because that sentence is broken across a line-break hyphen in the cached
        PDF extraction.
  - name: p.Ala99Thr
    type: MISSENSE
    clinical_significance: PATHOGENIC
    description: >-
      A third patient missense allele, characterised biochemically alongside
      p.Pro81Leu and p.Asp128Asn. Like them it converts the enzyme to a monomer
      with reduced substrate affinity and catalytic efficiency.

      Which patient carries this allele is deliberately NOT asserted.
      PMID:34926941 states that four variants have been identified in human
      patients without assigning them to individuals, and the only two families
      whose genotypes are individually published (PMID:34918187,
      PMID:40696808) carry p.Pro81Leu and p.Asp128Asn. It is therefore likely
      that p.Ala99Thr and the frameshift belong to the two siblings of
      PMID:31271740, whose specific variants are not named in the cached
      abstract, but that is an inference from elimination and is recorded here
      as such rather than curated as fact. Resolving it requires the Clin Chim
      Acta full text, which is not open-access and was not obtained for this
      entry.
    evidence:
    - reference: PMID:34926941
      reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Four TMPK variants (P81L, A99T, D128N, and a frameshift) have been
        identified in human patients who suffered from severe neurodegenerative
        diseases.
      explanation: >-
        Names the complete set of four patient alleles known at the time,
        including this one, without assigning them to individuals.
  - name: DTYMK frameshift allele (position not specified in cached sources)
    type: FRAMESHIFT
    clinical_significance: PATHOGENIC
    description: >-
      A frameshift allele reported among the four patient variants
      characterised by PMID:34926941. The cached sources for this entry name it
      only as a frameshift; no cDNA or protein coordinate is given in any text
      quoted here, so none is asserted.

      This variant record intentionally carries no HGVS name. The deep-research
      report for this entry proposed c.287_320del p.Asp96fs on the basis of a
      ClinVar lookup, and that may well be correct, but ClinVar was not
      independently queried during this curation and no cached reference states
      that coordinate. Naming it here would be asserting an identifier this
      entry cannot support. A curator with ClinVar access should complete this
      record.
    evidence:
    - reference: PMID:34926941
      reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Four TMPK variants (P81L, A99T, D128N, and a frameshift) have been
        identified in human patients who suffered from severe neurodegenerative
        diseases.
      explanation: >-
        The only statement in any cached source that a frameshift allele exists
        in this patient population.
diagnosis:
- name: Molecular diagnosis by exome sequencing
  description: >-
    All three published families were diagnosed by exome sequencing. There is no
    clinically distinctive gestalt and no abnormal metabolite: extensive
    metabolic work-up was normal in every individual in whom it was performed,
    including urinary organic acids, purines and pyrimidines, plasma amino
    acids, acylcarnitines, very-long-chain fatty acids, lactate and CSF amino
    acids. Molecular testing therefore establishes the diagnosis rather than
    confirming a biochemical suspicion.
  diagnosis_term:
    preferred_term: whole exome sequencing
    term:
      id: NCIT:C101295
      label: Whole Exome Sequencing
  evidence:
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Clinical evaluation, neuroimaging studies, and genetic analysis using WES
      followed by Sanger sequencing were performed.
    explanation: >-
      States the diagnostic route actually used in the fifth reported case,
      exome sequencing with Sanger confirmation.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Extensive metabolic investigations were performed
    explanation: >-
      Supports the claim that biochemical investigation was tried and was not
      what made the diagnosis in individual I; the paragraph that follows this
      sentence lists the normal results.
- name: dTMPK enzyme activity assay in cultured fibroblasts
  description: >-
    Direct measurement of dTMP kinase activity in cultured skin fibroblasts is
    the functional confirmation of a candidate DTYMK genotype. In PMID:34918187
    the affected individual had 0.62 pmol/min/mg protein against 43.65 and 31.08
    in the heterozygous mother and father. The assay is a research method, not a
    clinical service, and requires a skin biopsy.
  diagnosis_term:
    preferred_term: dTMP kinase enzyme activity assay in cultured fibroblasts
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      dTMPK enzyme activity of the individual is significantly lower than those
      of the parents
    explanation: >-
      Shows the assay discriminates an affected biallelic individual from
      heterozygous carriers, which is what makes it useful for variant
      interpretation.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In cells of affected individuals, dTMPK enzyme activity was minimal, along
      with impaired DNA replication.
    explanation: >-
      Confirms that the biochemical readout in patient cells is a near-complete
      loss of activity.
- name: Brain MRI showing progressive cerebral and basal ganglia atrophy
  description: >-
    Serial imaging is what makes the disorder recognisable as neurodegenerative.
    The characteristic sequence is a near-normal or only mildly abnormal
    neonatal scan followed within months by severe hemispheric and basal ganglia
    atrophy with ventricular and subarachnoid enlargement, while the thalamus,
    brainstem and cerebellum look comparatively preserved. A single scan can be
    mistaken for a static encephalopathy; two scans cannot.
  diagnosis_term:
    preferred_term: magnetic resonance imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Brain MRI at 6 months of age showed dramatic atrophy of the cerebral
      hemispheres with severe enlargement of the lateral ventricles and
      subarachnoid spaces
    explanation: >-
      Documents the imaging appearance at the age at which it becomes
      unmistakable.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      with severe underdevelopment of the putamen
    explanation: >-
      The neonatal scan at 3 weeks in individual I showed only slight
      underdevelopment of the caudate and frontal cortex, with the putamen the
      one structure already severely affected. That focal early finding is the
      diagnostically useful part: the neonatal scan is otherwise close to normal
      and gives no hint of the devastation visible three months later. The
      sentence opening is not quoted because the cached PDF extraction
      hyphenates "underdevelopment" across a line break.
biochemical:
- name: Deficient dTMPK activity in cultured fibroblasts
  presence: ABNORMAL
  context: >-
    An in vitro dTMPK assay on cultured skin fibroblasts from family I of
    PMID:34918187 gave 0.62 pmol/min/mg protein in the affected individual
    against 43.65 in the heterozygous mother and 31.08 in the heterozygous
    father, that is roughly 1.4 to 2.0 per cent of parental activity. The same
    assay in the zebrafish model gave 1.80 pmol/min/mg in mutant larvae against
    38.55 in siblings and 41.43 in unrelated wildtype larvae.
  readouts:
  - target: Loss of dTMP Kinase Catalytic Activity
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      The assay is a direct measurement of the enzymatic step the disease
      abolishes, so a near-zero value in a biallelic individual with clearly
      detectable activity in both carriers is the functional confirmation of a
      candidate genotype.
  notes: >-
    A research assay, not a clinical service, and it requires a skin biopsy. The
    numbers come from ONE family: n = 1 affected, 2 carriers, so there is no
    reference interval and no `reference_ranges` block is asserted. The
    heterozygous parents' values differ from each other by about 30 per cent
    with no stated measurement error, which is why no carrier range is claimed
    either. The zebrafish figures are recorded here because they are the same
    assay run as an internal control on the model, not as human data; the
    corresponding evidence item is tagged MODEL_ORGANISM.

    Quoting note: the sentence reporting the maternal value breaks the word
    "measured" across a line in the cached PDF extraction, so the quotable
    fragment stops before it.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In fibroblasts of the parents, dTMPK activity was readily detectable.
    explanation: >-
      Establishes the carrier baseline against which the affected value is
      interpreted.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In the mother, an activity of 43.65 pmol/min/mg protein
    explanation: >-
      The maternal carrier value.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      whereas the cells of the father showed lower activity: 31.08 pmol/min/mg
      protein.
    explanation: >-
      The paternal carrier value.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      was hardly detectable: 0.62 pmol/min/mg protein.
    explanation: >-
      The affected individual's value. The subject of the sentence is quoted
      separately above because the cached PDF extraction breaks "individual"
      across a line at this point.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Dtymk mutant embryos on the other hand had barely detectable activity:
      1.80 pmol/min/mg protein.
    explanation: >-
      The same assay in the zebrafish model, included because it shows the human
      result is reproduced in an independent system rather than being an assay
      artefact.
- name: Normal routine metabolic work-up
  presence: NORMAL
  context: >-
    A normal biochemical screen is diagnostically load-bearing in this disorder
    rather than merely unremarkable. Glucose, lactate, ammonia, biotinidase,
    creatine kinase, acylcarnitines, amino acids, very long-chain fatty acids
    and urinary organic acids were all normal in individual II of PMID:34918187,
    and extensive metabolic investigation in individual I was likewise
    unrevealing. The corollary is that no first-line metabolic panel will raise
    this diagnosis and that a normal screen does not exclude it.
  readouts:
  - target: Block of Canonical dTTP Biosynthetic Flux
    relationship: READOUT_OF
    direction: PRESENT_ABSENT
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Read together with the separately curated finding that steady-state dTTP
      pools are normal, the normal metabolic screen is what forces the
      mechanistic claim to be about FLUX rather than about a measurable
      metabolite abnormality. There is no analyte to test for.
  notes: >-
    Curated as a normal finding on purpose. This is the biochemical counterpart
    of the diagnosis section's statement that molecular testing establishes the
    diagnosis rather than confirming a biochemical suspicion. Denominator: the
    itemised panel is reported for individual II only; individual I is covered
    by a general statement that extensive metabolic investigations were
    performed. No purine/pyrimidine or dNTP-panel result is quoted here because
    the dTTP measurement is curated on the pathophysiology node it constrains.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Metabolic work-up including glucose, lactate, ammonia, biotinidase,
      creatine kinase, acylcarnitines, amino acids, very long-chain fatty acids
      and urinary organic acids profile were all normal.
    explanation: >-
      The itemised normal panel in individual II.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Extensive metabolic investigations were performed
    explanation: >-
      Documents that biochemical investigation was undertaken in individual I
      and did not make the diagnosis.
histopathology:
- name: Global neuronal loss with sparing of dentate nucleus and brainstem
  description: >-
    Autopsy of individual I in PMID:34918187 showed severe atrophy of the
    neocortex, cerebral white matter and basal ganglia with massive neuronal
    dropout, while the brainstem, cerebellar dentate nucleus and the gross size
    of the cerebellum were preserved. The sparing pattern is the diagnostically
    informative part: this is not a uniform encephaloclastic process but a
    selective one that leaves specific structures intact, matching the imaging
    observation that brainstem and cerebellum look comparatively normal on MRI.
  diagnostic: true
  notes: >-
    No finding_term is bound. The HistopathologyFindingTerm binding admits only
    NCIT terms reachable from the Histopathology Result branch (NCIT:C83490)
    plus a handful of HP rosette terms, and OAK searches of the NCIT
    Morphologic Finding branch on 2026-08-01 returned no term for neuronal loss
    or for a regional sparing pattern (candidates audited and rejected:
    NCIT:C50774 Tissue Degeneration and NCIT:C120874 Degeneration and Atrophy,
    both too generic to carry the sparing claim, which is the whole point of
    this record). The corresponding clinical phenotype is separately bound to
    HP:0002529 in the phenotypes section.

    Neuropathology exists for exactly ONE of the five published individuals, so
    no frequency is asserted for any entry in this section.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Gross neuropathological examination showed severe atrophy of the
      neocortex,
    explanation: >-
      Opening of the gross neuropathology description. The sentence continues
      "cerebral white matter and basal ganglia", which cannot be quoted
      contiguously because the cached PDF extraction breaks "matter" across a
      line.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      with normal size of brainstem and cerebellum
    explanation: >-
      The gross sparing of brainstem and cerebellum, in the same sentence.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      only sparing the dentate nucleus and brain stem.
    explanation: >-
      The authors' own summary of the sparing pattern. The clause preceding this
      one is not quoted because the extraction breaks "massive" across a line.
- name: Anisomorphic astrogliosis of the cerebral cortex
  description: >-
    The cortex of individual I showed intense anisomorphic astrogliosis with
    only a minimal degree of vascular proliferation, and reactive gliosis was
    also present in the neostriatum and thalamus alongside neuronal loss.
  finding_term:
    preferred_term: anisomorphic astrogliosis
    term:
      id: NCIT:C26783
      label: Gliosis
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      intense anisomorphic astrogliosis
    explanation: >-
      The cortical gliosis finding.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      show loss of neurons and reactive gliosis.
    explanation: >-
      The same reaction in the neostriatum and thalamus.
- name: Oligodendrocyte loss by apoptosis with paucity of myelin
  description: >-
    Deep periventricular white matter showed loss of oligodendrocytes with
    moderate microglial activation; the more peripheral hemispheric white matter
    showed massive ameboid microglial activation, lack of myelin and loss of
    oligodendrocytes by apoptosis, with paucity of myelin throughout the
    hemispheres and capsules. Caspase-3 was among the stains used. This is the
    histological evidence that the oligodendroglial arm of the disease is
    apoptotic rather than purely hypomyelinating.
  finding_term:
    preferred_term: apoptotic loss of oligodendrocytes
    term:
      id: NCIT:C176399
      label: Increased Apoptosis
  notes: >-
    The myelin and microglial components of this finding have no bindable term
    in the NCIT Histopathology Result branch (NCIT:C117277 Demyelination was
    audited on 2026-08-01 and is NOT reachable from NCIT:C83490 or NCIT:C35867,
    so it cannot be used here), so the record is bound to the apoptosis finding
    and the rest is carried in the description.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      and loss of oligodendrocytes by apoptosis
    explanation: >-
      The apoptotic mechanism of oligodendrocyte loss.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      spheric white matter shows massive activation of microglia with ameboid
      morphology
    explanation: >-
      The microglial reaction in peripheral white matter. The quote starts
      mid-word because the cached PDF extraction breaks "hemispheric" across a
      line immediately before it.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      show paucity of myelin throughout the cerebral hemispheres and capsules
    explanation: >-
      The myelin deficit, on whole mounts of the cerebral hemispheres.
- name: Cerebellar granular and Purkinje cell layer neuronal loss
  description: >-
    Microscopy of a cerebellum that was of normal gross size, and that had
    looked normal on MRI, nevertheless showed loss of neurons in the granular
    and Purkinje cell layers with a moderate Bergmann glial reaction. The
    cerebellum is therefore involved microscopically even where imaging and
    gross examination suggest it is spared, which is a caution against reading
    normal cerebellar imaging as normal cerebellum.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      shows loss of neurons in the granular and Purkinje cell layer
    explanation: >-
      The cerebellar microscopic finding.
treatments:
- name: Supportive and symptomatic management
  action_category: THERAPEUTIC
  therapeutic_modality: OTHER
  description: >-
    No disease-modifying therapy exists and none has been trialled. All reported
    management has been symptomatic and is curated as separate atomic entries
    below: anti-seizure pharmacotherapy, nasogastric tube feeding, and blood
    transfusion for the anaemia in individual II, with genetic counselling
    recorded as a non-therapeutic action. Both individuals with reported
    outcomes nonetheless died in early childhood after intercurrent infection.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  notes: >-
    This entry is the umbrella statement that management is supportive only; the
    individual interventions are curated one per entry below rather than bundled
    here. No cached reference for this entry uses the words "supportive care",
    "palliative" or "multidisciplinary" — literal case-insensitive searches for
    `supportiv`, `palliat`, `symptomatic`, `multidisciplinary`, `no cure`,
    `no specific`, `no effective` and `no disease-modif` across
    references_cache/PMID_34918187.md, PMID_40696808.md, PMID_31271740.md and
    PMID_34926941.md on 2026-08-01 all returned zero hits. The NCIT:C15747
    binding is therefore a curatorial roll-up of the individually evidenced
    symptomatic interventions, not a quoted characterisation, and no separate
    "multidisciplinary/palliative care" treatment entry has been created because
    nothing in the cached literature would support one.

