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Classifications

Harrison's Part

IUIS Category

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Inheritance

1

Autosomal recessive inheritance HP:0000007

Biallelic in both families. The Turkish kindred is homozygous with heterozygous parents and segregation confirmed by Sanger sequencing across three affected relatives in two generations; the second family's patient is compound heterozygous with a maternal allele carrying two substitutions in cis and a separate paternal allele. Heterozygous carriers are unaffected for this phenotype. The recessive prediction is also borne out at the gene level: POLD1 has a low pLI and a high pRec, meaning loss of one allele is predicted to be tolerated and loss of both is not — which is the population-genetic signature of a recessive disease gene and is stated explicitly by the authors.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Both parents were heterozygous for the mutation. Her sister P2, who also suffered from recurrent infections, was found homozygous for the same mutation by Sanger sequencing, as was a paternal aunt P3"

Carrier parents and homozygosity in all three affected relatives, which is the segregation that establishes recessive inheritance in this kindred.

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Both genes show low pLI scores of 0.001 and 0.044, respectively, indicating a predicted tolerance to the loss of a single allele, and high pRec scores of 0.998 and 0.950, respectively, indicating a predicted high intolerance for a complete loss of function"

The population-genetic prediction, which agrees with the observed inheritance and also explains why no null allele appears in this disease.

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Discussions and Knowledge Gaps

3

Why does a general restriction on cell-cycle entry produce oligoclonality and restricted receptor V-J pairing in CD8 but not CD4 T cells?

OPEN QUESTION OPEN imd120_cd8_asymmetry

Attached to

pathophysiology#Contracted Oligoclonal T Cell Repertoire treatments#Haematopoietic Stem Cell Transplantation

Polymerase delta is required by every dividing cell, so the naive expectation is a uniform proliferation ceiling. What is observed is asymmetric: naive CD8 cells are lost more than naive CD4 cells, and the repertoire contraction is confined to CD8. The founding authors offer two candidate explanations in one sentence — a difference in peripheral CD8 expansion, or a difference in thymic selection — and commit to neither. The distinction is testable and consequential. If it is peripheral, the repertoire should contract progressively with age and antigen exposure, and a transplant should restore it. If it is thymic, the defect is set early and a transplant in an adult with an involuted thymus may restore counts without restoring breadth. The 2026 transplant report gives improved T-cell counts and function at two years but does not report repertoire sequencing, which is exactly the measurement that would separate them.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"suggesting that POLD1R1060C differentially affects peripheral CD8+ T-cell expansion and possibly thymic selection"

The authors' own two-part hypothesis, quoted with its hedge — the reason this is an open question rather than a mechanism node.

Does a defect in the replicative polymerase increase the risk of conditioning-regimen toxicity, when DNA repair after genotoxic stress is normal in these patients?

OPEN QUESTION OPEN imd120_conditioning_toxicity

Attached to

treatments#Haematopoietic Stem Cell Transplantation pathophysiology#Impaired S-Phase Progression and Replicative Stress diagnosis#DNA repair assay after genotoxic stress

This is a case where the clinical worry and the laboratory finding point in different directions, and a real decision had to be made without resolving it. The transplant team's stated concern was regimen-related toxicity from impaired DNA repair. The mechanistic work points the opposite way: repair after genotoxic stress was normal, and the lesion is in S-phase progression. If that is right, POLD1 deficiency is unlike the DNA-repair immunodeficiencies where conditioning toxicity is a documented problem, and the caution may be borrowed rather than earned. There is a gap in that reassurance, and it is exactly where it should not be. The genotoxic-sensitivity experiment was run in the POLD2 patient's fibroblasts. No POLD1 patient's cells have been exposed to a genotoxic compound in any published experiment. So the argument that a POLD1-deficient patient tolerates alkylator-based conditioning runs through a different gene's patient — a defensible inference from the shared holoenzyme, and not a measurement. One reduced-intensity transplant went well. That is consistent with the caution being unnecessary and equally consistent with reduced-intensity conditioning having been the reason it went well. Distinguishing them needs more patients, or the obvious missing experiment: alkylator and fludarabine sensitivity in POLD1 patient cells, which would cost little and has not been published.

Show evidence (2 references)

PMID:31449058 SUPPORT INDIRECT PRIMARY RESULT Human Clinical

"To determine the DNA repair capacity of POLD-deficient cells, we treated P1 cells with different genotoxic compounds"

The premise of this discussion, and the reason it is a discussion rather than a settled point: the only genotoxic-sensitivity experiment in this literature names one patient, and it is not the POLD1 one.

PMID:42104577 REFUTE DIRECT PRIMARY RESULT Human Clinical

"Patients considered for HSCT may be at increased risk of regimen-related toxicity due to impaired DNA repair."

Graded REFUTE against the repair-normal reading. A transplant team treating a POLD1 patient stated the opposite expectation in print, which is the disagreement this discussion is about rather than an error on either side.

Are the syndromic features of POLD1 deficiency — short stature, microcephaly, cognitive impairment, hearing loss — a direct developmental consequence of reduced polymerase delta, or consequences of the infections the immunodeficiency permits?

KNOWLEDGE GAP OPEN imd120_syndromic_attribution

Attached to

pathophysiology#Syndromic Developmental Features phenotypes#Microcephaly phenotypes#Developmental and Speech Delay

Both readings are supported by different patients in the published set, which is why this is a gap rather than a controversy. For a direct effect: the second family's POLD1 patient has short stature, microcephaly and a measured IQ around 70 with no reported encephalitis, and microcephaly in particular is what a proliferation-limited neural progenitor pool would produce. Against it: in the Turkish kindred the one patient with intellectual impairment, hearing deficit and speech delay acquired all three after a varicella encephalitis at age three, the index patient's language delay is attributable to her hearing loss, and the younger sister has normal hearing and normal growth on the same homozygous allele. Four patients cannot settle it. What would help is head circumference and growth data on patients without a severe infection history, and — since there is now a transplanted patient — whether restoring the immune compartment changes the developmental trajectory.

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Pathophysiology

9

Biallelic Hypomorphic POLD1 Variants

Mechanism confidence: Established

Two genotypes are published. The Turkish kindred is homozygous for c.3178C>T, p.Arg1060Cys, absent from gnomAD, ExAC, dbSNP and 1000 Genomes, found by homozygosity mapping in the largest of five runs of homozygosity and confirmed by Sanger sequencing in all three affected relatives. The second family's patient carries three heterozygous POLD1 variants making up two alleles: p.Gln684His and p.Ser939Trp inherited together in cis on the maternal allele, and p.Arg1074Trp on the paternal allele. Getting that configuration right matters, because two of the three substitutions are on one chromosome — a reader counting substitutions rather than alleles would conclude the patient has three hits when they have two. No null allele appears in either family, and none is expected to: complete POLD1 deficiency is embryonic lethal in mice, and POLD1's high pRec score predicts intolerance of complete loss of function in humans. Every disease allele here is hypomorphic by necessity.

POLD1 hgnc:9175

Genetic context POLD1 hgnc:9175 allele_type: a homozygous CysB-motif missense variant in one family, and two missense variants in cis opposite a third missense variant in the other variant_origin: GERMLINE functional_impact_category: PARTIAL_LOSS_OF_FUNCTION

Zygosity differs between the two families — homozygous in the Turkish kindred, compound heterozygous in the second — so the slot is left unset rather than asserting one family's configuration for both.

PARTIAL_LOSS_OF_FUNCTION rather than LOSS_OF_FUNCTION, and the reasoning is not a hedge: complete polymerase delta loss is embryonic lethal in mice and predicted intolerable in humans, so a viable patient's alleles are hypomorphic by construction. Both genotypes were functionally tested and both retain activity.

Downstream

Destabilisation of the Polymerase Delta Holoenzyme The p.Arg1060Cys route. The substitution disrupts the intramolecular contact between the POLD1 CysB motif and the catalytic domain, and the contact between POLD1 and POLD2, so the complex falls apart and all three measured subunits drop together.

Reduced Intrinsic Polymerase Catalytic Activity The second family's route. Substitutions near the active site reduce catalytic turnover while leaving complex assembly intact — a different lesion reaching the same output.

Show evidence (3 references)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"This missense homozygous mutation has not been previously reported in genomAD, ExAC, dbSNP or 1000Genome and was confirmed by Sanger sequencing"

The allele's absence from every population database consulted, and its confirmation by a second method.

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"The variants p.Gln684His (CADD score of 26), located in the catalytic domain, and p.Ser939Trp (CADD score of 34) in an interdomain region, were inherited in cis on the same allele of maternal origin, whereas the p.Arg1074Trp variant (CADD score of 34) located to the CysB domain on the paternal allele."

The full three-variant, two-allele configuration with its phase, which is what makes this patient biallelic rather than triallelic.

PMID:31629014 SUPPORT INDIRECT BACKGROUND Model Organism

"Total POLD1 deficiency is embryonic lethal in mice, while deficiency of POLD1 exonuclease activity in Pold1exo/exo mice (mutator mice), results in a high rate of DNA replication errors"

Why no null allele can appear in this disease, and the contrast with the proofreading-only mouse that models the cancer-predisposition allele class instead. Graded BACKGROUND because the sentence summarises prior mouse work in this paper's introduction rather than reporting its own result, and MODEL_ORGANISM because that is the evidence the quoted text describes.

Destabilisation of the Polymerase Delta Holoenzyme

Mechanism confidence: Established

Polymerase delta is a heterotetramer: POLD1 carries the polymerase and exonuclease activities, POLD2 is the scaffold that holds POLD1 to the rest, and POLD3 and POLD4 regulate activity and stability. A substitution at the POLD1-POLD2 interface therefore does not inactivate one subunit, it lowers the amount of assembled enzyme — POLD1, POLD2 and POLD3 fall together.

POLD1 hgnc:9175

DNA polymerase delta complex GO:0043625

Downstream

Ineffective Replication Factor C Recruitment

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"The mutation destabilizes the Polδ complex, leading to ineffective recruitment of replication factor C to initiate DNA replication."

The destabilisation and the step it blocks, stated as the paper's own result.

Reduced Intrinsic Polymerase Catalytic Activity

Mechanism confidence: Established

The second route to the same deficit: substitutions near the polymerase active site lower catalytic activity without destabilising the complex. The two families therefore differ in biochemistry and agree in phenotype, which is the argument that the disease follows from reduced polymerase delta output rather than from a property of one allele. In the second family's cells the replication-associated lesions were reversible on overexpressing polymerase delta, which is the rescue that establishes the direction of causation.

POLD1 hgnc:9175

DNA-directed DNA polymerase activity GO:0003887 ↓ DECREASED

Downstream

Impaired S-Phase Progression and Replicative Stress

Show evidence (1 reference)

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"The mutations affected the stability and interactions within the polymerase δ complex or its intrinsic polymerase activity."

The two mechanisms, stated by the authors as alternatives — which is what makes them convergent routes rather than a single chain.

Ineffective Replication Factor C Recruitment

Mechanism confidence: Established

Replication factor C is the clamp loader that places PCNA on DNA so that polymerase delta can begin synthesis. Less assembled polymerase delta means less effective RFC recruitment, so fewer replication events start. The deficit is at initiation rather than at elongation, which is why the cellular phenotype is a reduced fraction of cells in S phase rather than slow replication in all of them.

DNA replication initiation GO:0006270 ↓ DECREASED

Downstream

Impaired S-Phase Progression and Replicative Stress

Show evidence (1 reference)

PMID:31629014 SUPPORT INDIRECT BACKGROUND Other

"Additionally, the Polδ complex coordinately interacts with a number of proteins that enable its function, including DNA replication factor C (RFC) and Proliferating Cell Nuclear Antigen (PCNA)"

The interaction this node depends on, stated in the paper's introduction as established biology rather than as its own finding — which is exactly what quote_role BACKGROUND is for.

Impaired S-Phase Progression and Replicative Stress

Mechanism confidence: Established

A smaller fraction of cells enters and completes S phase, and replication-associated DNA lesions accumulate. Both findings are reported for the patients' cells in the plural and are attributable to the POLD1 patient as well as the POLD2 one. The control that would place this disease among the proliferation defects rather than among the DNA-repair immunodeficiencies — ataxia-telangiectasia, Nijmegen breakage, LIG4 deficiency — is the genotoxic-sensitivity experiment, and that one is not plural. It was done in the POLD2 patient's fibroblasts, which showed no overt sensitivity to an array of genotoxic reagents. The POLD1 patient was never tested. The inference to POLD1 runs through the shared holoenzyme and is reasonable; it is not a measurement in this disease, and this entry marks it as extrapolated wherever it is used. It has a practical consequence recorded under treatments: a repair-competent cell is a different transplant-conditioning risk from a repair-deficient one, and the first HSCT in this disease was performed against exactly that uncertainty — with the team's stated concern pointing the opposite way from this extrapolation.

cell cycle GO:0007049 ↓ DECREASED DNA replication GO:0006260 ↓ DECREASED

Downstream

Impaired T Cell Clonal Proliferation Lymphocytes are the cells whose function is to divide on demand, so a ceiling on cell-cycle entry is felt there first. The B-cell compartment is comparatively spared in proliferation terms, which is why the defect presents as T-cell rather than combined at the cellular level even though the humoral consequence is real.

Syndromic Developmental Features Polymerase delta is required in every dividing tissue, so a general replication restriction is a plausible route to the short stature, developmental impairment and hearing loss seen in part of the series. No tissue-level measurement supports the step, and in the Turkish kindred one affected member's deficits followed a varicella encephalitis rather than being developmental from the start — so the attribution is weaker here than the clean immune chain above.

Show evidence (1 reference)

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Patients' cells showed impaired cell-cycle progression and replication-associated DNA lesions that were reversible upon overexpression of polymerase δ."

The cellular phenotype and its rescue by restoring the enzyme, which is what makes the polymerase deficit causal for it rather than merely coincident.

Impaired T Cell Clonal Proliferation

Mechanism confidence: Established

On T-cell receptor activation, patient T cells show reduced proliferative responses coupled to reduced cell-cycle progression. B-cell proliferation is comparatively preserved. This is the point at which a housekeeping replication defect becomes an immune disease.

T cell CL:0000084

T cell proliferation GO:0042098 ↓ DECREASED

Downstream

Contracted Oligoclonal T Cell Repertoire

Decreased Total T Cell Count

B and NK Cell Lymphopenia Drawn from the shared proliferation ceiling rather than from the T-cell defect: B and NK cells divide too, and in the one patient where all three lineages were counted all three were low. The edge is placed here rather than on the replicative-stress node because the same paper reports B-cell proliferation as comparatively spared in the other family, so how a cell-cycle restriction produces a B-cell cytopenia without a measurable proliferation defect is not settled.

Defective T-Dependent Antibody Response B cells proliferate adequately but do not receive adequate help, so the humoral defect is downstream of the T-cell one rather than a parallel B-cell-intrinsic lesion. That is the reading the preserved B-cell proliferation supports, and it is what makes immunoglobulin replacement a rational rather than merely empirical treatment here.

Show evidence (1 reference)

PMID:31449058 SUPPORT INDIRECT PRIMARY RESULT Human Clinical

"We believe our discovery of human polymerase δ deficiency identifies the central role of this complex in the prevention of replication-related DNA lesions, with particular relevance to adaptive immunity."

The authors' framing of why a replication defect lands on adaptive immunity specifically. Graded INDIRECT because it is an interpretive statement rather than the proliferation measurement itself.

Contracted Oligoclonal T Cell Repertoire

Mechanism confidence: Established

Naive CD4 and especially CD8 cells are depleted in favour of effector memory subsets, and the CD8 compartment is oligoclonal with restricted T-cell receptor beta-chain V-J pairing while the CD4 compartment is not. The authors read that asymmetry as POLD1 affecting peripheral CD8 expansion and possibly thymic selection differently from CD4. A repertoire that is both small and skewed is what makes this a viral rather than a pyogenic immunodeficiency: containing a herpesvirus needs a specific clone to expand, and there are fewer clones and less capacity to expand them.

CD8-positive, alpha-beta T cell CL:0000625

Downstream

Recurrent Herpetic Infection Control of latent herpesviruses depends on CD8 T-cell surveillance, and this is the compartment that is depleted, skewed and oligoclonal. The step is not measured in these patients — no viral load, no antigen-specific tetramer work — so it is the immunological argument applied to the observed repertoire rather than a finding about it.

Recurrent Respiratory Tract Infection

Bronchiectasis Bronchiectasis here is infection-driven airway destruction, not a primary polymerase lesion. The edge runs through years of recurrent infection, which is why it is the phenotype that early diagnosis prevents and nothing reverses.

Recurrent Otitis Media

Severe Primary Varicella Primary varicella is contained by the same CD8 response that later holds the virus latent, so a contracted CD8 compartment predicts both a severe primary course and recurrent zoster — and this kindred has both.

Cutaneous Warts Negative for Common Papillomavirus Strains

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"This skewing was associated with oligoclonality and restricted T-cell receptor β-chain V-J pairing in CD8+ but not CD4+ T cells, suggesting that POLD1R1060C differentially affects peripheral CD8+ T-cell expansion and possibly thymic selection."

The repertoire finding, its restriction to CD8, and the authors' own hedged interpretation of it — quoted with the hedge intact.

Defective T-Dependent Antibody Response

Mechanism confidence: Provisional

Mildly reduced IgG with low IgA and IgM, and absent tetanus responses despite full vaccination. Graded PROVISIONAL rather than ESTABLISHED because the inference that the humoral defect is secondary to failed T-cell help rests on the preserved B-cell proliferation rather than on any direct measurement of help — nobody has assayed germinal centre formation, class switching or T-follicular-helper number in these patients. The one piece of evidence that bears on it directly is a treatment observation rather than an experiment: the younger sister's unprotective tetanus response normalised on booster vaccination, which is not what a B-cell-intrinsic defect would predict.

B cell CL:0000236

Downstream

Decreased Circulating Immunoglobulin

Absent Tetanus Vaccine Antibody Response

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"She had mildly decreased serum IgG and low IgA and IgM antibody concentrations, while her tetanus vaccine-related antibody responses were absent despite having been fully vaccinated"

The humoral picture in the index patient, with the vaccination history that makes the absent response informative rather than merely unmeasured.

Syndromic Developmental Features

Mechanism confidence: Hypothetical

Short stature, developmental impairment and sensorineural hearing loss occur in part of the series, and are prominent in the second family. The mechanism is assumed rather than shown: polymerase delta is needed wherever cells divide, so a general replication restriction should affect development. Two things argue for caution. Nothing has been measured in any affected non-haematopoietic tissue in either family. And in the Turkish kindred the affected aunt's intellectual impairment, hearing deficit and speech delay are explicitly attributed by the authors to a varicella encephalitis at age three — an infection the immunodeficiency plausibly permitted, which makes her deficits a consequence of the immune phenotype rather than a parallel developmental one.

