Bachmann-Bupp Syndrome

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Classifications

Harrison's Chapter

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Inheritance

2

Autosomal dominant HP:0000006

Heterozygous ODC1 variants are sufficient; reported cases have been de novo, so recurrence risk to siblings is presumed low.

Autosomal dominant inheritance

Show evidence (2 references)

PMID:36007106 SUPPORT Human Clinical

"BABS is expressed in an autosomal dominant manner and typically caused by a de novo ODC1 pathogenic variant."

GeneReviews states the autosomal dominant mode and the de novo origin of the causative variant.

PMID:36443247 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (OMIM #619075) is a novel autosomal dominant disorder caused by variants in the c-terminus of the ornithine decarboxylase 1 gene, resulting in increased levels of ornithine decarboxylase."

Independent confirmation of autosomal dominant transmission and of the C-terminal location of the causative variants.

De novo occurrence HP:0003745

All reported probands have carried de novo heterozygous ODC1 variants rather than inherited alleles.

Sporadic

Show evidence (1 reference)

PMID:30475435 SUPPORT Human Clinical

"In this report, we present four patients with a distinct neurometabolic disorder associated with de novo heterozygous, gain-of-function variants in the ODC1 gene."

A four-patient cohort in which every causative allele arose de novo.

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Discussions and Knowledge Gaps

2

The K6/ODC mouse reproduces the alopecia and follicular cysts of BABS and predicted the DFMO response, but it also develops skin tumours and is skin-restricted. Does whole-body expression of stabilised ODC in BABS patients carry a tumour risk, and does the absence of a whole-body model mean the neurodevelopmental arm of the disease has never been modelled?

HUMAN MODEL MISMATCH OPEN babs_k6odc_model_scope_and_cancer_risk

Attached to

pathophysiology#Dysregulated Neural Progenitor Proliferation

The only well-characterised animal model of this exact lesion targets the transgene to hair follicle keratinocytes. Its tumour phenotype has been interpreted as evidence that polyamine excess promotes tumorigenesis, and the index human cohort report raised cancer surveillance as a consideration on that basis. But no BABS patient tumour series exists, GeneReviews does not recommend tumour surveillance, and there is no whole-body C-terminally-truncated-ODC model in which the neurodevelopmental phenotype could be studied. The mismatch matters in both directions: it risks over-calling a cancer risk that has not been observed in patients, and it leaves the central neurodevelopmental mechanism without an in vivo model.

Proposed experiments

Whole-body or CNS-conditional Odc1 C-terminal truncation knock-in

exp_babs_whole_body_truncation_knockin

Generate a mouse carrying a knock-in of a human-equivalent C-terminally truncated Odc1 allele expressed ubiquitously or conditionally in neural lineages, rather than under a keratin 6 promoter, and characterise cortical progenitor proliferation, brain growth, white matter development and response to eflornithine started at different postnatal ages.

Prospective tumour-surveillance registry across the BABS cohort

exp_babs_tumour_surveillance_registry

Assemble a prospective, standardised tumour-surveillance registry across the international BABS cohort to establish whether the mouse skin-tumour phenotype has any human counterpart, and whether long-term eflornithine exposure modifies it.

Show evidence (2 references)

PMID:30475435 SUPPORT Human Clinical

"As the ODC1 gene has been implicated in neoplasia, cancer surveillance may be important in this disorder."

The index cohort raises cancer surveillance as a hypothesis, phrased as a possibility rather than a recommendation.

PMID:41925768 SUPPORT Model Organism

"However, unlike the K6/ODC mouse where this mutation was directed to the skin, the ODC mutation is expressed in all tissues of BABS patients resulting in macrosomia, macrocephaly, neurodevelopmental delay, spasticity, hypotonia, delayed visual maturation, and sensorineural hearing loss"

States the exact scope difference between the model and the human disease.

Does earlier initiation of eflornithine, for example in a neonate diagnosed before neurological damage accrues, change the neurodevelopmental trajectory of BABS?

KNOWLEDGE GAP OPEN babs_treatment_window_neonatal_initiation

Attached to

pathophysiology#Abnormal Brain Development

All reported treated patients started eflornithine after developmental delay was already established; the index patient was 4 years and 8 months old. The treating team explicitly identified neonatal initiation as the untested question of greatest consequence. Prenatal diagnosis of BABS has now been reported, which makes pre-symptomatic treatment a realistic prospect.

Proposed experiments

Natural-history cohort comparing early versus late eflornithine initiation

exp_babs_early_versus_late_initiation_cohort

Establish a prospective international natural-history cohort with standardised developmental assessment at fixed ages, then compare developmental trajectories, MRI findings and N-acetylputrescine normalisation between patients started on eflornithine before and after 12 months of age.

Show evidence (1 reference)

PMID:34282722 SUPPORT Human Clinical

"This could be especially consequential if we could initiate therapy in a neonate diagnosed early before neurological damage occurs."

The treating team states the open question directly.

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Pathophysiology

11

ODC1 C-Terminal Truncating Variant

A de novo heterozygous variant at the 3-prime end of ODC1 introduces a premature stop codon in the last exon, removing the carboxy-terminal residues of ornithine decarboxylase. The variants cluster in this region across reported patients, and the index allele c.1342A>T removes the last 14 amino acids.

ODC1 hgnc:8109 ⚠ ABNORMAL

Downstream

Escape from Antizyme-Mediated Proteasomal Degradation Loss of the C-terminal degron removes the signal that normally targets ODC for ubiquitin-independent proteasomal turnover.

Show evidence (4 references)

PMID:37469105 SUPPORT Human Clinical

"The condition is caused by 3'-end mutations of the ornithine decarboxylase 1 (ODC1) gene, which produce carboxy (C)-terminally truncated variants of ODC, a pyridoxal 5'-phosphate-dependent enzyme."

Names the location of the causative variants and the protein consequence that defines this node.

PMID:30239107 SUPPORT Human Clinical

"Here, we report an 32-month-old Caucasian female with a heterozygous de novo nonsense mutation in the ODC1 gene that leads to a premature abrogation of 14-aa residues at the ODC protein c-terminus."

The index case defines the specific lesion: a de novo nonsense variant truncating the last 14 residues.

PMID:34477286 SUPPORT Human Clinical

"Variants continue to cluster, providing support to a universal biochemical mechanism related to elevated ODC protein, enzyme activity, and abnormalities in polyamine levels."

Establishes that the reported variants cluster in one region and converge on a single biochemical mechanism.

+ 1 more reference

Escape from Antizyme-Mediated Proteasomal Degradation

Wild-type ODC is one of the shortest-lived mammalian proteins because its C-terminus acts as a degron for ubiquitin-independent, antizyme-dependent proteasomal degradation. The truncated BABS enzyme cannot be cleared by this route, so it escapes normal turnover. This is a stability defect, not a catalytic defect.

proteasomal ubiquitin-independent protein catabolic process GO:0010499 ↓ DECREASED

Downstream

ODC Protein Accumulation A protein that cannot be degraded accumulates in the cell.

Show evidence (7 references)

PMID:40382142 SUPPORT Human Clinical

"These shortened ODC proteins remain enzymatically active and are not cleared by the proteasome, therefore leading to ODC protein accumulation in cells."

States both halves of this node: preserved catalysis and failed proteasomal clearance.

PMID:31249027 SUPPORT In Vitro

"We hypothesized that this new mutation (c.1342 A>T) leads to a C-terminal truncation variant of the ODC protein that is resistant to normal proteasomal degradation, leading to putrescine accumulation in cells."

States the degradation-resistance hypothesis that the same study then tested in patient-derived cells.

PMID:41925768 SUPPORT Model Organism

"a premature stop codon at position 427 in the mouse ODC cDNA was placed downstream of the K6 promoter resulting in a carboxyl-truncated ODC protein with a much longer in vivo half-life than the full-length ODC protein"

The engineered mouse allele demonstrates that C-terminal truncation alone extends the half-life of the ODC protein.

+ 4 more references

ODC Protein Accumulation

Stabilised ODC protein accumulates to large excess in patient cells, demonstrated in primary dermal fibroblasts and in red blood cells.

fibroblast CL:0000057 erythrocyte CL:0000232

Downstream

Elevated ODC Enzyme Activity Because the accumulated protein retains catalytic competence, more enzyme means proportionally more activity.

Show evidence (2 references)

PMID:31249027 SUPPORT In Vitro

"In this study, we show that primary dermal fibroblasts derived from a skin biopsy of a 3-year-old patient contain large amounts of ODC protein and putrescine compared with primary dermal (neonatal and adult) fibroblast control cells."

Direct measurement of accumulated ODC protein in patient-derived fibroblasts.

PMID:30239107 SUPPORT Human Clinical

"Red blood cells obtained from our patient showed elevated ODC protein and polyamine levels compared to healthy controls."

Confirms ODC protein accumulation in a second, circulating patient cell type.