    The DTYMK inhibitors developed in the oncology literature are conceptually
    contraindicated in a loss-of-function disorder and are deliberately not
    curated. Deoxynucleoside substrate-enhancement therapy is curated
    separately below, with its mechanistic caveat, because unlike the inhibitors
    it is genuinely on the table.
  evidence:
  - reference: PMID:40696808
    reference_title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Further functional studies are needed to elucidate the mechanisms linking
      DTYMK dysfunction to neurodegeneration.
    explanation: >-
      The most recent report still frames the mechanism as incompletely
      understood, which is the state of play that precludes any targeted
      therapy.
- name: Anti-seizure pharmacotherapy
  action_category: THERAPEUTIC
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Both individuals in PMID:34918187 received an anti-seizure drug: individual
    I was treated with phenobarbital for recurrent febrile seizures at 6 months,
    reported as successful, and individual II was treated with carbamazepine for
    severe myoclonic jerks at 15 months, with no response stated. These are the
    only two anti-seizure agents named anywhere in the DTYMK literature and the
    phenobarbital response is the only treatment response reported for this
    disease.
  treatment_term:
    preferred_term: anti-seizure pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: phenobarbital
      term:
        id: CHEBI:8069
        label: phenobarbital
    - preferred_term: carbamazepine
      term:
        id: CHEBI:3387
        label: carbamazepine
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  - preferred_term: Myoclonic seizure
    term:
      id: HP:0032794
      label: Myoclonic seizure
  notes: >-
    Two agents used in two children in one case report. This is a record of what
    was done, not a treatment recommendation, and no comparative or sequential
    data exist. The deep-research artefact for this entry raises the concern
    that carbamazepine can exacerbate myoclonic seizures; that pharmacological
    claim appears in NO cached reference for this entry and is recorded here as
    an unsourced caveat rather than curated as fact. What the cached text does
    establish is only that a clinician chose carbamazepine for individual II's
    myoclonic jerks and that no response was reported.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      She developed recurrent febrile seizures with flat trace EEG at 6 months
      of age which were successfully treated with phenobarbital.
    explanation: >-
      Documents symptomatic anti-seizure treatment and its effect in individual
      I. It is the only treatment response reported anywhere in this literature.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      He developed severe myoclonic jerks at 15 months of age, which were
      treated with carbamazepine.
    explanation: >-
      Documents carbamazepine use for individual II's myoclonic seizures.
      Curated as PARTIAL because the sentence records only that the drug was
      given; unlike the phenobarbital sentence it makes no claim about seizure
      control, so it supports the intervention but not any efficacy.
- name: Nasogastric tube feeding
  action_category: THERAPEUTIC
  description: >-
    Individual I of PMID:34918187 required nasogastric tube feeding for the
    early feeding failure and tolerated it well. This is the only nutritional
    intervention reported in the DTYMK literature.
  treatment_term:
    preferred_term: nasogastric tube feeding
    term:
      id: NCIT:C93322
      label: Enteral Tube Feeding
  target_phenotypes:
  - preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  notes: >-
    No therapeutic_modality is asserted. Enteral tube feeding is not one of the
    platforms in TherapeuticModalityEnum, and CLAUDE.md explicitly warns against
    mechanically tagging nutritional-support actions as BEHAVIORAL. NCIT:C93322
    Enteral Tube Feeding was chosen over the broader NCIT:C15433 Nutritional
    Support because the cached text names the route (naso-gastric tube)
    specifically; both are reachable from NCIT:C25218, verified with OAK on
    2026-08-01.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Nutrition with naso-gastric tube was needed and well tolerated.
    explanation: >-
      Documents the feeding intervention used for the early feeding failure.
- name: Blood transfusion for anaemia
  action_category: THERAPEUTIC
  therapeutic_modality: OTHER
  description: >-
    Individual II of PMID:34918187 was admitted at 7 months with fever and
    vomiting, was found to have severe anaemia, and was treated with blood
    transfusion. Repeated later testing continued to show microcytic hypochromic
    anaemia, so the transfusion addressed an episode rather than the underlying
    haematological abnormality.
  treatment_term:
    preferred_term: blood transfusion
    term:
      id: NCIT:C15192
      label: Blood Transfusion
  target_phenotypes:
  - preferred_term: Hypochromic microcytic anemia
    term:
      id: HP:0004840
      label: Hypochromic microcytic anemia
  notes: >-
    A single transfusion episode in one of five published individuals. Whether
    the anaemia is mechanistically part of the disease (a plausible consequence
    of a dTTP-supply defect in a proliferative lineage) or an incidental
    nutritional iron deficiency is not resolved by any cached reference; see the
    Hypochromic Microcytic Anemia phenotype entry, which records that
    uncertainty. The transfusion is therefore curated as symptomatic management
    of an observed anaemia and implies nothing about its cause.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Severe anemia was detected and treated by blood transfusion.
    explanation: >-
      Documents the transfusion given to individual II.
- name: Genetic counselling
  action_category: COUNSELING_INFORMATIONAL
  therapeutic_modality: OTHER
  description: >-
    Individual II of PMID:34918187 was referred for genetic counselling at 30
    months of age, which is how the diagnosis was pursued. Counselling is
    relevant to this disorder because it is autosomal recessive with a 25 per
    cent recurrence risk for siblings, and because both reported families were
    consanguineous.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  notes: >-
    Curated with action_category COUNSELING_INFORMATIONAL and therefore
    deliberately without target_phenotypes or target_mechanisms, per the
    MedicalActionCategoryEnum guidance that counselling actions do not modify
    pathophysiology. The evidence documents that a referral happened in one
    family; no cached reference states counselling content, recurrence-risk
    figures given to a family, or any prenatal or carrier-testing offer. The
    inheritance and recurrence-risk statements in the description are drawn from
    this entry's own inheritance block, not from a treatment-specific source.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At 30 months of age, the boy was referred for genetic counseling.
    explanation: >-
      Documents that genetic counselling was part of this individual's care
      pathway. It is the only mention of counselling in the DTYMK literature.
- name: Deoxycytidine plus deoxythymidine substrate-enhancement therapy (investigational)
  action_category: THERAPEUTIC
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: deoxynucleoside substrate-enhancement pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: deoxycytidine
      term:
        id: CHEBI:15698
        label: 2'-deoxycytidine
    - preferred_term: thymidine
      term:
        id: CHEBI:17748
        label: thymidine
  description: >-
    An open-label phase II trial of oral deoxycytidine plus deoxythymidine for
    mitochondrial DNA depletion disorders lists DTYMK among its eligible
    genotypes. This is the only interventional study anywhere that names DTYMK.
    No result specific to a DTYMK-mutant participant has been published, and no
    DTYMK patient is known to have been enrolled.
  notes: >-
    This is curated as an investigational eligibility, NOT as an evidenced
    treatment, and the mechanistic caveat is the point of the entry. Substrate
    enhancement with deoxythymidine works in TK2 deficiency because TK2 performs
    the FIRST salvage step, so supplying thymidine downstream of the defective
    kinase restores flux. In DTYMK deficiency the block is at dTMP to dTDP,
    which is DOWNSTREAM of where supplemental thymidine enters the pathway.
    Supplying more thymidine therefore adds substrate proximal to the block and
    has no obvious route to restoring dTTP. Supplemental deoxycytidine could in
    principle relieve pyrimidine pool imbalance, but that is speculation.
    Additionally, the trial's rationale is mtDNA depletion, and mtDNA depletion
    has never been demonstrated in a DTYMK patient (see the
    dtymk-mtdna-depletion mechanistic hypothesis). The inclusion of DTYMK in the
    eligibility list appears to follow from the 2019 paper's title rather than
    from demonstrated mtDNA depletion. Nothing here should be read as a
    recommendation.

    The trial record is quoted from the cached ClinicalTrials.gov summary at
    references_cache/clinicaltrials_NCT04802707.md, which already existed in
    this repository and was not created for this entry.
  evidence:
  - reference: clinicaltrials:NCT04802707
    reference_title: "A Phase II, Monocenter, Single Arm Study To Assess The Safety and Efficacy Of Combination Deoxycytidine and Deoxythymidine For Mitochondrial Depletion Disorders"
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The subjects included are children (0-18Y), with positive MDS diagnosis
      and express mutations in one of the following genes: POLG, POLG2, C10orf2,
      RRM2B, MPV17, SUCLA2, SUCLG1, FBXL4, DTYMK.
    explanation: >-
      Documents that DTYMK is an eligible genotype for this deoxynucleoside
      trial. Curated as PARTIAL because eligibility is not efficacy and the
      trial's mitochondrial rationale is itself contested for this gene.
differential_diagnoses:
- name: Aicardi-Goutieres syndrome
  disease_term:
    preferred_term: Aicardi-Goutieres syndrome
    term:
      id: MONDO:0018866
      label: Aicardi-Goutieres syndrome
  description: >-
    The closest clinical and mechanistic mimic, and the comparison the primary
    paper itself draws. AGS also presents with progressive microcephaly,
    psychomotor retardation, white matter destruction, brain atrophy and death
    in early childhood, and at the mechanistic level both disorders are
    characterised by elevated ribonucleotide incorporation into genomic DNA -
    in AGS because RNase H2 cannot excise them, in DTYMK deficiency because the
    dTTP shortage causes them to be inserted in the first place.
  distinguishing_features:
  - >-
    Molecular: AGS is genetically heterogeneous (RNASEH2A/B/C, TREX1, SAMHD1,
    ADAR, IFIH1 and others) and is a type 1 interferonopathy; DTYMK deficiency
    is a single-gene nucleotide-biosynthesis defect with no interferon
    signature reported.
  - >-
    Imaging and laboratory: intracranial calcification and CSF lymphocytosis are
    characteristic of AGS and are not reported in DTYMK deficiency. Systemic
    features of AGS such as thrombocytopenia and hepatosplenomegaly are also
    absent.
  - >-
    Directionality of the ribonucleotide defect: in AGS, ribonucleotides
    accumulate because ribonucleotide excision repair fails. In DTYMK
    deficiency they accumulate because the replication machinery substitutes
    them for the missing deoxynucleotide. The shared readout has opposite
    upstream causes.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      White matter destruction and brain atrophy are shared phenotypic features
      of AGS and DTYMK deficiency.
    explanation: >-
      The primary paper's own statement of the clinical overlap that makes AGS
      the leading differential.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      at the mechanistic level, AGS and DTYMK deficiency are similar as both are
      characterized by elevated ribonucleotide incorporation in the genome
    explanation: >-
      Establishes the shared mechanistic readout, which is why the two are
      confusable at the level of pathophysiology and not only at the bedside.
- name: CAD-related developmental and epileptic encephalopathy 50
  disease_term:
    preferred_term: developmental and epileptic encephalopathy 50 (CAD-related)
    term:
      id: MONDO:0014647
      label: developmental and epileptic encephalopathy, 50
  description: >-
    The other neurodegenerative disorder of the dTTP pathway, caused by
    biallelic CAD variants (HGNC:1424, verified by OAK on MONDO:0014647). CAD
    performs the first steps of de novo pyrimidine synthesis, several enzymatic
    steps upstream of dTMPK. Like DTYMK deficiency it is autosomal recessive,
    progressive, neurodegenerative, and begins in the first months or years of
    life with early-onset seizures and developmental regression; it also
    features anaemia.
  distinguishing_features:
  - >-
    Molecular: CAD (HGNC:1424, MONDO:0014647) versus DTYMK (HGNC:3061,
    MONDO:0859241). Different genes, different MONDO entities.
  - >-
    Position in the pathway: CAD acts at the entry to de novo pyrimidine
    synthesis, so its loss can in principle be bypassed by the salvage pathway.
    DTYMK sits downstream of the point where de novo and salvage converge, so
    its loss cannot be bypassed at all. This is the reason uridine
    supplementation is a rational therapy in CAD deficiency and is not one here.
  - >-
    Anaemia type: DEE50 features normocytic anaemia, whereas the one DTYMK
    individual with anaemia had microcytic hypochromic indices.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Another human neurodegenerative disease, linked to dTTP metabolism and
      caused by pathogenic variants in CAD
    explanation: >-
      The primary paper names the CAD disorder as the comparator within the same
      metabolic pathway.
- name: TYMP-related mitochondrial neurogastrointestinal encephalomyopathy (MNGIE)
  disease_term:
    preferred_term: MNGIE (TYMP-related, MTDPS1)
    term:
      id: MONDO:0011283
      label: mitochondrial DNA depletion syndrome 1
  description: >-
    The third dTTP-pathway disorder named by the primary paper, caused by
    biallelic TYMP variants (HGNC:3148, verified by OAK on MONDO:0011283).
    Thymidine phosphorylase loss causes thymidine and dTTP to ACCUMULATE, which
    produces a dNTP pool imbalance and mtDNA depletion. This is the mirror image
    of DTYMK deficiency, where dTTP is depleted.
  distinguishing_features:
  - >-
    Molecular: TYMP (HGNC:3148, MONDO:0011283) versus DTYMK (HGNC:3061,
    MONDO:0859241).
  - >-
    Direction of the metabolic lesion: thymidine and dTTP accumulate in MNGIE
    and are depleted in DTYMK deficiency, so plasma thymidine and deoxyuridine
    are diagnostically elevated in MNGIE and are not a feature here.
  - >-
    Clinical: MNGIE is a multisystem disorder dominated by gastrointestinal
    dysmotility, cachexia, ptosis and ophthalmoplegia, peripheral neuropathy and
    leukoencephalopathy, typically with onset in the second or third decade.
    DTYMK deficiency is an infantile brain-restricted degeneration with no
    gastrointestinal or neuromuscular signature reported.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thymidine phosphorylase (TP) deficiency causes MNGIE
    explanation: >-
      The primary paper names MNGIE as the thymidine-pathway comparator.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      When accumulation of dTTP occurs, dNTP pool imbalance is promoted, leading
      to mtDNA depletion
    explanation: >-
      States the accumulation-driven mechanism of MNGIE, which is the opposite
      of the depletion-driven mechanism curated for DTYMK deficiency.
- name: Autosomal recessive primary microcephaly (MCPH)
  disease_term:
    preferred_term: autosomal recessive primary microcephaly
    term:
      id: MONDO:0016660
      label: autosomal recessive primary microcephaly
  description: >-
    The differential that the disease name itself is built to exclude. Both are
    autosomal recessive, both present with severe microcephaly and profound
    developmental impairment in a consanguineous family, and both will be
    referred for exome sequencing on that basis. MCPH is a neurodevelopmental
    disorder in which the brain is small from the outset because too few neurons
    were generated; DTYMK deficiency is a neurodegenerative disorder in which a
    near-normal head circumference at birth is followed by destruction of brain
    already built.
  distinguishing_features:
  - >-
    Timing: MCPH is primary or congenital microcephaly, present at birth by
    definition. In DTYMK deficiency head circumference is at or near the normal
    range at birth and then falls away from the centiles, reaching minus 7.6 SD
    at 9 months in individual I and minus 7.4 SD at 26 months in individual II
    (see the Progressive Microcephaly phenotype, where those figures are
    evidenced). This is the single most discriminating feature and is why the
    disorder is named for PROGRESSIVE microcephaly.
  - >-
    Trajectory: MCPH is classified as a neurodevelopmental disorder, not a
    degenerative one. DTYMK deficiency is degenerative - progressive
    neurodevelopmental regression is documented in the fifth reported case
    (PMID:40696808) and both individuals with reported outcomes died in early
    childhood. Note the honest limit here: in the two individuals of
    PMID:34918187 no milestone was ever gained, so regression could not be
    observed in them; the degenerative character in those two rests on serial
    imaging and on autopsy, not on skill loss. See the Developmental Regression
    phenotype, which records the same limitation.
  - >-
    Imaging: what separates the two is SERIAL imaging, not a single scan. DTYMK
    deficiency shows a near-normal or only mildly abnormal neonatal scan
    followed within months by severe hemispheric and basal ganglia atrophy with
    ventricular and subarachnoid enlargement (see the brain-MRI diagnosis
    entry). A single small-brain scan in a microcephalic infant does not
    discriminate; two scans months apart do. No cached reference in this entry
    describes MCPH imaging, so no positive imaging claim is made about MCPH
    here.
  - >-
    Molecular: MCPH is caused by variants in centrosomal and mitotic-spindle
    genes such as ASPM, WDR62 and MCPH1 (MONDO:0016660), whereas DTYMK
    deficiency is a nucleotide-biosynthesis defect (MONDO:0859241).
  notes: >-
    Added on review. The distinguishing features above are drawn from claims
    already evidenced elsewhere in this entry (the onset, progression and
    imaging sections) plus the two quoted MCPH statements below. Nothing new is
    asserted about DTYMK deficiency here.