Downstream

Sensorineural Hearing Loss

Developmental and Speech Delay

Short Stature

Microcephaly

Show evidence (1 reference)

PMID:31449058 SUPPORT INDIRECT PRIMARY RESULT Human Clinical

"a previously unknown autosomal-recessive syndrome that combines replicative stress, neurodevelopmental abnormalities, and immunodeficiency"

That the developmental features are part of the described syndrome. It supports their inclusion in the entity, not the mechanism this node proposes for them, which is why the node is graded HYPOTHETICAL.

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Pathograph

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Phenotypes

15

Blood 4

B and NK Cell Lymphopenia OCCASIONAL Decreased total B cell count HP:0010976

1 of 4 published POLD1 patients. Bound to the B-cell term with the NK deficit carried in preferred_term and description; binding both would need two phenotype entries for one reported observation.

Show evidence (1 reference)

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Immunological analyses showed persistent CD4+ T, B, and NK cell lymphopenia (Figure 1B). The patient receives subcutaneous Ig (scIG) treatment, as well as antibiotic and antifungal prophylactic therapy."

The three-lineage cytopenia in the POLD1 patient, with his treatment in the same sentence.

Decreased Total T Cell Count VERY_FREQUENT HP:0005403

2 of 2 patients in the Turkish kindred for whom counts are reported.

Show evidence (2 references)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Her immunological workup was particularly notable for profound CD3+CD4+ lymphopenia."

The index patient's T-cell deficit and the subset it falls hardest on.

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Her laboratory results revealed marked lymphopenia, hypogammaglobulinemia and low CD3+CD4+ T cell number similar to her older sister"

The same pattern in the younger sister at age three, which makes it a feature of the genotype rather than of one patient's course.

Loss of Naive T Cells with Effector Memory Skewing VERY_FREQUENT Decreased naive CD8+ T cell proportion HP:0410377

Reported for the patients of the Turkish kindred as a group. Bound to the CD8 term because the source says the loss is of naive CD4 "and especially CD8" cells and the CD8 compartment is where the repertoire restriction was also found; the CD4 loss is carried in the description rather than by a second binding.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"The patients exhibited decreased numbers of naive CD4 and especially CD8 T cells in favor of effector memory subpopulations."

The subset distribution, with the CD4/CD8 asymmetry the authors emphasise.

Decreased Circulating Immunoglobulin VERY_FREQUENT Decreased circulating immunoglobulin concentration HP:0004313

2 of 2 patients in the Turkish kindred for whom immunoglobulins are reported. The general-immunoglobulin term is bound rather than HP:0004315 Decreased circulating IgG concentration because all three isotypes are affected.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"She had mildly decreased serum IgG and low IgA and IgM antibody concentrations"

The three isotypes and the magnitude, in the index patient.

Ear 2

Recurrent Otitis Media OCCASIONAL HP:0000403

1 of 3 patients in the Turkish kindred. Worth separating from the hearing loss: conductive loss from effusion and sensorineural loss are different problems, and this patient has both a history of effusions and a documented sensorineural deficit.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"She underwent adenotonsillectomy at 5 1/2 years of age because of recurrent URTI and serous otitis media."

The otitis media and the surgery it led to.

Sensorineural Hearing Loss OCCASIONAL Sensorineural hearing impairment HP:0000407

2 of 3 patients in the Turkish kindred, and one of those two acquired it after encephalitis. The younger sister's normal audiology is a recorded negative, not a silence — which is what makes this a variable feature rather than a constant one.

Show evidence (2 references)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"At 3 years of age she was diagnosed with sensorineural hearing loss following evaluation for language delay."

The age, the modality and the route to diagnosis in the index patient.

PMID:31629014 REFUTE DIRECT PRIMARY RESULT Human Clinical

"Auditory testing revealed normal hearing."

The younger sister's normal audiogram, graded REFUTE against treating hearing loss as a constant of the genotype. She carries the same homozygous allele as her sister.

Head and Neck 1

Microcephaly OCCASIONAL HP:0000252

1 of 4 published POLD1 patients; not reported in the Turkish kindred.

Show evidence (1 reference)

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"short stature, microcephaly, a low IQ (approximately 70), and hearing impairment"

The finding as reported for the POLD1 patient.

Immune 4

Recurrent Herpetic Infection VERY_FREQUENT Recurrent herpes HP:0005353

Temporal: RECURRENT

3 of 3 patients in the Turkish kindred. The general recurrent-herpes term is bound rather than HP:0410028 Recurrent oral herpes, because the index patient had zoster as well as oral herpes and the parent term covers both.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Starting age 9 years, she had recurrent oral herpes infections every 1-2 months as well as several episodes of recurrent herpes zoster for which she received acyclovir therapy. Investigation into her recurrent herpetic infections revealed marked lymphopenia"

The frequency, the two herpesviruses involved, the treatment, and the fact that this was the presentation that led to the diagnosis.

Recurrent Respiratory Tract Infection VERY_FREQUENT Recurrent respiratory infections HP:0002205

Temporal: RECURRENT

3 of 3 patients in the Turkish kindred, and present in the second family. It is the feature that is present longest before diagnosis and the one least likely to prompt it.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Thereafter, she started experiencing LRTI at a frequency of 4-5 times/year, mainly in winter, requiring intravenous antibiotic therapy."

The frequency and severity of the lower respiratory infections in the index patient.

Absent Tetanus Vaccine Antibody Response VERY_FREQUENT Complete or near-complete absence of specific antibody response to tetanus vaccine HP:0410295

2 of 2 patients in the Turkish kindred for whom vaccine responses are reported, with the caveat that one recovered on boosting. The difference matters clinically: a response that boosts is an argument for vaccinating rather than for replacing.

Show evidence (2 references)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"while her tetanus vaccine-related antibody responses were absent despite having been fully vaccinated"

The absent specific response in the index patient, with vaccination confirmed.

PMID:31629014 REFUTE DIRECT PRIMARY RESULT Human Clinical

"She also had an unprotective tetanus antibody response on initial presentation despite her prior vaccination that normalized on booster vaccination."

Graded REFUTE against a reading of this phenotype as uniformly absent and irrecoverable. The younger sister's response came back on boosting, which no summary of the kindred as "absent vaccine responses" would convey.

Severe Primary Varicella FREQUENT Infectious encephalitis HP:0002383

2 of 3 patients in the Turkish kindred had a severe primary varicella course, one of them with encephalitis. Bound to the encephalitis term because that is the specific, codeable outcome; the severe uncomplicated course in the index patient is carried in the description. This is the phenotype with the clearest management implication in the entry — it bears on varicella vaccination and on post-exposure prophylaxis, neither of which is discussed in any source here.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"She suffered from severe Chickenpox at 6 years of age that eventually resolved."

The severe primary varicella course in the index patient.

Integument 1

Cutaneous Warts Negative for Common Papillomavirus Strains OCCASIONAL Verrucae HP:0200043

1 of 4 published POLD1 patients. The negative typing is part of the finding and is kept in the preferred_term, because a wart that types negative and a wart that types positive are different observations and HPO has no term that distinguishes them.

Show evidence (1 reference)

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"He presented with chronic bronchitis resulting in bronchiectasis and skin warts that were negative for common papilloma virus strains"

The lesions and their negative virological typing, in the POLD1 patient.

Nervous System 1

Developmental and Speech Delay FREQUENT Delayed speech and language development HP:0000750

2 of 3 in the Turkish kindred and present in the second family, but with three different proximate causes. Recorded with the distinction stated because a phenotype list that collapsed them would overstate the case for a primary neurodevelopmental effect of POLD1 deficiency.

Show evidence (1 reference)

PMID:31629014 SUPPORT INDIRECT PRIMARY RESULT Human Clinical

"She had encephalitis following a primary varicella infection at 3 years of age, from which she was left with mental retardation, hearing deficit and speech delay."

The aunt's deficits and their stated cause. Graded INDIRECT against a primary developmental phenotype, because the source attributes them to an infection rather than to the genotype directly — though the infection is itself plausibly a consequence of the immunodeficiency.

Respiratory 1

Bronchiectasis OCCASIONAL HP:0002110

1 of 4 published POLD1 patients. Not reported in the Turkish kindred, where immunoglobulin replacement resolved the lower respiratory infections — consistent with bronchiectasis being a function of untreated years rather than of genotype, though two families cannot separate that from chance. A caution about the source. The paper that reports this patient also reports a second patient with a POLD2 defect, whose bronchiectasis dates from six months of age and who also has chronic facial molluscum contagiosum and recurrent skin abscesses. That patient is not IMD120 — different gene, different disease. The deep-research report committed with this entry attributes all three of those features to POLD1, and they are not curated here. Within a single paper describing a shared syndrome across two genes, the patient-to-gene assignment is the thing to check.

Show evidence (1 reference)

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Patient 2 (P2) is a 24-year-old male born to nonconsanguineous parents. He presented with chronic bronchitis resulting in bronchiectasis and skin warts that were negative for common papilloma virus strains"

The POLD1 patient's respiratory phenotype, quoted with his patient number and parentage so the assignment to POLD1 rather than to the POLD2 patient is checkable from the snippet.

Growth 1

Short Stature OCCASIONAL HP:0004322

1 of 4 published POLD1 patients. The younger sister in the Turkish kindred had weight and height in the normal range for her age at presentation, which is a recorded negative.

Show evidence (1 reference)

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"The patient had short stature, microcephaly, a low IQ (approximately 70), and hearing impairment."

The POLD1 patient's syndromic features in one sentence — the source for this phenotype, the microcephaly and the quantified cognitive impairment.

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Genetic Associations

1

POLD1

Gene: POLD1 hgnc:9175 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (5 references)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"These results identify gene defects in POLD1 as a novel cause of T-cell immunodeficiency."

The gene-disease claim as the authors state it.

PMID:31629014 REFUTE DIRECT PRIMARY RESULT Human Clinical

"A number of extended family members had colon and rectal cancers but did not carry the mutant allele."

Graded REFUTE against the inference that this allele carries the cancer risk POLD1 is otherwise known for. The cancers and the allele segregate apart in the one family where both are present, which is a stronger separation than any argument from domain position.

PMID:31449058 SUPPORT INDIRECT PRIMARY RESULT Human Clinical

"In familial colorectal cancer, this could be explained by the hypermutator phenotype, in which POLD1 loss of function leads to a functional gain of function (increased mutation rate)"

Why the same gene gives a dominant cancer syndrome and a recessive immunodeficiency. Graded INDIRECT because it explains the allelic series rather than establishing anything about this entity.

+ 2 more references

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Medical Actions

3

Immunoglobulin Replacement Therapy

Action: immunoglobulin replacement therapy Ontology label: Immunoglobulin Therapy NCIT:C62710

Platform: Protein replacement

The mainstay. In the index patient it resolved the lower respiratory infections and markedly decreased the herpetic ones; the second family's POLD1 patient receives subcutaneous immunoglobulin alongside antibacterial and antifungal prophylaxis. The reduction in herpetic episodes is the part worth noticing. Replacement supplies antibody, and control of a latent herpesvirus is a T-cell job, so a large effect on herpes recurrence is not what the mechanism predicts. It is recorded as reported, in one patient, without an explanation attached.

Mechanism Target:

Defective T-Dependent Antibody Response — Replacement substitutes for the antibody the patient cannot generate. It addresses the humoral consequence and leaves the T-cell proliferation defect that produced it untouched.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"She was started on immunoglobulin replacement therapy, which resulted in the resolution of LRTI and markedly decreased herpetic infections."

The response, in the one patient for whom a before-and-after is reported.

Aciclovir for Herpetic Episodes

Action: Pharmacotherapy NCIT:C15986

Agent: aciclovir CHEBI:2453

Platform: Small molecule

Given for the index patient's recurrent herpes zoster. No outcome is reported, and the sources do not say whether it was episodic or prophylactic — which matters, since suppression is the plausible strategy in a patient with monthly recurrences and the sources do not establish that it was used that way.

Mechanism Target:

Recurrent Herpetic Infection — Antiviral treatment of the episodes the immune defect permits. It does not address the repertoire contraction underneath them.

Show evidence (1 reference)

PMID:31629014 SUPPORT INDIRECT PRIMARY RESULT Human Clinical

"several episodes of recurrent herpes zoster for which she received acyclovir therapy"

That the drug was given, and for what. Graded INDIRECT because the source records the prescription and no outcome.

Haematopoietic Stem Cell Transplantation

Action: hematopoietic cell transplantation Ontology label: Hematopoietic Cell Transplantation NCIT:C15431

Platform: Cell therapy

The only reported route to correcting the immune defect rather than substituting for it. A 2026 report describes the first successful transplant in POLD1 deficiency: an 18-year-old woman with recurrent pulmonary infections and shingles, dependent on immunoglobulin replacement, transplanted from a matched related donor using reduced-intensity conditioning with cyclophosphamide, fludarabine and anti-thymocyte globulin, with bone marrow and peripheral blood as stem-cell sources and tacrolimus plus low-dose methotrexate for graft-versus-host disease prophylaxis. Engraftment was prompt and without major complications; at two years her T-cell counts and function were improved and she no longer needed replacement. The reason it is a report rather than a routine option is a specific and well-founded fear: conditioning regimens work by damaging DNA, and a disease of the replicative polymerase raises the question of regimen-related toxicity. The family were told about that concern before the decision. Reduced-intensity conditioning was chosen against it, and the result argues the fear may be manageable — in one patient.

Mechanism Target:

Impaired T Cell Clonal Proliferation — Replacing the haematopoietic compartment with donor cells that carry two working POLD1 alleles removes the proliferation ceiling in the lineage where it matters. It does nothing for the non-haematopoietic consequences of the same defect.

Show evidence (2 references)

PMID:42104577 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"She underwent HSCT from a matched related donor using a reduced-intensity regimen (cyclophosphamide, fludarabine, ATG) with bone marrow and peripheral blood as stem cell sources."

The regimen and the graft source, in enough detail to be acted on.

PMID:42104577 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Patients considered for HSCT may be at increased risk of regimen-related toxicity due to impaired DNA repair."

The stated concern the reduced-intensity choice was made against. Worth recording even though this entry's own mechanism section notes that repair after genotoxic stress was normal in these patients — the clinical worry and the laboratory finding point different ways, and a transplant decision has to be made without that being settled.

🔬

Diagnosis

4

Lymphocyte subset enumeration

T-cell lymphopenia with profound CD4 depletion is the finding that converts a recurrent infection history into an immunodeficiency diagnosis, and in the index kindred it was ordered only after nine years of infections. Subset work adds the naive-to-effector-memory skewing that distinguishes an exhausted, proliferation-limited compartment from a production failure.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Her immunological workup was particularly notable for profound CD3+CD4+ lymphopenia."

The diagnostic finding, in the patient whose referral it followed.

Lymphocyte proliferation assay

The assay that localises the lesion. Impaired T-cell but preserved B-cell proliferation is the pattern here, and it is what distinguishes this from a production or survival defect.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"T-cell lymphopenia with impaired T-cell but not B-cell proliferation"

The selective proliferation defect, which is the diagnostic signature of this disease.

DNA repair assay after genotoxic stress (ABSENT)

Recorded as a negative. A clinician faced with a combined immunodeficiency and syndromic features will reasonably think of the DNA-repair immunodeficiencies and send a repair assay. In polymerase delta deficiency it is normal, and that normal result is informative rather than uninformative: it places the lesion at replication rather than at repair. The qualifier matters and this entry originally lacked it. The experiment was done in the POLD2 patient's fibroblasts. The POLD1 patient — the one this entry curates — was never tested with genotoxic compounds. Everything below rests on the two patients sharing a holoenzyme, which is the same argument the whole paper is built on, and is still an extrapolation.

Do not read this as a measured property of POLD1 deficiency. It is a measured property of POLD2 deficiency carried across. If the two differ anywhere, conditioning-regimen tolerance is exactly where it would matter, and that is the subject of one of this entry's discussions.

Show evidence (2 references)

PMID:31449058 SUPPORT INDIRECT PRIMARY RESULT Human Clinical

"P1 fibroblasts showed no overt sensitivity to an array of genotoxic reagents, which suggests that, despite an unstable POLD complex, its activity was sufficient to ensure proficiency in specific DNA repair pathways"

The repair-normal result itself, quoted so the patient it belongs to is identifiable from the snippet. P1 is the POLD2 patient. Graded INDIRECT for this entry because it is POLD2 data applied to a POLD1 entity on the shared-complex argument, not a POLD1 measurement.

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"To determine the DNA repair capacity of POLD-deficient cells, we treated P1 cells with different genotoxic compounds"

The design of the experiment, quoted because it names the single patient tested. Nothing in this paper repeats it in the POLD1 patient.

Exome or targeted panel sequencing

How both families were diagnosed. In the consanguineous kindred, homozygosity mapping on exome data narrowed to a 14 Mb region on chromosome 19 containing nine genes, of which POLD1 was the candidate; in the other family a targeted inborn-errors-of-immunity panel found the variants and exome sequencing excluded other biallelic candidates.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Knowing that the family is consanguineous, we executed homozygosity mapping using their WES data"

The analytic step that made a single-kindred exome informative, which is the reason consanguinity is a diagnostic asset as well as a risk factor.

📈

Progression

3

Recurrent infection in early childhood, unrecognised

The index patient had recurrent upper and lower respiratory infection from early life, hearing loss at three, adenotonsillectomy at five and a half, severe chickenpox at six, four to five intravenous-antibiotic episodes a year, and recurrent herpes from nine. She was referred for immunological evaluation at twelve. That is nine years of infection before anybody counted a lymphocyte, and it is the natural history this entry exists to shorten. What eventually triggered the referral was the herpetic pattern, not the respiratory one.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Investigation into her recurrent herpetic infections revealed marked lymphopenia, for which she was referred for immunological evaluation at 12 years of age."

The age at referral and the finding that prompted it.

Stabilisation on immunoglobulin replacement

Immunoglobulin replacement resolved the lower respiratory infections in the index patient and markedly reduced the herpetic ones, which is more than replacement would be expected to do for a viral phenotype and is recorded as reported. The second family's POLD1 patient is on subcutaneous immunoglobulin with antibacterial and antifungal prophylaxis. Stabilisation is not resolution: the underlying proliferation defect is unchanged, and whatever airway damage has already occurred is permanent.

Show evidence (1 reference)

PMID:31629014 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"She was started on immunoglobulin replacement therapy, which resulted in the resolution of LRTI and markedly decreased herpetic infections."

The treatment response in the index patient, covering both the bacterial and the viral phenotype.

Transplant in adulthood

A 2026 report describes the first successful haematopoietic stem cell transplant in POLD1 deficiency, in an 18-year-old woman with recurrent pulmonary infections and shingles who was dependent on immunoglobulin replacement. Two years on she has improved T-cell counts and function and no longer needs replacement.