Elevated ODC Enzyme Activity

Cellular ornithine decarboxylase activity is raised by one to two orders of magnitude, 12-17-fold in patient fibroblasts and 125-137-fold in patient red blood cells. ODC is the first, rate-limiting step of polyamine biosynthesis, so this is the point at which pathway flux is deregulated.

polyamine biosynthetic process GO:0006596 ↑ INCREASED

ornithine decarboxylase activity GO:0004586 ↑ INCREASED

Downstream

Putrescine Accumulation ODC converts ornithine to putrescine; excess enzyme activity drives putrescine accumulation.

Ornithine Substrate Depletion Sustained excess flux through the decarboxylation step draws down the ornithine pool.

Show evidence (3 references)

PMID:31249027 SUPPORT In Vitro

"Importantly, the accumulated ODC protein variant remained functionally active as we detected exceptionally high ODC enzyme activity in both primary dermal fibroblasts (12-17-fold of controls) and red blood cells (RBCs) (125-137-fold of controls), using a specific 14C radioactive ODC activity assay."

Quantifies the magnitude of the enzyme-activity gain in patient material.

PMID:41410504 SUPPORT Human Clinical

"Bachmann-Bupp syndrome results from heterozygous gain-of-function variants in the ornithine decarboxylase 1 (ODC1) gene, resulting in increased ornithine decarboxylase enzyme activity."

The polyaminopathy review states increased enzyme activity as the defining biochemical consequence.

PMID:30475435 SUPPORT Human Clinical

"Ornithine decarboxylase 1 (ODC1) is the rate-limiting enzyme in endogenous polyamine synthesis."

Establishes why a change in ODC activity controls flux through the whole polyamine pathway.

Putrescine Accumulation

Putrescine, the immediate product of ODC, accumulates in patient cells. It is the proximate biochemical lesion of BABS and the target of eflornithine therapy.

Downstream

Elevated N-Acetylputrescine Excess putrescine is acetylated, and it is the acetylated species that is measurable on clinical metabolomic profiling.

Hair Follicle Dysfunction with Bulge Stem Cell Recruitment Elevated follicular polyamines disrupt the hair cycle and recruit bulge stem cells out of quiescence.

Dysregulated Neural Progenitor Proliferation ODC1 expression tracks neural progenitor proliferation in fetal brain and cerebral organoids; gain of function is proposed to drive over-proliferation. The steps between the raised polyamine pool and the progenitor phenotype are not established.

Show evidence (4 references)

PMID:31249027 SUPPORT In Vitro

"In this study, we show that primary dermal fibroblasts derived from a skin biopsy of a 3-year-old patient contain large amounts of ODC protein and putrescine compared with primary dermal (neonatal and adult) fibroblast control cells."

Direct measurement of putrescine accumulation in patient-derived cells.

PMID:40382142 SUPPORT Human Clinical

"ODC is a key enzyme of polyamine biosynthesis by converting ornithine to putrescine, and if accumulated, can lead to high putrescine levels in human cells including red blood cells (RBCs) and primary dermal fibroblasts."

States that accumulated ODC leads to high putrescine in patient cell types.

PMID:30475435 PARTIAL Human Clinical

"Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels."

Marked PARTIAL and included as the specificity boundary on this node: the accumulation is putrescine-selective, and spermidine and spermine are not raised in plasma. A generic "polyamine excess" reading of BABS would be wrong.

+ 1 more reference

Ornithine Substrate Depletion

Plasma ornithine sat below the 2.5th percentile of a paediatric reference cohort before treatment in the first treated patient and normalised on eflornithine, consistent with excess consumption by the overactive enzyme.

Show evidence (2 references)

PMID:34282722 SUPPORT Human Clinical

"Ornithine andN-acetylarginine were below the 2.5th percentile at start of therapy and normalized to the larger pediatric values over the course of therapy."

Documents the pre-treatment ornithine deficit and its correction on ODC inhibition, which is what makes substrate drawdown by the overactive enzyme the most parsimonious explanation. The snippet reproduces a missing-space text-extraction artefact present in the cached source ("andN-acetylarginine") and is quoted byte-exactly rather than tidied.

PMID:34282722 SUPPORT Human Clinical

"Urea cycle components citrulline and arginine, along with other metabolites, remained at 1 to -1 standard deviation throughout the study period"

Shows that the metabolomic disturbance is confined to the polyamine arm and does not extend to the urea cycle, which bounds the scope of this node.

Elevated N-Acetylputrescine

N-acetylputrescine is the clinically measurable signature of the accumulated putrescine pool and is the metabolite that makes metabolomic profiling diagnostically suggestive of BABS. Other polyamine levels may be normal.

Show evidence (2 references)

PMID:30475435 SUPPORT Human Clinical

"Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels."

Establishes the elevation and its selectivity within the polyamine panel.

PMID:36007106 SUPPORT Human Clinical

"The finding of abnormal polyamine pathway metabolites (including increased N-acetylputrescine) on metabolomic profiling is suggestive of a diagnosis of BABS."

GeneReviews makes this metabolite the biochemical entry point to the diagnosis.

Hair Follicle Dysfunction with Bulge Stem Cell Recruitment

Excess ODC activity in outer root sheath keratinocytes disrupts the hair cycle. In the C-terminally-truncated-ODC mouse the first hair cycle is normal and hair is then lost completely, matching the human natural history of hair present at birth followed by shedding.

outer root sheath cell CL:0002561

hair cycle GO:0042633 ⚠ ABNORMAL

Downstream

Follicular Cyst Formation Hair follicles that cannot complete the cycle give rise to dermal follicular cysts.

Show evidence (2 references)

PMID:8618048 SUPPORT Model Organism

"These transgenic mice have a normal first hair cycle, but lose their hair completely beginning 2-3 wk after birth."

Establishes the hair-cycle-specific timing of the defect in the model that carries the same class of lesion.

PMID:8618048 SUPPORT Model Organism

"Mice that overexpress a mutated ornithine decarboxylase (ODC) transgene in outer root sheath keratinocytes of the hair follicle were used to study the role of this enzyme in regulating hair follicle structure and function."

Identifies the outer root sheath keratinocyte as the cell type in which excess ODC produces the follicular phenotype.

Follicular Cyst Formation

Recurrent follicular cysts form on the scalp, neck and back, beginning as small maculopapular pustules and enlarging to several centimetres, sometimes requiring surgical removal.

Show evidence (2 references)

PMID:34282722 SUPPORT Human Clinical

"Multiple lesions located on the posterior scalp and back that first were small maculopapular pustules slowly increased in size to approximately 6-7 cm in diameter"

Describes the natural history and size of the cysts in a genotyped patient.

PMID:7671221 SUPPORT Model Organism

"Effects observed include development of dermal follicular cysts, excessive skin wrinkling, enhanced nail growth, alopecia, and spontaneous tumor development."

The original transgenic report lists dermal follicular cysts alongside alopecia and accelerated nail growth, the ectodermal cluster later recognised in BABS patients.

Dysregulated Neural Progenitor Proliferation

ODC1 expression during fetal brain development and in cerebral organoids associates with neural progenitor cell proliferation, and gain-of-function variants are proposed to produce neural over-proliferation. This node is the weakest link in the chain: the human neurodevelopmental phenotype is not yet mechanistically connected to a measured progenitor abnormality in BABS patient tissue.

neural progenitor cell CL:0011020

neural precursor cell proliferation GO:0061351 ⚠ ABNORMAL

Downstream

Abnormal Brain Development Disturbed progenitor proliferation is the proposed route to the structural and functional brain abnormalities, but the intermediates are unknown.

Show evidence (1 reference)

PMID:33806076 SUPPORT Computational

"The linkage from the expression data of ODC1 in early neural progenitor proliferation to phenotypes of neurodevelopmental delay and to the connection of polyamine metabolites in brain function establish ODC1 as a bona fide neurodevelopmental disorder gene."

States the inferential chain from progenitor proliferation to neurodevelopmental delay on which this node rests.

Abnormal Brain Development

Structural neuroimaging findings are variable and inconsistent across patients, and include white matter abnormalities, prominent Virchow-Robin spaces, periventricular and subependymal cysts, and corpus callosum abnormalities. Absolute or relative macrocephaly is common.

Show evidence (2 references)

PMID:30475435 SUPPORT Human Clinical

"Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."

Enumerates the structural findings that define this node.

PMID:34477286 PARTIAL Human Clinical

"Neuroimaging abnormalities continue to be an inconsistent feature of the syndrome."

Marked PARTIAL because it qualifies the finding as inconsistent rather than obligate, which is why no frequency band is assigned.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

26

Cardiovascular 1

Abnormal heart morphology Abnormal heart morphology HP:0001627

Show evidence (1 reference)

PMID:36007106 SUPPORT Human Clinical

"Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay /..."

Congenital heart defects are named among the manifestations requiring standard treatment.