    Sourcing limits, stated rather than papered over. No cached reference for
    this entry mentions MCPH, ASPM or WDR62 - literal case-insensitive searches
    for `ASPM`, `WDR62`, `primary microcephaly`, `MCPH`, `congenital
    microcephaly` and `static` across references_cache/PMID_34918187.md and
    PMID_40696808.md on 2026-08-01 returned only a bibliography line. The MCPH
    side is therefore evidenced from PMID:35111754, an MCPH review already
    present in references_cache for the Autosomal_Recessive_Primary_Microcephaly
    entry; no new reference was fetched. That review states MCPH's congenital
    and neurodevelopmental character, which is what the contrast turns on, but
    it does NOT contain a sentence asserting that MCPH is non-progressive in so
    many words, so the "static" wording in the trajectory bullet is a curatorial
    reading of "neurodevelopmental" and "present at birth" and is not directly
    quoted. The gene list (ASPM, WDR62, MCPH1) is not quoted either; it is
    common knowledge for this disorder and is stated in the distinguishing
    feature rather than as an evidenced claim.
  evidence:
  - reference: PMID:35111754
    reference_title: "Autosomal Recessive Primary Microcephaly: Not Just a Small Brain."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Autosomal recessive primary microcephaly (MCPH) is the prototype of
      isolated primary (congenital) microcephaly, affecting predominantly the
      cerebral cortex.
    explanation: >-
      Establishes that MCPH is congenital microcephaly, which is the axis on
      which it separates from a disorder whose head circumference is near normal
      at birth. Tagged OTHER because the source is a narrative review rather
      than a primary human observation.
  - reference: PMID:35111754
    reference_title: "Autosomal Recessive Primary Microcephaly: Not Just a Small Brain."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      MCPH is a group of rare heterogeneous neurodevelopmental disorders
      characterized by intellectual disability
    explanation: >-
      Classifies MCPH as neurodevelopmental rather than neurodegenerative, the
      second half of the contrast.
clinical_trials:
- name: NCT04802707
  phase: PHASE_II
  description: >-
    Open-label, monocentre, single-arm phase II study of combination oral
    deoxycytidine and deoxythymidine in children aged 0-18 years with
    mitochondrial DNA depletion syndrome. DTYMK is named in the eligible-genotype
    list alongside POLG, POLG2, C10orf2, RRM2B, MPV17, SUCLA2, SUCLG1 and FBXL4.
    This is the only interventional study anywhere that names DTYMK. No result
    specific to a DTYMK-mutant participant has been published and no DTYMK
    patient is known to have been enrolled.
  target_phenotypes:
  - preferred_term: Absent neurodevelopmental progress
    term:
      id: HP:0001263
      label: Global developmental delay
  notes: >-
    No `status` is asserted. The cached ClinicalTrials.gov summary at
    references_cache/clinicaltrials_NCT04802707.md carries the study description
    only; it contains no recruitment-status field, and guessing one would be
    fabrication. Phase II is taken from the registered study title.

    Recorded here as well as under `treatments` so that it is queryable as a
    trial. The mechanistic objection - that deoxythymidine enters the pathway
    UPSTREAM of the dTMP-to-dTDP block, so substrate enhancement has no obvious
    route to restoring dTTP in this gene, unlike in TK2 deficiency - is set out
    in full in the corresponding treatment entry and applies equally here. The
    target_phenotype is the trial's stated neurological target expressed with
    the nearest term this entry already uses; the registry text says only
    "Subjects with MDS expressing neurological phenotypes dysfunction" and names
    no specific phenotype, so nothing more granular is claimed.
  evidence:
  - reference: clinicaltrials:NCT04802707
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The subjects included are children (0-18Y), with positive MDS diagnosis
      and express mutations in one of the following genes: POLG, POLG2, C10orf2,
      RRM2B, MPV17, SUCLA2, SUCLG1, FBXL4, DTYMK.
    explanation: >-
      Documents DTYMK as an eligible genotype. PARTIAL because eligibility is
      not efficacy, and because the trial's mitochondrial rationale is itself
      contested for this gene.
  - reference: clinicaltrials:NCT04802707
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In this phase II Trial a mix of Deoxynucleosides Pyrimidine (Deoxycytidine
      dC and Deoxythymidine dT) will be used as early treatment of MDS.
    explanation: >-
      States the intervention and the phase.
mechanistic_hypotheses:
- hypothesis_group_id: dtymk-nuclear-genome-instability
  hypothesis_label: Nuclear genome instability from dTTP depletion
  status: CANONICAL
  description: >-
    The accepted model. Loss of dTMPK collapses the dTTP pool, which impairs
    nuclear DNA replication, drives ribonucleotide misincorporation into genomic
    DNA, and leaves DNA damage unrepaired. Neurons and oligodendrocytes die by
    apoptosis and the brain atrophies postnatally. This model is supported by
    patient enzymology, patient fibroblast replication assays and an independent
    zebrafish knockout.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified loss-of-function of DTYMK as the cause of a severe
      postnatal neurodegenerative disease and highlight the essential nature of
      dTTP synthesis in the maintenance of genome stability and neuronal
      survival
    explanation: >-
      The authors' own statement of the canonical model.
- hypothesis_group_id: dtymk-mtdna-depletion
  hypothesis_label: Mitochondrial DNA depletion
  status: ALTERNATIVE
  description: >-
    The original 2019 proposal was that DTYMK belongs to the mitochondrial DNA
    depletion syndrome gene set, on the basis of an in silico inference of mtDNA
    depletion in the more severely affected of two siblings. The 2022 study
    tested this directly in patient fibroblasts and found normal mtDNA copy
    number, no mtDNA deletions on long-range PCR, and normal respiratory chain
    complex I-V activities, alongside normal lactate and alanine in its own two
    individuals. The hypothesis is nevertheless kept as ALTERNATIVE rather than
    DEPRECATED for two reasons. First, the 2022 authors themselves state the
    caveat that fibroblast or blood mtDNA copy number is not representative of
    affected tissue and that they had no muscle biopsy. Second, and more
    substantively, the 2021 enzymology paper showed that in the same patient
    fibroblasts the loss of TMPK activity is COMPLETE in mitochondria and only
    near-complete in cytosol, which is a positive biochemical reason to keep a
    mitochondrial arm on the table.
  notes: >-
    This is the single most consequential disagreement in the DTYMK literature,
    and it matters for curation as well as for biology: the 2019 paper's title
    calls DTYMK a mitochondrial DNA depletion syndrome gene, so any curator
    reading titles alone would classify this disease into the wrong mechanism
    class. Conversely, a curator reading only the 2022 paper would discard the
    mitochondrial arm entirely and miss that DTYMK is a listed eligible genotype
    in an active deoxynucleoside trial for mitochondrial depletion disorders
    (clinicaltrials:NCT04802707, curated under treatments). The evidence list
    below deliberately carries the original claim, the original authors' own
    hedge, the disconfirming experiment with supports REFUTE, and the
    compartment finding that partially rehabilitates it, so the disagreement is
    visible in the data rather than resolved silently in prose.

    An earlier revision of this entry set this hypothesis to DEPRECATED. That
    was wrong, and specifically it was wrong because it had been written before
    PMID:34926941 was read. The status is corrected to ALTERNATIVE here.
  evidence:
  - reference: PMID:31271740
    reference_title: "Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      Mitochondrial DNA depletion has been demonstrated in silico in the more
      severe sibling.
    explanation: >-
      The original claim, and its own abstract makes clear the evidence was in
      silico rather than measured.
  - reference: PMID:31271740
    reference_title: "Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      DTYMK may be the missing link in the mitochondrial nucleotide salvage
      pathway but further characterization and additional evidence would be
      needed.
    explanation: >-
      The original authors' own hedge, which the later disconfirmation should be
      read against.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: >-
      In conclusion, we find no significant indications of mitochondrial
      dysfunction in fibroblasts of individual I.
    explanation: >-
      Direct experimental disconfirmation in patient-derived cells, covering
      mtDNA copy number, mtDNA integrity and respiratory chain function.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      They predicted mitochondrial depletion in one of the affected
      individuals, but functional data to support a mitochondrial defect was not
      provided
    explanation: >-
      The 2022 authors' explicit characterisation of the evidentiary status of
      the 2019 claim.
  - reference: PMID:34926941
    reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: >-
      the P81L and D128N mutations led to a complete loss of TMPK activity in
      mitochondria and extremely low and unstable TMPK activity in cytosol
    explanation: >-
      A compartment-resolved measurement in the same patient fibroblasts showing
      the mitochondrial loss is total. This is a biochemical reason to keep the
      mitochondrial arm open, but it is curated as PARTIAL because loss of
      mitochondrial TMPK activity is not the same claim as mtDNA depletion, and
      this paper does not measure mtDNA.
discussions:
- discussion_id: dtymk-mtdna-controversy
  prompt: >-
    Is DTYMK deficiency a mitochondrial DNA depletion syndrome, as its first
    description asserted, or a nuclear genome instability disorder?
  kind: CONTROVERSY
  status: OPEN
  rationale: >-
    PMID:31271740 titles DTYMK a novel gene for mitochondrial DNA depletion
    syndrome on the basis of an in silico inference. PMID:34918187 measured
    mtDNA copy number, mtDNA integrity and respiratory chain activity in patient
    fibroblasts and found all normal, and instead demonstrated a nuclear
    phenotype: impaired DNA replication, ribonucleotide misincorporation and a
    persistent DNA damage response. The question is not fully closed because the
    2022 authors concede that fibroblast mtDNA copy number does not represent
    affected tissue and that muscle would be needed to settle it.
  proposed_experiments:
  - experiment_id: exp_dtymk_mtdna_affected_tissue
    name: mtDNA copy number in affected tissue rather than fibroblasts
    description: >-
      Measure mtDNA copy number in post-mortem brain and in skeletal muscle from
      an affected individual, the tissues in which depletion would actually
      matter. PMID:34918187 explicitly states that fibroblast and blood copy
      number is not representative and that muscle is required, so this is the
      experiment its own authors nominate.
  - experiment_id: exp_dtymk_dntp_pool_in_neurons
    name: Direct dNTP pool measurement in patient-derived neurons
    description: >-
      Quantify the dNTP pool, including dTTP, directly in patient-derived
      neurons or cerebral organoids. Existing measurements were made in
      fibroblasts and whole zebrafish larvae and were normal; the cell type that
      actually dies has never been assayed.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Unfortunately, we do not have access to muscle tissue of the described
      individuals.
    explanation: >-
      The 2022 authors state that the tissue in which mtDNA depletion could
      actually have been assessed was unavailable to them, which is why their
      negative fibroblast result does not formally close the question. Their
      fuller statement of the caveat, that fibroblast and blood copy number is
      not representative of affected tissue, is broken across a line-break
      hyphen in the cached PDF extraction and so is paraphrased in this
      discussion's rationale rather than quoted.
- discussion_id: dtymk-zebrafish-eye-mismatch
  prompt: >-
    How much weight should the dtymk zebrafish eye phenotype carry for the human
    disease?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  rationale: >-
    The dtymk knockout zebrafish has small, deformed eyes lacking four of the
    six retinal layers, plus absent Meckel's cartilage. Neither human individual
    had a structural eye abnormality; their visual deficit was central, and
    formal ophthalmologic examination in individual II was normal. The model
    reproduces the microcephaly, neuronal apoptosis and early lethality
    faithfully, so it is a good model of the neurodegeneration, but its ocular
    and craniofacial readouts should not be back-projected onto the human
    phenotype. This matters for curation because it would be easy to add
    microphthalmia and a jaw anomaly to the human entry on the strength of a
    persuasive figure.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      A notable difference between the human phenotype and the dtymk-deficient
      zebrafish model is the degree in which eye development is affected.
    explanation: >-
      The authors flag the human-model divergence themselves.
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      However, the eyes were morphologically normal in both individuals.
    explanation: >-
      Establishes that the human eye is structurally normal, which is the basis
      for excluding the ocular terms from the phenotype list.
- discussion_id: dtymk-viability-paradox
  prompt: >-
    How is any cell viable when the only route to dTTP is blocked?
  kind: KNOWLEDGE_GAP
  status: OPEN
  rationale: >-
    dTMPK sits downstream of the convergence of the de novo and salvage
    pathways, so a complete block should abolish dTTP entirely and be
    incompatible with life. Affected individuals nonetheless survived 18 and 32
    months; patient fibroblasts still cycle and in one study proliferated at a
    normal rate; and measured dTTP levels in both patient fibroblasts and mutant
    zebrafish were normal. The primary authors call this remarkable without
    explaining it and state that a compensatory pathway remains to be proven.
    Two candidate explanations have been advanced and one has been excluded.
    CMPK2 (UMP-CMP kinase 2, sometimes called TMPK2) was considered and rejected
    by PMID:34918187 on the grounds that it cannot use dTMP as a substrate. An
    unidentified TMPK-like activity remains open: PMID:35346037 reports a
    TMPK-like enzyme in zebrafish at later developmental stages with similar
    biochemical properties to Dtymk but not recognised by the Dtymk antibody,
    and PMID:34926941 independently infers a hitherto unknown compensatory
    TMPK-like enzyme from the normal proliferation of patient fibroblasts.
    Whether a human counterpart exists is unknown. Resolving this would also
    explain why the brain is selectively vulnerable, since a compensating enzyme
    with restricted expression is one of the two hypotheses PMID:34918187 offers
    for the tissue selectivity.
  proposed_experiments:
  - experiment_id: exp_dtymk_identify_compensatory_tmpk
    name: Biochemical identification of the compensatory TMPK-like activity
    description: >-
      Identify the postulated compensatory TMPK-like activity in human tissue,
      and test whether its expression is low in forebrain-derived structures.
      A compensating enzyme with restricted expression is one of the two
      explanations PMID:34918187 offers for why the brain is selectively
      vulnerable, so this experiment would resolve the compensation gap and the
      tissue-selectivity question at once.
  - experiment_id: exp_dtymk_residual_activity_ultrasensitive
    name: Ultrasensitive residual-activity assay of the patient alleles
    description: >-
      Determine the residual catalytic activity of recombinant p.Pro81Leu and
      p.Asp128Asn dTMPK with an assay sensitive well below the 0.62
      pmol/min/mg floor reported in patient fibroblasts, to test whether
      survival is explained by sub-detection-threshold residual activity rather
      than by a separate compensating enzyme.
  evidence:
  - reference: PMID:34918187
    reference_title: "DTYMK is essential for genome integrity and neuronal survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Thus, a compensatory pathway for dTTP generation remains to be proven.
    explanation: >-
      The primary authors state the gap directly, in the same paragraph in which
      they exclude CMPK2 as the candidate.
  - reference: PMID:34926941
    reference_title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      surprisingly the proliferation rate of the patient-derived fibroblasts was
      normal, suggesting the existence of an alternative and hitherto unknown
      compensatory TMPK-like enzyme for dTTP synthesis
    explanation: >-
      An independent group reaches the same conclusion from a different
      observation, normal fibroblast proliferation despite absent enzyme
      activity.
  - reference: PMID:35346037
    reference_title: "Differential expression of enzymes in thymidylate biosynthesis in zebrafish at different developmental stages: implications for dtymk mutation-caused neurodegenerative disorders."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Furthermore, there is a novel TMPK-like enzyme expressed at later stages
      of development.
    explanation: >-
      Identifies the candidate alternative activity that could in principle
      explain residual dTTP synthesis, in the zebrafish model.
references:
- reference: PMID:34918187
  title: "DTYMK is essential for genome integrity and neuronal survival."
- reference: PMID:31271740
  title: "Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome."
- reference: PMID:40696808
  title: "Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease."
- reference: PMID:35346037
  title: "Differential expression of enzymes in thymidylate biosynthesis in zebrafish at different developmental stages: implications for dtymk mutation-caused neurodegenerative disorders."
- reference: PMID:34926941
  title: "Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity."
- reference: PMID:38621447
  title: "DTYMK is an essential gene in mice and heterozygosity does not cause neural tube defects."
- reference: PMID:35111754
  title: "Autosomal Recessive Primary Microcephaly: Not Just a Small Brain."
- reference: clinicaltrials:NCT04802707
  title: "A Phase II, Monocenter, Single Arm Study To Assess The Safety and Efficacy Of Combination Deoxycytidine and Deoxythymidine For Mitochondrial Depletion Disorders"

📚

References & Deep Research

References

8

PMID:34918187

DTYMK is essential for genome integrity and neuronal survival.