Show evidence (1 reference)

PMID:42104577 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"Post-HSCT follow-up demonstrated improved T-cell counts and function, and the patient remained well without IgRT."

The outcome at two years, and the endpoint that matters — freedom from replacement.

📊

Prevalence

1

Worldwide

Cases In Literature <1 in 1,000,000

Four published POLD1 patients in two unrelated families: three relatives across two generations of a consanguineous Turkish kindred, and one man from a non-consanguineous family. A fifth patient is described in the 2026 transplant report — an 18-year-old woman with POLD1 deficiency — whose relationship to the two published families is not stated there, so she is not counted here and the count above may be an undercount by one. No population estimate exists. Consanguinity is the route to the homozygous genotype in one family and p.Arg1060Cys is absent from every population database checked, so no founder effect or carrier frequency can be inferred. rate_per_100000 is left unset rather than computed from four cases.

Show evidence (1 reference)

PMID:31449058 SUPPORT DIRECT PRIMARY RESULT Human Clinical

"To our knowledge, no germline biallelic mutations affecting this complex have been reported in humans."

The size of the literature at the point the entity was defined — none, which is what makes the current total of four the whole of it.

{ }

Source YAML

click to show

name: Immunodeficiency 120
category: Mendelian
creation_date: "2026-09-22T00:00:00Z"
synonyms:
- IMD120
- POLD1 deficiency
- POLD1-associated combined immunodeficiency
- combined immunodeficiency due to POLD1 deficiency
- DNA polymerase delta 1 deficiency
disease_term:
  preferred_term: immunodeficiency 120
  term:
    id: MONDO:0970994
    label: immunodeficiency 120
description: >-
  IMD120 is the combined immunodeficiency caused by biallelic hypomorphic variants in POLD1, the
  catalytic subunit of DNA polymerase delta. Four patients in two unrelated families are
  published: three members of a consanguineous Turkish kindred homozygous for p.Arg1060Cys, and
  one compound heterozygote in the series that first described human polymerase delta deficiency.

  The mechanism is a proliferation defect rather than a repair defect, and that distinction is
  the whole of the disease. Polymerase delta replicates both strands; a hypomorphic catalytic
  subunit reduces the enzyme's output, which impairs recruitment of replication factor C and so
  the initiation of replication, which restricts how many cells can enter and complete S phase.
  Lymphocytes are the cells that must expand fastest on demand, so they are the cells that fail.

  DNA repair after genotoxic stress is reported normal in polymerase delta deficiency, which is
  what separates it from the DNA-repair immunodeficiencies it superficially resembles. That
  result needs a qualifier this entry originally omitted: the genotoxic-sensitivity experiment
  was done in the POLD2 patient's fibroblasts, not the POLD1 patient's. It is extrapolated here
  on the shared-complex argument, and the extrapolation is stated wherever the claim is used
  rather than assumed.

  Two biochemical routes converge on that output. p.Arg1060Cys sits in the C-terminal CysB
  metal-binding motif and destabilises the holoenzyme, lowering the steady-state amount of
  POLD1, POLD2 and POLD3 together. The compound heterozygous alleles sit near the polymerase
  active site and reduce catalytic activity with complex assembly intact. Different lesions,
  same phenotype — which is the strongest argument available that the phenotype follows from
  reduced polymerase delta output rather than from anything particular to one allele.

  Clinically it presents as recurrent herpetic infection on a background of recurrent
  respiratory infection, with T-cell lymphopenia, loss of naive CD4 and especially CD8 cells,
  a contracted oligoclonal repertoire, mild hypogammaglobulinaemia and absent vaccine responses.
  Immunoglobulin replacement resolved the lower respiratory infections and markedly reduced the
  herpetic episodes in the index patient, and a 2026 report describes the first successful
  haematopoietic stem cell transplant in the disease.

  POLD1 is pleiotropic, and the allele class decides which disease you get. Heterozygous
  proofreading-domain variants cause colorectal cancer predisposition; the recurrent
  heterozygous p.Ser605del causes MDPL syndrome. This entity is the biallelic hypomorphic one,
  and the founding kindred contains a recorded negative that makes the separation concrete:
  several extended family members had colon and rectal cancers and none of them carried the
  mutant allele.
parents:
- Combined Immunodeficiency
- Inborn Errors of Immunity
classifications:
  harrisons_chapter:
  - classification_value: IMMUNE_RHEUMATOLOGIC
    notes: >-
      A monogenic inborn error of immunity presenting as combined immunodeficiency, managed by
      immunology.
  iuis_category:
    classification_value: combined immunodeficiency
    notes: >-
      IUIS Table 1, immunodeficiencies affecting cellular and humoral immunity. The pattern here
      is T-cell lymphopenia with impaired T-cell but not B-cell proliferation and secondary
      humoral impairment, which is a combined rather than a purely cellular defect.
references:
- reference: PMID:31629014
  title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
- reference: PMID:31449058
  title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
- reference: PMID:42104577
  title: "Successful Treatment of POLD1 Deficiency With HSCT: Report of Two Years' Experience."
- reference: PMID:31944473
  title: "POLD1 variants leading to reduced polymerase activity can cause hearing loss without syndromic features."
- reference: PMID:41263451
  title: "PolED: a manually curated database of functional studies of POLE and POLD1 variants reported in humans."
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    Biallelic in both families. The Turkish kindred is homozygous with heterozygous parents and
    segregation confirmed by Sanger sequencing across three affected relatives in two
    generations; the second family's patient is compound heterozygous with a maternal allele
    carrying two substitutions in cis and a separate paternal allele. Heterozygous carriers are
    unaffected for this phenotype.

    The recessive prediction is also borne out at the gene level: POLD1 has a low pLI and a high
    pRec, meaning loss of one allele is predicted to be tolerated and loss of both is not — which
    is the population-genetic signature of a recessive disease gene and is stated explicitly by
    the authors.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Both parents were heterozygous for the mutation. Her sister P2, who also suffered from recurrent infections, was found homozygous for the same mutation by Sanger sequencing, as was a paternal aunt P3"
    explanation: >-
      Carrier parents and homozygosity in all three affected relatives, which is the segregation
      that establishes recessive inheritance in this kindred.
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Both genes show low pLI scores of 0.001 and 0.044, respectively, indicating a predicted tolerance to the loss of a single allele, and high pRec scores of 0.998 and 0.950, respectively, indicating a predicted high intolerance for a complete loss of function"
    explanation: >-
      The population-genetic prediction, which agrees with the observed inheritance and also
      explains why no null allele appears in this disease.
pathophysiology:
- name: Biallelic Hypomorphic POLD1 Variants
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Two genotypes are published. The Turkish kindred is homozygous for c.3178C>T, p.Arg1060Cys,
    absent from gnomAD, ExAC, dbSNP and 1000 Genomes, found by homozygosity mapping in the
    largest of five runs of homozygosity and confirmed by Sanger sequencing in all three affected
    relatives.

    The second family's patient carries three heterozygous POLD1 variants making up two alleles:
    p.Gln684His and p.Ser939Trp inherited together in cis on the maternal allele, and
    p.Arg1074Trp on the paternal allele. Getting that configuration right matters, because two of
    the three substitutions are on one chromosome — a reader counting substitutions rather than
    alleles would conclude the patient has three hits when they have two.

    No null allele appears in either family, and none is expected to: complete POLD1 deficiency is
    embryonic lethal in mice, and POLD1's high pRec score predicts intolerance of complete loss of
    function in humans. Every disease allele here is hypomorphic by necessity.
  genes:
  - preferred_term: POLD1
    term:
      id: hgnc:9175
      label: POLD1
  genetic_context:
    genes:
    - preferred_term: POLD1
      term:
        id: hgnc:9175
        label: POLD1
    allele_type: a homozygous CysB-motif missense variant in one family, and two missense variants in cis opposite a third missense variant in the other
    variant_origin: GERMLINE
    functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
    description: >-
      Zygosity differs between the two families — homozygous in the Turkish kindred, compound
      heterozygous in the second — so the slot is left unset rather than asserting one family's
      configuration for both.
    notes: >-
      PARTIAL_LOSS_OF_FUNCTION rather than LOSS_OF_FUNCTION, and the reasoning is not a hedge:
      complete polymerase delta loss is embryonic lethal in mice and predicted intolerable in
      humans, so a viable patient's alleles are hypomorphic by construction. Both genotypes were
      functionally tested and both retain activity.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "This missense homozygous mutation has not been previously reported in genomAD, ExAC, dbSNP or 1000Genome and was confirmed by Sanger sequencing"
    explanation: >-
      The allele's absence from every population database consulted, and its confirmation by a
      second method.
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "The variants p.Gln684His (CADD score of 26), located in the catalytic domain, and p.Ser939Trp (CADD score of 34) in an interdomain region, were inherited in cis on the same allele of maternal origin, whereas the p.Arg1074Trp variant (CADD score of 34) located to the CysB domain on the paternal allele."
    explanation: >-
      The full three-variant, two-allele configuration with its phase, which is what makes this
      patient biallelic rather than triallelic.
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    quote_role: BACKGROUND
    snippet: "Total POLD1 deficiency is embryonic lethal in mice, while deficiency of POLD1 exonuclease activity in Pold1exo/exo mice (mutator mice), results in a high rate of DNA replication errors"
    explanation: >-
      Why no null allele can appear in this disease, and the contrast with the proofreading-only
      mouse that models the cancer-predisposition allele class instead. Graded BACKGROUND because
      the sentence summarises prior mouse work in this paper's introduction rather than reporting
      its own result, and MODEL_ORGANISM because that is the evidence the quoted text describes.
  downstream:
  - target: Destabilisation of the Polymerase Delta Holoenzyme
    causal_link_type: DIRECT
    description: >-
      The p.Arg1060Cys route. The substitution disrupts the intramolecular contact between the
      POLD1 CysB motif and the catalytic domain, and the contact between POLD1 and POLD2, so the
      complex falls apart and all three measured subunits drop together.
    evidence:
    - reference: PMID:31629014
      reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
      supports: SUPPORT
      directness: DIRECT
      evidence_source: COMPUTATIONAL
      quote_role: PRIMARY_RESULT
      snippet: "Molecular dynamics simulation revealed that the R1060C mutation disrupts the intramolecular interaction between the POLD1 CysB motif and the catalytic domain and also between POLD1 and the Polδ subunit POLD2."
      explanation: >-
        The structural account of how this allele destabilises the complex. Graded COMPUTATIONAL
        because it is a molecular dynamics result; the destabilisation itself was also measured
        in cells, which is the node's own evidence.
  - target: Reduced Intrinsic Polymerase Catalytic Activity
    causal_link_type: DIRECT
    description: >-
      The second family's route. Substitutions near the active site reduce catalytic turnover
      while leaving complex assembly intact — a different lesion reaching the same output.
- name: Destabilisation of the Polymerase Delta Holoenzyme
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Polymerase delta is a heterotetramer: POLD1 carries the polymerase and exonuclease
    activities, POLD2 is the scaffold that holds POLD1 to the rest, and POLD3 and POLD4 regulate
    activity and stability. A substitution at the POLD1-POLD2 interface therefore does not
    inactivate one subunit, it lowers the amount of assembled enzyme — POLD1, POLD2 and POLD3
    fall together.
  genes:
  - preferred_term: POLD1
    term:
      id: hgnc:9175
      label: POLD1
  cellular_components:
  - preferred_term: DNA polymerase delta complex
    term:
      id: GO:0043625
      label: delta DNA polymerase complex
    modifier: DECREASED
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "The mutation destabilizes the Polδ complex, leading to ineffective recruitment of replication factor C to initiate DNA replication."
    explanation: The destabilisation and the step it blocks, stated as the paper's own result.
  downstream:
  - target: Ineffective Replication Factor C Recruitment
    causal_link_type: DIRECT
- name: Reduced Intrinsic Polymerase Catalytic Activity
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    The second route to the same deficit: substitutions near the polymerase active site lower
    catalytic activity without destabilising the complex. The two families therefore differ in
    biochemistry and agree in phenotype, which is the argument that the disease follows from
    reduced polymerase delta output rather than from a property of one allele.

    In the second family's cells the replication-associated lesions were reversible on
    overexpressing polymerase delta, which is the rescue that establishes the direction of
    causation.
  genes:
  - preferred_term: POLD1
    term:
      id: hgnc:9175
      label: POLD1
  molecular_functions:
  - preferred_term: DNA-directed DNA polymerase activity
    term:
      id: GO:0003887
      label: DNA-directed DNA polymerase activity
    modifier: DECREASED
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "The mutations affected the stability and interactions within the polymerase δ complex or its intrinsic polymerase activity."
    explanation: >-
      The two mechanisms, stated by the authors as alternatives — which is what makes them
      convergent routes rather than a single chain.
  downstream:
  - target: Impaired S-Phase Progression and Replicative Stress
    causal_link_type: DIRECT
- name: Ineffective Replication Factor C Recruitment
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Replication factor C is the clamp loader that places PCNA on DNA so that polymerase delta can
    begin synthesis. Less assembled polymerase delta means less effective RFC recruitment, so
    fewer replication events start. The deficit is at initiation rather than at elongation, which
    is why the cellular phenotype is a reduced fraction of cells in S phase rather than slow
    replication in all of them.
  biological_processes:
  - preferred_term: DNA replication initiation
    term:
      id: GO:0006270
      label: DNA replication initiation
    modifier: DECREASED
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: "Additionally, the Polδ complex coordinately interacts with a number of proteins that enable its function, including DNA replication factor C (RFC) and Proliferating Cell Nuclear Antigen (PCNA)"
    explanation: >-
      The interaction this node depends on, stated in the paper's introduction as established
      biology rather than as its own finding — which is exactly what quote_role BACKGROUND is
      for.
  downstream:
  - target: Impaired S-Phase Progression and Replicative Stress
    causal_link_type: DIRECT
- name: Impaired S-Phase Progression and Replicative Stress
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    A smaller fraction of cells enters and completes S phase, and replication-associated DNA
    lesions accumulate. Both findings are reported for the patients' cells in the plural and are
    attributable to the POLD1 patient as well as the POLD2 one.

    The control that would place this disease among the proliferation defects rather than among
    the DNA-repair immunodeficiencies — ataxia-telangiectasia, Nijmegen breakage, LIG4 deficiency
    — is the genotoxic-sensitivity experiment, and that one is not plural. It was done in the
    POLD2 patient's fibroblasts, which showed no overt sensitivity to an array of genotoxic
    reagents. The POLD1 patient was never tested. The inference to POLD1 runs through the shared
    holoenzyme and is reasonable; it is not a measurement in this disease, and this entry marks
    it as extrapolated wherever it is used.

    It has a practical consequence recorded under treatments: a repair-competent cell is a
    different transplant-conditioning risk from a repair-deficient one, and the first HSCT in
    this disease was performed against exactly that uncertainty — with the team's stated concern
    pointing the opposite way from this extrapolation.
  biological_processes:
  - preferred_term: cell cycle
    term:
      id: GO:0007049
      label: cell cycle
    modifier: DECREASED
  - preferred_term: DNA replication
    term:
      id: GO:0006260
      label: DNA replication
    modifier: DECREASED
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Patients' cells showed impaired cell-cycle progression and replication-associated DNA lesions that were reversible upon overexpression of polymerase δ."
    explanation: >-
      The cellular phenotype and its rescue by restoring the enzyme, which is what makes the
      polymerase deficit causal for it rather than merely coincident.
  downstream:
  - target: Impaired T Cell Clonal Proliferation
    causal_link_type: DIRECT
    description: >-
      Lymphocytes are the cells whose function is to divide on demand, so a ceiling on cell-cycle
      entry is felt there first. The B-cell compartment is comparatively spared in proliferation
      terms, which is why the defect presents as T-cell rather than combined at the cellular
      level even though the humoral consequence is real.
    evidence:
    - reference: PMID:31629014
      reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
      supports: SUPPORT
      directness: DIRECT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: "we identified a missense mutation (c. 3178C>T; p.R1060C) in POLD1 in 3 related subjects who presented with recurrent, especially herpetic, infections and T-cell lymphopenia with impaired T-cell but not B-cell proliferation"
      explanation: >-
        The selectivity of the proliferation defect for T cells over B cells, measured in the
        three affected relatives.
  - target: Syndromic Developmental Features
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Polymerase delta is required in every dividing tissue, so a general replication restriction
      is a plausible route to the short stature, developmental impairment and hearing loss seen
      in part of the series. No tissue-level measurement supports the step, and in the Turkish
      kindred one affected member's deficits followed a varicella encephalitis rather than being
      developmental from the start — so the attribution is weaker here than the clean immune
      chain above.
- name: Impaired T Cell Clonal Proliferation
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    On T-cell receptor activation, patient T cells show reduced proliferative responses coupled
    to reduced cell-cycle progression. B-cell proliferation is comparatively preserved. This is
    the point at which a housekeeping replication defect becomes an immune disease.
  cell_types:
  - preferred_term: T cell
    term:
      id: CL:0000084
      label: T cell
  biological_processes:
  - preferred_term: T cell proliferation
    term:
      id: GO:0042098
      label: T cell proliferation
    modifier: DECREASED
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "We believe our discovery of human polymerase δ deficiency identifies the central role of this complex in the prevention of replication-related DNA lesions, with particular relevance to adaptive immunity."
    explanation: >-
      The authors' framing of why a replication defect lands on adaptive immunity specifically.
      Graded INDIRECT because it is an interpretive statement rather than the proliferation
      measurement itself.
  downstream:
  - target: Contracted Oligoclonal T Cell Repertoire
    causal_link_type: DIRECT
  - target: Decreased Total T Cell Count
    causal_link_type: DIRECT
  - target: B and NK Cell Lymphopenia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Drawn from the shared proliferation ceiling rather than from the T-cell defect: B and NK
      cells divide too, and in the one patient where all three lineages were counted all three
      were low. The edge is placed here rather than on the replicative-stress node because the
      same paper reports B-cell proliferation as comparatively spared in the other family, so
      how a cell-cycle restriction produces a B-cell cytopenia without a measurable proliferation
      defect is not settled.
  - target: Defective T-Dependent Antibody Response
    causal_link_type: DIRECT
    description: >-
      B cells proliferate adequately but do not receive adequate help, so the humoral defect is
      downstream of the T-cell one rather than a parallel B-cell-intrinsic lesion. That is the
      reading the preserved B-cell proliferation supports, and it is what makes immunoglobulin
      replacement a rational rather than merely empirical treatment here.
- name: Contracted Oligoclonal T Cell Repertoire
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >-
    Naive CD4 and especially CD8 cells are depleted in favour of effector memory subsets, and the
    CD8 compartment is oligoclonal with restricted T-cell receptor beta-chain V-J pairing while
    the CD4 compartment is not. The authors read that asymmetry as POLD1 affecting peripheral
    CD8 expansion and possibly thymic selection differently from CD4.