Digestive 2

Feeding difficulties Feeding difficulties HP:0011968

Show evidence (2 references)

PMID:36007106 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."

GeneReviews lists feeding difficulties among the defining characteristics.

PMID:36007106 SUPPORT Human Clinical

"Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay /..."

The management recommendation reflects the clinical weight of the feeding problem.

Constipation Constipation HP:0002019

Show evidence (1 reference)

PMID:36007106 SUPPORT Human Clinical

"Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay /..."

GeneReviews management lists a full constipation treatment ladder, indicating this is an expected manifestation.

Ear 2

Conductive hearing impairment VERY_RARE Conductive hearing impairment HP:0000405

Show evidence (1 reference)

PMID:36007106 SUPPORT Human Clinical

"Rare findings may include seizures with onset in later childhood and conductive hearing loss."

GeneReviews explicitly classifies conductive hearing loss as a rare finding, mapping to VERY_RARE.

Sensorineural hearing impairment Sensorineural hearing impairment HP:0000407

Show evidence (2 references)

PMID:30239107 SUPPORT Human Clinical

"Phenotypic manifestations include macrosomia, macrocephaly, developmental delay, alopecia, spasticity, hypotonia, cutaneous vascular malformation, delayed visual maturation, and sensorineural hearing loss."

The index case report documents sensorineural, not conductive, hearing loss.

PMID:41925768 SUPPORT Human Clinical

"the ODC mutation is expressed in all tissues of BABS patients resulting in macrosomia, macrocephaly, neurodevelopmental delay, spasticity, hypotonia, delayed visual maturation, and sensorineural hearing loss"

A review restates sensorineural hearing loss among the multisystem consequences of ubiquitous expression of the mutant enzyme.

Eye 1

Strabismus Strabismus HP:0000486

Show evidence (1 reference)

PMID:36007106 SUPPORT Human Clinical

"Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay /..."

Strabismus is named among the manifestations requiring standard treatment.

Head and Neck 2

Macrocephaly Macrocephaly HP:0000256

Show evidence (2 references)

PMID:30475435 SUPPORT Human Clinical

"This disorder presents with global developmental delay, ectodermal abnormalities including alopecia, absolute or relative macrocephaly, and characteristic facial dysmorphisms."

Establishes that macrocephaly may be absolute or only relative to body size.

PMID:34477286 SUPPORT Human Clinical

"BABS is characterized by developmental delay, macrocephaly, macrosomia, and an unusual pattern of non-congenital alopecia."

Independent cohort listing macrocephaly among the defining features.

Dysmorphic facial features Abnormal facial shape HP:0001999

Show evidence (2 references)

PMID:36007106 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."

GeneReviews lists nonspecific dysmorphic features among the defining characteristics.

PMID:30475435 PARTIAL Human Clinical

"This disorder presents with global developmental delay, ectodermal abnormalities including alopecia, absolute or relative macrocephaly, and characteristic facial dysmorphisms."

Marked PARTIAL because this cohort calls the dysmorphisms characteristic whereas GeneReviews calls them nonspecific; the two sources disagree on specificity.

Integument 3

Alopecia VERY_FREQUENT Alopecia HP:0001596

Show evidence (4 references)

PMID:36007106 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."

GeneReviews places a distinctive alopecia first among the defining characteristics, which maps to the VERY_FREQUENT band under the GeneReviews prose-to-enum convention for a feature the disorder is "characterized by".

PMID:36007106 SUPPORT Human Clinical

"Hair is typically present at birth but may be sparse and of an unexpected color with subsequent loss of hair in large clumps within the first few weeks of life."

Gives the natural history that distinguishes this alopecia from congenital atrichia.

PMID:37469105 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (BABS) is a neurodevelopmental disorder characterized by developmental delay, hypotonia, and varying forms of non-congenital alopecia."

Independent review confirming the non-congenital character and variable form of the alopecia.

+ 1 more reference

Capillary malformation Capillary malformation HP:0025104

Show evidence (1 reference)

PMID:30239107 PARTIAL Human Clinical

"Phenotypic manifestations include macrosomia, macrocephaly, developmental delay, alopecia, spasticity, hypotonia, cutaneous vascular malformation, delayed visual maturation, and sensorineural hearing loss."

Marked PARTIAL because the report says "cutaneous vascular malformation" without specifying the vessel type, so the binding to a capillary malformation term is the closest available rather than an exact match.

Epidermoid cyst Epidermoid cyst HP:0200040

Show evidence (3 references)

PMID:36007106 SUPPORT Human Clinical

"Complete skin evaluation for follicular cysts at least annually."

GeneReviews makes annual follicular cyst surveillance a standing recommendation.

PMID:34282722 SUPPORT Human Clinical

"She had a history of recurring follicular cyst formation and enlargement."

Patient-level documentation of recurrent follicular cyst formation.

PMID:36443247 SUPPORT Human Clinical

"In both patients, treatment with difluoromethylornithine has resulted in improved dermatologic signs, including regrowth of eyebrow and scalp hair and cessation of recurrent follicular cyst development."

Two further genotyped patients with recurrent follicular cysts.

Musculoskeletal 2

Hypotonia VERY_FREQUENT Hypotonia HP:0001252

Show evidence (2 references)

PMID:36007106 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."

GeneReviews lists hypotonia among the defining characteristics, mapping to VERY_FREQUENT.

PMID:40167220 SUPPORT Human Clinical

"First described in 2018, Bachmann-Bupp Syndrome (BABS) is a rare neurodevelopmental disorder that is caused by gain-of-function variants in the ornithine decarboxylase (ODC1) gene and is characterized by developmental delay, hypotonia, and alopecia."

Independent confirmation of hypotonia as one of the three core clinical features.

Spasticity Spasticity HP:0001257

Show evidence (1 reference)

PMID:30239107 SUPPORT Human Clinical

"Phenotypic manifestations include macrosomia, macrocephaly, developmental delay, alopecia, spasticity, hypotonia, cutaneous vascular malformation, delayed visual maturation, and sensorineural hearing loss."

The index case report documents spasticity alongside hypotonia.

Nervous System 6

Global developmental delay VERY_FREQUENT Global developmental delay HP:0001263

Show evidence (3 references)

PMID:36007106 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."

GeneReviews names global developmental delay in the moderate to severe range as a defining characteristic, mapping to VERY_FREQUENT.

PMID:34282722 SUPPORT Human Clinical

"Prior to therapy, she had delayed development which manifested with no standing, cruising, or sitting, and limited fine motor skills."

Patient-level description of the functional severity of the delay before treatment.

PMID:30475435 SUPPORT Human Clinical

"This disorder presents with global developmental delay, ectodermal abnormalities including alopecia, absolute or relative macrocephaly, and characteristic facial dysmorphisms."

Independent four-patient cohort with global developmental delay as the leading feature.

Autistic behavior Autistic behavior HP:0000729

Show evidence (2 references)

PMID:36007106 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."

GeneReviews names autism spectrum disorder explicitly among the behavioural abnormalities.

PMID:36007106 SUPPORT Human Clinical

"Behavioral assessment for signs of autism spectrum disorder, attention, and aggressive or self-injurious behaviors annually."

The surveillance recommendation confirms autism spectrum disorder is expected frequently enough to warrant annual screening.

Attention deficit hyperactivity disorder Attention deficit hyperactivity disorder HP:0007018

Show evidence (1 reference)

PMID:36007106 SUPPORT Human Clinical

"Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."

GeneReviews names attention-deficit/hyperactivity disorder explicitly.

Seizure VERY_RARE Seizure HP:0001250

Show evidence (2 references)

PMID:36007106 SUPPORT Human Clinical

"Rare findings may include seizures with onset in later childhood and conductive hearing loss."

GeneReviews explicitly classifies seizures as a rare finding, which maps to the VERY_RARE band under the GeneReviews prose-to-enum convention.

PMID:34477286 SUPPORT Human Clinical

"Recent diagnosis of four more BABS patients provides further characterization of the phenotype of this syndrome including late-onset seizures in the oldest reported patient at 23 years of age, representing the first report for this phenotype in BABS."

Documents the single index observation of late-onset seizures in the published series.

Abnormal cerebral white matter morphology Abnormal cerebral white matter morphology HP:0002500

Show evidence (2 references)

PMID:30475435 SUPPORT Human Clinical

"Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."

Lists white matter abnormalities first among the neuroimaging findings.

PMID:34282722 SUPPORT Human Clinical

"A neonatal brain MRI showed abnormal cerebral white matter and subependymal cysts"

Patient-level neonatal MRI documentation of the white matter abnormality.

Abnormal corpus callosum morphology Abnormal corpus callosum morphology HP:0001273

Show evidence (1 reference)

PMID:30475435 SUPPORT Human Clinical

"Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."

Names corpus callosum abnormalities among the neuroimaging findings.