No top-level findings curated for this source.

PMID:31271740

Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome.

No top-level findings curated for this source.

PMID:40696808

Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease.

No top-level findings curated for this source.

PMID:35346037

Differential expression of enzymes in thymidylate biosynthesis in zebrafish at different developmental stages: implications for dtymk mutation-caused neurodegenerative disorders.

No top-level findings curated for this source.

PMID:34926941

Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity.

No top-level findings curated for this source.

PMID:38621447

DTYMK is an essential gene in mice and heterozygosity does not cause neural tube defects.

No top-level findings curated for this source.

PMID:35111754

Autosomal Recessive Primary Microcephaly: Not Just a Small Brain.

No top-level findings curated for this source.

clinicaltrials:NCT04802707

A Phase II, Monocenter, Single Arm Study To Assess The Safety and Efficacy Of Combination Deoxycytidine and Deoxythymidine For Mitochondrial Depletion Disorders

No top-level findings curated for this source.

Deep Research

1

Claude Code ▸

DTYMK-Related Neurodegeneration — Comprehensive Research Report

claude-haiku-4-5-20251001, claude-opus-5[1m] 21 citations 2026-08-01T14:12:23.437936

DTYMK-Related Neurodegeneration — Comprehensive Research Report

Preferred disease name: Childhood-onset neurodegeneration with progressive microcephaly (CONPM) Target MONDO ID: MONDO:0859241 Category: Mendelian, autosomal recessive, ultra-rare (≤5 reported patients worldwide as of 2025) Report date: 2026-08-01

⚠️ Curation Preflight Warnings (read before using this report)

1. Named-Entity / topic confusion risk is HIGH for this gene. A PubMed query for DTYMK returns ~58 records, of which the large majority are cancer-bioinformatics papers (hepatocellular carcinoma prognostic signatures, lung adenocarcinoma pan-cancer analyses, uveal melanoma, colorectal cancer). Only five primary records concern the human neurodegenerative disease. A deep-research tool asked about "DTYMK" will very plausibly return a coherent, well-cited, snippet-validating report about DTYMK as an oncology biomarker rather than about CONPM. Per the repo NEC preflight (CLAUDE.md §2b), the identity anchors for this entry are: gene DTYMK / HGNC:3061 / OMIM *188345, phenotype OMIM #619847, locus 2q37.3. Any report whose dominant subject is tumor prognosis is off-target.

2. Second NEC-adjacent risk: the first clinical report (Lam et al. 2019, PMID:31271740) framed DTYMK as a mitochondrial DNA depletion syndrome (MDDS) gene, not as a nuclear-genome-instability disorder. The two framings coexist in the literature and are not the same mechanistic claim. Do not blend them into a single unqualified causal chain — see §6.

3. Quote provenance. Abstract text reproduced below under "verbatim abstract" was fetched from NCBI E-utilities and is quotable. Sentences marked [full-text] were extracted from PMC full text by an intermediate summarizer and must be re-verified against the source before being used as an evidence snippet: — they are reported here as leads, not as validated quotes.

4. Ontology IDs suggested throughout are candidates. Every one must be verified with just validate-terms / OAK before commit.

1. Disease Information

Overview

CONPM is an ultra-rare autosomal recessive neurometabolic/neurodegenerative disorder caused by biallelic loss-of-function variants in DTYMK, which encodes deoxythymidylate kinase (thymidylate kinase, TMPK; EC 2.7.4.9). TMPK catalyses the penultimate step of dTTP biosynthesis (dTMP → dTDP). Because both the de novo (thymidylate synthase) and the salvage (thymidine kinase) routes to dTTP converge on dTMP upstream of TMPK, loss of TMPK constitutes a complete block of the canonical dTTP supply — a fact the discovery paper explicitly calls remarkable given that affected children are born alive.

Clinically the disorder presents as congenital-to-infantile onset, severe and progressive (postnatal-worsening) microcephaly, profound global developmental delay or frank developmental regression, early-onset seizures, spasticity with pyramidal signs, cortical blindness/absent visual tracking, feeding failure, and death in early childhood in the severe form, with a milder end of the spectrum (small head circumference, severe intellectual disability, hypotonia, poor speech, motor delay) documented in the sibling pair reported by Lam et al.

The neuroimaging signature is distinctive: profound generalized cerebral atrophy with severe ventricular and subarachnoid space enlargement, shrinkage/"disappearance" of the basal ganglia, and relative sparing of brainstem and cerebellum.

Key identifiers

Resource	Identifier	Notes
OMIM (phenotype)	#619847 — NEURODEGENERATION, CHILDHOOD-ONSET, WITH PROGRESSIVE MICROCEPHALY; CONPM
OMIM (gene)	*188345 — DEOXYTHYMIDYLATE KINASE; DTYMK	2q37.3
MONDO	MONDO:0859241	Label: "Neurodegeneration, childhood-onset, with progressive microcephaly"; xrefs GARD:0027309, MEDGEN:1801540, OMIM:619847, UMLS:C5676972. No definition and no synonyms in MONDO — a curation gap worth noting.
MedGen	UID 1801540 / CUI C5676972
GARD	0027309
UMLS	C5676972
Orphanet	No dedicated ORPHA code identified. Searches of Orphanet and of the local dismech Orphanet cache (`references_cache/ORPHA_*.md`) returned no DTYMK/CONPM entry. Treat Orphanet epidemiology as unavailable rather than substituting a near-miss ORPHA code.
ICD-10	No specific code. In practice coded under G31.8/G31.9 (other/unspecified degenerative disease of nervous system) with Q02 (microcephaly) and G40.x (epilepsy) as needed. Approximate — verify against local coding practice before asserting.
ICD-11	No specific code identified. Nearest foundation concepts are the hereditary degenerative CNS disease and microcephaly stems. Not verified; do not assert a specific code.
MeSH	No dedicated descriptor. Indexed via Microcephaly (D008831), Neurodegenerative Diseases (D019636), Nucleoside-Phosphate Kinase / thymidylate kinase concepts.

Synonyms and alternative names

Childhood-onset neurodegeneration with progressive microcephaly (CONPM) — OMIM/MONDO preferred
DTYMK-related neurodegeneration
DTYMK deficiency; thymidylate kinase (TMPK) deficiency; dTMP kinase deficiency
Deoxythymidylate kinase deficiency
DTYMK-related mitochondrial DNA depletion syndrome (Lam et al. framing; not an OMIM-recognized MDDS numbered subtype)

Provenance of information

Aggregated disease-level resources plus individual-patient case reports. There is no registry, no natural-history cohort, and no EHR-derived data for this disorder. All human phenotype information derives from five individually described patients in three publications. HPO annotations for OMIM:619847 are denominator-annotated over n=2 or n=4 individuals (see §3), which is itself a useful signal that all "frequencies" are case-count fractions, not population estimates.

2. Etiology

Disease causal factors

Purely genetic (monogenic, autosomal recessive). Biallelic loss-of-function variants in DTYMK (HGNC:3061). No environmental, infectious, or acquired etiology is known or postulated. No somatic mechanism in this disease (somatic DTYMK dysregulation is an oncology topic — see §12 note — and is mechanistically unrelated).

Primary quote (verbatim abstract, PMID:34918187):

"Here, we describe two unrelated children with bi-allelic variants in DTYMK, encoding dTMPK, which catalyzes the penultimate step in dTTP biosynthesis." "In summary, by combining genetic and biochemical approaches in multiple models we identified loss-of-function of DTYMK as the cause of a severe postnatal neurodegenerative disease and highlight the essential nature of dTTP synthesis in the maintenance of genome stability and neuronal survival."

Genetic risk factors

Causal variants: biallelic (homozygous or compound heterozygous) DTYMK variants — see §4.
Consanguinity is a documented risk contributor: Individual II of Vanoevelen et al. was born to consanguineous Egyptian parents and was homozygous for p.Pro81Leu [full-text]. The 2025 Mexican case was likewise homozygous for p.Pro81Leu (PMID:40696808).
Carrier status: heterozygous carriers are unaffected. Mouse data support this directly — heterozygous Dtymk mice show ~3-fold reduced expression with no neural tube defects (PMID:38621447).
No susceptibility loci, GWAS signals, or modifier genes have been reported. GWAS Catalog / PheGenI contain nothing relevant to CONPM.

Environmental risk factors

None identified. No toxin, exposure, lifestyle, occupational, maternal, or seasonal factor has been implicated. Age, sex, and parity are not risk factors (see §9 for the sex distribution caveat: n is too small to interpret).

One negative environmental experiment is informative: Tiani & Stover fed heterozygous Dtymk dams three different diets (folate-manipulated) and found no diet-dependent increase in neural tube defect risk in het offspring (PMID:38621447) — i.e., no demonstrated folate/one-carbon dietary modifier of Dtymk haploinsufficiency in mouse.

Protective factors

None identified. No protective allele, modifier, dietary, or lifestyle factor is documented.

However, there is one striking endogenous compensatory phenomenon that functions like a protective mechanism at the cellular level and is arguably the central unresolved question of this disease: non-neural tissues appear to be substantially spared, and patient fibroblasts proliferate normally despite undetectable TMPK activity. This is discussed as a mechanism/knowledge-gap in §6 rather than a protective factor, because the responsible enzyme is unidentified.

Verbatim abstract (PMID:34926941, ACS Omega 2021):

"In conclusion, TMPK mutations identified in patients represent loss of function mutations but surprisingly the proliferation rate of the patient-derived fibroblasts was normal, suggesting the existence of an alternative and hitherto unknown compensatory TMPK-like enzyme for dTTP synthesis."

Verbatim abstract (PMID:34994281, Nucleosides Nucleotides Nucleic Acids 2022):

"Deficiency in TMPK activity due to genetic alterations of DTYMK, i.e., the gene coding for TMPK, causes severe microcephaly in humans. However, no defects were observed in other tissues, suggesting the existence of a compensatory enzyme for dTTP synthesis." "…because of its low activity, isoform 6 is unlikely be able to compensate for the loss of TMPK activity caused by deletions and/or point mutations of the DTYMK gene."

Gene–environment interactions

None documented. CTD, PheGenI, and the primary literature contain no GxE evidence for DTYMK/CONPM. Theoretically plausible but untested interactions worth flagging as knowledge gaps: (i) thymidine/deoxynucleoside availability (relevant to the NCT04802707 trial, §12); (ii) antifolate or nucleoside-analogue drug exposure in carriers, given that the pathway is the target of 5-FU/methotrexate-class agents; (iii) genotoxic exposure (UV/ionizing radiation) given the demonstrated DNA-damage-response defect. None of these are supported by data — do not curate as evidence-backed.

3. Phenotypes

3.1 HPO annotations for OMIM:619847 (authoritative, with case-count frequencies)

Retrieved from the HPO annotation API (ontology.jax.org/api/network/annotation/OMIM:619847). Frequencies are n-of-N counts over the reported cases, not population frequencies. Denominators of 4 indicate annotation across both clinical reports (Vanoevelen n=2 + Lam n=2); denominators of 2 indicate a single report.

HP ID	Phenotype	Count	Suggested dismech FrequencyEnum
HP:0001263	Global developmental delay	4/4	OBLIGATE / VERY_FREQUENT
HP:0002059	Cerebral atrophy	3/4	VERY_FREQUENT
HP:0011451	Primary microcephaly	2/2	VERY_FREQUENT
HP:0000252	Microcephaly	1/2	(redundant with above; prefer HP:0011451 + progressive qualifier)
HP:0001252	Hypotonia	2/2	VERY_FREQUENT
HP:0012704	Widened subarachnoid space	2/2	VERY_FREQUENT
HP:0003593	Infantile onset	2/2	— (onset, not phenotype)
HP:0003577	Congenital onset	2/2	— (onset)
HP:0003819	Death in childhood	2/2	VERY_FREQUENT
HP:0002151	Increased circulating lactate	2/2	VERY_FREQUENT
HP:0000028	Cryptorchidism	2/4	FREQUENT (males only)
HP:0001249	Intellectual disability	1/1	(only assessable in survivors)
HP:0001250	Seizure	1/2	FREQUENT
HP:0002133	Status epilepticus	1/2	FREQUENT
HP:0002373	Febrile seizure (3 mo–6 y)	1/2	FREQUENT
HP:0001336	Myoclonus	1/2	FREQUENT
HP:0002376	Developmental regression	1/2	FREQUENT
HP:0001257	Spasticity	1/2	FREQUENT
HP:0002510	Spastic tetraplegia	1/2	FREQUENT
HP:0001276	Hypertonia	1/2	FREQUENT
HP:0002179	Opisthotonus	1/2	FREQUENT
HP:0001347	Hyperreflexia	1/2	FREQUENT
HP:0002169	Clonus	1/2	FREQUENT
HP:0003487	Babinski sign	1/2	FREQUENT
HP:0002451	Limb dystonia	1/2	FREQUENT
HP:0100021	Cerebral palsy	1/2	FREQUENT
HP:0002171	Gliosis	1/2	FREQUENT (neuropathology)
HP:0006956	Lateral ventricle dilatation	1/2	FREQUENT
HP:0100704	Cerebral visual impairment	1/2	FREQUENT
HP:0000407	Sensorineural hearing impairment	1/2	FREQUENT
HP:0011968	Feeding difficulties	1/2	FREQUENT
HP:0033454	Tube feeding	1/2	FREQUENT
HP:0002015	Dysphagia	1/2	FREQUENT
HP:0001601	Laryngomalacia	1/2	FREQUENT
HP:0002878	Respiratory failure	1/2	FREQUENT
HP:0004322	Short stature	1/2	FREQUENT
HP:0001518	Small for gestational age	1/2	FREQUENT
HP:0003348	Hyperalaninemia	1/2	FREQUENT
HP:0000054	Micropenis	1/2	FREQUENT (males)
HP:0000341	Narrow forehead	1/2	FREQUENT
HP:0000293	Full cheeks	1/2	FREQUENT
HP:0001561	Polyhydramnios	1/2	FREQUENT (prenatal)
HP:0001623	Breech presentation	1/2	FREQUENT (prenatal)
HP:0000007	Autosomal recessive inheritance	—	inheritance slot

Phenotypes documented in the literature but NOT in the current HPO annotation set (candidate HPO-annotation gaps worth flagging upstream):

Phenotype	Suggested HP term	Source
Basal ganglia atrophy / "disappearance of the basal ganglia"	HP:0006979 (Abnormal basal ganglia morphology) or HP:0002135 (Abnormality of the basal ganglia) — the specific "basal ganglia atrophy" concept should be verified with OAK	PMID:34918187 abstract, verbatim: "Brain imaging revealed severe cerebral atrophy and disappearance of the basal ganglia."
Absent visual tracking / no eye contact	HP:0000618 (Blindness) or HP:0007843? — prefer HP:0100704 (cerebral visual impairment, already annotated)	PMID:34918187 [full-text]
Cerebellar atrophy	HP:0001272	PMID:40696808 (Mexican case reports "cortical and cerebellar atrophy" — note this CONTRADICTS the cerebellar sparing in Vanoevelen; see §7 discrepancy note)
Microcytic hypochromic anemia	HP:0004840 (verify)	PMID:34918187 [full-text], Individual II
Elevated hepatic transaminases	HP:0002910	PMID:34918187 [full-text], Individual II
Failure to thrive / growth retardation	HP:0001508	PMID:34918187 abstract: "severe microcephaly and growth retardation with minimal neurodevelopment"
Epilepsy (as distinct from single seizures)	HP:0001250 with `temporality: RECURRENT`	PMID:40696808
Absent speech	HP:0001344	Lam et al. milder sibling phenotype (per OMIM summary)

3.2 Phenotype characteristics by domain

Neurodevelopmental / cognitive - Type: clinical sign + developmental - Onset: congenital to infantile (HP:0003577 2/2; HP:0003593 2/2). Feeding problems from day 3 of life in Individual I [full-text]. - Severity: severe to profound in the Vanoevelen/Hernández-Carreto cases (essentially no milestones achieved); moderate-severe intellectual disability with poor speech in the Lam siblings. - Progression: progressive with frank regression — this is the defining feature separating CONPM from static primary microcephaly. Individual I was hypotonic at birth then "developed spasticity with opisthotonus within 1 year of age" [full-text]. - QoL: catastrophic. Total dependence for all activities of daily living; no communication; tube feeding; recurrent aspiration/respiratory illness. No formal QoL instrument (EQ-5D, PROMIS, PedsQL) has been applied — a genuine data gap.