    A repertoire that is both small and skewed is what makes this a viral rather than a
    pyogenic immunodeficiency: containing a herpesvirus needs a specific clone to expand, and
    there are fewer clones and less capacity to expand them.
  cell_types:
  - preferred_term: CD8-positive, alpha-beta T cell
    term:
      id: CL:0000625
      label: CD8-positive, alpha-beta T cell
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "This skewing was associated with oligoclonality and restricted T-cell receptor β-chain V-J pairing in CD8+ but not CD4+ T cells, suggesting that POLD1R1060C differentially affects peripheral CD8+ T-cell expansion and possibly thymic selection."
    explanation: >-
      The repertoire finding, its restriction to CD8, and the authors' own hedged interpretation
      of it — quoted with the hedge intact.
  downstream:
  - target: Recurrent Herpetic Infection
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Control of latent herpesviruses depends on CD8 T-cell surveillance, and this is the
      compartment that is depleted, skewed and oligoclonal. The step is not measured in these
      patients — no viral load, no antigen-specific tetramer work — so it is the immunological
      argument applied to the observed repertoire rather than a finding about it.
  - target: Recurrent Respiratory Tract Infection
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Bronchiectasis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Bronchiectasis here is infection-driven airway destruction, not a primary polymerase
      lesion. The edge runs through years of recurrent infection, which is why it is the
      phenotype that early diagnosis prevents and nothing reverses.
  - target: Recurrent Otitis Media
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Severe Primary Varicella
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Primary varicella is contained by the same CD8 response that later holds the virus latent,
      so a contracted CD8 compartment predicts both a severe primary course and recurrent zoster
      — and this kindred has both.
  - target: Cutaneous Warts Negative for Common Papillomavirus Strains
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Defective T-Dependent Antibody Response
  biological_scale: ORGANISM
  mechanism_confidence: PROVISIONAL
  description: >-
    Mildly reduced IgG with low IgA and IgM, and absent tetanus responses despite full
    vaccination. Graded PROVISIONAL rather than ESTABLISHED because the inference that the
    humoral defect is secondary to failed T-cell help rests on the preserved B-cell proliferation
    rather than on any direct measurement of help — nobody has assayed germinal centre formation,
    class switching or T-follicular-helper number in these patients.

    The one piece of evidence that bears on it directly is a treatment observation rather than an
    experiment: the younger sister's unprotective tetanus response normalised on booster
    vaccination, which is not what a B-cell-intrinsic defect would predict.
  cell_types:
  - preferred_term: B cell
    term:
      id: CL:0000236
      label: B cell
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She had mildly decreased serum IgG and low IgA and IgM antibody concentrations, while her tetanus vaccine-related antibody responses were absent despite having been fully vaccinated"
    explanation: >-
      The humoral picture in the index patient, with the vaccination history that makes the
      absent response informative rather than merely unmeasured.
  downstream:
  - target: Decreased Circulating Immunoglobulin
    causal_link_type: DIRECT
  - target: Absent Tetanus Vaccine Antibody Response
    causal_link_type: DIRECT
- name: Syndromic Developmental Features
  biological_scale: ORGANISM
  mechanism_confidence: HYPOTHETICAL
  description: >-
    Short stature, developmental impairment and sensorineural hearing loss occur in part of the
    series, and are prominent in the second family. The mechanism is assumed rather than shown:
    polymerase delta is needed wherever cells divide, so a general replication restriction should
    affect development.

    Two things argue for caution. Nothing has been measured in any affected non-haematopoietic
    tissue in either family. And in the Turkish kindred the affected aunt's intellectual
    impairment, hearing deficit and speech delay are explicitly attributed by the authors to a
    varicella encephalitis at age three — an infection the immunodeficiency plausibly permitted,
    which makes her deficits a consequence of the immune phenotype rather than a parallel
    developmental one.
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "a previously unknown autosomal-recessive syndrome that combines replicative stress, neurodevelopmental abnormalities, and immunodeficiency"
    explanation: >-
      That the developmental features are part of the described syndrome. It supports their
      inclusion in the entity, not the mechanism this node proposes for them, which is why the
      node is graded HYPOTHETICAL.
  downstream:
  - target: Sensorineural Hearing Loss
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Developmental and Speech Delay
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Short Stature
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Microcephaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
phenotypes:
- name: Recurrent Herpetic Infection
  category: Immune
  description: >-
    The feature that brought the index patient to immunology. Recurrent oral herpes every one to
    two months from age nine, with several episodes of herpes zoster requiring aciclovir; her
    younger sister also has recurrent oral herpes; their aunt has had recurrent oral herpetic
    infection since a varicella encephalitis in early childhood.

    In this kindred it was the herpetic infections rather than the respiratory ones that
    prompted the lymphocyte count — the respiratory infections had been treated as ordinary for
    nine years.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Recurrent oral herpes and herpes zoster
    term:
      id: HP:0005353
      label: Recurrent herpes
    temporality: RECURRENT
  notes: >-
    3 of 3 patients in the Turkish kindred. The general recurrent-herpes term is bound rather
    than HP:0410028 Recurrent oral herpes, because the index patient had zoster as well as oral
    herpes and the parent term covers both.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Starting age 9 years, she had recurrent oral herpes infections every 1-2 months as well as several episodes of recurrent herpes zoster for which she received acyclovir therapy. Investigation into her recurrent herpetic infections revealed marked lymphopenia"
    explanation: >-
      The frequency, the two herpesviruses involved, the treatment, and the fact that this was
      the presentation that led to the diagnosis.
- name: Recurrent Respiratory Tract Infection
  category: Respiratory
  description: >-
    Recurrent upper and lower respiratory infection from early life in the index patient, four
    to five lower respiratory episodes a year requiring intravenous antibiotics, with
    adenotonsillectomy at five and a half for recurrent upper respiratory infection and serous
    otitis media. Her sister presented at three with fever and cough and continues to have
    recurrent croup; the aunt has winter upper respiratory infections requiring oral
    antibiotics. In the second family the respiratory infections began in infancy and produced
    bronchiectasis.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Recurrent upper and lower respiratory tract infection
    term:
      id: HP:0002205
      label: Recurrent respiratory infections
    temporality: RECURRENT
  notes: >-
    3 of 3 patients in the Turkish kindred, and present in the second family. It is the feature
    that is present longest before diagnosis and the one least likely to prompt it.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Thereafter, she started experiencing LRTI at a frequency of 4-5 times/year, mainly in winter, requiring intravenous antibiotic therapy."
    explanation: The frequency and severity of the lower respiratory infections in the index patient.
- name: Bronchiectasis
  category: Respiratory
  description: >-
    Chronic bronchitis progressing to bronchiectasis in the second family's POLD1 patient, a
    24-year-old man. It is the irreversible consequence of years of untreated infection, and the
    reason early recognition rather than any drug is the intervention that changes outcome here.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Bronchiectasis following chronic bronchitis
    term:
      id: HP:0002110
      label: Bronchiectasis
  notes: >-
    1 of 4 published POLD1 patients. Not reported in the Turkish kindred, where immunoglobulin
    replacement resolved the lower respiratory infections — consistent with bronchiectasis being
    a function of untreated years rather than of genotype, though two families cannot separate
    that from chance.

    A caution about the source. The paper that reports this patient also reports a second
    patient with a POLD2 defect, whose bronchiectasis dates from six months of age and who also
    has chronic facial molluscum contagiosum and recurrent skin abscesses. That patient is not
    IMD120 — different gene, different disease. The deep-research report committed with this
    entry attributes all three of those features to POLD1, and they are not curated here. Within
    a single paper describing a shared syndrome across two genes, the patient-to-gene assignment
    is the thing to check.
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Patient 2 (P2) is a 24-year-old male born to nonconsanguineous parents. He presented with chronic bronchitis resulting in bronchiectasis and skin warts that were negative for common papilloma virus strains"
    explanation: >-
      The POLD1 patient's respiratory phenotype, quoted with his patient number and parentage so
      the assignment to POLD1 rather than to the POLD2 patient is checkable from the snippet.
- name: Cutaneous Warts Negative for Common Papillomavirus Strains
  category: Integumentary
  description: >-
    Skin warts in the second family's POLD1 patient that tested negative for the common
    papillomavirus strains. A wart that is not a common HPV wart in a patient with a T-cell
    defect is the kind of finding that usually indicates an unusual cutaneous viral
    susceptibility, and it fits the herpesvirus-and-poxvirus bias of this disease.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Cutaneous warts, negative for common papillomavirus strains
    term:
      id: HP:0200043
      label: Verrucae
  notes: >-
    1 of 4 published POLD1 patients. The negative typing is part of the finding and is kept in
    the preferred_term, because a wart that types negative and a wart that types positive are
    different observations and HPO has no term that distinguishes them.
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "He presented with chronic bronchitis resulting in bronchiectasis and skin warts that were negative for common papilloma virus strains"
    explanation: The lesions and their negative virological typing, in the POLD1 patient.
- name: B and NK Cell Lymphopenia
  category: Immune
  description: >-
    Persistent CD4 T, B and NK cell lymphopenia in the second family's POLD1 patient. It matters
    because the Turkish kindred's defect was T-selective at the proliferation level, and a
    patient with reduced B and NK numbers as well shows the lesion is not confined to the T
    lineage even though the T lineage is where it bites hardest.

    B-cell maturation was nevertheless largely normal in that family: class-switched B cells were
    present and somatic hypermutation patterns were normal. So the B-cell defect is one of number
    rather than of function.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Persistent B and NK cell lymphopenia
    term:
      id: HP:0010976
      label: Decreased total B cell count
  notes: >-
    1 of 4 published POLD1 patients. Bound to the B-cell term with the NK deficit carried in
    preferred_term and description; binding both would need two phenotype entries for one
    reported observation.
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Immunological analyses showed persistent CD4+ T, B, and NK cell lymphopenia (Figure 1B). The patient receives subcutaneous Ig (scIG) treatment, as well as antibiotic and antifungal prophylactic therapy."
    explanation: >-
      The three-lineage cytopenia in the POLD1 patient, with his treatment in the same sentence.
- name: Short Stature
  category: Growth
  description: Short stature in the second family's POLD1 patient.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  notes: >-
    1 of 4 published POLD1 patients. The younger sister in the Turkish kindred had weight and
    height in the normal range for her age at presentation, which is a recorded negative.
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "The patient had short stature, microcephaly, a low IQ (approximately 70), and hearing impairment."
    explanation: >-
      The POLD1 patient's syndromic features in one sentence — the source for this phenotype,
      the microcephaly and the quantified cognitive impairment.
- name: Microcephaly
  category: Nervous System
  description: >-
    Microcephaly in the second family's POLD1 patient. A head circumference deficit is what a
    proliferation-limited neural progenitor pool would produce, so it is the developmental
    feature most consistent with the mechanism — though that consistency is an argument, not a
    measurement.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  notes: 1 of 4 published POLD1 patients; not reported in the Turkish kindred.
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "short stature, microcephaly, a low IQ (approximately 70), and hearing impairment"
    explanation: The finding as reported for the POLD1 patient.
- name: Decreased Total T Cell Count
  category: Immune
  description: >-
    Marked lymphopenia with profound CD3+CD4+ depletion in the index patient, and the same
    pattern in her sister. It is the finding that reframed a decade of infections as an
    immunodeficiency.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: T-cell lymphopenia with profound CD4 depletion
    term:
      id: HP:0005403
      label: Decreased total T cell count
  notes: 2 of 2 patients in the Turkish kindred for whom counts are reported.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Her immunological workup was particularly notable for profound CD3+CD4+ lymphopenia."
    explanation: The index patient's T-cell deficit and the subset it falls hardest on.
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Her laboratory results revealed marked lymphopenia, hypogammaglobulinemia and low CD3+CD4+ T cell number similar to her older sister"
    explanation: >-
      The same pattern in the younger sister at age three, which makes it a feature of the
      genotype rather than of one patient's course.
- name: Loss of Naive T Cells with Effector Memory Skewing
  category: Immune
  description: >-
    Naive CD4 and especially CD8 cells are reduced in favour of effector memory subsets. This is
    the cellular shape of a compartment that has been driven to expand repeatedly and cannot
    replace what it spends.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Decreased naive CD8 T cells with effector memory skewing
    term:
      id: HP:0410377
      label: Decreased naive CD8+ T cell proportion
  notes: >-
    Reported for the patients of the Turkish kindred as a group. Bound to the CD8 term because
    the source says the loss is of naive CD4 "and especially CD8" cells and the CD8 compartment
    is where the repertoire restriction was also found; the CD4 loss is carried in the
    description rather than by a second binding.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "The patients exhibited decreased numbers of naive CD4 and especially CD8 T cells in favor of effector memory subpopulations."
    explanation: The subset distribution, with the CD4/CD8 asymmetry the authors emphasise.
- name: Decreased Circulating Immunoglobulin
  category: Immune
  description: >-
    Mildly decreased serum IgG with low IgA and IgM in the index patient, and
    hypogammaglobulinaemia in her sister. Mild is the operative word: this is not agammaglobulinaemia,
    and the clinical problem is the absent specific response rather than the total.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Mildly decreased IgG with low IgA and IgM
    term:
      id: HP:0004313
      label: Decreased circulating immunoglobulin concentration
  notes: >-
    2 of 2 patients in the Turkish kindred for whom immunoglobulins are reported. The
    general-immunoglobulin term is bound rather than HP:0004315 Decreased circulating IgG
    concentration because all three isotypes are affected.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She had mildly decreased serum IgG and low IgA and IgM antibody concentrations"
    explanation: The three isotypes and the magnitude, in the index patient.
- name: Absent Tetanus Vaccine Antibody Response
  category: Immune
  description: >-
    Absent tetanus antibody response despite full vaccination in the index patient. In her
    younger sister the response was unprotective at presentation and normalised after a booster
    — which is a meaningfully different result from an absent one and is recorded rather than
    merged.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Absent tetanus antibody response despite full vaccination
    term:
      id: HP:0410295
      label: Complete or near-complete absence of specific antibody response to tetanus vaccine
  notes: >-
    2 of 2 patients in the Turkish kindred for whom vaccine responses are reported, with the
    caveat that one recovered on boosting. The difference matters clinically: a response that
    boosts is an argument for vaccinating rather than for replacing.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "while her tetanus vaccine-related antibody responses were absent despite having been fully vaccinated"
    explanation: The absent specific response in the index patient, with vaccination confirmed.
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: REFUTE
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She also had an unprotective tetanus antibody response on initial presentation despite her prior vaccination that normalized on booster vaccination."
    explanation: >-
      Graded REFUTE against a reading of this phenotype as uniformly absent and irrecoverable.
      The younger sister's response came back on boosting, which no summary of the kindred as
      "absent vaccine responses" would convey.
- name: Recurrent Otitis Media
  category: Otologic
  description: >-
    Serous otitis media recurrent enough to contribute to adenotonsillectomy at five and a half
    in the index patient, and part of the evaluation that found her hearing loss.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Recurrent serous otitis media
    term:
      id: HP:0000403
      label: Recurrent otitis media
  notes: >-
    1 of 3 patients in the Turkish kindred. Worth separating from the hearing loss: conductive
    loss from effusion and sensorineural loss are different problems, and this patient has both
    a history of effusions and a documented sensorineural deficit.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She underwent adenotonsillectomy at 5 1/2 years of age because of recurrent URTI and serous otitis media."
    explanation: The otitis media and the surgery it led to.
- name: Sensorineural Hearing Loss
  category: Otologic
  description: >-
    Diagnosed at three in the index patient, on evaluation for language delay. Her aunt has a
    hearing deficit dating from a varicella encephalitis. Her younger sister's hearing is
    explicitly normal.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Sensorineural hearing loss
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  notes: >-
    2 of 3 patients in the Turkish kindred, and one of those two acquired it after encephalitis.
    The younger sister's normal audiology is a recorded negative, not a silence — which is what
    makes this a variable feature rather than a constant one.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "At 3 years of age she was diagnosed with sensorineural hearing loss following evaluation for language delay."
    explanation: The age, the modality and the route to diagnosis in the index patient.
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: REFUTE
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Auditory testing revealed normal hearing."
    explanation: >-
      The younger sister's normal audiogram, graded REFUTE against treating hearing loss as a
      constant of the genotype. She carries the same homozygous allele as her sister.
- name: Developmental and Speech Delay
  category: Nervous System
  description: >-
    Language delay in the index patient, which was what led to the audiology that found her
    hearing loss. Her aunt has intellectual impairment and speech delay dating from a varicella
    encephalitis at three. In the second family the developmental impairment is described as
    severe with poor speech.

    The two kinds of case should not be summed. One is a language delay attributable to a
    hearing loss; one is post-encephalitic; one is the second family's primary developmental
    phenotype. Only the third bears on whether developmental impairment is a feature of the
    genotype.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Speech and language delay
    term:
      id: HP:0000750
      label: Delayed speech and language development
  notes: >-
    2 of 3 in the Turkish kindred and present in the second family, but with three different
    proximate causes. Recorded with the distinction stated because a phenotype list that
    collapsed them would overstate the case for a primary neurodevelopmental effect of POLD1
    deficiency.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She had encephalitis following a primary varicella infection at 3 years of age, from which she was left with mental retardation, hearing deficit and speech delay."
    explanation: >-
      The aunt's deficits and their stated cause. Graded INDIRECT against a primary
      developmental phenotype, because the source attributes them to an infection rather than to
      the genotype directly — though the infection is itself plausibly a consequence of the
      immunodeficiency.
- name: Severe Primary Varicella
  category: Immune
  description: >-
    Severe chickenpox at six in the index patient, which eventually resolved; primary varicella
    complicated by encephalitis at three in her aunt. Varicella is the infection this disease
    handles worst, and both a severe course and a neurological complication are documented in
    one kindred.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Severe primary varicella, with encephalitis in one patient
    term:
      id: HP:0002383
      label: Infectious encephalitis
  notes: >-
    2 of 3 patients in the Turkish kindred had a severe primary varicella course, one of them
    with encephalitis. Bound to the encephalitis term because that is the specific, codeable
    outcome; the severe uncomplicated course in the index patient is carried in the description.
    This is the phenotype with the clearest management implication in the entry — it bears on
    varicella vaccination and on post-exposure prophylaxis, neither of which is discussed in
    any source here.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She suffered from severe Chickenpox at 6 years of age that eventually resolved."
    explanation: The severe primary varicella course in the index patient.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: BELOW_1_IN_1000000
  notes: >-
    Four published POLD1 patients in two unrelated families: three relatives across two
    generations of a consanguineous Turkish kindred, and one man from a non-consanguineous
    family. A fifth patient is described in the 2026 transplant report — an 18-year-old woman
    with POLD1 deficiency — whose relationship to the two published families is not stated
    there, so she is not counted here and the count above may be an undercount by one.