Growth 2

Macrosomia Overgrowth HP:0001548

Show evidence (2 references)

PMID:34477286 SUPPORT Human Clinical

"BABS is characterized by developmental delay, macrocephaly, macrosomia, and an unusual pattern of non-congenital alopecia."

Names macrosomia among the four defining features of the syndrome.

PMID:30239107 SUPPORT Human Clinical

"Phenotypic manifestations include macrosomia, macrocephaly, developmental delay, alopecia, spasticity, hypotonia, cutaneous vascular malformation, delayed visual maturation, and sensorineural hearing loss."

The index case report lists macrosomia first among the phenotypic manifestations.

Obesity Obesity HP:0001513

Show evidence (1 reference)

PMID:36007106 SUPPORT Human Clinical

"Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay /..."

GeneReviews management explicitly provides for nutritional intervention in those with obesity.

Other 5

Absent eyebrow Absent eyebrow HP:0002223

Show evidence (2 references)

PMID:34282722 SUPPORT Human Clinical

"One month into treatment, hair growth was noted, with eyebrows appearing first"

Eyebrow regrowth on treatment implies the pre-treatment absence of eyebrows in this genotyped patient.

PMID:36443247 SUPPORT Human Clinical

"In both patients, treatment with difluoromethylornithine has resulted in improved dermatologic signs, including regrowth of eyebrow and scalp hair and cessation of recurrent follicular cyst development."

Two further genotyped patients in whom eyebrow hair was absent and regrew on treatment.

Abnormal nail growth Abnormal nail growth HP:0030807

Show evidence (2 references)

PMID:41925768 SUPPORT Human Clinical

"Similar to the phenotypic abnormalities observed in K6/ODC transgenic mice, human patients with this ODC mutation also displayed alopecia, accelerated nail growth and skin cysts"

A review states that BABS patients, like the transgenic mice, show accelerated nail growth.

PMID:7671221 SUPPORT Model Organism

"Effects observed include development of dermal follicular cysts, excessive skin wrinkling, enhanced nail growth, alopecia, and spontaneous tumor development."

The corresponding mouse observation, recorded separately so the human and model evidence are not conflated.

Abnormality of refraction Abnormality of refraction HP:0000539

Show evidence (1 reference)

PMID:36007106 SUPPORT Human Clinical

"Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay /..."

Refractive error is named among the manifestations requiring standard treatment.

Dilation of Virchow-Robin spaces Dilation of Virchow-Robin spaces HP:0012520

Show evidence (1 reference)

PMID:30475435 SUPPORT Human Clinical

"Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."

Names prominent Virchow-Robin spaces among the neuroimaging findings.

Subependymal cysts Subependymal cysts HP:0002416

Show evidence (2 references)

PMID:34282722 SUPPORT Human Clinical

"A neonatal brain MRI showed abnormal cerebral white matter and subependymal cysts"

Documents subependymal cysts on the neonatal MRI of a genotyped patient.

PMID:30475435 PARTIAL Human Clinical

"Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."

Marked PARTIAL because this cohort describes the cysts as periventricular rather than specifically subependymal.

🧬

Genetic Associations

1

ODC1 (Causative)

Gene: ODC1 hgnc:8109 relationship_type: CAUSATIVE variant_origin: DE_NOVO

Autosomal dominant

Show evidence (7 references)

PMID:30239107 SUPPORT Human Clinical

"The ODC1 gene mutation (c.1342 A>T) was identified by whole-exome sequencing and confirmed by Sanger sequencing."

Names the index allele and the method by which it was identified and confirmed.

PMID:30475435 SUPPORT Human Clinical

"In this report, we present four patients with a distinct neurometabolic disorder associated with de novo heterozygous, gain-of-function variants in the ODC1 gene."

Independent replication establishing the gene-disease relationship in four further patients with de novo gain-of-function alleles.

PMID:36007106 SUPPORT Human Clinical

"Heterozygous pathogenic variants in ODC1 that cause BABS are typically gain-of-function variants."

GeneReviews states the direction of effect explicitly, which is the single most important fact to preserve when reading ODC1 literature.

+ 4 more references

💊

Medical Actions

4

Eflornithine (difluoromethylornithine, DFMO)

Action: Pharmacotherapy NCIT:C15986

Agent: eflornithine CHEBI:41948

Eflornithine is an irreversible ODC inhibitor and the mechanism-matched targeted therapy for BABS. It was repurposed from its existing indications (West African trypanosomiasis, paediatric neuroblastoma maintenance, and hirsutism) and first given to a BABS patient under a single-patient FDA Investigational New Drug application, 16 months after the syndrome was first published. The index regimen was an oral solution given by gastrostomy tube at 500 mg/m2 twice daily, escalated to 750 and then 1000 mg/m2 twice daily, alongside a low-polyamine diet. Reported outcomes include hair regrowth beginning with the eyebrows at one month, immediate cessation of follicular cyst formation, increased muscle bulk and tone, acquisition of head control, unsupported sitting and self-feeding, and normalisation of cerebral white matter signal with resolution of subependymal cysts on MRI. Eflornithine is not an FDA-approved treatment for BABS and remains a compassionate-use therapy. Paediatric dosing and safety were taken from the neuroblastoma maintenance literature rather than from any BABS trial.

Mechanism Target:

INHIBITS Elevated ODC Enzyme Activity — Eflornithine irreversibly inhibits ODC, so it suppresses the catalytic activity of the accumulated truncated enzyme rather than restoring its degradation.

Show evidence (1 reference)

PMID:31249027 SUPPORT In Vitro

"Exposure of primary dermal fibroblasts to ODC inhibitor α-difluoromethylornithine (DFMO) reduced the ODC activity and putrescine to levels observed in controls without adversely affecting cell morphology or inducing cell death."

Demonstrates in the patient's own cells that DFMO normalises the raised enzyme activity without cytotoxicity.

INHIBITS Putrescine Accumulation — Inhibiting the enzyme lowers the putrescine pool and its measurable acetylated derivative back toward the reference range.

Show evidence (1 reference)

PMID:34282722 SUPPORT Human Clinical

"Eflornithine normalized polyamine levels without disrupting other pathways."

In-patient confirmation that the drug corrects the polyamine disturbance selectively.

INHIBITS Hair Follicle Dysfunction with Bulge Stem Cell Recruitment — Suppressing follicular ODC activity restores hair growth, an effect first shown in the truncated-ODC mouse and then reproduced in patients.

Show evidence (1 reference)

PMID:8618048 SUPPORT Model Organism

"2-Difluoromethylornithine could also reactivate hair growth in animals with complete hair loss."

The model result that motivated trying the drug in patients with established alopecia.

Show evidence (10 references)

PMID:34282722 SUPPORT Human Clinical

"Eflornithine normalized polyamine levels without disrupting other pathways. She demonstrated remarkable improvement in both neurological symptoms and cortical architecture. She gained fine motor skills with the capacity to feed herself and sit with support."

The primary treated-patient report, giving biochemical, neurological and functional outcomes in the first patient treated.

PMID:34282722 SUPPORT Human Clinical

"At age 4 years and 8 months, we started eflornithine (Sanofi Aventis) treatment with 500 mg/m2/dose bid twice daily via a gastrostomy tube along with a low polyamine diet on November 14, 2019, for 3 months, increasing to 750 mg/m2/dose twice daily, and a final increase to 1000 mg/m2/dose twice..."

Documents the actual regimen, route and escalation schedule used in the index treated case.

PMID:34282722 SUPPORT Human Clinical

"Dosing was based on what had been demonstrated to be safe in pediatric patients in maintenance therapy for neuroblastoma treated with eflornithine (Saulnier Sholler et al., 2015)."

Records that the paediatric dose and safety basis was borrowed from the neuroblastoma maintenance literature, not generated in BABS.

+ 7 more references

Low-polyamine diet

Action: Dietary Intervention NCIT:C15447

Dietary restriction of polyamines was given alongside eflornithine in the index treated patient. It has never been tested as monotherapy in BABS, and the review literature raises dietary intervention and gut-flora-directed antibiotics only as candidate approaches to lowering putrescine.

Mechanism Target:

INHIBITS Putrescine Accumulation — Reducing dietary and gut-derived polyamine input is intended to lower the systemic putrescine burden.

Show evidence (1 reference)

PMID:30475435 PARTIAL Human Clinical

"Therapies aimed at reducing putrescine levels, including ODC1 inhibitors, dietary interventions, and antibiotics to reduce polyamine production by gastrointestinal flora could be considered as disease-modifying therapies."

Marked PARTIAL because this is a proposal for what could be considered, not a report of a tested dietary intervention.

Show evidence (1 reference)

PMID:34282722 PARTIAL Human Clinical

"At age 4 years and 8 months, we started eflornithine (Sanofi Aventis) treatment with 500 mg/m2/dose bid twice daily via a gastrostomy tube along with a low polyamine diet on November 14, 2019, for 3 months, increasing to 750 mg/m2/dose twice daily, and a final increase to 1000 mg/m2/dose twice..."