Microcephaly - Type: physical manifestation / clinical sign - Onset: congenital but predominantly postnatal-progressive. Individual I had OFC 31 cm at birth (2nd centile — i.e., borderline, not markedly microcephalic) and reached −7.6 SD by 9 months; Individual II reached −7.4 SD by 26 months [full-text]. This trajectory (near-normal at birth → extreme by 1–2 years) is the single most curation-relevant temporal detail and should drive a clinical_course: PROGRESSIVE qualifier. - Severity: extreme (−7 SD or worse). - Frequency: 2/2 in the severe cases; small head circumference in the milder siblings.

Seizures / epilepsy - Type: clinical sign - Onset: 6 months (febrile seizures, Individual I); 15 months (myoclonic jerks, Individual II) [full-text]; epilepsy present in the 2-year-old Mexican case (PMID:40696808). - Semiology: febrile seizures, myoclonic jerks, status epilepticus. - EEG: Individual I had a flat-trace EEG treated with phenobarbital [full-text] — consistent with profound cortical loss rather than a primary channelopathy. - Progression: progressive; drug response poor.

Motor / tone - Biphasic pattern: neonatal hypotonia → evolving spastic hypertonia with hyperreflexia, clonus, extensor plantar responses, spastic tetraplegia, opisthotonus, limb dystonia. Individual II retained "good control of the head" while having increased distal tone, bilateral clonus, and positive Babinski signs [full-text].

Visual - Absent visual tracking/eye contact from the first months; annotated as cerebral (cortical) visual impairment (HP:0100704). "No eye contact was ever made" (Individual I) [full-text].

Growth / feeding - SGA (1/2), short stature (1/2), poor feeding from the neonatal period requiring nasogastric tube, dysphagia, laryngomalacia. Individual II birth weight 2250 g (−1.8 SD) [full-text].

Laboratory abnormalities — important because they are the metabolic-workup handles - Increased circulating lactate (HP:0002151) — 2/2. LOINC: 2524-7 (Lactate [Moles/volume] in Serum or Plasma), 32693-4 (Lactate, blood); CSF lactate LOINC 2519-7. - Hyperalaninemia (HP:0003348) — 1/2. LOINC 26603-3 (Alanine [Moles/volume] in Plasma). The lactate+alanine pattern is the classic mitochondrial-disease screen and explains why the Lam siblings were worked up as MDDS. - Microcytic hypochromic anemia and elevated liver enzymes (Individual II) [full-text]. - Fibroblast dTMPK enzyme activity — the diagnostic functional assay (see §10).

Urogenital - Cryptorchidism 2/4, micropenis 1/2 — notable as the only consistent extra-CNS structural finding, and worth flagging mechanistically since gonadal/germline tissue is highly proliferative.

Neuropathology - Gliosis (HP:0002171). "Pathology in individual I confirms massive neuronal dropout, only sparing the dentate nucleus and brain stem." [full-text]

4. Genetic / Molecular Information

Gene

Field	Value
Symbol	DTYMK
HGNC	HGNC:3061 → dismech CURIE form `hgnc:3061` (lowercase per repo convention)
Approved name	deoxythymidylate kinase
Previous symbols	CDC8, TYMK, TMPK
Aliases	dTMP kinase, thymidylate (dTMP) kinase
Locus	2q37.3
NCBI Gene	1841
Ensembl	ENSG00000168393
RefSeq transcript	NM_012145.4 (isoform 1, the characterized functional enzyme)
UniProt	P23919 (thymidylate kinase / dTMP kinase), 212 aa
EC	2.7.4.9
OMIM gene	*188345

Protein: 212-aa homodimeric P-loop kinase of the thymidylate kinase family. Reaction: dTMP + ATP → dTDP + ADP (Mg²⁺-dependent). Localizes to cytosol, nucleus, and mitochondrion (UniProt P23919). Human Protein Atlas reports low tissue specificity (tau 0.29), detected in all tissues, assigned to the "Bone marrow – Nuclear processes" expression cluster, with HPA IF subcellular localization to mitochondria and moderate, non-distinctive expression across brain regions. Curation note: the absence of brain-enriched expression means the brain-restricted phenotype is not explained by expression pattern — it must be explained by the proliferative/repair demands of neurodevelopment plus the postmitotic vulnerability of neurons.

Reported pathogenic variants (all germline; ClinVar-verified)

cDNA (NM_012145.4)	Protein	Type	ClinVar VCV	Classification	Review status	Population AF
c.242C>T	p.Pro81Leu	missense	VCV001686905	Likely pathogenic	criteria provided, single submitter	gnomAD 0.00001
c.382G>A	p.Asp128Asn	missense	VCV001686904	Pathogenic	no assertion criteria provided	gnomAD 0.00002; ExAC 0.00002; TOPMed 0.00001; ESP 0.00008; 1000G 0.00020
c.295G>A	p.Ala99Thr	missense	VCV001686903	Pathogenic	no assertion criteria provided	gnomAD 0.00003; gnomAD exomes 0.00001; TOPMed 0.00003
c.287_320del	p.Asp96fs	frameshift deletion (34 bp)	VCV001686902	Pathogenic	no assertion criteria provided	not reported
c.265_270del	p.Gln89_Gly90del	in-frame deletion	VCV004277573	Likely pathogenic	criteria provided, single submitter	not reported
c.239+1045_239+1050del	(deep intronic)	deletion	VCV003065236	VUS / VUS-high	criteria provided, multiple submitters, no conflicts	not reported

Genotype assignments by patient:

Patient	Ancestry	Genotype	Source
Individual I (F)	Dutch, non-consanguineous	compound heterozygous c.242C>T (p.Pro81Leu, paternal) / c.382G>A (p.Asp128Asn, maternal)	PMID:34918187 [full-text]
Individual II (M)	Egyptian, consanguineous	homozygous c.242C>T (p.Pro81Leu)	PMID:34918187 [full-text]
Lam siblings ×2	Chinese (Hong Kong)	compound heterozygous, two variants in trans — the ACS Omega functional paper identifies the four patient variants as "P81L, A99T, D128N, and a frameshift", and ClinVar links both c.295G>A (p.Ala99Thr) and c.287_320del (p.Asp96fs) to CONPM, so A99T + D96fs is the strongly-supported inferred pairing for the Lam siblings. Verify against the Clin Chim Acta full text before curating the phase assignment as fact.	PMID:31271740; PMID:34926941
Mexican case (M, 2 y)	Mexican	homozygous c.242C>T (p.Pro81Leu)	PMID:40696808 (verbatim abstract)

p.Pro81Leu is the recurrent allele, seen in 3 of 5 reported patients across Egyptian, Dutch, and Mexican ancestries — consistent with recurrent mutation rather than a founder effect (no shared haplotype reported; the three ancestries are unrelated).

Functional consequences — loss of function via loss of obligate dimerization

Verbatim abstract (PMID:34926941, ACS Omega 2021):

"Here we show that in fibroblasts derived from a patient, the P81L and D128N mutations led to a complete loss of TMPK activity in mitochondria and extremely low and unstable TMPK activity in cytosol. Despite the lack of TMPK activity, the patient-derived fibroblasts apparently grew normal. … The wild-type TMPK mainly exists as a dimer with high substrate binding affinity, that is, low KM value and high catalytic efficiency, that is, kcat/KM. In contrast, all mutants were present as monomers with dramatically reduced substrate binding affinity and catalytic efficiencies. Based on the human TMPK structure, none of the mutated amino acids interacted directly with the substrates."

Kinetics [full-text, Table 2 of PMID:34926941 — re-verify before use]:

Enzyme	dTMP KM (μM)	dTMP kcat (s⁻¹)	dTMP kcat/KM (M⁻¹s⁻¹)	ATP KM (μM)	ATP kcat/KM (M⁻¹s⁻¹)
WT	1.75 ± 0.88	3.24 ± 0.23	1.85 × 10⁶	1.11 ± 0.15	2.51 × 10⁶
A99T	24.6 ± 5.4	6.92 ± 0.42	0.28 × 10⁶ (−85%)	41.3 ± 4.03	0.11 × 10⁶ (−96%)
P81L	115.9 ± 31.2	17.2 ± 2.13	0.14 × 10⁶ (−92%)	43.1 ± 3.67	0.12 × 10⁶ (−95%)
D128N	too low for reliable kinetic analysis	—	—	—	—

Key mechanistic insight for the pathophysiology graph: the missense substitutions are not active-site contact residues. They act allosterically/structurally, converting the obligate homodimer into a catalytically crippled monomer. This is a dimerization-disruption LoF, not a substrate-binding LoF — a distinction worth capturing as a distinct MOLECULAR-scale pathophysiology node.

Cellular enzyme activity [full-text, PMID:34918187]: - Individual I fibroblasts: 0.62 pmol/min/mg protein (essentially undetectable) - Mother: 43.65 pmol/min/mg; Father: 31.08 pmol/min/mg (both normal) - Statistical significance: mother vs. proband p = 1.46 × 10⁻⁶; father vs. proband p = 5.77 × 10⁻⁶ - Compartment-specific finding: no detectable TMPK activity in mitochondria; low, unstable activity in cytosol (PMID:34926941 abstract, verbatim above).

Modifier genes

None identified. The most important open question in this space is not a modifier gene per se but the identity of the unknown compensatory TMPK-like enzyme postulated to sustain dTTP synthesis in non-neural tissue. Frisk et al. systematically excluded the five non-canonical DTYMK mRNA isoforms (isoforms 2–5 lack essential substrate-binding elements; isoform 6 retains intact catalytic centres but has <0.1% of isoform-1 activity) — PMID:34994281. Vanoevelen et al. considered and rejected CMPK2: "has no apparent capability to use dTMP as a substrate, it would appear unlikely that CMPK2 can fulfill this function. Thus, a compensatory pathway for dTTP generation remains to be proven." [full-text]

This is the single best KNOWLEDGE_GAP discussion item for the dismech entry.

Epigenetics

No DNA methylation, histone-modification, chromatin, or episignature data exist for CONPM. DTYMK is not on any published rare-disease episignature panel. Not applicable / no data.

Chromosomal abnormalities

None reported as a cause of CONPM. Note that DTYMK lies at 2q37.3, within the interval commonly deleted in 2q37 deletion / Brachydactyly–Mental Retardation syndrome (which dismech already curates as 2q37_Microdeletion_Syndrome.yaml, driven by HDAC4). There is no evidence that DTYMK haploinsufficiency contributes to the 2q37 deletion phenotype, and the mouse heterozygote data argue against it (PMID:38621447). Do not cross-link these two entries as mechanistically related without new evidence; a "same locus, different mechanism" note is appropriate if any link is made at all.

Population constraint

gnomAD constraint metrics (pLI / LOEUF / missense Z) for DTYMK could not be retrieved through available tooling in this session (the gnomAD browser is a JS app and the GraphQL endpoint requires POST). Do not assert a pLI or LOEUF value from memory. Fetch these directly before curating a constraint claim. The relevant biological constraint statement that IS evidenced: homozygous Dtymk knockout is embryonic lethal in mouse while heterozygotes are normal (PMID:38621447) — i.e., recessive essentiality, not haploinsufficiency.

5. Environmental Information

Environmental factors: none. No entries in CTD linking environmental chemicals to CONPM. (CTD does contain DTYMK–chemical interactions from toxicogenomic screens, but these are gene-expression associations in unrelated experimental contexts and are not disease-etiologic — do not curate them as risk factors.)
Lifestyle factors: not applicable (congenital-onset monogenic disorder).
Infectious agents: not causal. Infection is however a major proximate cause of death: Individual I died at 18 months from cardiopulmonary arrest following a respiratory illness; Individual II died at 32 months from pneumonia and coma [full-text]. Curate these as complications/terminal events (§11), not as etiology.
Fever as a trigger: Individual I had recurrent febrile seizures (HP:0002373) [full-text]. Whether fever is a genuine decompensation trigger (as in some intoxication-type IEMs) is unstudied — a legitimate hypothesis-flagged item, not an evidenced claim.

6. Mechanism / Pathophysiology

6.1 The causal chain (proposed pathograph, upstream → downstream)

[MOLECULAR] Biallelic DTYMK LoF variants (p.Pro81Leu / p.Asp128Asn / p.Ala99Thr / p.Asp96fs)
     │
     ▼
[MOLECULAR] Loss of TMPK homodimerization → monomeric, catalytically crippled enzyme
     │  (kcat/KM reduced 85–96%; D128N below detection)
     ▼
[MOLECULAR] Loss of dTMP → dTDP phosphorylation (EC 2.7.4.9); COMPLETE block of the
     │  canonical dTTP supply, because de novo (TYMS) and salvage (TK1/TK2) both
     │  converge on dTMP UPSTREAM of TMPK
     ▼
[CELLULAR] dTTP insufficiency in cells with high replicative/repair demand
     │        ├──► Impaired DNA replication; S-phase collapse (patient fibroblasts 2.8% S-phase
     │        │     vs. 23.65%/16.03% in parents) [full-text]
     │        ├──► Nucleotide-pool imbalance → RIBONUCLEOTIDE MISINCORPORATION into genomic DNA
     │        │     (dtymk⁻/⁻ zebrafish gDNA fragility comparable to Rnaseh2⁻/⁻ mouse) [full-text]
     │        └──► Impaired DNA damage response (persistent γH2AX 24 h post-UV) [full-text]
     ▼
[CELLULAR] Genome instability in the developing and mature CNS
     ▼
[CELLULAR] Neuronal apoptosis / neuronal dropout
     │  (dtymk mutant zebrafish: significantly more apoptotic cells in forebrain,
     │   p = 6.45 × 10⁻⁶ vs. wild type) [full-text]
     ▼
[TISSUE] Progressive cerebral and striatal atrophy with gliosis;
     │  relative sparing of brainstem, cerebellum, dentate nucleus
     ▼
[ORGANISM] Progressive microcephaly, developmental regression, epilepsy, spastic
    tetraplegia, cortical blindness → early childhood death

┌─ PARALLEL / CONTESTED ARM (Lam et al. 2019) ─────────────────────┐
│ Mitochondrial TMPK activity loss → mitochondrial dTTP pool       │
│ depletion → mtDNA replication failure → mtDNA DEPLETION →        │
│ OXPHOS deficiency → lactic acidemia (HP:0002151, 2/2) and        │
│ hyperalaninemia (HP:0003348, 1/2)                                │
│ STATUS: mtDNA depletion shown "in silico" only in one sibling;   │
│ mitochondrial TMPK activity loss confirmed biochemically         │
│ (PMID:34926941). Curate as an EMERGING mechanistic_hypothesis.   │
└──────────────────────────────────────────────────────────────────┘

┌─ UNRESOLVED COMPENSATION (the central paradox) ──────────────────┐
│ Unknown "TMPK-like" enzyme sustains dTTP in non-neural tissue →  │
│ near-normal bulk dNTP pools; normal fibroblast proliferation;    │
│ viability to birth despite complete canonical-pathway block.     │
│ Identity unknown. CMPK2 and DTYMK isoform 6 both excluded.       │
│ Curate as KNOWLEDGE_GAP.                                         │
└──────────────────────────────────────────────────────────────────┘

6.2 Molecular pathways

Pyrimidine deoxyribonucleotide biosynthesis — KEGG hsa00240 (Pyrimidine metabolism). Reactome hosts the reaction under pyrimidine deoxyribonucleotide biosynthesis (the Reactome ContentService returned 403 in this session; fetch and verify the exact stable ID before curating — do not assert an R-HSA ID from memory).
De novo arm: dUMP —(TYMS, folate-dependent)→ dTMP
Salvage arm: thymidine —(TK1 cytosolic / TK2 mitochondrial)→ dTMP
Convergence point: dTMP —(DTYMK/TMPK, blocked)→ dTDP —(NME/NDPK)→ dTTP
Downstream: DNA replication, DNA repair, mtDNA replication.