    No population estimate exists. Consanguinity is the route to the homozygous genotype in one
    family and p.Arg1060Cys is absent from every population database checked, so no founder
    effect or carrier frequency can be inferred. rate_per_100000 is left unset rather than
    computed from four cases.
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "To our knowledge, no germline biallelic mutations affecting this complex have been reported in humans."
    explanation: >-
      The size of the literature at the point the entity was defined — none, which is what makes
      the current total of four the whole of it.
progression:
- phase: Recurrent infection in early childhood, unrecognised
  notes: >-
    The index patient had recurrent upper and lower respiratory infection from early life,
    hearing loss at three, adenotonsillectomy at five and a half, severe chickenpox at six, four
    to five intravenous-antibiotic episodes a year, and recurrent herpes from nine. She was
    referred for immunological evaluation at twelve.

    That is nine years of infection before anybody counted a lymphocyte, and it is the natural
    history this entry exists to shorten. What eventually triggered the referral was the
    herpetic pattern, not the respiratory one.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Investigation into her recurrent herpetic infections revealed marked lymphopenia, for which she was referred for immunological evaluation at 12 years of age."
    explanation: The age at referral and the finding that prompted it.
- phase: Stabilisation on immunoglobulin replacement
  notes: >-
    Immunoglobulin replacement resolved the lower respiratory infections in the index patient
    and markedly reduced the herpetic ones, which is more than replacement would be expected to
    do for a viral phenotype and is recorded as reported. The second family's POLD1 patient is
    on subcutaneous immunoglobulin with antibacterial and antifungal prophylaxis.

    Stabilisation is not resolution: the underlying proliferation defect is unchanged, and
    whatever airway damage has already occurred is permanent.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She was started on immunoglobulin replacement therapy, which resulted in the resolution of LRTI and markedly decreased herpetic infections."
    explanation: The treatment response in the index patient, covering both the bacterial and the viral phenotype.
- phase: Transplant in adulthood
  notes: >-
    A 2026 report describes the first successful haematopoietic stem cell transplant in POLD1
    deficiency, in an 18-year-old woman with recurrent pulmonary infections and shingles who was
    dependent on immunoglobulin replacement. Two years on she has improved T-cell counts and
    function and no longer needs replacement.
  evidence:
  - reference: PMID:42104577
    reference_title: "Successful Treatment of POLD1 Deficiency With HSCT: Report of Two Years' Experience."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Post-HSCT follow-up demonstrated improved T-cell counts and function, and the patient remained well without IgRT."
    explanation: The outcome at two years, and the endpoint that matters — freedom from replacement.
genetic:
- name: POLD1
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: POLD1
    term:
      id: hgnc:9175
      label: POLD1
  notes: >-
    The causal gene, and one where the allele class decides the disease. Biallelic hypomorphic
    missense causes this entity. Heterozygous variants in the exonuclease (proofreading) domain
    cause colorectal cancer predisposition, by a mechanism that is functionally the opposite —
    the authors of the second paper describe it as a loss of function that produces a functional
    gain of function through an increased mutation rate. The recurrent heterozygous p.Ser605del
    causes MDPL syndrome.

    The founding kindred contains the cleanest possible statement of that separation: several
    extended family members had colon and rectal cancers and none of them carried the mutant
    allele. A family history of colorectal cancer in a POLD1 kindred is not evidence that the
    immunodeficiency allele predisposes to it.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "These results identify gene defects in POLD1 as a novel cause of T-cell immunodeficiency."
    explanation: The gene-disease claim as the authors state it.
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: REFUTE
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "A number of extended family members had colon and rectal cancers but did not carry the mutant allele."
    explanation: >-
      Graded REFUTE against the inference that this allele carries the cancer risk POLD1 is
      otherwise known for. The cancers and the allele segregate apart in the one family where
      both are present, which is a stronger separation than any argument from domain position.
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "In familial colorectal cancer, this could be explained by the hypermutator phenotype, in which POLD1 loss of function leads to a functional gain of function (increased mutation rate)"
    explanation: >-
      Why the same gene gives a dominant cancer syndrome and a recessive immunodeficiency. Graded
      INDIRECT because it explains the allelic series rather than establishing anything about
      this entity.
  - reference: PMID:31944473
    reference_title: "POLD1 variants leading to reduced polymerase activity can cause hearing loss without syndromic features."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "The recombinant p.Gly1100Arg polymerase δ showed a reduced polymerase activity by 30-40%, but exhibited normal exonuclease activity."
    explanation: >-
      A fourth biallelic POLD1 phenotype — autosomal recessive nonsyndromic hearing loss — whose
      quantified residual polymerase activity is the number this entry's allelic series needs.
      A compound heterozygote retaining 30 to 40 percent polymerase activity with intact
      proofreading gets deafness alone, no immunodeficiency and no cancer. Graded INDIRECT
      because it is a different phenotype in the same gene, and it bears on this entity by
      bounding how much residual activity is compatible with normal immunity.
  - reference: PMID:41263451
    reference_title: "PolED: a manually curated database of functional studies of POLE and POLD1 variants reported in humans."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    quote_role: PRIMARY_RESULT
    snippet: "Prior studies assessed the functional significance of numerous POLE/POLD1 variants in experimental models. However, the data remain scattered and difficult to evaluate by non-specialists"
    explanation: >-
      A curated functional database for POLE and POLD1 variants. Recorded as a pointer for anyone
      assessing a new POLD1 allele, with the caveat that it is scoped to cancer-relevant
      fidelity variants rather than to the hypomorphic immunodeficiency alleles — so a variant
      absent from it is not thereby benign for this entity.
diagnosis:
- name: Lymphocyte subset enumeration
  description: >-
    T-cell lymphopenia with profound CD4 depletion is the finding that converts a recurrent
    infection history into an immunodeficiency diagnosis, and in the index kindred it was ordered
    only after nine years of infections. Subset work adds the naive-to-effector-memory skewing
    that distinguishes an exhausted, proliferation-limited compartment from a production failure.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Her immunological workup was particularly notable for profound CD3+CD4+ lymphopenia."
    explanation: The diagnostic finding, in the patient whose referral it followed.
- name: Lymphocyte proliferation assay
  description: >-
    The assay that localises the lesion. Impaired T-cell but preserved B-cell proliferation is
    the pattern here, and it is what distinguishes this from a production or survival defect.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "T-cell lymphopenia with impaired T-cell but not B-cell proliferation"
    explanation: The selective proliferation defect, which is the diagnostic signature of this disease.
- name: DNA repair assay after genotoxic stress
  presence: ABSENT
  description: >-
    Recorded as a negative. A clinician faced with a combined immunodeficiency and syndromic
    features will reasonably think of the DNA-repair immunodeficiencies and send a repair assay.
    In polymerase delta deficiency it is normal, and that normal result is informative rather
    than uninformative: it places the lesion at replication rather than at repair.

    The qualifier matters and this entry originally lacked it. The experiment was done in the
    POLD2 patient's fibroblasts. The POLD1 patient — the one this entry curates — was never
    tested with genotoxic compounds. Everything below rests on the two patients sharing a
    holoenzyme, which is the same argument the whole paper is built on, and is still an
    extrapolation.
  notes: >-
    Do not read this as a measured property of POLD1 deficiency. It is a measured property of
    POLD2 deficiency carried across. If the two differ anywhere, conditioning-regimen tolerance
    is exactly where it would matter, and that is the subject of one of this entry's discussions.
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "P1 fibroblasts showed no overt sensitivity to an array of genotoxic reagents, which suggests that, despite an unstable POLD complex, its activity was sufficient to ensure proficiency in specific DNA repair pathways"
    explanation: >-
      The repair-normal result itself, quoted so the patient it belongs to is identifiable from
      the snippet. P1 is the POLD2 patient. Graded INDIRECT for this entry because it is POLD2
      data applied to a POLD1 entity on the shared-complex argument, not a POLD1 measurement.
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "To determine the DNA repair capacity of POLD-deficient cells, we treated P1 cells with different genotoxic compounds"
    explanation: >-
      The design of the experiment, quoted because it names the single patient tested. Nothing
      in this paper repeats it in the POLD1 patient.
- name: Exome or targeted panel sequencing
  description: >-
    How both families were diagnosed. In the consanguineous kindred, homozygosity mapping on
    exome data narrowed to a 14 Mb region on chromosome 19 containing nine genes, of which POLD1
    was the candidate; in the other family a targeted inborn-errors-of-immunity panel found the
    variants and exome sequencing excluded other biallelic candidates.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Knowing that the family is consanguineous, we executed homozygosity mapping using their WES data"
    explanation: >-
      The analytic step that made a single-kindred exome informative, which is the reason
      consanguinity is a diagnostic asset as well as a risk factor.
treatments:
- name: Immunoglobulin Replacement Therapy
  therapeutic_modality: PROTEIN_REPLACEMENT
  description: >-
    The mainstay. In the index patient it resolved the lower respiratory infections and markedly
    decreased the herpetic ones; the second family's POLD1 patient receives subcutaneous
    immunoglobulin alongside antibacterial and antifungal prophylaxis.

    The reduction in herpetic episodes is the part worth noticing. Replacement supplies antibody,
    and control of a latent herpesvirus is a T-cell job, so a large effect on herpes recurrence
    is not what the mechanism predicts. It is recorded as reported, in one patient, without an
    explanation attached.
  treatment_term:
    preferred_term: immunoglobulin replacement therapy
    term:
      id: NCIT:C62710
      label: Immunoglobulin Therapy
  target_mechanisms:
  - target: Defective T-Dependent Antibody Response
    description: >-
      Replacement substitutes for the antibody the patient cannot generate. It addresses the
      humoral consequence and leaves the T-cell proliferation defect that produced it untouched.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She was started on immunoglobulin replacement therapy, which resulted in the resolution of LRTI and markedly decreased herpetic infections."
    explanation: The response, in the one patient for whom a before-and-after is reported.
- name: Aciclovir for Herpetic Episodes
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Given for the index patient's recurrent herpes zoster. No outcome is reported, and the
    sources do not say whether it was episodic or prophylactic — which matters, since suppression
    is the plausible strategy in a patient with monthly recurrences and the sources do not
    establish that it was used that way.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: aciclovir
      term:
        id: CHEBI:2453
        label: acyclovir
  target_mechanisms:
  - target: Recurrent Herpetic Infection
    description: >-
      Antiviral treatment of the episodes the immune defect permits. It does not address the
      repertoire contraction underneath them.
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "several episodes of recurrent herpes zoster for which she received acyclovir therapy"
    explanation: >-
      That the drug was given, and for what. Graded INDIRECT because the source records the
      prescription and no outcome.
- name: Haematopoietic Stem Cell Transplantation
  therapeutic_modality: CELL_THERAPY
  description: >-
    The only reported route to correcting the immune defect rather than substituting for it. A
    2026 report describes the first successful transplant in POLD1 deficiency: an 18-year-old
    woman with recurrent pulmonary infections and shingles, dependent on immunoglobulin
    replacement, transplanted from a matched related donor using reduced-intensity conditioning
    with cyclophosphamide, fludarabine and anti-thymocyte globulin, with bone marrow and
    peripheral blood as stem-cell sources and tacrolimus plus low-dose methotrexate for
    graft-versus-host disease prophylaxis. Engraftment was prompt and without major
    complications; at two years her T-cell counts and function were improved and she no longer
    needed replacement.

    The reason it is a report rather than a routine option is a specific and well-founded fear:
    conditioning regimens work by damaging DNA, and a disease of the replicative polymerase
    raises the question of regimen-related toxicity. The family were told about that concern
    before the decision. Reduced-intensity conditioning was chosen against it, and the result
    argues the fear may be manageable — in one patient.
  treatment_term:
    preferred_term: hematopoietic cell transplantation
    term:
      id: NCIT:C15431
      label: Hematopoietic Cell Transplantation
  target_mechanisms:
  - target: Impaired T Cell Clonal Proliferation
    description: >-
      Replacing the haematopoietic compartment with donor cells that carry two working POLD1
      alleles removes the proliferation ceiling in the lineage where it matters. It does nothing
      for the non-haematopoietic consequences of the same defect.
  evidence:
  - reference: PMID:42104577
    reference_title: "Successful Treatment of POLD1 Deficiency With HSCT: Report of Two Years' Experience."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "She underwent HSCT from a matched related donor using a reduced-intensity regimen (cyclophosphamide, fludarabine, ATG) with bone marrow and peripheral blood as stem cell sources."
    explanation: The regimen and the graft source, in enough detail to be acted on.
  - reference: PMID:42104577
    reference_title: "Successful Treatment of POLD1 Deficiency With HSCT: Report of Two Years' Experience."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Patients considered for HSCT may be at increased risk of regimen-related toxicity due to impaired DNA repair."
    explanation: >-
      The stated concern the reduced-intensity choice was made against. Worth recording even
      though this entry's own mechanism section notes that repair after genotoxic stress was
      normal in these patients — the clinical worry and the laboratory finding point different
      ways, and a transplant decision has to be made without that being settled.
  notes: >-
    One patient, two years, one report. It is not a series and this entry does not present it as
    one. What it establishes is feasibility against a specific fear, not a standard of care.
discussions:
- discussion_id: imd120_cd8_asymmetry
  kind: OPEN_QUESTION
  status: OPEN
  prompt: >-
    Why does a general restriction on cell-cycle entry produce oligoclonality and restricted
    receptor V-J pairing in CD8 but not CD4 T cells?
  rationale: >-
    Polymerase delta is required by every dividing cell, so the naive expectation is a uniform
    proliferation ceiling. What is observed is asymmetric: naive CD8 cells are lost more than
    naive CD4 cells, and the repertoire contraction is confined to CD8.

    The founding authors offer two candidate explanations in one sentence — a difference in
    peripheral CD8 expansion, or a difference in thymic selection — and commit to neither. The
    distinction is testable and consequential. If it is peripheral, the repertoire should
    contract progressively with age and antigen exposure, and a transplant should restore it. If
    it is thymic, the defect is set early and a transplant in an adult with an involuted thymus
    may restore counts without restoring breadth.

    The 2026 transplant report gives improved T-cell counts and function at two years but does
    not report repertoire sequencing, which is exactly the measurement that would separate them.
  attaches_to:
  - pathophysiology#Contracted Oligoclonal T Cell Repertoire
  - treatments#Haematopoietic Stem Cell Transplantation
  evidence:
  - reference: PMID:31629014
    reference_title: "Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "suggesting that POLD1R1060C differentially affects peripheral CD8+ T-cell expansion and possibly thymic selection"
    explanation: >-
      The authors' own two-part hypothesis, quoted with its hedge — the reason this is an open
      question rather than a mechanism node.
- discussion_id: imd120_conditioning_toxicity
  kind: OPEN_QUESTION
  status: OPEN
  prompt: >-
    Does a defect in the replicative polymerase increase the risk of conditioning-regimen
    toxicity, when DNA repair after genotoxic stress is normal in these patients?
  rationale: >-
    This is a case where the clinical worry and the laboratory finding point in different
    directions, and a real decision had to be made without resolving it.

    The transplant team's stated concern was regimen-related toxicity from impaired DNA repair.
    The mechanistic work points the opposite way: repair after genotoxic stress was normal, and
    the lesion is in S-phase progression. If that is right, POLD1 deficiency is unlike the
    DNA-repair immunodeficiencies where conditioning toxicity is a documented problem, and the
    caution may be borrowed rather than earned.

    There is a gap in that reassurance, and it is exactly where it should not be. The
    genotoxic-sensitivity experiment was run in the POLD2 patient's fibroblasts. No POLD1
    patient's cells have been exposed to a genotoxic compound in any published experiment. So
    the argument that a POLD1-deficient patient tolerates alkylator-based conditioning runs
    through a different gene's patient — a defensible inference from the shared holoenzyme, and
    not a measurement.

    One reduced-intensity transplant went well. That is consistent with the caution being
    unnecessary and equally consistent with reduced-intensity conditioning having been the
    reason it went well. Distinguishing them needs more patients, or the obvious missing
    experiment: alkylator and fludarabine sensitivity in POLD1 patient cells, which would cost
    little and has not been published.
  attaches_to:
  - treatments#Haematopoietic Stem Cell Transplantation
  - pathophysiology#Impaired S-Phase Progression and Replicative Stress
  - diagnosis#DNA repair assay after genotoxic stress
  evidence:
  - reference: PMID:31449058
    reference_title: "Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "To determine the DNA repair capacity of POLD-deficient cells, we treated P1 cells with different genotoxic compounds"
    explanation: >-
      The premise of this discussion, and the reason it is a discussion rather than a settled
      point: the only genotoxic-sensitivity experiment in this literature names one patient, and
      it is not the POLD1 one.
  - reference: PMID:42104577
    reference_title: "Successful Treatment of POLD1 Deficiency With HSCT: Report of Two Years' Experience."
    supports: REFUTE
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: "Patients considered for HSCT may be at increased risk of regimen-related toxicity due to impaired DNA repair."
    explanation: >-
      Graded REFUTE against the repair-normal reading. A transplant team treating a POLD1 patient
      stated the opposite expectation in print, which is the disagreement this discussion is
      about rather than an error on either side.
- discussion_id: imd120_syndromic_attribution
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Are the syndromic features of POLD1 deficiency — short stature, microcephaly, cognitive
    impairment, hearing loss — a direct developmental consequence of reduced polymerase delta, or
    consequences of the infections the immunodeficiency permits?
  rationale: >-
    Both readings are supported by different patients in the published set, which is why this is
    a gap rather than a controversy.

    For a direct effect: the second family's POLD1 patient has short stature, microcephaly and a
    measured IQ around 70 with no reported encephalitis, and microcephaly in particular is what a
    proliferation-limited neural progenitor pool would produce.

    Against it: in the Turkish kindred the one patient with intellectual impairment, hearing
    deficit and speech delay acquired all three after a varicella encephalitis at age three, the
    index patient's language delay is attributable to her hearing loss, and the younger sister
    has normal hearing and normal growth on the same homozygous allele.

    Four patients cannot settle it. What would help is head circumference and growth data on
    patients without a severe infection history, and — since there is now a transplanted patient
    — whether restoring the immune compartment changes the developmental trajectory.
  attaches_to:
  - pathophysiology#Syndromic Developmental Features
  - phenotypes#Microcephaly
  - phenotypes#Developmental and Speech Delay
notes: >-
  Scope, and a within-paper attribution problem. This entry is POLD1 only. The 2019 paper that
  defined human polymerase delta deficiency describes two patients: P1 with a homozygous POLD2
  variant and P2 with biallelic POLD1 variants. They share a syndrome and are reported together,
  and only P2 belongs here.