Marked PARTIAL because the diet was co-administered with eflornithine, so no independent effect can be attributed to it.

Supportive and symptom-directed management

Action: Supportive Care NCIT:C15747

Standard multidisciplinary care for the individual manifestations: feeding therapy with a low threshold for gastrostomy placement, nutritional intervention for obesity, a constipation ladder of stool softeners, prokinetics, osmotic agents and laxatives, and standard treatment for epilepsy, developmental delay and intellectual disability, refractive error, strabismus, hearing loss, follicular cysts and congenital heart defects.

Show evidence (2 references)

PMID:36007106 SUPPORT Human Clinical

"Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay /..."

The GeneReviews management paragraph is the source for every element of this supportive-care package.

PMID:36007106 SUPPORT Human Clinical

"Ophthalmology and audiology evaluations annually or as clinically indicated."

Specifies the recommended sensory surveillance cadence.

Genetic counseling

Action: Genetic Counseling NCIT:C15240

BABS is autosomal dominant and typically de novo, so the recurrence risk to other family members is presumed low. Once the familial ODC1 variant is known, prenatal and preimplantation genetic testing are possible.

Show evidence (1 reference)

PMID:36007106 SUPPORT Human Clinical

"Therefore, the risk to other family members is presumed to be low. Once an ODC1 pathogenic variant has been identified in an affected family member, prenatal testing and preimplantation genetic testing are possible."

GeneReviews states the recurrence-risk counselling message and the reproductive testing options.

🔬

Biochemical Markers

3

Elevated plasma N-acetylputrescine (INCREASED)

Show evidence (3 references)

PMID:30475435 SUPPORT Human Clinical

"Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels."

Establishes the elevation in plasma and its selectivity within the polyamine panel.

PMID:34282722 SUPPORT Human Clinical

"N-acetylputrescine, the only polyamine that meets CAP/CLIA standards in this analysis, served as the primary indicator of putrescine levels."

Explains why this metabolite, rather than putrescine itself, is the clinical readout.

PMID:36007106 SUPPORT Human Clinical

"The finding of abnormal polyamine pathway metabolites (including increased N-acetylputrescine) on metabolomic profiling is suggestive of a diagnosis of BABS."

GeneReviews uses this metabolite as the biochemical trigger for genetic confirmation.

Elevated erythrocyte and fibroblast ODC enzyme activity (INCREASED)

Show evidence (2 references)

PMID:31249027 SUPPORT In Vitro

"Importantly, the accumulated ODC protein variant remained functionally active as we detected exceptionally high ODC enzyme activity in both primary dermal fibroblasts (12-17-fold of controls) and red blood cells (RBCs) (125-137-fold of controls), using a specific 14C radioactive ODC activity assay."

Supplies the quantitative fold-change and the assay used.

PMID:40382142 SUPPORT Human Clinical

"Here we describe how to quantitatively measure ODC enzymatic activity and the polyamines by a radiolabeled 14C-ornithine assay and by reverse phase (RP)-HPLC, respectively."

Documents the standardised protocol for measuring the enzyme activity and polyamines in BABS patient samples.

Elevated erythrocyte polyamines (INCREASED)

Show evidence (1 reference)

PMID:30239107 SUPPORT Human Clinical

"Red blood cells obtained from our patient showed elevated ODC protein and polyamine levels compared to healthy controls."

Direct measurement of raised polyamines in a patient's circulating cells.

🔀

Differential Diagnoses

6

Conditions with similar clinical presentations that must be differentiated from Bachmann-Bupp Syndrome:

Alopecia-intellectual disability syndrome 4 (LSS-related) Not Yet Curated MONDO:0030009

Overlapping Features The closest clinical mimic outside the polyamine pathway, and the one that matters most at the bedside: a recessive neuroectodermal syndrome caused by biallelic LSS (lanosterol synthase) variants that pairs alopecia with intellectual disability or developmental delay, exactly the pairing that defines the BABS gestalt. The discriminator is the timing of the hair loss. In LSS-related disease the alopecia is CONGENITAL - total alopecia with sparse eyelashes and eyebrows is present at birth - whereas in BABS hair is typically present at birth and is then shed in large clumps within the first weeks of life. LSS disease is also autosomal recessive, frequently epileptic, and often accompanied by ichthyosis or erythroderma, and it sits in cholesterol rather than polyamine biosynthesis, so the BABS biochemical signature of raised N-acetylputrescine is absent and eflornithine is not rational therapy.

Distinguishing Features

Caused by biallelic LSS (lanosterol synthase) variants, not by ODC1
Autosomal recessive, not de novo autosomal dominant
Alopecia is CONGENITAL and total at birth, whereas BABS hair is present at birth and shed in clumps within weeks - this is the single most useful discriminator
Early-onset epilepsy is frequent, whereas seizures are a rare and typically late-onset finding in BABS
Ichthyosis and erythroderma are common; the BABS skin phenotype is recurrent follicular cysts
Cholesterol-biosynthesis rather than polyamine-pathway disorder, so ODC activity, putrescine and N-acetylputrescine are not elevated
Microcephaly is reported rather than the macrocephaly and macrosomia of BABS

Show evidence (3 references)

PMID:30723320 SUPPORT Human Clinical

"It is a rare autosomal recessive condition characterized by hypotrichosis and intellectual disability (ID) or developmental delay (DD), frequently associated with early-onset epilepsy and other dermatological features."

Gives the inheritance mode and the alopecia-plus-developmental-delay core that make this the closest non-polyaminopathy mimic of BABS.

PMID:30723320 SUPPORT Human Clinical

"Total alopecia with sparse eyelashes and eyebrows was noted at birth in all affected individuals."

Establishes the congenital timing of the alopecia, the discriminator against the non-congenital clump shedding of BABS.

PMID:36007106 SUPPORT Human Clinical

"Hair is typically present at birth but may be sparse and of an unexpected color with subsequent loss of hair in large clumps within the first few weeks of life."

The BABS side of the same discriminator, stated by GeneReviews: hair is present at birth and lost afterwards.

Snyder-Robinson syndrome Not Yet Curated MONDO:0010664

Overlapping Features The first-described and best-known polyaminopathy, and the disorder whose prior research the BABS team explicitly credits with accelerating BABS from discovery to treatment. It shares intellectual disability and hypotonia with BABS, and its literature uses the same polyamine-pathway vocabulary, so mechanism sentences are easily misattributed between the two. It is separated from BABS by the affected enzyme (spermine synthase, several steps downstream of ODC), by the direction of effect (loss of function, not gain), and by X-linked hemizygous rather than autosomal dominant transmission. Alopecia is not its presenting feature.

Distinguishing Features

Caused by SMS (spermine synthase), not ODC1
Loss-of-function with decreased or absent enzyme activity, the opposite direction of effect to the ODC1 gain of function in BABS
X-linked, affecting hemizygous males, rather than de novo autosomal dominant
Osteoporosis, kyphoscoliosis, unsteady gait and facial asymmetry dominate; the non-congenital clump alopecia and macrocephaly/macrosomia of BABS are not its core
No ODC inhibitor therapy - inhibiting ODC would worsen an already spermine-deficient pathway

Show evidence (2 references)

PMID:41410504 SUPPORT Human Clinical

"Snyder-Robinson syndrome results from hemizygous loss-of-function variants in the spermine synthase (SMS) gene, resulting in decreased or complete loss of spermine synthase enzyme activity."

Gives the gene, the zygosity and the direction of effect that separate Snyder-Robinson syndrome from BABS.

PMID:37092498 SUPPORT Human Clinical

"Recent identification of four additional polyaminopathies, including Bachmann-Bupp syndrome, have benefited from previous research on Snyder-Robinson syndrome in order to advance from research to treatment more quickly."

Documents the direct research lineage between the two disorders, which is precisely why their literatures are intertwined and confusable.

Faundes-Banka syndrome Not Yet Curated MONDO:0859163

Overlapping Features A polyaminopathy of the hypusination arm of the pathway, caused by heterozygous loss-of-function variants in EIF5A. Like BABS it is a heterozygous, recently described neurodevelopmental polyaminopathy, so the two are routinely tabulated side by side and their "heterozygous variants in a polyamine-pathway gene" framing is easy to conflate. The discriminators are the gene, the direction of effect (loss, not gain), and the affected step: EIF5A acts on eIF5A hypusination downstream of spermidine, not on polyamine synthesis itself, so ODC activity and putrescine are not elevated and eflornithine is not rational therapy.

Distinguishing Features

Caused by EIF5A, not ODC1
Loss-of-function impairing eIF5A protein function, not gain-of-function enzyme stabilisation
Affects the hypusination branch downstream of spermidine rather than the rate-limiting decarboxylation step
No elevated ODC activity, no putrescine or N-acetylputrescine elevation, so the BABS biochemical signature is absent
The BABS non-congenital clump alopecia is not a feature

Show evidence (2 references)

PMID:41410504 SUPPORT Human Clinical

"Faundes-Banka syndrome results from heterozygous loss-of-function variants in the eukaryotic translation initiation factor 5A (EIF5A) gene, impairing eIF5A protein function."