6.3 Cellular processes and GO term suggestions

Process	Suggested GO term	Modifier
dTMP kinase activity (molecular function)	GO:0004798 dTMP kinase activity	DECREASED / ABSENT
ATP binding	GO:0005524	—
dTDP biosynthetic process	GO:0006233	DECREASED
dTTP biosynthetic process	GO:0006235	DECREASED
Thymidine biosynthetic process	GO:0046105	DECREASED
DNA replication	GO:0006260	DECREASED
DNA repair	GO:0006281	DECREASED
Cellular response to DNA damage stimulus / DDR signal transduction	GO:0006974 / GO:0000077	DECREASED (impaired resolution)
Apoptotic process / neuron apoptotic process	GO:0006915 / GO:0051402	INCREASED
Mitochondrial DNA replication	GO:0006264	DECREASED (hypothesis arm)
Brain development / forebrain development	GO:0007420 / GO:0030900	DECREASED
Cell cycle / G1-S transition	GO:0007049 / GO:0000082	DECREASED
Protein homodimerization activity	GO:0042803	DECREASED (the LoF mechanism)

All GO IDs above are candidates — verify each with uv run runoak -i sqlite:obo:go info GO:XXXXXXX -O obo before commit.

6.4 Protein dysfunction

Loss of function via failure of obligate homodimerization. Not misfolding-aggregation, not gain of function, not dominant-negative (heterozygous parents and heterozygous mice are unaffected). Structural rationale: the substituted residues (P81, A99, D128) do not contact substrate; structural modelling explains how each substitution destabilizes the dimer interface / catalytic architecture (PMID:34926941). Structure resources: PDB entries for human TMPK exist (search "human thymidylate kinase" in PDB); AlphaFold model AF-P23919.

6.5 Metabolic changes

Profound reduction of dTDP/dTTP synthetic flux through the canonical route.
Paradox to curate carefully: measured steady-state dNTP pools in patient fibroblasts and in zebrafish mutant larvae "resemble those of normal controls" [full-text]. The disease is therefore best modeled as a flux/compartment/demand-limited defect, not a bulk pool-depletion defect. This distinction matters for any downstream biomarker claim — a normal fibroblast dNTP panel does not exclude CONPM.
Secondary systemic markers: elevated lactate (2/2) and hyperalaninemia (1/2) → a mitochondrial-disease-like biochemical signature that will route these patients into an MDDS workup.
CHEBI candidates (verify with OAK): dTMP CHEBI:17013, dTDP CHEBI:58369, dTTP CHEBI:37568, ATP CHEBI:30616, thymidine CHEBI:17748, deoxycytidine CHEBI:15698, L-lactate CHEBI:16651, L-alanine CHEBI:16977.

6.6 Immune system involvement

None known. No autoimmunity, immunodeficiency, or interferonopathy has been reported. This is worth an explicit negative note because the mechanism — ribonucleotide misincorporation into genomic DNA, explicitly benchmarked in the paper against Rnaseh2-null mouse DNA — is the exact molecular lesion of Aicardi–Goutières syndrome type 4 (RNASEH2B/C/A), which is a type I interferonopathy. Whether CONPM has an unrecognized cGAS-STING/interferon component is an explicitly attractive, entirely untested hypothesis and an excellent KNOWLEDGE_GAP / proposed_experiments item (measure interferon signature in patient fibroblasts and dtymk zebrafish).

6.7 Tissue damage mechanisms

Neuronal apoptosis and neuronal dropout with reactive gliosis; not oxidative stress, ischemia, or fibrosis. Zebrafish histology showed "empty spaces, indicative of neurodegeneration" in brain [full-text]. Human neuropathology: "massive neuronal dropout, only sparing the dentate nucleus and brain stem" [full-text].

6.8 Biochemical abnormalities

Enzyme deficiency (EC 2.7.4.9). Diagnostic assay: dTMPK activity in cultured fibroblasts (see §10). No receptor or ion-channel defect.

6.9 Epigenetic changes

No data.

6.10 Molecular profiling

Transcriptomics: no patient RNA-seq published for CONPM. GTEx/HPA show broad, non-tissue-specific DTYMK expression.
Proteomics / metabolomics / lipidomics: no disease-specific studies. No MetaboLights or PRIDE datasets for CONPM.
Single-cell / spatial: none.
Functional genomics screens: DTYMK is a common essential gene in DepMap CRISPR screens (consistent with the mouse embryonic lethality) — verify the current DepMap common-essential call before citing. The uveal-melanoma study demonstrates pharmacological DTYMK inhibition (YMU1) synergizing with PARP1 inhibition (pamiparib) (PMID:39195238), which is independent orthogonal support for the "DTYMK loss → DNA repair burden" arm of the mechanism, in a cancer rather than neuronal context.

Verbatim abstract (PMID:39195238, Cells 2024):

"Our hypothesis of the double hit into tumoral DNA metabolism as a possible therapeutic option in uveal melanoma was confirmed since combined targeting of DTYMK and PARP1 affected all tested cytophysiological parameters with the highest efficiency."

7. Anatomical Structures Affected

Organ level

Primary: brain (central nervous system). UBERON:0000955 (brain).
Secondary: none primarily; respiratory (aspiration pneumonia, respiratory failure, laryngomalacia), GI (dysphagia, feeding failure), haematological (microcytic anemia, 1 patient), hepatic (transaminase elevation, 1 patient), urogenital (cryptorchidism, micropenis).
Body systems: nervous (dominant); with secondary respiratory, digestive, and reproductive involvement.

Regional CNS involvement — the sparing pattern is diagnostically important

Structure	UBERON candidate	Involvement
Cerebral hemispheres / cerebral cortex	UBERON:0000956	Severely atrophic ("dramatic atrophy of the cerebral hemispheres")
Basal ganglia / striatum	UBERON:0002420 (basal ganglion); UBERON:0002435 (striatum)	Severely affected — "disappearance of the basal ganglia" (abstract, verbatim); "basal nuclei were small" [full-text]
Lateral ventricles	UBERON:0002285 (telencephalic ventricle)	Severely enlarged (ex vacuo)
Subarachnoid space	UBERON:0002450 (verify)	Widened, 2/2 (HP:0012704)
Thalamus	UBERON:0001897	"appeared to have a normal size" [full-text] — spared
Brainstem	UBERON:0002298	Spared (both patients)
Cerebellum	UBERON:0002037	Spared in Vanoevelen patients — but the 2025 Mexican case reports "cortical and cerebellar atrophy" (PMID:40696808 abstract, verbatim). Curate this as a documented inter-patient discrepancy, not as a resolved fact.
Dentate nucleus	UBERON:0002688	Spared on neuropathology [full-text]

Lateralization: bilateral and symmetric (generalized atrophy). No asymmetry reported.

Tissue and cell level

Cell type	CL candidate	Role
Neuron	CL:0000540	Primary target; apoptosis/dropout
CNS neuron (sensu Vertebrata)	CL:0000117	more specific alternative
Neural progenitor / neuronal stem cell	CL:0000047	Likely the proliferative compartment where dTTP demand is highest (mechanistically inferred; not directly demonstrated in human tissue — flag as inference)
Medium spiny neuron	CL:0000706 (verify)	Implied by striatal loss
Astrocyte	CL:0000127	Gliosis (HP:0002171)
Microglial cell	CL:0000129	Presumed reactive; not directly demonstrated
Fibroblast	CL:0000057	The ex vivo assay tissue; notably functionally spared despite enzyme loss

Key modeling caution: the phenotype has two temporally distinct cellular substrates — (a) a proliferative phase defect (neural progenitors, replication/S-phase) explaining microcephaly, and (b) a postmitotic defect (mature neurons, DNA repair burden) explaining progressive degeneration. These should be separate pathophysiology nodes with distinct biological_scale: CELLULAR tags, not bundled.

Subcellular level

Compartment	GO CC	Note
Nucleus	GO:0005634	genomic DNA replication/repair; site of ribonucleotide misincorporation
Cytosol	GO:0005829	residual, unstable TMPK activity in patient cells
Mitochondrion	GO:0005739	Complete loss of TMPK activity in patient fibroblast mitochondria (PMID:34926941) — the anchor for the mtDNA-depletion hypothesis arm

8. Temporal Development

Onset

Congenital onset (HP:0003577) 2/2 and infantile onset (HP:0003593) 2/2 — both annotated, reflecting that prenatal/neonatal features (SGA, polyhydramnios, breech, neonatal feeding failure, neonatal hypotonia) precede the overt neurological syndrome.
Prenatal signals are nonspecific: polyhydramnios 1/2, breech presentation 1/2, SGA 1/2. Head circumference is near-normal at birth (Individual I: 31 cm, 2nd centile) — CONPM is not reliably detectable by prenatal or newborn OFC.
Onset pattern: insidious/chronic-progressive with a subacute regression phase in infancy.

Progression

Rate: rapid by neurodegenerative standards. OFC crosses from ~2nd centile to −7.6 SD within 9 months (Individual I) and to −7.4 SD by 26 months (Individual II) [full-text].
Course: relentlessly progressive; no remission, no relapsing-remitting pattern, no plateau documented in the severe form.
Stages (proposed, for curation):
Neonatal (0–3 mo): hypotonia, feeding failure, NG-tube dependence, absent visual fixation. OFC near-normal.
Infantile decline (3–15 mo): rapid OFC deceleration, spasticity replacing hypotonia, opisthotonus, seizure onset, no milestones acquired/loss of acquired milestones.
Advanced (15 mo–death): spastic tetraplegia, myoclonus, status epilepticus, flat-trace EEG, complete cortical/striatal atrophy on imaging, respiratory and swallowing failure.
Terminal: intercurrent respiratory infection → pneumonia/cardiopulmonary arrest.
Duration: lifelong; life-limiting. Death in childhood 2/2 (HP:0003819) — ages 18 and 32 months in the two severe cases.
Milder end of spectrum: the Lam siblings survived to allow assessment of intellectual disability and speech, indicating a genuinely broader survival range. Precise ages/outcomes require the Clin Chim Acta full text.

Patterns

Remission: none, spontaneous or treatment-induced.
Critical periods: the first 12 months — the window during which OFC collapses and the atrophy becomes established. Any disease-modifying intervention would almost certainly need to act prenatally or in the first months. Curate this as the therapeutic window, and note that no such intervention exists.
Fever/illness as a decompensation trigger: suggested by febrile seizures and by the fact that both deaths followed intercurrent respiratory infection, but not established as a metabolic-decompensation mechanism.

9. Inheritance and Population

Epidemiology

Prevalence: not documented. No ORPHA prevalence class is available (no Orphanet entry found). For a dismech Prevalence record the honest structured encoding is:
measure_type: CASES_IN_LITERATURE
prevalence_class: ULTRA_RARE (or NOT_YET_DOCUMENTED)
notes: "Five patients reported worldwide as of 2025 (Vanoevelen 2022 n=2; Lam 2019 n=2; Hernández-Carreto 2025 n=1)."
Do not populate rate_per_100000.
Incidence: unknown.
Verbatim abstract (PMID:40696808): "Only four cases have been reported in the literature to date. This paper's objective is to describe the fifth globally reported case of CONPM and the first documented in a Mexican patient…"

Genetic epidemiology

Parameter	Value	Evidence
Inheritance	Autosomal recessive — HP:0000007	HPO annotation; OMIM #619847; all patients biallelic; parents unaffected heterozygotes
Penetrance	Appears complete for biallelic LoF; n too small for a formal estimate	5/5 biallelic individuals affected
Expressivity	Variable — this is explicit in the OMIM summary: severe (no milestones, death <3 y) vs. milder (small head, severe ID, poor speech, motor delay). Genotype–phenotype correlation is not established; note that p.Pro81Leu homozygotes span the severe end (Egyptian, Mexican cases)	OMIM #619847; PMID:34918187; PMID:31271740
Genetic anticipation	Not applicable (no repeat expansion)	—
Germline mosaicism	Not reported	—
Founder effect	None demonstrated. p.Pro81Leu recurs across three unrelated ancestries (Dutch, Egyptian, Mexican) without a reported shared haplotype — favours recurrent mutation	ClinVar; PMID:34918187; PMID:40696808
Consanguinity	Contributory in at least the Egyptian case (documented consanguinity, homozygous P81L) and presumptively in the Mexican homozygous case	PMID:34918187 [full-text]; PMID:40696808
Carrier frequency	Not established. Individual allele frequencies in gnomAD are ~1–3 × 10⁻⁵; the aggregate carrier frequency for pathogenic DTYMK alleles has not been computed and should not be estimated here	ClinVar/gnomAD

Population demographics

Affected populations: Dutch, Egyptian, Chinese (Hong Kong), Mexican — i.e., no ethnic clustering; the disorder is pan-ethnic and its rarity is a function of allele rarity, not population structure.
Geographic distribution: none (case reports from Europe, North Africa, East Asia, Latin America).
Variant geography: p.Pro81Leu reported in Netherlands, Egypt, Mexico; p.Asp128Asn in the Netherlands; p.Ala99Thr and p.Asp96fs in Hong Kong.
Sex ratio: among the fully characterized cases, 1 female (Individual I) and 2 males (Individual II, Mexican case); the Lam siblings' sexes require the full text. n = 5 is far too small to infer a sex ratio — curate as "no sex bias reported" rather than a ratio.
Age distribution: all affected individuals identified in infancy/early childhood; no adult-onset or adult-diagnosed cases.

10. Diagnostics

Clinical / laboratory tests

Test	Finding	LOINC / notes
Plasma lactate	Elevated, 2/2 (HP:0002151)	LOINC 2524-7 / 32693-4
Plasma amino acids (alanine)	Hyperalaninemia, 1/2 (HP:0003348)	LOINC 26603-3
CBC	Microcytic hypochromic anemia (1 patient) [full-text]
Liver enzymes	Elevated (1 patient) [full-text]	ALT LOINC 1742-6; AST 1920-8
Fibroblast dTMPK enzyme activity	The confirmatory functional assay. Patient 0.62 pmol/min/mg vs. parents 43.65 and 31.08 pmol/min/mg [full-text]. Available only as a research assay.	No LOINC code identified
Subcellular fractionation TMPK assay	Absent mitochondrial activity; low/unstable cytosolic activity (PMID:34926941)	research assay
Fibroblast dNTP pool quantification	Normal or near-normal — a NEGATIVE result does not exclude the diagnosis [full-text]	research assay; important caveat
Cell-cycle/S-phase analysis of fibroblasts	Reduced S-phase fraction (2.8% vs. 16–24% parental) [full-text]	research assay
mtDNA copy number (muscle/blood)	mtDNA depletion asserted "in silico" in one Lam sibling — i.e., inferred, not directly quantified (PMID:31271740 verbatim). Direct qPCR mtDNA copy-number quantification in patient tissue is an outstanding validation experiment.	LOINC not established

Imaging

Brain MRI is the highest-yield diagnostic modality. Expected findings: - Profound generalized cerebral atrophy (HP:0002059) - Marked lateral ventricular dilatation (HP:0006956) and widened subarachnoid spaces (HP:0012704) - Small/"disappeared" basal ganglia — the most distinctive feature - Normal-sized thalamus, brainstem, and (usually) cerebellum - Serial imaging showing progression is more informative than a single study.

Verbatim (PMID:34918187 abstract): "Brain imaging revealed severe cerebral atrophy and disappearance of the basal ganglia."

Electrophysiology

EEG: abnormal; flat trace documented in the advanced stage of Individual I [full-text]. No pathognomonic pattern.
EMG/NCS/ECG: no reported abnormalities; peripheral nerve involvement not described.

Biopsy / pathology

Neuropathology (post-mortem, Individual I): massive neuronal dropout with sparing of dentate nucleus and brainstem; gliosis [full-text].
Skin biopsy for fibroblast culture is the key diagnostic specimen (enables the enzyme assay).
Muscle biopsy: no characteristic ragged-red/COX-negative findings reported; if the MDDS hypothesis is pursued, muscle mtDNA quantification would be the test.