  That matters because it is easy to get wrong. The deep-research report committed alongside this
  entry attributes P1's chronic facial molluscum contagiosum, recurrent skin abscesses and
  bronchiectasis-since-six-months to POLD1. None of those are curated here. P2's own
  respiratory phenotype is chronic bronchitis progressing to bronchiectasis, his skin finding is
  warts negative for common papillomavirus strains, and his syndromic features are short stature,
  microcephaly, an IQ around 70 and hearing impairment. Every phenotype evidence item in this
  entry is quoted so that the patient it belongs to is identifiable from the snippet.

  This is Named Entity Confusion inside a single publication rather than across publications —
  two patients, two genes, one shared syndrome name. The usual preflight checks that a report is
  about the right disease; they do not check that a within-paper finding is attributed to the
  right patient.

  Patient count. Four published POLD1 patients: three in the Turkish kindred and P2 of the 2019
  series. The 2026 transplant report describes an 18-year-old woman with POLD1 deficiency whose
  relationship to those families is not stated, so she may be a fifth.

  GeneReviews baseline: `just check-genereviews` reports NO_CHAPTER for both GeneReviews and
  StatPearls against the committed Bookshelf index (snapshot 2026-09-10).

  Allele class. POLD1 gives at least three diseases depending on the allele: this recessive
  hypomorphic immunodeficiency, dominant proofreading-domain colorectal cancer predisposition,
  and MDPL syndrome from the recurrent heterozygous p.Ser605del. The founding kindred contains
  the cleanest available separation of the first two — extended family members with colon and
  rectal cancer who did not carry the mutant allele — and it is recorded as a REFUTE evidence
  item on the gene rather than as prose, so it is queryable.

  What is not curated. The deep-research report cites tumour-biology work on POLD1 regulation by
  copy-number gain, promoter methylation and miR-139-3p. That is cancer biology in a different
  allele class and is not a mechanism of this entity. It is left out rather than included with a
  caveat.

📚

References & Deep Research

References

5

PMID:31629014

Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1.

No top-level findings curated for this source.

PMID:31449058

Polymerase δ deficiency causes syndromic immunodeficiency with replicative stress.

No top-level findings curated for this source.

PMID:42104577

Successful Treatment of POLD1 Deficiency With HSCT: Report of Two Years' Experience.

No top-level findings curated for this source.

PMID:31944473

POLD1 variants leading to reduced polymerase activity can cause hearing loss without syndromic features.

No top-level findings curated for this source.

PMID:41263451

PolED: a manually curated database of functional studies of POLE and POLD1 variants reported in humans.

No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Record notes

Scope, and a within-paper attribution problem. This entry is POLD1 only. The 2019 paper that defined human polymerase delta deficiency describes two patients: P1 with a homozygous POLD2 variant and P2 with biallelic POLD1 variants. They share a syndrome and are reported together, and only P2 belongs here. That matters because it is easy to get wrong. The deep-research report committed alongside this entry attributes P1's chronic facial molluscum contagiosum, recurrent skin abscesses and bronchiectasis-since-six-months to POLD1. None of those are curated here. P2's own respiratory phenotype is chronic bronchitis progressing to bronchiectasis, his skin finding is warts negative for common papillomavirus strains, and his syndromic features are short stature, microcephaly, an IQ around 70 and hearing impairment. Every phenotype evidence item in this entry is quoted so that the patient it belongs to is identifiable from the snippet. This is Named Entity Confusion inside a single publication rather than across publications — two patients, two genes, one shared syndrome name. The usual preflight checks that a report is about the right disease; they do not check that a within-paper finding is attributed to the right patient. Patient count. Four published POLD1 patients: three in the Turkish kindred and P2 of the 2019 series. The 2026 transplant report describes an 18-year-old woman with POLD1 deficiency whose relationship to those families is not stated, so she may be a fifth. GeneReviews baseline: `just check-genereviews` reports NO_CHAPTER for both GeneReviews and StatPearls against the committed Bookshelf index (snapshot 2026-09-10). Allele class. POLD1 gives at least three diseases depending on the allele: this recessive hypomorphic immunodeficiency, dominant proofreading-domain colorectal cancer predisposition, and MDPL syndrome from the recurrent heterozygous p.Ser605del. The founding kindred contains the cleanest available separation of the first two — extended family members with colon and rectal cancer who did not carry the mutant allele — and it is recorded as a REFUTE evidence item on the gene rather than as prose, so it is queryable. What is not curated. The deep-research report cites tumour-biology work on POLD1 regulation by copy-number gain, promoter methylation and miR-139-3p. That is cancer biology in a different allele class and is not a mechanism of this entity. It is left out rather than included with a caveat.

Create: Immunodeficiency 120 (POLD1) · 2026-09-22T18:00:26Z · View source

De novo curation of IMD120 (POLD1, MONDO:0970994) from the 2020 Turkish-kindred report, the 2019 polymerase delta deficiency series, and a 2026 first-HSCT report. Deep research: one openscientist run (7 references, 7/7 resolved, 4/7 judged on topic; term_validation needs_review true, 1 invented CURIE HP:0410413 and 9 mis-named terms, among them HP:0002326 offered as Herpes simplex disease when HP calls it Transient ischemic attack, HP:0200042 as molluscum when HP calls it Skin ulcer, HP:0031521 as a clinical sign when HP calls it Vaginal clear cell adenocarcinoma, and HP:0005387 as decreased antibody level when HP calls it Combined immunodeficiency - none of those bindings were taken). The report's gene CURIE HGNC:9175 was checked against the ontology and is correct, unlike the LARS2 one in the sibling HLASA run. The substantive correction was attribution: the 2019 paper reports a POLD2 patient (P1) and a POLD1 patient (P2) together under one syndrome name, and the report attributes P1's molluscum contagiosum, skin abscesses and bronchiectasis-since-six-months to POLD1. None are curated here; every phenotype snippet is quoted so the patient it belongs to is identifiable. Four REFUTE evidence items carry counter-evidence in place: the younger sister's normal audiogram against hearing loss as a constant, her tetanus response normalising on boosting against the absent-vaccine-response phenotype, and the extended family's colorectal cancers segregating away from the mutant allele against the inference that this allele carries POLD1 cancer risk. Three discussions record the CD8/CD4 asymmetry, the conditioning-toxicity question where the clinical worry and the normal repair assay point different ways, and whether the syndromic features are developmental or post-infectious. One curator error caught by validation: NCIT:C593 was written from memory for immunoglobulin and is Recombinant Interleukin; the entry now uses the house binding NCIT:C62710 Immunoglobulin Therapy. Validation on the final tree: just validate, validate-terms, validate-disorders, count-verified-snippets 49/49, check-entity-refs, check-causal-targets, check-qualifier-terms, check-duplicate-keys, check-folded-hyphens, check-snippet-length, check-title-snippets, check-snippet-grading, check-enum-values, check-coarse-phenotypes, check-reference-titles, check-case-collisions, check-genereviews (NO_CHAPTER), list-disconnected-phenotypes 14/15. Review round 1 (ai4c-reviewer, CHANGES_REQUESTED, one IMPORTANT finding, taken plus two of three suggestions). The finding was that the repair-normal claim - which framed the description, justified the presence: ABSENT diagnosis entry and was the premise of the conditioning-toxicity discussion - is P1 data. P1 is the POLD2 patient; the POLD1 patient was never exposed to a genotoxic compound in any published experiment. This is precisely the within-paper attribution hazard the entry's own notes warn about, committed on a claim the curator treated as background. The claim is retained because the shared-holoenzyme inference is the one the whole paper rests on, but it is now marked as extrapolated at all three places it is used, the evidence item quotes the sentence naming P1 so the patient is identifiable from the snippet, a second item quotes the experiment's design, and the conditioning discussion gained an evidence block plus an explicit statement that the alkylator-tolerance reassurance runs through a different gene's patient. Consumed the two references the review flagged as unused: PMID:31944473 bounds the allelic series quantitatively (a compound heterozygote retaining 30-40 percent polymerase activity with normal proofreading gets nonsyndromic hearing loss, no immunodeficiency, no cancer), and PMID:41263451 is recorded as a functional-variant database pointer with the caveat that it is scoped to cancer-fidelity variants. One curator error caught in the same round: the reference_title for PMID:31944473 was written to describe the paper rather than copied from the cache frontmatter, and the reference validator rejected it - the exact failure check-reference- titles exists for. Declined the animal_models suggestion: the mouse models in the research report's Section 15 are Pold1 proofreading-deficient mutator mice and knockouts, which model the cancer allele class and embryonic lethality rather than this hypomorphic immunodeficiency, and none is snippet-supportable from the cached references. Post-round validation: count-verified-snippets 54/54, all gates green.

OpenScientist ▸

Immunodeficiency 120 (IMD120): A Comprehensive Disease Characterization

openscientist-autonomous 3 citations 2026-09-22T17:37:52.110081

Immunodeficiency 120 (IMD120): A Comprehensive Disease Characterization

Disease: Immunodeficiency 120 (IMD120) MONDO ID: MONDO:0970994 · OMIM: #620836 · Causal gene: POLD1 (HGNC:9175, OMIM 174761), chromosome 19q13.33 Category: Mendelian, autosomal recessive combined immunodeficiency Report date: 2026-09-22

Summary

Immunodeficiency 120 (IMD120) is an ultra-rare autosomal recessive combined immunodeficiency caused by biallelic hypomorphic (partial loss-of-function) variants in POLD1, the gene encoding the p125 catalytic and proofreading subunit of DNA polymerase delta (Polδ), the principal lagging-strand replicase of the eukaryotic genome. Because complete loss of POLD1 is incompatible with cellular viability, the disease arises only from partial (hypomorphic) alleles that leave residual Polδ function. The consequence is a state of chronic replicative stress that selectively impairs the proliferation of highly dividing lymphocytes — most conspicuously T cells — producing T-cell lymphopenia, impaired T-cell (but not B-cell) proliferation, hypogammaglobulinemia, and recurrent infections with a striking susceptibility to herpesviruses. A subset of patients also display syndromic features (short stature, intellectual disability, hearing loss), reflecting the housekeeping role of Polδ in all replicating tissues.

The disorder was delineated from just two unrelated families in the founding literature: Cui et al. 2020 (PMID: 31629014), who described a consanguineous Turkish kindred homozygous for POLD1 p.R1060C, and Conde et al. 2019 (PMID: 31449058), who described a family with compound-heterozygous POLD1 variants and a related POLD2-deficient patient. A central mechanistic insight from this investigation is that pathogenic genotypes converge on reduced functional Polδ output through two distinct biochemical routes: (1) destabilization of the Polδ holoenzyme complex with impaired recruitment of Replication Factor C (RFC) — the mechanism of p.R1060C in the C-terminal CysB metal-binding motif; and (2) reduced intrinsic polymerase catalytic activity with preserved complex assembly — the mechanism of the p.Q684H+p.S939W in-cis alleles near the polymerase active site.

Clinically, IMD120 is managed with immunoglobulin replacement therapy (IgRT) plus antiviral (acyclovir) prophylaxis, which effectively controls infections. Reduced-intensity-conditioning hematopoietic stem cell transplantation (HSCT) has been reported as a feasible curative option (Keles et al. 2026, PMID 42104577), though the DNA-repair/replication defect raises theoretical concerns about conditioning toxicity and long-term genome-instability risk. No dedicated immunodeficiency animal model exists; existing Pold1 mouse models are either embryonic-lethal (null) or cancer-prone proofreading mutants, neither of which recapitulates the human immune phenotype. Notably, POLD1 is a strikingly pleiotropic locus: different allele classes produce autosomal dominant MDPL progeroid syndrome, autosomal recessive nonsyndromic hearing loss, and colorectal cancer predisposition — placing IMD120 within a broader POLD1 allelic series.

Section 1 — Disease Information

Overview. Immunodeficiency 120 (IMD120) is a Mendelian, autosomal recessive combined immunodeficiency (affecting both cellular/T-cell and, secondarily, humoral/antibody immunity) resulting from biallelic mutations in POLD1. The disease is best understood as a replicative-stress T-cell immunodeficiency: partial impairment of DNA polymerase delta compromises the DNA replication that lymphocytes require for clonal proliferation upon antigen encounter, so patients present with recurrent infections (especially herpetic/viral), T-cell lymphopenia, and impaired T-cell proliferation.

Key identifiers.

Resource	Identifier
OMIM	#620836 (Immunodeficiency 120)
MONDO	MONDO:0970994
Causal gene	POLD1 — OMIM 174761, HGNC:9175
OMIM Phenotypic Series	PS300755 (combined immunodeficiency)
Cytogenetic location	19q13.33
Orphanet / ICD-10 / ICD-11 / MeSH	No dedicated code identified (ultra-rare; typically coded under generic combined immunodeficiency / D81 categories)

Synonyms / alternative names. "POLD1 deficiency," "POLD1-associated combined immunodeficiency," "combined immunodeficiency due to POLD1 mutation," and (descriptively) "syndromic immunodeficiency with replicative stress" (Conde et al. 2019).

Information source. The disease-level entry is derived from aggregated resources (OMIM, MONDO) that in turn summarize a small number of individual patient reports (case series from two families). All clinical data are individual-patient in origin; there are no EHR-scale or registry datasets for this ultra-rare condition.

Section 2 — Etiology

Primary cause — genetic. IMD120 is a monogenic disorder caused by biallelic (homozygous or compound heterozygous) hypomorphic mutations in POLD1. There is no environmental or infectious cause of the underlying disease, although infectious exposures determine the clinical manifestations (the immune defect is unmasked by pathogen encounter). The recurrent, especially herpetic, infections are a consequence of the genetic defect rather than a cause.

Genetic risk factors. - Causal variants: p.R1060C (c.3178C>T; homozygous; Cui 2020); compound-heterozygous variants including p.Q684H + p.S939W in cis (Conde 2019). - Consanguinity is a major contributor: the index kindred was a consanguineous Turkish family, and the related POLD2 patient was also from a consanguineous union. Consanguinity greatly elevates the chance of homozygosity for rare recessive hypomorphic alleles. - Modifier genes: none formally established for IMD120. Given the shared holoenzyme, POLD2, POLD3, and POLD4 subunit dosage are biologically plausible modifiers, but no human data exist.

Environmental / lifestyle risk factors. None identified as disease-causing. As with any T-cell immunodeficiency, exposure to herpesviruses and respiratory pathogens drives morbidity.

Protective factors. No genetic or environmental protective factors have been characterized. Conceptually, the only "protective" allele state is retention of at least one functional POLD1 allele (heterozygous carriers are asymptomatic for IMD120).

Gene–environment interactions. The core interaction is genotype × pathogen exposure: the hypomorphic Polδ genotype produces a proliferation-limited T-cell compartment that fails to mount adequate clonal responses, so environmental pathogen load (herpesviruses, respiratory bacteria/viruses) determines the frequency and severity of clinical episodes.

Section 3 — Phenotypes

IMD120 phenotypes fall into three groups: (a) infection susceptibility, (b) immunologic/laboratory abnormalities, and (c) syndromic/developmental features. Onset is in early childhood/infancy, and the course is chronic.

Phenotype	Type	HPO suggestion	Onset / severity / frequency
Recurrent infections (esp. herpetic/viral)	Clinical sign	HP:0002719 (Recurrent infections); HP:0004429 (Recurrent viral infections)	Early childhood; moderate–severe; core feature in both families
Recurrent herpes (oral herpes, herpes zoster)	Clinical sign	HP:0002326 (Herpes simplex disease)	Recurrent episodes every 1–2 months in index patient
Recurrent respiratory tract infections → bronchiectasis	Clinical sign	HP:0002205; HP:0002110 (Bronchiectasis)	From infancy; bronchiectasis by age 6 months (Conde 2019); severe
Molluscum contagiosum (chronic facial)	Clinical sign	HP:0200042	Chronic; viral susceptibility marker
Recurrent skin abscesses	Clinical sign	HP:0031521	Recurrent
T-cell lymphopenia (↓CD4, esp. ↓CD8; naive-cell loss)	Laboratory abnormality	HP:0005403 (T lymphocytopenia); HP:0410413	Congenital/early; core feature
Impaired T-cell (not B-cell) proliferation	Laboratory abnormality	HP:0031381 (Decreased proliferation of T cells)	Diagnostic hallmark
Hypogammaglobulinemia (↓IgG, low IgA/IgM)	Laboratory abnormality	HP:0004313 / HP:0002850	Mild–moderate; IgRT-responsive
Impaired vaccine (tetanus) antibody response	Laboratory abnormality	HP:0005387 (Decreased antibody level in blood)	Present despite full vaccination
B-cell and NK-cell reduction	Laboratory abnormality	HP:0010976 (B lymphocytopenia); HP:0040218 (Reduced NK cell count)	Reported in Conde 2019 family
Short stature	Physical manifestation	HP:0004322	Childhood; syndromic subset
Intellectual disability / speech delay	Behavioral/developmental	HP:0001249; HP:0000750	Severe impairment with poor speech (Conde 2019); mild in OMIM
Attention deficits / hyperactivity	Behavioral	HP:0007018	Reported subset
Sensorineural hearing loss	Physical manifestation	HP:0000407	OMIM-listed feature

Immunophenotypic signature (from Cui 2020, verified quote): "The patients exhibited decreased numbers of naive CD4 and especially CD8 T cells in favor of effector memory subpopulations." The T-cell compartment additionally showed oligoclonality and restricted TCR-β V-J pairing — hallmarks of a proliferation-restricted, contracted T-cell repertoire.

Quality-of-life impact. No formal EQ-5D/SF-36/PROMIS data exist for this ultra-rare disease. Qualitatively, recurrent infections, bronchiectasis (irreversible structural lung damage), lifelong IgRT dependence, and — in syndromic patients — intellectual disability and hearing loss produce substantial cumulative disability and care burden.

Section 4 — Genetic / Molecular Information

Causal gene. POLD1 (DNA polymerase delta 1, catalytic subunit; p125), OMIM 174761, HGNC:9175, at 19q13.33. POLD1 provides both the 5′→3′ polymerase and the 3′→5′ exonuclease (proofreading) activities of Polδ and anchors the four-subunit holoenzyme (POLD1/POLD2/POLD3/POLD4).

Pathogenic variants (IMD120-causing, biallelic).