Gives the gene and the direction of effect that separate Faundes-Banka syndrome from BABS.

PMID:41410504 SUPPORT Human Clinical

"The five known syndromes associated with the polyamine pathway share many similar clinical phenotypes, and yet patients with each syndrome present with distinctive syndromic features."

Establishes that the five polyaminopathies overlap clinically, which is the condition under which their evidence gets mixed up.

Deoxyhypusine synthase (DHPS) deficiency Not Yet Curated MONDO:0032775

Overlapping Features An autosomal recessive polyaminopathy caused by bi-allelic hypomorphic DHPS variants. It sits on the same hypusination branch as Faundes-Banka syndrome and, like BABS, presents as a Mendelian neurodevelopmental disorder with seizures and developmental impairment, so it appears in the same polyaminopathy tables. It is separated from BABS by the gene, by recessive rather than dominant inheritance, and by reduced rather than increased enzyme activity.

Distinguishing Features

Caused by DHPS (deoxyhypusine synthase), not ODC1
Autosomal recessive with bi-allelic hypomorphic variants, not de novo heterozygous
Reduced enzyme activity, the opposite direction of effect to BABS
Acts on the spermidine-dependent hypusination of eIF5A rather than on polyamine synthesis, so putrescine and N-acetylputrescine are not the diagnostic signature
Seizures and speech and walking impairment define the phenotype; the BABS alopecia and macrocephaly/macrosomia combination is not its core

Show evidence (1 reference)

PMID:41410504 SUPPORT Human Clinical

"DHPS (deoxyhypusine synthase) deficiency is an autosomal recessive disease and results from bi-allelic hypomorphic variants in the deoxyhypusine synthase (DHPS) gene, which results in reduced deoxyhypusine synthase enzyme activity."

Gives the gene, the inheritance mode and the direction of effect that separate DHPS deficiency from BABS.

Deoxyhypusine hydroxylase (DOHH) disorder Not Yet Curated MONDO:0859293

Overlapping Features The fifth recognised polyaminopathy, caused by bi-allelic loss-of-function DOHH variants, and the second step of the hypusination branch. It is the newest member of the family and is grouped with BABS in every polyaminopathy review, which is the setting in which its findings can be misattributed. It is separated from BABS by the gene, by autosomal recessive inheritance, by decreased rather than increased enzyme activity, and by a microcephaly-with-cerebral-atrophy brain phenotype that is close to the inverse of the BABS macrocephaly.

Distinguishing Features

Caused by DOHH (deoxyhypusine hydroxylase), not ODC1
Autosomal recessive bi-allelic loss of function, not de novo heterozygous gain of function
Decreased enzyme activity, the opposite direction of effect to BABS
Microcephaly with cerebral atrophy and visual impairment, the inverse of the absolute or relative macrocephaly and macrosomia of BABS
Hypusination branch, so no ODC/putrescine elevation and no rationale for an ODC inhibitor

Show evidence (1 reference)

PMID:41410504 SUPPORT Human Clinical

"Finally, DOHH (deoxyhypusine hydroxylase) disorder is an autosomal recessive disorder caused by bi-allelic loss-of-function variants in the deoxyhypusine hydroxylase (DOHH) gene, which causes decreased deoxyhypusine hydroxylase enzyme activity."

Gives the gene, the inheritance mode and the direction of effect that separate DOHH disorder from BABS.

ODC1 loss-of-function neurological phenotype

Overlapping Features The single most dangerous confusion for this entry, because it involves the same gene. Hypomorphic and loss-of-function ODC1 alleles, exemplified by the G84R missense variant present in roughly 1 percent of South Asian individuals and reducing enzyme function 2.5-fold, have been connected to intellectual disability and seizures. This is NOT Bachmann-Bupp syndrome: the direction of effect is opposite, the predicted consequence for neural progenitors is depletion rather than over-proliferation, the ODC-activity and putrescine elevations that define BABS are absent, and inhibiting ODC with eflornithine would be expected to aggravate rather than treat it. Importing ODC1 knockout or loss-of-function findings into a BABS mechanism graph is the specific error this differential exists to prevent.

Distinguishing Features

Same gene as BABS, so gene-level literature searches return both
Loss of function or hypomorphic missense (for example G84R) rather than C-terminal truncation
Reduced ODC enzyme activity, so the 12-17-fold fibroblast and 125-137-fold red cell activity elevations of BABS are absent
Predicted neural progenitor depletion rather than over-proliferation
Not associated with the BABS alopecia, macrocephaly or macrosomia
Eflornithine, the BABS therapy, would be mechanistically contraindicated

Show evidence (3 references)

PMID:33806076 SUPPORT Computational

"An analysis of variants from ClinVar, Geno2MP, TOPMed, gnomAD, and COSMIC revealed an intellectual disability and seizure connected loss-of-function variant, ODC G84R (rs138359527, NC_000002.12:g.10444500C > T)."

Identifies the loss-of-function allele and the neurological phenotype connected to it.

PMID:33806076 SUPPORT Computational

"The missense variant is found in ~1% of South Asian individuals and results in 2.5-fold decrease in enzyme function."

Quantifies the direction and magnitude of the functional change, which is the opposite of the BABS gain of function.

PMID:33806076 SUPPORT Computational

"Further dissection of RNA-Seq during fetal brain development and within cerebral organoids showed an association of ODC1 expression with cell proliferation of neural progenitor cells, suggesting gain-of-function variants with neural over-proliferation and loss-of-function variants with neural depletion."

States that the two allele classes have opposite predicted consequences for neural progenitors, which is the mechanistic reason they must not be merged.

{ }

Source YAML

click to show

name: Bachmann-Bupp Syndrome
creation_date: '2026-08-01T00:00:00Z'
category: Mendelian
synonyms:
- BABS
- NEDABA
- neurodevelopmental disorder with alopecia and brain abnormalities
- global developmental delay-alopecia-macrocephaly-facial dysmorphism-structural brain
  anomalies syndrome
description: >-
  Bachmann-Bupp syndrome (BABS) is an ultra-rare autosomal dominant
  neurodevelopmental disorder caused by de novo heterozygous variants at the
  3-prime end of ODC1 that truncate the carboxy terminus of ornithine
  decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis. The
  mechanism is gain of function, not loss of function: the truncated enzyme
  remains catalytically active but loses the C-terminal degron required for
  ubiquitin-independent, antizyme-mediated proteasomal turnover, so ODC protein
  accumulates and cellular ODC activity rises by one to two orders of magnitude,
  driving putrescine accumulation. The clinical picture combines a distinctive
  non-congenital alopecia (hair present at birth, then shed in clumps), global
  developmental delay in the moderate to severe range, hypotonia, absolute or
  relative macrocephaly, macrosomia, nonspecific facial dysmorphism, recurrent
  follicular cysts, feeding difficulties and behavioural abnormalities, with
  variable and inconsistent structural neuroimaging findings. BABS is one of the
  few neurodevelopmental disorders with a mechanism-matched repurposed therapy:
  the ODC inhibitor eflornithine (alpha-difluoromethylornithine, DFMO), given on
  a compassionate-use basis, has produced hair regrowth, cessation of follicular
  cyst formation, improved muscle tone and developmental gains in treated
  patients.
disease_term:
  preferred_term: Bachmann-Bupp syndrome
  term:
    id: MONDO:0033642
    label: neurodevelopmental disorder with alopecia and brain abnormalities
parents:
- Disorder of polyamine metabolism
- Mendelian neurodevelopmental disorder
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:36007106
      reference_title: Bachmann-Bupp Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The diagnosis is established in a proband with suggestive findings and a heterozygous pathogenic variant in ODC1 identified by molecular genetic testing."
      explanation: >-
        A monogenic disorder established by molecular genetic testing of a single
        gene belongs to the genetics chapter.
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:37469105
      reference_title: Bachmann-Bupp syndrome and treatment.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Bachmann-Bupp syndrome (BABS) is a neurodevelopmental disorder characterized by developmental delay, hypotonia, and varying forms of non-congenital alopecia."
      explanation: >-
        The disease-specific review classifies BABS as a neurodevelopmental
        disorder with developmental delay and hypotonia as core features.
  - classification_value: DERMATOLOGY
    evidence:
    - reference: PMID:36443247
      reference_title: Improvement of dermatological symptoms in patients with Bachmann-Bupp
        syndrome using difluoromethylornithine treatment.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In both patients, treatment with difluoromethylornithine has resulted in improved dermatologic signs, including regrowth of eyebrow and scalp hair and cessation of recurrent follicular cyst development."
      explanation: >-
        Alopecia and recurrent follicular cysts are defining, often presenting
        manifestations that are managed dermatologically.
  - classification_value: ENDOCRINOLOGY_METABOLISM
    evidence:
    - reference: PMID:30475435
      reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic
        neurodevelopmental disorder associated with macrocephaly, alopecia, dysmorphic
        features, and neuroimaging abnormalities.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In this report, we present four patients with a distinct neurometabolic disorder associated with de novo heterozygous, gain-of-function variants in the ODC1 gene."
      explanation: >-
        The index cohort report characterises BABS as a neurometabolic disorder
        of endogenous polyamine synthesis.
  icimd_category:
  - classification_value: polyamine_metabolism
    evidence:
    - reference: PMID:41410504
      reference_title: "Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Bachmann-Bupp syndrome results from heterozygous gain-of-function variants in the ornithine decarboxylase 1 (ODC1) gene, resulting in increased ornithine decarboxylase enzyme activity."
      explanation: >-
        The polyaminopathy review places BABS within the family of disorders of
        polyamine metabolism.
notes: >-
  Scope, provenance and named-entity-confusion notes for this entry.