Genetic testing

Recommended first-tier approach: whole-exome sequencing (WES) or whole-genome sequencing (WGS) with trio analysis. All five reported patients were diagnosed by exome sequencing. WES is what identified the Mexican case ("confirmed through whole-exome sequencing (WES)", PMID:40696808 verbatim) and the Lam siblings ("whole exome sequencing is often needed for their diagnoses", PMID:31271740 verbatim).
Gene panels: DTYMK should be — and in some laboratories now is — included on (a) progressive/primary microcephaly panels, (b) neurodegeneration-in-childhood panels, and (c) mitochondrial DNA depletion syndrome panels. Its inclusion is inconsistent across vendors; verify panel content in GTR for any specific lab before recommending. Confirm current listings at https://www.ncbi.nlm.nih.gov/gtr/.
Single-gene testing: appropriate only for targeted familial-variant testing / cascade screening after a proband diagnosis.
Sanger confirmation + segregation in both parents is essential to establish biallelic status and phase (as done in PMID:40696808).
CMA / karyotype / FISH: low yield for CONPM itself. CMA remains reasonable as part of a general microcephaly workup and would detect a 2q37.3 deletion contributing one allele in a compound-heterozygous configuration — worth explicitly considering, since a whole-gene deletion in trans with a point variant would be missed by exome-only analysis.
mtDNA testing: mtDNA sequencing and copy-number quantification are indicated given the MDDS differential and the lactate/alanine profile.
Repeat expansion testing: not indicated.
RNA-seq: useful as a second-tier tool to resolve the deep-intronic VUS (c.239+1045_239+1050del, VCV003065236) or other candidate splice-affecting alleles.

Clinical criteria and differential diagnosis

No consensus diagnostic criteria exist (too few patients). Diagnosis = compatible phenotype + biallelic DTYMK variants (± functional confirmation).

Differential diagnosis — the most useful section for a curator, because CONPM's imaging and biochemical profile overlaps several well-known entities:

Differential	Distinguishing features
Primary autosomal recessive microcephaly (MCPH; ASPM, WDR62, etc.)	MCPH is congenital and largely static; CONPM head circumference is near-normal at birth then collapses postnatally, with frank degeneration and basal ganglia loss
Mitochondrial DNA depletion syndromes (TK2, DGUOK, POLG, RRM2B, SUCLA2, MPV17, FBXL4, TWNK)	Overlapping lactate/alanine elevation and nucleotide-metabolism logic; distinguish by mtDNA copy number and gene. This is the single highest-risk misclassification — Lam et al. explicitly proposed DTYMK as an MDDS gene
Aicardi–Goutières syndrome (RNASEH2A/B/C, TREX1, SAMHD1, ADAR, IFIH1)	Mechanistically adjacent (ribonucleotide misincorporation / nucleic-acid metabolism), also causes progressive microcephaly with basal ganglia involvement — but AGS has intracranial calcification, CSF pleocytosis, raised CSF interferon-α, and an interferon signature, none of which have been reported (or, importantly, looked for) in CONPM
Pontocerebellar hypoplasia (TSEN54 etc.)	PCH has cerebellar/pontine hypoplasia; CONPM classically spares brainstem and cerebellum
Congenital infection (TORCH/CMV/Zika)	Serology/PCR; intracranial calcification; non-Mendelian
Other serine/nucleotide/one-carbon IEMs (PYCR2, PNKP, serine biosynthesis defects)	Distinguished genetically; PNKP is another DNA-repair microcephaly with epileptic encephalopathy and is a close clinical mimic
Molybdenum cofactor deficiency / sulfite oxidase deficiency	Early catastrophic encephalopathy with cystic cerebral destruction; distinguished by urine sulfite/S-sulfocysteine, low urate

Screening

Newborn screening: not applicable. There is no analyte biomarker, no treatment, and head circumference is near-normal at birth. CONPM fails standard Wilson–Jungner criteria.
Carrier screening: DTYMK is not on standard expanded carrier screening panels. Its inclusion would be defensible only in the context of a known family.
Cascade screening: targeted variant testing of at-risk relatives and reproductive partners after a proband diagnosis — this is the highest-value screening application.

11. Outcome / Prognosis

Survival and mortality

Death in childhood (HP:0003819) in 2/2 of the severely affected annotated individuals.
Documented ages at death: 18 months (Individual I, cardiopulmonary arrest following respiratory illness) and 32 months (Individual II, pneumonia and coma) [full-text].
The milder Lam siblings survived long enough for formal intellectual assessment, establishing that survival beyond early childhood occurs at the mild end. Precise survival data require the primary full text.
No 5-/10-year survival statistics, no life-expectancy estimate, no mortality rate — n is too small. For dismech, curate "death in early childhood in the severe form; survival documented in the milder form" with the two specific ages, rather than any derived rate.
Disease-specific mortality: deaths are attributable to the disease via its complications (respiratory infection, aspiration, respiratory failure) rather than to a single organ failure.

Morbidity and function

Profound, permanent, global disability: no independent sitting, rolling, vocalizing, or smiling in the severe form ("he did not roll over, sit, vocalize, or smile") [full-text]; total care dependence; enteral feeding; refractory epilepsy; cortical blindness; spastic tetraplegia.
No quality-of-life instrument has been applied. No EQ-5D, PedsQL, PROMIS, or CPCHILD data exist. Do not populate QoL scores.
GBD/WHO carry no disease-specific burden estimate.

Complications

Aspiration and recurrent respiratory infection → pneumonia (a documented cause of death); respiratory failure (HP:0002878); laryngomalacia (HP:0001601); dysphagia (HP:0002015) with tube-feeding dependence (HP:0033454); status epilepticus (HP:0002133); failure to thrive/short stature; contractures secondary to spastic tetraplegia (expected, not explicitly reported); microcytic anemia; transaminase elevation.

Recovery potential

None. Neuronal loss is irreversible; no disease-modifying therapy exists; no recovery or plateau has been documented in the severe form.

Prognostic factors

No validated prognostic model. Observationally suggestive (all low-confidence, n=5): - Rate of OFC decline in the first year is the most face-valid clinical prognostic index. - Age at seizure onset (6 months vs. 15 months, both severe). - Residual enzyme activity: biochemically plausible as the primary determinant (p.Ala99Thr retains the highest residual kcat/KM of the characterized missense alleles, and the Lam siblings carrying A99T are at the milder end — an appealing but unproven genotype–phenotype correlation with n=2; explicitly flag as a hypothesis, not a finding). - Prognostic biomarkers: none validated.

12. Treatment

There is no disease-specific or disease-modifying therapy. Management is entirely supportive.

Pharmacotherapy

Treatment	Purpose	Evidence	NCIT candidate
Phenobarbital	Seizure control (used in Individual I) [full-text]	Case-level, n=1	`NCIT:C15986` Pharmacotherapy + `therapeutic_agent` CHEBI:8069 phenobarbital (verify)
Carbamazepine	Myoclonic jerks (used in Individual II) [full-text]	Case-level, n=1. Clinical caveat worth recording: carbamazepine can exacerbate myoclonic seizures; the choice reflects a single clinician's decision, not a guideline.	`NCIT:C15986` + CHEBI:3387 carbamazepine (verify)
Antiseizure medication (general)	Refractory epilepsy	No CONPM-specific efficacy data	`NCIT:C15986`

Pharmacogenomics: no CPIC/PharmGKB guidance specific to DTYMK. A worth-noting theoretical consideration (unstudied — do not curate as evidence): the affected pathway is the target of thymidylate-synthase inhibitors (5-FU, capecitabine) and antifolates (methotrexate); whether DTYMK carriers or patients have altered sensitivity is unknown.

Advanced therapeutics

Gene therapy: none. No preclinical AAV or gene-replacement program identified. DTYMK is small (212 aa CDS, well within AAV capacity) and the disease is recessive LoF — i.e., theoretically tractable — but the postnatal-degeneration timeline and the near-complete atrophy by 12–24 months make the therapeutic window extremely narrow, and no program exists.
Gene editing / cell therapy / mRNA / siRNA / ASO: none. ASO is mechanistically inapplicable (missense LoF, not a splice or knockdown target — with the possible exception of the deep-intronic VUS if it proves splice-altering).
Enzyme replacement: not feasible — TMPK is an intracellular, nuclear/cytosolic/mitochondrial kinase acting on a phosphorylated, membrane-impermeant substrate.

Substrate/nucleoside supplementation — the one active clinical-trial handle, with a critical mechanistic caveat

NCT04802707 — "Deoxynucleosides Pyrimidines as Treatment for Mitochondrial Depletion Syndrome", Phase II, open-label, single-centre, recruiting; deoxycytidine (dC) + deoxythymidine (dT) orally, escalating over 22 days then maintained at 400 mg/kg; ages 0–60; up to ~200 participants. This trial explicitly lists DTYMK among its eligible genotypes.

The record is already present in the dismech reference cache (references_cache/clinicaltrials_NCT04802707.md), and the following is a verified quotable snippet from that cached file:

"The subjects included are children (0-18Y), with positive MDS diagnosis and express mutations in one of the following genes: POLG, POLG2, C10orf2, RRM2B, MPV17, SUCLA2, SUCLG1, FBXL4, DTYMK."

⚠️ Mechanistic caveat that MUST accompany this trial in the knowledge base. Deoxynucleoside substrate-enhancement therapy works in TK2 deficiency because supplying dThd/dCtd bypasses a kinase-limited first salvage step. In DTYMK deficiency the block is at dTMP → dTDP, i.e., downstream of where supplemental thymidine enters the pathway (thymidine → TK1/TK2 → dTMP → [BLOCK]). Supplying more dThd therefore increases the substrate that is already accumulating proximal to the block and has no obvious mechanistic route to restoring dTTP. Supplemental dCtd could in principle relieve dNTP-pool imbalance on the pyrimidine side, but that is speculative.

Recommended curation: record NCT04802707 as a clinical trial whose eligibility includes DTYMK, and attach an explicit discussions entry of kind: KNOWLEDGE_GAP (or a mechanistic_hypotheses entry with status: EMERGING) stating that the substrate-bypass rationale is not established for DTYMK given the position of the enzymatic block, with proposed_experiments = measure dTTP pools and mtDNA copy number in DTYMK-deficient cells ± dT/dC. Do not curate dC/dT as an evidenced treatment for CONPM.

Surgical and interventional

Gastrostomy (PEG) for tube-feeding dependence — clinically standard for this level of dysphagia (NG tube documented; PEG not explicitly reported). NCIT:C15329 Surgical Procedure; consider a gastrostomy-specific NCIT term.
Orchidopexy for cryptorchidism, where clinically indicated. NCIT:C16186 Orthopedic Surgical Procedure is not correct here — look up a urological/orchidopexy NCIT term.
Airway management for laryngomalacia and respiratory failure.

Supportive and rehabilitative

Intervention	NCIT candidate	`therapeutic_modality`
Multidisciplinary supportive/palliative care	`NCIT:C15747` Supportive Care	OTHER
Nutritional support / enteral feeding	`NCIT:C15433` Nutritional Support	do not auto-tag BEHAVIORAL — see CLAUDE.md backfill guidance; here it is enteral nutrition, closest to OTHER/BEHAVIORAL — decide per entry
Physical therapy (spasticity, contracture prevention)	`NCIT:C15302` Physical Therapy	BEHAVIORAL
Occupational therapy	`NCIT:C121351` Occupational Therapy	BEHAVIORAL
Seizure management	`NCIT:C15986` Pharmacotherapy	SMALL_MOLECULE
Respiratory care / aspiration prevention	`NCIT:C15747` Supportive Care	OTHER
Genetic counselling	`NCIT:C15240` Genetic Counseling	OTHER

All NCIT IDs must be verified with uv run runoak -i sqlite:obo:ncit info NCIT:Cxxxxx -O obo.

Treatment outcomes, adverse events, algorithms

No response-rate data (no disease-specific therapy has been trialled in CONPM).
No CONPM-specific adverse-event data. FAERS contains nothing indexed to this disease.
No treatment algorithm, guideline, NCCN/society pathway, or GeneReviews chapter exists for CONPM. Management follows generic severe-neurodegenerative-encephalopathy principles.
Personalized medicine: the only genotype-guided element currently available is reproductive (see §13).

13. Prevention

Primary prevention

Not achievable for an affected fetus/child — the disorder is determined at conception. Prevention is entirely reproductive: - Genetic counselling for at-risk couples: 25% recurrence risk per pregnancy, 50% carrier risk for unaffected sibs, standard AR counselling. NCIT:C15240. - Carrier testing of the proband's parents and extended family (particularly relevant in consanguineous kindreds). - Prenatal diagnosis by CVS or amniocentesis with targeted testing of the known familial variants. - Preimplantation genetic testing for monogenic disease (PGT-M) — technically straightforward once the familial variants are known. - Consanguinity counselling in populations where first-cousin union is common.

Secondary prevention (early detection)

No population screening is justified or available. Newborn screening is not applicable (no analyte, no treatment, normal birth OFC).
The practical "early detection" measure is serial head-circumference monitoring in infancy, which will flag the OFC deceleration and trigger a workup — but this detects the disease after neuronal loss has begun and does not alter outcome.
Cascade testing within a known family is the only genuinely effective early-detection route.

Tertiary prevention (preventing complications) — this is where real clinical benefit lies

Aspiration prevention: early swallow assessment, thickened feeds, timely conversion from NG to gastrostomy. Directly targets the documented cause of death (pneumonia).
Respiratory infection prophylaxis: routine immunizations, influenza and RSV prophylaxis, pneumococcal vaccination, chest physiotherapy, prompt treatment of intercurrent infection.
Seizure control to prevent status epilepticus.
Contracture and positioning management for spastic tetraplegia.
Nutritional optimization to prevent iron-deficiency/microcytic anemia and further growth failure.

Immunization

No disease-specific vaccine. Routine childhood immunization plus respiratory-pathogen prophylaxis is a high-value intervention given that both documented deaths followed respiratory infection. NCIT:C15346 Vaccination.

Public health and environmental interventions

Not applicable. No environmental modifiable risk exists.

14. Other Species / Natural Disease

Orthologs (Alliance of Genome Resources, all high-confidence "best score")

Species	NCBITaxon	Gene	Database ID
Mouse (Mus musculus)	NCBITaxon:10090	Dtymk	MGI:108396
Rat (Rattus norvegicus)	NCBITaxon:10116	Dtymk	RGD:1309614
Zebrafish (Danio rerio)	NCBITaxon:7955	dtymk	ZFIN:ZDB-GENE-990603-11
Fruit fly (Drosophila melanogaster)	NCBITaxon:7227	Dtymk	FB:FBgn0034299
Nematode (C. elegans)	NCBITaxon:6239	dtmk-1	WB:WBGene00011272
Budding yeast (S. cerevisiae)	NCBITaxon:4932	*CDC8*	SGD:S000003818
Xenopus laevis	NCBITaxon:8355	dtymk.S	Xenbase:XB-GENE-1004312
Xenopus tropicalis	NCBITaxon:8364	dtymk	Xenbase:XB-GENE-1004306

The yeast ortholog name CDC8 (cell division cycle 8) — which is also the human gene's legacy alias — is a direct historical signal of the gene's core cell-cycle function and of deep evolutionary conservation.

Naturally occurring disease in other species

None known. A search of OMIA and the veterinary literature identified no naturally occurring DTYMK-related disease in companion animals, livestock, or wildlife. No breed-associated variant; no VBO breed identifier applicable. No zoonotic potential and no cross-species transmission (this is a Mendelian metabolic disorder, not a transmissible condition).

Comparative biology

Evolutionary conservation is exceptionally deep — a functional TMPK ortholog is present from yeast through humans, consistent with dTTP synthesis being a universal requirement.
Comparative pathology diverges in an interesting and curation-relevant way:
Mouse: homozygous null is embryonic lethal (PMID:38621447) — mouse does NOT recapitulate the human "viable but neurodegenerative" phenotype.
Zebrafish: homozygous mutant is viable through early larval stages with microcephaly and neurodegeneration, then lethal — this is the closest phenocopy.
Human: viable to birth with normal-sized head, then postnatal neurodegeneration.
This species gradient (mouse lethal < zebrafish larval-lethal < human postnatal-degenerative) is itself evidence that the hypothesized compensatory dTTP pathway differs in capacity across species — an elegant framing for the HUMAN_MODEL_MISMATCH discussion.
Enzymatic substrate specificity diverges too: Drosophila TMPK phosphorylates dTMP, dUMP, and also dGMP and dIMP (at low efficiency), unlike human TMPK (PMID:38518117 abstract, verbatim below) — relevant if a fly model is used, because compensation logic may differ.