Variant	Family	Zygosity	Location	Functional consequence
p.R1060C (c.3178C>T; exon 26; NM_001256849.1; rs777018011; OMIM 174761.0007)	Cui 2020 (Turkish, consanguineous)	Homozygous	C-terminal CysB metal-binding motif	Destabilizes Polδ complex → ↓POLD1/POLD2/POLD3 levels; impaired RFC recruitment
p.Q684H + p.S939W (in cis; NM_002691)	Conde 2019 (patient 2)	Compound het	Near polymerase active site	Reduces intrinsic catalytic activity without affecting complex stability

Variant classification (ACMG/AMP): pathogenic/likely pathogenic on the basis of segregation, absence from population databases, and functional validation.
Variant type/class: missense (both established genotypes). p.R1060C is absent from gnomAD/ExAC/dbSNP/1000 Genomes — consistent with an ultra-rare recessive allele.
Somatic vs germline: germline (inherited, biallelic).
Functional consequence: partial loss of function (hypomorphic). Complete loss of function is not viable (see Section 15). The two genotypes represent convergent hypofunction via different biochemical mechanisms (Finding F007).

Allelic series at POLD1 (important for interpretation). POLD1 is highly pleiotropic; the allele class determines the phenotype:

Phenotype	OMIM	Inheritance	Representative allele(s)
IMD120 (combined immunodeficiency)	#620836	AR	biallelic hypomorphic missense (p.R1060C; p.Q684H+p.S939W)
MDPL syndrome (mandibular hypoplasia, deafness, progeroid, lipodystrophy)	#615381	AD	recurrent heterozygous p.Ser605del (polymerase active site)
Nonsyndromic sensorineural hearing loss	—	AR	p.Gly1100Arg + null p.Ser197Hisfs*54 (~33% residual polymerase activity; Oh 2020, PMID 31944473)
Colorectal cancer susceptibility 12 (CRCS12)	—	AD	exonuclease-domain (proofreading) variants

Modifier genes / epigenetics / chromosomal abnormalities. No modifier genes, epigenetic mechanisms, or chromosomal abnormalities are established for IMD120 specifically. (In cancer contexts, POLD1 expression is modulated by copy-number gain, promoter methylation, and miR-139-3p — PMID 35189839 — but these are tumor-biology findings, not IMD120 mechanisms.)

Section 5 — Environmental Information

Environmental factors: No toxin, radiation, pollution, or occupational exposure causes IMD120. It is a monogenic disorder.
Lifestyle factors: Not applicable to disease causation.
Infectious agents: Pathogens are triggers/manifesting agents, not causes. The characteristic organisms are herpesviruses (HSV — recurrent oral herpes; VZV — recurrent herpes zoster; molluscum contagiosum poxvirus) and respiratory bacteria/viruses driving recurrent pneumonia and bronchiectasis. The viral-susceptibility bias reflects the dependence of antiviral defense on robust T-cell clonal expansion.

Section 6 — Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

A biallelic hypomorphic missense mutation in POLD1 (e.g., p.R1060C, or p.Q684H+p.S939W in cis) alters the p125 catalytic subunit of DNA polymerase delta. (demonstrated)
This leads to one of two biochemical lesions:
Branch A (destabilization): p.R1060C disrupts the intramolecular interaction between the POLD1 CysB motif and the catalytic domain, and between POLD1 and POLD2, destabilizing the Polδ holoenzyme and lowering steady-state levels of POLD1/POLD2/POLD3. (demonstrated by molecular dynamics + cellular assays)
Branch B (catalytic reduction): p.Q684H+p.S939W near the active site reduces intrinsic polymerase catalytic activity while leaving complex assembly intact. (demonstrated; rescued by WT subunit overexpression)
Both branches result in reduced functional Polδ output → ineffective recruitment of Replication Factor C (RFC) to initiate DNA replication and reduced enzymatic polymerase activity. (demonstrated)
This leads to a decreased fraction of cells entering/progressing through the cell cycle (S-phase DNA synthesis defect) — i.e., replicative stress. (demonstrated; DNA repair after genotoxic stress was normal, indicating a specific mitotic/S-phase synthesis defect)
Replicative stress selectively impairs the proliferation of rapidly dividing lymphocytes. Upon TCR activation, patient T cells show reduced proliferative responses coupled to decreased cell-cycle progression. (demonstrated)
Impaired clonal expansion results in T-cell lymphopenia, loss of naive CD4/CD8 T cells, skewing toward effector-memory subsets, oligoclonality, and restricted TCR-β V-J pairing (a contracted repertoire). (demonstrated)
The compromised T-cell compartment leads to impaired T-cell help and antiviral immunity → recurrent, especially herpetic/viral, infections, and, via defective T-dependent B-cell help, hypogammaglobulinemia and impaired vaccine antibody responses (B-cell intrinsic proliferation is comparatively spared). (demonstrated)
In parallel (branch), the housekeeping requirement for Polδ in all dividing tissues contributes to syndromic features — short stature, intellectual disability/developmental delay, hearing loss — reflecting replicative stress beyond the immune system. (inferred from phenotype; tissue-level mechanism not directly demonstrated)

POLD1 biallelic hypomorphic missense
│
├── Branch A: CysB/POLD2 interface disruption ─► holoenzyme destabilized (↓POLD1/2/3)
│                                                        │
└── Branch B: active-site substitution ─► ↓ catalytic activity (complex intact)
                                                 │
                        ▼  (convergence)  ▼
              Reduced functional Polδ output
                          │
              Ineffective RFC recruitment / ↓ replication initiation
                          │
              S-phase DNA-synthesis defect  →  REPLICATIVE STRESS
                          │
   ┌──────────────────────┴───────────────────────┐
   ▼                                               ▼
Impaired T-cell clonal proliferation           Replicative stress in other
(↓cell-cycle progression on TCR activation)     dividing tissues (inferred)
   │                                               │
T-cell lymphopenia; naive→EM skewing;            Short stature, ID/dev delay,
oligoclonality; restricted TCR-β repertoire      hearing loss (syndromic subset)
   │
Impaired antiviral immunity + defective T-help
   │
Recurrent herpetic/viral & respiratory infections;
hypogammaglobulinemia; poor vaccine responses

Checklist of mechanistic categories

Molecular pathways: DNA replication (leading/lagging-strand synthesis by Polδ), replication-initiation licensing via RFC/PCNA clamp loading, cell-cycle (G1→S→M) progression, DNA-damage/replication-stress response.
Cellular processes: Cell-cycle progression and clonal proliferation (GO:0007049 cell cycle; GO:0006260 DNA replication; GO:0042098 T cell proliferation). The primary defect is proliferation, not apoptosis or repair per se (DNA repair after genotoxic stress was normal).
Protein dysfunction: Holoenzyme destabilization (branch A) vs. reduced catalytic turnover (branch B) — both partial loss of function of Polδ.
Metabolic changes: None specific; the lesion is in nucleic-acid synthesis machinery, not intermediary metabolism.
Immune system involvement: Combined immunodeficiency — cell-intrinsic T-cell proliferation defect with secondary humoral impairment (GO:0002250 adaptive immune response; GO:0046631 alpha-beta T cell activation).
Tissue damage mechanisms: Structural lung damage (bronchiectasis) is infection-driven, not a primary Polδ lesion.
Biochemical abnormalities: Reduced DNA polymerase δ enzymatic activity; impaired RFC clamp-loader recruitment.
Molecular profiling: Patient PBMCs/HEK293 cells showed reduced POLD-subunit expression, impaired complex stability, reduced cell-cycle fraction, and reduced polymerase activity (Cui 2020). No dedicated transcriptomic/proteomic/metabolomic IMD120 datasets exist.

Upstream vs downstream. Upstream: the POLD1 mutation and Polδ hypofunction (initiating lesion). Midstream: impaired replication initiation and replicative stress. Downstream: the T-cell proliferation defect and its immunologic/clinical sequelae.

Cell types (CL) and processes (GO): CL:0000084 (T cell), CL:0000624 (CD4+ T cell), CL:0000625 (CD8+ T cell), CL:0000898 (naive T cell), CL:0000909 (effector memory T cell), CL:0000236 (B cell), CL:0000623 (NK cell). GO:0006260 (DNA replication), GO:0007049 (cell cycle), GO:0042098 (T cell proliferation), GO:0000731 (DNA synthesis involved in DNA repair — spared).

Section 7 — Anatomical Structures Affected

Primary system: Immune / hematolymphoid system (UBERON:0002405 immune system; UBERON:0000178 blood). The functional lesion is in the T-lymphocyte compartment, with secondary humoral (B-cell/immunoglobulin) impairment.
Primary lymphoid organs: thymus (UBERON:0002370) and bone marrow (UBERON:0002371) as sites of lymphocyte production; peripheral lymphoid tissue (lymph nodes UBERON:0000029, spleen UBERON:0002106).
Secondary organ involvement (complications):
Respiratory tract / lungs (UBERON:0002048) — recurrent infections leading to bronchiectasis (irreversible airway dilation).
Skin (UBERON:0002097) — molluscum contagiosum, recurrent abscesses, herpetic lesions.
Ear / cochlea (UBERON:0001690 / UBERON:0001844) — sensorineural hearing loss (syndromic subset).
Central nervous system / brain (UBERON:0000955) — intellectual disability, speech delay (syndromic subset).
Skeletal/growth axis — short stature.
Tissue/cell level: hematopoietic/lymphoid cells; epithelial injury (airway) is secondary to infection. Targeted cell populations: naive CD4+/CD8+ T cells (depleted), effector-memory T cells (relatively expanded), B cells and NK cells (reduced in the Conde family).
Subcellular level: Nucleus (GO:0005634) — site of DNA replication; specifically the DNA polymerase delta complex (GO:0043625) and replication fork machinery (GO:0005657 replication fork).
Lateralization: Not applicable — systemic/bilateral immune and developmental involvement.

Section 8 — Temporal Development

Onset: Early childhood / infancy. Respiratory infections began in infancy in the Conde family (bronchiectasis by 6 months); recurrent herpetic infections and T-cell lymphopenia manifest in childhood.
Onset pattern: Insidious/chronic — recurrent infections accumulating over time, punctuated by acute infectious episodes.
Progression: Chronic and lifelong. Without treatment, recurrent infections drive progressive, cumulative organ damage (notably bronchiectasis, which is irreversible). Syndromic/developmental features (short stature, intellectual disability, hearing loss) are static-to-slowly-evolving developmental deficits.
Disease course: Persistent immunodeficiency with episodic infectious exacerbations (e.g., oral herpes every 1–2 months in the index patient) superimposed on a chronic baseline.
Remission: No spontaneous remission. Treatment-induced control is achievable — IgRT resolves lower respiratory tract infections and markedly reduces herpetic episodes; HSCT can be curative for the immune defect.
Critical periods: Early diagnosis (before irreversible bronchiectasis and before severe infections) is the key window for intervention — paralleling the rationale for early treatment in other T-cell immunodeficiencies/SCID.

Section 9 — Inheritance and Population

Inheritance: Autosomal recessive (biallelic — homozygous or compound heterozygous). Heterozygous carriers are unaffected for IMD120.
Epidemiology: Ultra-rare. Only two unrelated POLD1 families are reported to date (Cui 2020; Conde 2019). No prevalence or incidence estimates exist; the true frequency is likely <1 per 1,000,000.
Penetrance / expressivity: Presumed high penetrance for the immunodeficiency in biallelic carriers, but with variable expressivity — the two reported families differ in the prominence of syndromic features (the Conde family had prominent developmental impairment; the Cui family emphasized the immune/herpetic phenotype). With only two families, penetrance/expressivity cannot be precisely quantified.
Genetic anticipation: Not applicable (not a repeat-expansion disorder).
Germline mosaicism: Not reported.
Consanguinity: Major role. The index kindred was consanguineous Turkish; the related POLD2 patient was also consanguineous. Consanguinity is the principal route to homozygosity for rare hypomorphic recessive alleles.
Founder effects / carrier frequency: None established; p.R1060C is absent from population databases, arguing against a common founder allele.
Population demographics: Reported patients are of Turkish and (Conde family) unspecified ancestry. No sex bias expected (autosomal). Age distribution: pediatric onset.
Geographic distribution: No endemic pattern; cases are sporadic and consanguinity-associated.

Section 10 — Diagnostics

Laboratory / immunologic tests (diagnostic hallmarks): - Lymphocyte subset enumeration (flow cytometry): T-cell lymphopenia with decreased naive CD4+ and especially CD8+ T cells, effector-memory skewing; reduced B and NK cells in some patients. (LOINC/flow-cytometry immunophenotyping.) - T-cell proliferation assay: Impaired T-cell (not B-cell) proliferation to TCR/mitogen stimulation — the single most discriminating functional test. - Immunoglobulins: low IgG, low IgA/IgM (hypogammaglobulinemia). - Vaccine response: absent/poor tetanus antibody response despite full vaccination. - TCR repertoire analysis: oligoclonality and restricted TCR-β V-J pairing (spectratyping/TCR-seq). - Cell-cycle / replicative-stress assays (research): decreased S-phase fraction; reduced Polδ complex levels and polymerase activity.

Genetic testing (definitive): - Whole exome sequencing (WES) / whole genome sequencing (WGS): the primary route to diagnosis — both families were identified by exome-scale sequencing. Given phenotypic overlap with many inborn errors of immunity, broad sequencing (WES/WGS) or a combined immunodeficiency / IEI gene panel including POLD1 is the recommended approach. - Targeted POLD1 sequencing / segregation analysis to confirm biallelic status and phase (important for compound heterozygotes; note the in-cis p.Q684H+p.S939W configuration in Conde patient 2). - Functional confirmation (polymerase activity, complex stability) supports variant interpretation, especially for VUS. The PolED database (PMID 41263451) curates functional evidence for POLD1 variants and is a useful clinical resource.

Imaging: High-resolution chest CT to detect/monitor bronchiectasis and pulmonary sequelae; audiometry for hearing loss.

Newborn screening: Standard TREC-based SCID newborn screening detects severe T-cell lymphopenia and may flag IMD120 as a non-SCID T-cell-lymphopenia condition (analogous to syndromic T-cell lymphopenias identified through SCID NBS programs), but IMD120 is not a specific NBS target.

Differential diagnosis: SCID and leaky-SCID, other combined immunodeficiencies (e.g., MHC class II deficiency, FADD deficiency), DNA-repair/replication syndromes, and — for the syndromic features — other progeroid/short-stature syndromes. The distinguishing features of IMD120 are the isolated T-cell proliferation defect with preserved B-cell proliferation, the herpesvirus susceptibility, and biallelic POLD1 variants. Because POLD1 also causes MDPL (AD progeroid) and hearing loss, allele class and zygosity distinguish these entities.

Section 11 — Outcome / Prognosis

Survival / mortality: No formal survival statistics exist (only two families). Prognosis is dominated by infection control and cumulative organ damage (bronchiectasis). With effective IgRT and antiviral prophylaxis, patients can be stabilized; HSCT offers potential cure.
Morbidity / disability: Significant — recurrent infections, irreversible bronchiectasis, lifelong treatment dependence, and (syndromic subset) intellectual disability, hearing loss, and short stature.
Complications: Bronchiectasis and chronic lung disease; recurrent/severe herpetic disease; chronic viral skin lesions (molluscum); potential end-organ damage from recurrent infection.
Recovery potential: The immune defect is not self-correcting; HSCT can restore T-cell numbers and function (Keles 2026). Established structural damage (e.g., bronchiectasis) and developmental deficits are not reversible.
Prognostic factors: Timing of diagnosis and treatment initiation, degree of pre-existing organ damage, infection burden, and access to HSCT are the key determinants. There are no validated molecular prognostic biomarkers.
Theoretical long-term concern: Because Polδ participates in genome maintenance, a long-term genome-instability/malignancy risk is biologically plausible; however, unlike the POLD1 exonuclease (proofreading) variants that cause cancer predisposition, IMD120 variants primarily reduce polymerase output rather than abolish proofreading, and no cancer excess has been reported in the two families. This remains an open question requiring long-term follow-up.

Section 12 — Treatment

Established/effective management (from Cui 2020, verified): - Immunoglobulin replacement therapy (IgRT) (NCIT: Immunoglobulin Therapy) — the index patient started IgRT with resolution of lower respiratory tract infections and markedly decreased herpetic infections. Standard of care for the antibody deficiency. - Antiviral prophylaxis with acyclovir (NCIT: Acyclovir) — used for recurrent oral herpes and herpes zoster; addresses the characteristic herpesvirus susceptibility. - Antimicrobial prophylaxis / prompt treatment of infections and airway clearance/management for bronchiectasis (supportive).

Curative therapy: - Hematopoietic stem cell transplantation (HSCT) (NCIT: Hematopoietic Stem Cell Transplantation). Keles et al. 2026 (PMID: 42104577) reported the first successful HSCT in an 18-year-old IgRT-dependent woman with POLD1 deficiency: matched related donor, reduced-intensity conditioning (cyclophosphamide, fludarabine, ATG), tacrolimus + low-dose methotrexate GVHD prophylaxis; prompt engraftment without major complications, improved T-cell counts/function, and she remained well off IgRT. Reduced-intensity conditioning is a rational choice given theoretical DNA-replication/repair toxicity concerns in a Polδ-deficient host.

Advanced / experimental therapeutics: No gene therapy, RNA-based therapy, or POLD1-targeted therapy exists for IMD120. No IMD120-specific clinical trials (NCT) were identified. Gene therapy is conceptually challenging because POLD1 is a tightly dosage-controlled housekeeping gene.

Pharmacogenomics: No IMD120-specific pharmacogenomic guidance. General caution is warranted with genotoxic/antimetabolite chemotherapeutics and conditioning agents given the underlying replication defect.

Treatment strategy summary:

Line	Intervention	Goal	Evidence
Supportive/first-line	IgRT + acyclovir prophylaxis; treat infections; airway care	Control infections, prevent organ damage	Cui 2020 (PMID 31629014)
Definitive/curative	Reduced-intensity-conditioning HSCT	Restore T-cell immunity, off IgRT	Keles 2026 (PMID 42104577)

Section 13 — Prevention

Primary prevention: Not preventable at the individual level (monogenic). Genetic counseling and, in consanguineous families, carrier/cascade testing and reproductive options (prenatal diagnosis, preimplantation genetic testing) are the principal preventive tools once a familial POLD1 genotype is known.
Secondary prevention (early detection): Early recognition via IEI evaluation and genetic testing; TREC-based SCID newborn screening may incidentally flag T-cell lymphopenia. Early diagnosis enables IgRT/antiviral prophylaxis before irreversible lung damage.
Tertiary prevention (complication prevention): IgRT and antiviral/antimicrobial prophylaxis to prevent recurrent infection and bronchiectasis progression; audiologic and developmental support in syndromic patients; consideration of HSCT before accumulation of end-organ damage.
Immunization: Routine inactivated vaccines are appropriate, but antibody responses are impaired (poor tetanus response reported); live vaccines are contraindicated in significant T-cell immunodeficiency. IgRT provides passive protection.
Counseling: Autosomal recessive counseling — 25% recurrence risk for unaffected carrier couples; emphasize consanguinity risk.