  (1) GeneReviews baseline. A GeneReviews chapter exists (PMID:36007106,
  "Bachmann-Bupp Syndrome", Bupp, Michael, VanSickle, Rajasekaran and Bachmann,
  2022 Aug 25) and was used as the mandatory phenotype baseline. Every clinical
  feature named in its Clinical Characteristics paragraph is represented in
  the phenotypes block: the distinctive alopecia, global developmental delay in
  the moderate to severe range, hypotonia, nonspecific dysmorphic features,
  behavioural abnormalities (autism spectrum disorder and
  attention-deficit/hyperactivity disorder are curated as two separate
  phenotype entries), feeding difficulties, the birth-hair-then-clump-loss
  natural history, and the rare findings of later-childhood seizures and
  conductive hearing loss. Features named only in its Management paragraph
  (obesity, constipation, refractive error, strabismus, follicular cysts,
  congenital heart defects) are also curated, sourced to that same paragraph.
  Nothing in the GeneReviews abstract is knowingly omitted. The cached record
  is the structured PubMed abstract, not the full chapter body, so features
  present only in the chapter body may still be missing.


  (2) Named-entity-confusion discipline - this is the central risk for ODC1.
  ODC1 is a heavily studied oncology and polyamine-pharmacology gene, and the
  overwhelming majority of its literature is cancer biology, DFMO
  chemoprevention or basic polyamine metabolism with no bearing on this
  neurodevelopmental disorder. Every citation in this entry was checked to be
  either (a) about genotyped human BABS patients, (b) the disease-specific
  review literature from the International Center for Polyamine Disorders, or
  (c) the C-terminally-truncated-ODC animal model that is the accepted
  mechanistic model of this exact lesion. No chemoprevention trial (colorectal
  adenoma, skin cancer) and no neuroblastoma efficacy trial is cited as
  evidence for a BABS claim; the neuroblastoma literature is referred to only
  where the BABS papers themselves invoke it as the source of the paediatric
  dose and safety data, and that is stated explicitly in the eflornithine
  treatment entry rather than cited directly.


  (3) The direction-of-effect trap. BABS is a GAIN-of-function disorder. ODC1
  knockout and loss-of-function data must not be imported as if they modelled
  the patient state, and none is. The one loss-of-function observation that is
  curated (the ODC G84R hypomorph in PMID:33806076) is deliberately modelled as
  a differential-diagnosis entry and as a contrast, never as support for a BABS
  mechanism, because the same paper reports that the two directions have
  opposite predicted consequences for neural progenitors: gain-of-function with
  over-proliferation and loss-of-function with depletion. Likewise the mouse
  evidence used here is the K6/ODC transgenic, which carries a premature stop
  codon producing a carboxyl-truncated, stabilised ODC - the same class of
  lesion as the human variants - and not an Odc1 null.


  (4) Mouse-model fidelity and its limits. The K6/ODC mouse (PMID:8618048,
  reviewed in PMID:41925768) reproduces the alopecia and follicular cysts and
  their reversal with DFMO, and was the direct basis for the drug-repurposing
  decision. It is a keratin-6-promoter-driven, skin-restricted transgenic,
  whereas BABS patients express the truncated enzyme in every tissue, so it
  models only the cutaneous arm. All neurodevelopmental claims in this entry
  therefore rest on human evidence, and the mouse evidence carries
  evidence_source MODEL_ORGANISM and is confined to the hair-follicle and
  follicular-cyst nodes.


  (5) Frequency derivation. Frequency bands are recorded on only five
  phenotypes and are omitted everywhere else. The five that carry a band are
  derived from GeneReviews qualitative language using the standard
  prose-to-FrequencyEnum mapping: features the chapter says the syndrome "is
  characterized by" (alopecia, global developmental delay, hypotonia) take
  VERY_FREQUENT, and features it explicitly calls "rare findings" (later-onset
  seizures, conductive hearing loss) take VERY_RARE. No numeric denominator
  underlies these bands. The published case denominators are tiny and
  inconsistent: PMID:30475435 reported four patients, PMID:30239107 one,
  PMID:34477286 four more, PMID:37092498 two more, and PMID:34282722 described
  the cohort as "less than 10 known cases". The deep-research report surfaced a
  per-feature frequency table (n=9) from the body of the GeneReviews chapter,
  giving alopecia 9/9, dysmorphic features 9/9, developmental delay 8/8,
  hypotonia 8/8, macrocephaly 6/9 and seizures 1/8. Those numbers are
  consistent with the bands recorded here, but the cached PubMed record for
  PMID:36007106 contains only the structured abstract, so the table itself
  could not be verified byte-exactly and its numbers are therefore NOT asserted
  as evidence anywhere in this entry. A future curator with access to the full
  chapter should be able to upgrade these bands to denominator-backed ones.


  (5a) Two phenotypes that the deep-research report supports but this entry
  does NOT curate, because no cached abstract contains a quotable sentence for
  them. Polyhydramnios (reported at 55-80% of pregnancies) and the HPO
  annotation set for OMIM:619075 (hypertelorism, high forehead, sparse
  eyelashes, cryptorchidism, ptosis and others) are both real and both
  well-attested in the sources the report cites, but grepping every cached
  reference used by this entry for "polyhydramnios" returns zero hits, and the
  HPOA annotations are database records rather than quotable abstract text.
  They are omitted rather than sourced to a citation that does not contain
  them. This is a recorded gap, not a claim that the evidence does not exist.


  (6) Prevalence derivation. No population-based rate has ever been published.
  The prevalence record therefore uses the qualitative ULTRA_RARE tier with the
  case-count denominators recorded in its notes. The counts themselves conflict
  across sources and are not summed into a single asserted total.


  (7) No structured-source (ORPHA:544488, CGGV, CGDS) citation is included.
  Neither an ORPHA_544488 nor any ClinGen cache file for ODC1 is present in
  references_cache, and generating one would require a data MANIFEST bump,
  which is blocked by the stale, un-refreshable pins tracked in #7622. The
  structured-source citation is skipped rather than fabricated.


  (8) Two claims that are true in the literature but are NOT asserted here for
  lack of a quotable BABS-specific source. First, an exact number of reported
  BABS patients: the sources disagree and none of the cached abstracts states a
  current cumulative total, so no total is asserted. Second, an oncology
  surveillance recommendation: PMID:30475435 raises cancer surveillance only as
  a suggestion ("cancer surveillance may be important in this disorder") and the
  GeneReviews surveillance paragraph does not include tumour screening, so this
  is curated as a discussion item and an explicitly hedged treatment note
  rather than as a recommendation.


  (9) Prenatal presentation. PMID:41931584 reports a prenatally diagnosed BABS
  fetus with macrocephaly and a ventricular septal defect. That record has no
  abstract in PubMed - fetching it yields only a bibliographic header with no
  quotable body - so it is not cited for any evidence item and its cache file
  is deliberately not committed. The congenital heart defect phenotype is
  instead sourced to the GeneReviews management paragraph, which does list
  congenital heart defects. The same applies to PMID:34318586 (LSS
  hypotrichosis families), which also has no abstract; the LSS differential is
  therefore sourced to PMID:30723320 instead.