Verbatim abstract (PMID:38518117):

"Unlike human TMPK, DmTMPK phosphorylated not only dTMP and dUMP but also dGMP and dIMP although with low efficiency. ATP and dATP are the most efficient phosphate donor but at higher concentration (>1 mM) ATP inhibited DmTMPK activity."

15. Model Organisms

15.1 Zebrafish — the flagship model (best phenocopy)

Allele: CRISPR-generated 5-bp deletion in exon 4, producing a premature stop codon 19 amino acids downstream [full-text]. Source: Vanoevelen et al., PMID:34918187. Should be registered/lookup-able at ZFIN (ZDB-GENE-990603-11).

Phenotype recapitulation — strong:

Feature	Zebrafish dtymk⁻/⁻	Human CONPM	Recapitulates?
Microcephaly	Head size significantly smaller than siblings (p = 1.52 × 10⁻¹³)	Severe progressive microcephaly	✅
Neurodegeneration	"Empty spaces, indicative of neurodegeneration" in brain	Massive neuronal dropout	✅
Neuronal apoptosis	Significantly more apoptotic cells in forebrain (p = 6.45 × 10⁻⁶ vs. WT)	Neuronal apoptosis inferred	✅
Seizure-like activity	"Twitching movements, reminiscent of epileptic seizures" from 3 dpf	Seizures from 6–15 months	✅ (behavioral proxy)
Enzyme loss	1.80 pmol/min/mg vs. sibling 38.55 / WT 41.43	0.62 vs. parental 31–44	✅ (quantitatively parallel)
Early lethality	>40% dead by 5 dpf	Death at 18–32 months	✅ (accelerated)
Ribonucleotide misincorporation	gDNA migrates lower + broad smear on alkaline gel; comparable to Rnaseh2⁻/⁻ mouse DNA	Not measured in humans	⚠️ model-only
Impaired DDR	Persistent γH2AX 24 h post-UV	Not measured in humans	⚠️ model-only
Small eyes, pericardial/intestinal edema, brain edema (2/3), absent Meckel's cartilage	Present	Not features of human disease	❌ model-specific

Limitations: (i) the fish shows non-CNS malformations (cardiac/intestinal edema, absent Meckel's cartilage, microphthalmia) that are not part of the human phenotype, suggesting a broader requirement in fish; (ii) the compressed larval timeline cannot model postnatal progressive degeneration over months–years; (iii) the two mechanistically most novel findings — ribonucleotide misincorporation and defective DDR — are demonstrated only in fish, never in human tissue. → This is a textbook HUMAN_MODEL_MISMATCH discussion item (evidence exists in a model; human translational validity is the open question), not a plain KNOWLEDGE_GAP.

Verbatim abstract (PMID:34918187):

"In addition, we generated dtymk mutant zebrafish that replicate this phenotype of microcephaly, neuronal cell death and early lethality. An increase of ribonucleotide incorporation in the genome as well as impaired responses to DNA damage were observed in dtymk mutant zebrafish, providing novel pathophysiological insights."

Supporting zebrafish developmental work (PMID:35346037, BMC Neuroscience 2022) — verbatim abstract excerpts:

"Our findings reveal that maternal-stored dNTPs are only sufficient for 6 cell division cycles, and the levels of dNTPs are inversely correlated to cell cycle length during early embryogenesis. TMPK and TK activities are prominent in the cytosol of embryos, larvae and adult fish and brain contains the highest TMPK activity." "Our results suggest that active dNTP synthesis in early embryogenesis is vital and that Dtymk is essential for neurodevelopment, which is supported by a recent study of dtymk knockout zebrafish with neurological disorder and lethal outcomes. Furthermore, there is a novel TMPK-like enzyme expressed at later stages of development."

Note the last sentence — it is independent, orthogonal support for the "unknown compensatory TMPK-like enzyme," this time from a developmental-stage expression study rather than from patient cells.

15.2 Mouse — essentiality established, disease NOT modeled

Tiani & Stover, Arch Biochem Biophys 2024, PMID:38621447, DOI 10.1016/j.abb.2024.109991.

Homozygous Dtymk knockout is embryonic lethal.
Heterozygotes across three dietary conditions showed no open neural tube defects, despite ~3-fold reduced dTYMK expression.
Implication: the standard mouse null is not a usable CONPM model. A viable model would require a hypomorphic knock-in (e.g., the human p.Pro81Leu or p.Ala99Thr allele) or a conditional/neural-specific conditional knockout (Nestin-Cre, Emx1-Cre). No such mouse has been reported — this is the single most valuable missing reagent in the field and a strong proposed_experiments entry.
Resources to check for existing alleles: MGI (MGI:108396), IMPC, KOMP/EuMMCR, IMSR.

15.3 Drosophila — characterized enzyme, no disease model yet

PMID:38518117 (Hu Frisk & Wang 2024) cloned, expressed, purified, and kinetically characterized DmTMPK, explicitly as groundwork for a fly disease model: "Drosophila has been used as an animal model to study pathogenic mechanism of neurological disorders… This study has laid a solid foundation for future study of TMPK function in Drosophila." No Dtymk mutant fly phenotype has been published. Caveat: broader substrate specificity than human TMPK (see §14).

15.4 In vitro / cellular models

Patient-derived dermal fibroblasts (Individual I) — the workhorse. Available from the Vanoevelen/Bierau group (Maastricht). Used for enzyme assay, subcellular fractionation, S-phase analysis, dNTP pools. Key limitation: fibroblasts proliferate normally and thus do not phenocopy the disease — they are a biochemical readout, not a disease model.
Recombinant TMPK (WT, P81L, A99T, D128N) expressed and purified for kinetics and size-exclusion dimerization analysis (PMID:34926941).
iPSC / neural organoids: none reported. Given that (a) the phenotype is neuron-specific, (b) fibroblasts are spared, and (c) the compensating enzyme is unknown, patient-iPSC-derived cortical neurons and cerebral organoids are the obvious highest-value missing model. This is also directly relevant to MorPhiC-style cellular-phenotype curation (§CLAUDE.md MorPhiC pattern): a DTYMK-null iPSC line with category: Cellular phenotypes and evidence_source: IN_VITRO would be a natural future annotation — but note that DTYMK is not among the current MorPhiC anchor genes (ISL1, EOMES, GCM1, NKX2-1), so no MorPhiC data exist today.
Cancer cell lines: MP41/MP46 uveal melanoma with the TMPK inhibitor YMU1 (PMID:39195238) — a pharmacological loss-of-function system, useful as orthogonal mechanistic support but not a neurodegeneration model.

15.5 Yeast

S. cerevisiae CDC8 — the classical cell-division-cycle mutant. Historically the source of the "TMPK is required for cell-cycle progression" understanding. Not used as a CONPM model but valuable for conservation arguments.

Appendix A — Master citation list

PMID	Citation	DOI	Relevance
34918187	Vanoevelen JM, Bierau J, Grashorn JC, et al. DTYMK is essential for genome integrity and neuronal survival. Acta Neuropathol. 2022.	10.1007/s00401-021-02394-0	Landmark / disease-defining paper. 2 patients, enzymology, zebrafish model, ribonucleotide misincorporation, DDR defect
31271740	Lam CW, Yeung WL, Ling TK, Wong KC, Law CY. Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome. Clin Chim Acta. 2019 Sep;496:93-99.	10.1016/j.cca.2019.06.028	First clinical report (2 siblings); MDDS framing; milder end of spectrum
40696808	Hernández-Carreto R, Acosta-Rodríguez-Bueno PC, Barragán-Arevalo T, et al. Childhood-Onset Neurodegeneration With Progressive Microcephaly (CONPM) due to a DTYMK Homozygous Pathogenic Variant: Outlining the Phenotype of an Ultra-Rare Disease. Am J Med Genet A. 2025.	10.1002/ajmg.a.64187	Fifth reported case; establishes "only four cases prior"; homozygous P81L; cerebellar atrophy discrepancy
34926941	Frisk JH, Vanoevelen JM, Bierau J, Pejler G, Eriksson S, Wang L. Biochemical Characterizations of Human TMPK Mutations Identified in Patients with Severe Microcephaly: Single Amino Acid Substitutions Impair Dimerization and Abolish Their Catalytic Activity. ACS Omega. 2021.	10.1021/acsomega.1c05288	Definitive functional/variant characterization; kinetics; dimerization mechanism; mitochondrial vs cytosolic activity; compensatory-enzyme paradox
34994281	Hu Frisk J, Pejler G, Eriksson S. Structural and functional analysis of human thymidylate kinase isoforms. Nucleosides Nucleotides Nucleic Acids. 2022.	10.1080/15257770.2021.2023748	Excludes DTYMK isoforms as the compensating enzyme; "no defects were observed in other tissues"
35346037	Frisk JH, Örn S, Pejler G, et al. Differential expression of enzymes in thymidylate biosynthesis in zebrafish at different developmental stages: implications for dtymk mutation-caused neurodegenerative disorders. BMC Neurosci. 2022.	10.1186/s12868-022-00704-0	Developmental dNTP demand; brain has highest TMPK activity; independent evidence for a novel TMPK-like enzyme
38621447	Tiani KA, Stover PJ. DTYMK is an essential gene in mice and heterozygosity does not cause neural tube defects. Arch Biochem Biophys. 2024.	10.1016/j.abb.2024.109991	Mouse essentiality; heterozygote tolerance; negative diet/NTD result
38518117	Hu Frisk J, Wang L. *Molecular characterization of Drosophila melanogaster* thymidylate kinase.** Nucleosides Nucleotides Nucleic Acids. 2024;43(8):734-742.	10.1080/15257770.2024.2332410	Fly model groundwork; substrate-specificity divergence
39195238	Oziębło S, Mizera J, Górska A, et al. Co-Targeting of DTYMK and PARP1 as a Potential Therapeutic Approach in Uveal Melanoma. Cells. 2024;13(16):1348.	10.3390/cells13161348	Orthogonal pharmacological support for the DTYMK–DNA-repair axis (oncology context)
NCT04802707	Deoxynucleosides Pyrimidines as Treatment for Mitochondrial Depletion Syndrome. Phase II, recruiting.	—	Only trial with DTYMK eligibility; already in `references_cache/clinicaltrials_NCT04802707.md`

Database records: OMIM #619847; OMIM *188345; MONDO:0859241; MedGen C5676972 / UID 1801540; HGNC:3061; UniProt P23919; ClinVar VCV001686902/3/4/5, VCV004277573, VCV003065236; Human Protein Atlas ENSG00000168393; Alliance of Genome Resources HGNC:3061 orthology; HPO annotation set for OMIM:619847.

Appendix B — Curation checklist and flagged gaps for the dismech entry

Verification required before commit 1. Run just fetch-reference for every PMID above; verify every snippet is an exact substring. All [full-text]-marked sentences in this report came through an intermediate summarizer and must be re-verified against the PMC source (PMC8742820, PMC8679000) before use as evidence. 2. Run just validate-terms on every HP/GO/CL/UBERON/CHEBI/NCIT ID suggested here — none have been OAK-verified in this session. 3. Fetch gnomAD constraint values directly; do not assert pLI/LOEUF from this report (retrieval failed). 4. Verify the Reactome stable ID for pyrimidine deoxyribonucleotide biosynthesis (ContentService returned 403). 5. Obtain the Lam 2019 full text to confirm (a) the phase/pairing of A99T + D96fs, (b) the siblings' sexes and ages, (c) whether mtDNA depletion was measured or only inferred.

Recommended discussions entries - kind: KNOWLEDGE_GAP — identity of the compensatory TMPK-like enzyme. Attaches to the dTTP-biosynthesis-block node. Supported by three independent papers (PMID:34926941, 34994281, 35346037). Proposed experiments: unbiased biochemical purification of dTMP-kinase activity from patient fibroblasts; CRISPR screen for synthetic lethality with DTYMK loss. - kind: HUMAN_MODEL_MISMATCH — ribonucleotide misincorporation and DDR failure are shown only in zebrafish, never in human neurons or patient tissue; and mouse null is embryonic lethal while humans reach term. Proposed experiments: patient-iPSC cortical neurons/organoids; alkaline-gel and γH2AX assays in human cells; humanized hypomorphic knock-in mouse. - kind: KNOWLEDGE_GAP — interferon signature untested, despite the mechanistic parallel to RNASEH2-deficient AGS explicitly drawn in the primary paper. - mechanistic_hypotheses (status: EMERGING) — mtDNA depletion arm (Lam 2019, mitochondrial TMPK activity loss in PMID:34926941). Edges from the mitochondrial-TMPK-loss node should opt into this hypothesis group. Flag that the mtDNA depletion itself was shown "in silico" only. - kind: KNOWLEDGE_GAP — deoxynucleoside (dC/dT) substrate therapy rationale is not established for DTYMK, because the enzymatic block lies downstream of thymidine entry; yet NCT04802707 lists DTYMK as eligible. - Inter-patient discrepancy: cerebellar sparing (Vanoevelen) vs. cerebellar atrophy (Hernández-Carreto 2025).

Suggested biological_scale tags for pathophysiology nodes MOLECULAR — DTYMK LoF variants; loss of homodimerization; loss of dTMP kinase activity; dTTP biosynthesis block. CELLULAR — impaired DNA replication / S-phase collapse; ribonucleotide misincorporation; impaired DNA damage response; neuronal apoptosis. TISSUE — cerebral and striatal atrophy with gliosis. ORGANISM — progressive microcephaly; developmental regression; lactic acidemia; early childhood death.

Module conformance candidates: none of the existing dismech modules is a clean fit. genome_instability_mutation covers a genome-maintenance-defect → mutator-phenotype chain but is scoped to oncogenesis, and CONPM's output is neuronal apoptosis rather than clonal evolution — do not force conformance. If a module is warranted later, the natural one would be a new "nucleotide-pool-imbalance genome instability" or "replication-stress neurodegeneration" module shared with AGS/RNASEH2, PNKP, and the MDDS nucleotide-salvage disorders.

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Classifications

Inheritance

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Histopathology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Biochemical Markers

Differential Diagnoses

Clinical Trials

Source YAML

References & Deep Research

References

Deep Research

DTYMK-Related Neurodegeneration — Comprehensive Research Report

⚠️ Curation Preflight Warnings (read before using this report)

1. Disease Information

Overview

Key identifiers

Synonyms and alternative names

Provenance of information

2. Etiology

Disease causal factors

Genetic risk factors

Environmental risk factors

Protective factors

Gene–environment interactions

3. Phenotypes

3.1 HPO annotations for OMIM:619847 (authoritative, with case-count frequencies)

3.2 Phenotype characteristics by domain

4. Genetic / Molecular Information

Gene

Reported pathogenic variants (all germline; ClinVar-verified)

Functional consequences — loss of function via loss of obligate dimerization

Modifier genes

Epigenetics

Chromosomal abnormalities

Population constraint

5. Environmental Information

6. Mechanism / Pathophysiology

6.1 The causal chain (proposed pathograph, upstream → downstream)

6.2 Molecular pathways

6.3 Cellular processes and GO term suggestions

6.4 Protein dysfunction

6.5 Metabolic changes

6.6 Immune system involvement

6.7 Tissue damage mechanisms

6.8 Biochemical abnormalities

6.9 Epigenetic changes

6.10 Molecular profiling

7. Anatomical Structures Affected

Organ level

Regional CNS involvement — the sparing pattern is diagnostically important

Tissue and cell level

Subcellular level

8. Temporal Development

Onset

Progression

Patterns

9. Inheritance and Population

Epidemiology

Genetic epidemiology

Population demographics

10. Diagnostics

Clinical / laboratory tests

Imaging

Electrophysiology

Biopsy / pathology

Genetic testing

Clinical criteria and differential diagnosis

Screening

11. Outcome / Prognosis

Survival and mortality

Morbidity and function

Complications