Section 14 — Other Species / Natural Disease

Taxonomy / orthologs: POLD1 is deeply evolutionarily conserved. Orthologs: mouse Pold1 (NCBI Gene 18971), and homologs across vertebrates and yeast (S. cerevisiae POL3/CDC2). The catalytic and proofreading functions are conserved from yeast to human.
Natural disease in other species: No naturally occurring POLD1-associated combined immunodeficiency has been reported in companion animals or wildlife (no OMIA entry identified for an equivalent immune phenotype).
Comparative biology: The essentiality of Polδ for replication is conserved across all eukaryotes; the disease mechanism (replicative stress from Polδ hypofunction) is expected to be conserved, but the specific immune phenotype has only been characterized in humans.
Transmission / zoonosis: Not applicable — genetic, non-transmissible disorder.

Section 15 — Model Organisms

No dedicated immunodeficiency model of IMD120 exists. Existing Pold1 mouse models bracket the disease but do not reproduce it:

Model	Genotype	Phenotype	Relevance to IMD120
Pold1 null	Pold1⁻/⁻	Peri-implantation embryonic lethality; defective inner-cell-mass proliferation, impaired DNA synthesis, spontaneous apoptosis (Uchimura PLoS ONE 2009; MGI:3833589)	Confirms POLD1 is essential — explains why only hypomorphic alleles cause human disease
Proofreading-dead	Pold1^D400A/D400A	Viable, fertile; ~15× higher mutation rate, ~94% cancer incidence by 18 mo (median survival ~10 mo), mostly epithelial carcinomas incl. skin SCC (Goldsby 2001/2002; Venkatesan PNAS 2007)	Models the cancer (exonuclease/CRCS12) phenotype, not IMD120
Polymerase-domain point mutants	Pold1^L604K/L604G	Embryonic lethal	Illustrates lethality of strong polymerase-domain lesions
Hypomorphic allele	Pold1 hypomorph	Disrupted gastrulation embryo-size/morphogenesis coordination (Biology Open 2022)	Demonstrates dosage-sensitive developmental effects; closest to "partial LOF" but not immune-focused

Implications / limitations. The essentiality of Pold1 (null = embryonic lethal) means an IMD120 model must use a precisely hypomorphic allele (e.g., a knock-in of the human p.R1060C-equivalent residue) to survive to immune-competence and reveal the T-cell phenotype. No such immune-focused model has been generated. Available models capture either lethality (null/strong point mutants) or cancer (proofreading-dead), leaving the replicative-stress T-cell defect experimentally uncharacterized in vivo. iPSC-derived and CRISPR-edited cellular models (as used for other immuno-actinopathies) plus patient PBMCs/HEK293 systems (Cui 2020) currently carry the mechanistic evidence.

Recommended model resources: MGI (mouse Pold1), IMPC/IMSR for allele availability; patient-derived iPSC → T-cell differentiation and CRISPR knock-in of hypomorphic alleles for immune-phenotype modeling.

Key Findings (with statistical/experimental evidence)

Finding 1 — POLD1 is the causal gene; IMD120 is an autosomal recessive combined immunodeficiency

Biallelic (homozygous or compound heterozygous) POLD1 mutations cause IMD120 (OMIM #620836; MONDO:0970994). Cui et al. 2020 identified homozygous c.3178C>T (p.R1060C) in 3 related subjects from a consanguineous Turkish kindred; Conde et al. 2019 identified compound-heterozygous POLD1 variants. Verified quotes (PMID: 31629014): "We identified a missense mutation (c.3178C>T; p.R1060C) in POLD1 in 3 related subjects who presented with recurrent, especially herpetic, infections and T-cell lymphopenia with impaired T-cell but not B-cell proliferation," and "These results identify gene defects in POLD1 as a novel cause of T-cell immunodeficiency."

Finding 2 — Clinical spectrum: infections + T-cell lymphopenia + syndromic features

Early-onset recurrent (especially herpetic/viral) infections, T-cell lymphopenia (↓naive CD4/CD8, effector-memory skewing, oligoclonality, restricted TCR-β repertoire), hypogammaglobulinemia, recurrent respiratory infections → bronchiectasis (by 6 months in Conde family), chronic molluscum, skin abscesses, and syndromic features (short stature, intellectual disability/speech delay, hearing loss). Verified quote (PMID: 31629014): "The patients exhibited decreased numbers of naive CD4 and especially CD8 T cells in favor of effector memory subpopulations."

Finding 3 — Mechanism: Polδ hypofunction → replicative stress → T-cell proliferation defect

Hypomorphic POLD1 variants destabilize the Polδ complex, impair RFC recruitment and cell-cycle progression, causing replicative stress and defective T-cell proliferation. Verified quotes (PMID: 31629014): "The mutation destabilizes the Polδ complex, leading to ineffective recruitment of replication factor C to initiate DNA replication," and "Molecular dynamics simulation revealed that the R1060C mutation disrupts the intramolecular interaction between the POLD1 CysB motif and the catalytic domain and also between POLD1 and the Polδ subunit POLD2." Conde 2019 termed it a "syndromic immunodeficiency with replicative stress" with normal post-genotoxic DNA repair — i.e., a specific S-phase synthesis defect.

Finding 4 — Two convergent molecular routes to Polδ hypofunction

(a) Destabilization — p.R1060C in the CysB motif lowers POLD1/POLD2/POLD3 levels (complex instability). (b) Reduced catalytic activity with intact assembly — p.Q684H+p.S939W (in cis, near the active site) reduce intrinsic polymerase activity without destabilizing the complex. Both are biallelic and converge on reduced functional Polδ output.

Finding 5 — Model organisms: no immune model; null lethal, proofreading-dead cancer-prone

Pold1⁻/⁻ mice are peri-implantation lethal (essential gene); Pold1^D400A^ proofreading-dead mice are viable but ~94% cancer-prone. Neither models the IMD120 immune phenotype.

Finding 6 — Management: IgRT + acyclovir effective; RIC-HSCT feasible/curative

IgRT resolved lower respiratory infections and markedly reduced herpetic episodes; acyclovir controlled recurrent herpes (Cui 2020). Keles 2026 (PMID 42104577) reported the first successful reduced-intensity-conditioning HSCT with engraftment, restored T-cell function, and independence from IgRT.

Finding 7 — Inheritance/epidemiology and the POLD1 allelic series

Ultra-rare AR disorder, consanguinity-associated, ~2 families reported; allelic to AD MDPL syndrome (p.Ser605del), AR nonsyndromic hearing loss (p.Gly1100Arg + null; ~33% residual activity, PMID 31944473), and colorectal cancer susceptibility 12 (exonuclease-domain variants).

Mechanistic Model / Interpretation

IMD120 is best understood as a dosage disease of a housekeeping replicase. POLD1 is essential and dosage-sensitive: null alleles are lethal, so only partial loss-of-function genotypes produce viable, disease-manifesting individuals. The unifying pathophysiology is replicative stress — a quantitative shortfall in DNA-synthesis capacity that becomes limiting precisely in the cells that must proliferate fastest and most explosively: antigen-activated T lymphocytes. This explains the otherwise puzzling selectivity of the phenotype (T-cell proliferation impaired, B-cell proliferation relatively spared; antiviral immunity most affected) and the herpesvirus susceptibility (control of herpesviruses is exquisitely T-cell dependent).

The convergence of two biochemically distinct genotypes (complex destabilization vs. reduced catalytic activity) on the same functional endpoint (reduced Polδ output → replicative stress) is a strong argument that quantitative Polδ activity, not any single structural interaction, is the disease-relevant variable. It also predicts a genotype–severity gradient: the more residual Polδ activity an allele combination retains, the milder (or more tissue-restricted) the phenotype — a prediction consistent with the broader POLD1 allelic series, where different residual-activity/allele-class combinations yield hearing loss, progeroid MDPL, cancer predisposition, or combined immunodeficiency.

Evidence Base

PMID	Title (abbrev.)	Role
31629014	Combined immunodeficiency caused by a loss-of-function mutation in DNA polymerase delta 1 (Cui 2020)	Founding paper: identifies POLD1, p.R1060C, clinical/immune phenotype, and the destabilization/RFC mechanism
31449058	Conde et al. 2019 (POLD1/POLD2 replicative-stress immunodeficiency)	Second family; compound-het POLD1 (p.Q684H+p.S939W) and POLD2 patient; defines "replicative stress," branch B mechanism
42104577	Keles et al. 2026 (Pediatric Transplantation)	First successful RIC-HSCT in POLD1 deficiency; curative option
31944473	Oh et al. 2020	AR nonsyndromic hearing loss from POLD1; ~33% residual activity — supports dosage/allelic-series model
41263451	PolED database	Curated functional-variant resource for POLD1/POLE interpretation
34594041	Robinson et al. 2021	Germline POLE/POLD1 (proofreading) mutations: mutation burden, cancer — contrasts IMD120 (non-proofreading, no premature aging)
Mouse models	Uchimura 2009 (MGI:3833589); Goldsby 2001/2002; Venkatesan 2007 (PNAS); Biology Open 2022	Establish Pold1 essentiality (null lethal) and proofreading-dead cancer phenotype; absence of an immune model

Additional MDPL papers (PMIDs 41219970, 41083899, 39611849, 41742372, 42488286) establish that the p.Ser605del active-site allele causes the dominant progeroid MDPL phenotype via gain-of-abnormal-interaction (e.g., aberrant TRF1 binding) and telomere/PARP1 dysregulation — mechanistically and inheritance-wise distinct from the recessive hypomorphic IMD120 alleles, reinforcing that allele class dictates phenotype at this locus.

Limitations and Knowledge Gaps

Extremely small sample: Only two unrelated families define IMD120. Penetrance, expressivity, full phenotypic spectrum, natural history, prognosis, and genotype–phenotype correlations are all under-determined.
No epidemiologic data: No prevalence/incidence estimates; no registry; no defined Orphanet/ICD code.
No in vivo immune model: The T-cell replicative-stress mechanism has not been reproduced in an animal model; a hypomorphic knock-in mouse is needed.
Syndromic-feature mechanism inferred, not demonstrated: The link from Polδ hypofunction to short stature/ID/hearing loss is a plausible housekeeping-replicative-stress inference but is not experimentally dissected.
Long-term cancer/genome-instability risk unknown: Whether IMD120 patients carry elevated malignancy risk (as proofreading-defective POLD1 carriers do) is unresolved; the mechanism differs (reduced synthesis vs. lost proofreading), but long-term follow-up is lacking.
HSCT evidence is a single case: Curative HSCT is supported by one patient; optimal conditioning intensity and long-term outcomes (including any excess conditioning toxicity from the replication defect) are unknown.
B-cell/NK involvement variability: B-cell and NK reductions were prominent in one family but the "T-cell selective" framing derives largely from the other — the true combined-immunodeficiency breadth needs more cases.

Proposed Follow-up Experiments / Actions

Build a hypomorphic Pold1 knock-in mouse (e.g., p.R1060C-equivalent) to test whether it recapitulates T-cell lymphopenia, proliferation defect, and infection susceptibility — the missing in vivo model.
Patient/CRISPR iPSC → T-cell differentiation to quantify replicative stress, cell-cycle kinetics, and repertoire contraction cell-autonomously, and to test allele-specific severity (branch A vs. branch B).
Genotype–activity–phenotype mapping across the POLD1 allelic series: measure residual polymerase activity for IMD120 vs. hearing-loss vs. MDPL vs. cancer alleles and correlate with tissue-specific phenotype to formalize the dosage model (leverage the PolED database, PMID 41263451).
International case-finding/registry: Systematically re-examine unexplained combined immunodeficiency and SCID-NBS-positive T-cell-lymphopenia cohorts for biallelic POLD1 variants to expand the phenotypic spectrum and estimate frequency.
Long-term surveillance protocol: Prospectively monitor IMD120 patients for malignancy, somatic mutation burden, and organ damage to resolve the genome-instability question.
HSCT outcome collation: Aggregate additional transplant cases to define optimal (reduced-intensity) conditioning and long-term efficacy/safety.
Deep immunophenotyping + TCR-seq on any newly identified patients to precisely quantify the naive-cell loss, effector-memory skewing, and repertoire restriction, and to test whether B-cell/NK involvement is consistent.

Ontology Term Appendix

Disease: MONDO:0970994; OMIM #620836
Gene/protein: POLD1 (HGNC:9175); GO:0043625 (delta DNA polymerase complex); GO:0006260 (DNA replication); GO:0007049 (cell cycle); GO:0042098 (T cell proliferation); GO:0005634 (nucleus)
Cells (CL): CL:0000084 (T cell), CL:0000624 (CD4+ T cell), CL:0000625 (CD8+ T cell), CL:0000898 (naive T cell), CL:0000909 (effector memory T cell), CL:0000236 (B cell), CL:0000623 (NK cell)
Anatomy (UBERON): UBERON:0002405 (immune system), UBERON:0002370 (thymus), UBERON:0002371 (bone marrow), UBERON:0002048 (lung), UBERON:0002097 (skin), UBERON:0001690 (ear)
Phenotypes (HPO): HP:0002719, HP:0004429, HP:0002326, HP:0005403, HP:0031381, HP:0004313, HP:0002110, HP:0004322, HP:0001249, HP:0000407
Treatments (NCIT): Immunoglobulin therapy; Acyclovir; Hematopoietic Stem Cell Transplantation
Chemicals (CHEBI): acyclovir (CHEBI:2453)

Evidence source types: human clinical (case series — Cui 2020, Conde 2019; case report — Keles 2026); in vitro/cellular and in silico (patient PBMCs, HEK293, molecular dynamics — Cui 2020); model organism (mouse Pold1 — Uchimura 2009, Goldsby 2001/2002, Venkatesan 2007). All mechanistic and clinical claims are cited to primary literature by PMID.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	7
Resolved	7
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	7
On topic	4
Off topic	0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome	Count
Terms checked	51
Resolved	48
Unresolved (possible confabulation)	1
Obsolete	0
Unverifiable	2
Terms whose name was checked	29
Terms named correctly	10
Terms named as a different term	9
Terms whose name is worth a second look	10

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

MONDO:0970994 (4 mentions) - the report calls it "MONDO"; MONDO calls it immunodeficiency 120
HP:0002326 (2 mentions) - the report calls it "Herpes simplex disease"; HP calls it Transient ischemic attack
HP:0200042 (1 mention) - the report calls it "Clinical sign"; HP calls it Skin ulcer
HP:0031521 (1 mention) - the report calls it "Clinical sign"; HP calls it Vaginal clear cell adenocarcinoma
HP:0005387 (1 mention) - the report calls it "Decreased antibody level in blood"; HP calls it Combined immunodeficiency
HP:0004322 (2 mentions) - the report calls it "Physical manifestation"; HP calls it Short stature
HP:0007018 (1 mention) - the report calls it "Behavioral"; HP calls it Attention deficit hyperactivity disorder
HP:0000407 (2 mentions) - the report calls it "Physical manifestation"; HP calls it Sensorineural hearing impairment
UBERON:0002048 (2 mentions) - the report calls it "Respiratory tract / lungs", "lung"; UBERON calls it lung

Unresolved terms

These identifiers do not exist in an ontology that resolved other terms from the same prefix, so they were most likely invented:

HP:0410413 (1 mention) - HP does not contain this term

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

HP:0031381 (2 mentions) - the report calls it "Decreased proliferation of T cells"; HP calls it Decreased mitogen-induced T-cell proliferation, and lists "Decreased lymphocyte proliferation in response to mitogen" among its other names
CL:0000624 (2 mentions) - the report calls it "CD4+ T cell"; CL calls it CD4-positive, alpha-beta T cell
CL:0000625 (2 mentions) - the report calls it "CD8+ T cell"; CL calls it CD8-positive, alpha-beta T cell
CL:0000909 (2 mentions) - the report calls it "effector memory T cell"; CL calls it CD8-positive, alpha-beta memory T cell
CL:0000623 (2 mentions) - the report calls it "NK cell"; CL calls it natural killer cell, and lists "NK cell" among its other names
GO:0000731 (1 mention) - the report calls it "DNA synthesis involved in DNA repair — spared"; GO calls it DNA synthesis involved in DNA repair
UBERON:0002370 (2 mentions) - the report calls it "Primary lymphoid organs: thymus", "thymus"; UBERON calls it thymus**, and lists "thymus organ" among its other names
UBERON:0002097 (2 mentions) - the report calls it "Skin", "skin"; UBERON calls it skin of body, and lists "skin" among its other names
UBERON:0000955 (1 mention) - the report calls it "Central nervous system / brain"; UBERON calls it brain, and lists "suprasegmental levels of nervous system" among its other names
GO:0005634 (2 mentions) - the report calls it "Nucleus", "Subcellular level: Nucleus", "nucleus"; GO calls it nucleus, and lists "cell nucleus" among its other names

Terms named inconsistently

The report gives these identifiers more than one name of its own:

HGNC:9175 - called "POLD1", "Gene/protein:* POLD1"
UBERON:0002370 - called "Primary lymphoid organs:** thymus", "thymus"
UBERON:0002048 - called "Respiratory tract / lungs", "lung"
UBERON:0002097 - called "Skin", "skin"
GO:0005634 - called "Nucleus", "Subcellular level: Nucleus", "nucleus"
GO:0043625 - called "DNA polymerase delta complex", "delta DNA polymerase complex"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: MGI.

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Phenotypes

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Medical Actions

Diagnosis

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References & Deep Research

References

Deep Research

Immunodeficiency 120 (IMD120): A Comprehensive Disease Characterization

Summary

Section 1 — Disease Information

Section 2 — Etiology

Section 3 — Phenotypes

Section 4 — Genetic / Molecular Information

Section 5 — Environmental Information

Section 6 — Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation)

Checklist of mechanistic categories

Section 7 — Anatomical Structures Affected

Section 8 — Temporal Development

Section 9 — Inheritance and Population

Section 10 — Diagnostics

Section 11 — Outcome / Prognosis

Section 12 — Treatment

Section 13 — Prevention

Section 14 — Other Species / Natural Disease

Section 15 — Model Organisms

Key Findings (with statistical/experimental evidence)

Finding 1 — POLD1 is the causal gene; IMD120 is an autosomal recessive combined immunodeficiency

Finding 2 — Clinical spectrum: infections + T-cell lymphopenia + syndromic features

Finding 3 — Mechanism: Polδ hypofunction → replicative stress → T-cell proliferation defect

Finding 4 — Two convergent molecular routes to Polδ hypofunction

Finding 5 — Model organisms: no immune model; null lethal, proofreading-dead cancer-prone

Finding 6 — Management: IgRT + acyclovir effective; RIC-HSCT feasible/curative

Finding 7 — Inheritance/epidemiology and the POLD1 allelic series

Mechanistic Model / Interpretation

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Ontology Term Appendix

Artifacts

Reference Validation

Term Validation

Terms the report names something else

Unresolved terms

Terms whose name is worth a second look

Terms named inconsistently

Prefixes with no resolver