  (10) Scope of differential_diagnoses. Six differentials are modelled. The
  four other recognised polyaminopathies (Snyder-Robinson syndrome,
  Faundes-Banka syndrome, DHPS deficiency and DOHH disorder) are bound to MONDO
  terms, because PMID:41410504 explicitly groups all five as one family that
  "share many similar clinical phenotypes" - which is exactly the setting in
  which evidence gets misattributed. Each is discriminated by its gene, its
  direction of effect and its position in the polyamine pathway. LSS-related
  alopecia-intellectual disability syndrome 4 is bound as the closest mimic
  outside the pathway, discriminated on congenital versus non-congenital
  alopecia. The sixth, the ODC1 loss-of-function/hypomorphic neurological
  phenotype, is left UNBOUND: it is the single most dangerous confusion for
  this entry because it involves the same gene, but it has no OMIM entry and no
  MONDO term of its own, so binding it to any existing term would be a
  fabrication. Note that MONDO:0800159 (disorder of polyamine metabolism) and
  MONDO:0100500 (Mendelian neurodevelopmental disorder) are this entry's own
  asserted superclasses and are therefore deliberately absent from the
  differential list. Four further differentials named in the GeneReviews
  differential table and relayed by the deep-research report (CHD3 / Snijders
  Blok-Campeau syndrome, DCAF17 / Woodhouse-Sakati syndrome, PAK1 / IDDMSSD and
  PTEN / Cowden syndrome) are NOT modelled here, because that table lives in the
  chapter body and not in the cached abstract, so no verbatim discriminating
  sentence is available for any of them from a reference this entry cites. They
  are named here so the next curator knows where to look rather than having to
  rediscover them.


  (11) Provenance of this entry. The deep-research provider was claude_code,
  run via `just research-disorder claude_code Bachmann-Bupp_Syndrome` on
  2026-08-01 (report at
  research/Bachmann-Bupp_Syndrome-deep-research-claude_code.md; 8 web searches,
  77 turns, 38 citations). The report was read in full and treated as leads
  rather than ground truth: every PMID it supplied was fetched with
  `just fetch-reference` and every snippet used here was copy-pasted from the
  cached file. Claims the report made that could not be verified against a
  cached abstract - the GeneReviews frequency table, the GeneReviews
  differential table, the cumulative case counts of 12 published / 18 worldwide
  across eight countries, polyhydramnios frequencies, ClinVar accessions and
  the full variant table - are recorded in these notes as leads and are not
  asserted as evidence anywhere in the entry.
inheritance:
- name: Autosomal dominant
  description: >-
    Heterozygous ODC1 variants are sufficient; reported cases have been de novo,
    so recurrence risk to siblings is presumed low.
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BABS is expressed in an autosomal dominant manner and typically caused by a de novo ODC1 pathogenic variant."
    explanation: >-
      GeneReviews states the autosomal dominant mode and the de novo origin of
      the causative variant.
  - reference: PMID:36443247
    reference_title: Improvement of dermatological symptoms in patients with Bachmann-Bupp
      syndrome using difluoromethylornithine treatment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (OMIM #619075) is a novel autosomal dominant disorder caused by variants in the c-terminus of the ornithine decarboxylase 1 gene, resulting in increased levels of ornithine decarboxylase."
    explanation: >-
      Independent confirmation of autosomal dominant transmission and of the
      C-terminal location of the causative variants.
- name: De novo occurrence
  description: >-
    All reported probands have carried de novo heterozygous ODC1 variants rather
    than inherited alleles.
  inheritance_term:
    preferred_term: Sporadic
    term:
      id: HP:0003745
      label: Sporadic
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this report, we present four patients with a distinct neurometabolic disorder associated with de novo heterozygous, gain-of-function variants in the ODC1 gene."
    explanation: >-
      A four-patient cohort in which every causative allele arose de novo.
prevalence:
- population: Worldwide, published cases
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Derivation: only case-level denominators exist and no population-based rate
    has ever been published, so no rate_per_100000 is recorded. PMID:30239107
    (2018) described the index patient; PMID:30475435 (2018) described four
    patients; PMID:34477286 (2021) added four more; PMID:37092498 (2023) added
    two more; PMID:34282722 (2021) described the condition as "less than 10
    known cases" at that time. The individual reports overlap and the reviews do
    not state a reconciled cumulative total, so the counts are recorded here
    rather than summed into an asserted number, and the qualitative ULTRA_RARE
    tier is used.
  evidence:
  - reference: PMID:37469105
    reference_title: Bachmann-Bupp syndrome and treatment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BABS is an ultra-rare condition with few reported cases, but it serves as a convincing example for drug repurposing therapy."
    explanation: >-
      The disease-specific review characterises BABS as ultra-rare with few
      reported cases.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The novel treatment of this ultra-rare (less than 10 known cases) genetic syndrome presented unique challenges for monitoring efficacy over time."
    explanation: >-
      Supplies the explicit published denominator underpinning the ultra-rare
      tier at the time of the first treated case.
  - reference: PMID:37092498
    reference_title: Two New Cases of Bachmann-Bupp Syndrome Identified through the International
      Center for Polyamine Disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This case study provides insights from two new patients diagnosed with Bachmann-Bupp syndrome, further expanding our understanding of this ultra-rare condition, as well as a general discussion about other known polyaminopathies."
    explanation: >-
      An incremental two-patient addition to the published series, again
      described as ultra-rare.
pathophysiology:
- name: ODC1 C-Terminal Truncating Variant
  biological_scale: MOLECULAR
  description: >-
    A de novo heterozygous variant at the 3-prime end of ODC1 introduces a
    premature stop codon in the last exon, removing the carboxy-terminal
    residues of ornithine decarboxylase. The variants cluster in this region
    across reported patients, and the index allele c.1342A>T removes the last
    14 amino acids.
  genes:
  - preferred_term: ODC1
    term:
      id: hgnc:8109
      label: ODC1
    modifier: ABNORMAL
  evidence:
  - reference: PMID:37469105
    reference_title: Bachmann-Bupp syndrome and treatment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The condition is caused by 3'-end mutations of the ornithine decarboxylase 1 (ODC1) gene, which produce carboxy (C)-terminally truncated variants of ODC, a pyridoxal 5'-phosphate-dependent enzyme."
    explanation: >-
      Names the location of the causative variants and the protein consequence
      that defines this node.
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we report an 32-month-old Caucasian female with a heterozygous de novo nonsense mutation in the ODC1 gene that leads to a premature abrogation of 14-aa residues at the ODC protein c-terminus."
    explanation: >-
      The index case defines the specific lesion: a de novo nonsense variant
      truncating the last 14 residues.
  - reference: PMID:34477286
    reference_title: "Expanding the phenotype: Four new cases and hope for treatment in Bachmann-Bupp syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Variants continue to cluster, providing support to a universal biochemical mechanism related to elevated ODC protein, enzyme activity, and abnormalities in polyamine levels."
    explanation: >-
      Establishes that the reported variants cluster in one region and converge
      on a single biochemical mechanism.
  - reference: PMID:40382142
    reference_title: Monitoring ODC activity and polyamines in Bachmann-Bupp syndrome
      patient biological samples.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ODC1 gene mutations that are linked to BABS always produce C-terminally truncated versions of the enzyme ornithine decarboxylase (ODC)."
    explanation: >-
      States that C-terminal truncation is an invariant feature of the BABS
      allele spectrum.
  downstream:
  - target: Escape from Antizyme-Mediated Proteasomal Degradation
    description: >-
      Loss of the C-terminal degron removes the signal that normally targets ODC
      for ubiquitin-independent proteasomal turnover.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37469105
      reference_title: Bachmann-Bupp syndrome and treatment.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "C-terminal truncation of ODC prevents its ubiquitin-independent proteasomal degradation and leads to cellular accumulation of ODC enzyme that remains catalytically active."
      explanation: >-
        Directly links the C-terminal truncation to failure of the degradation
        route.
- name: Escape from Antizyme-Mediated Proteasomal Degradation
  biological_scale: MOLECULAR
  description: >-
    Wild-type ODC is one of the shortest-lived mammalian proteins because its
    C-terminus acts as a degron for ubiquitin-independent, antizyme-dependent
    proteasomal degradation. The truncated BABS enzyme cannot be cleared by this
    route, so it escapes normal turnover. This is a stability defect, not a
    catalytic defect.
  biological_processes:
  - preferred_term: proteasomal ubiquitin-independent protein catabolic process
    term:
      id: GO:0010499
      label: proteasomal ubiquitin-independent protein catabolic process
    modifier: DECREASED
  evidence:
  - reference: PMID:40382142
    reference_title: Monitoring ODC activity and polyamines in Bachmann-Bupp syndrome
      patient biological samples.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These shortened ODC proteins remain enzymatically active and are not cleared by the proteasome, therefore leading to ODC protein accumulation in cells."
    explanation: >-
      States both halves of this node: preserved catalysis and failed
      proteasomal clearance.
  - reference: PMID:31249027
    reference_title: Biochemical features of primary cells from a pediatric patient with
      a gain-of-function ODC1 genetic mutation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We hypothesized that this new mutation (c.1342 A>T) leads to a C-terminal truncation variant of the ODC protein that is resistant to normal proteasomal degradation, leading to putrescine accumulation in cells."
    explanation: >-
      States the degradation-resistance hypothesis that the same study then
      tested in patient-derived cells.
  - reference: PMID:41925768
    reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "a premature stop codon at position 427 in the mouse ODC cDNA was placed downstream of the K6 promoter resulting in a carboxyl-truncated ODC protein with a much longer in vivo half-life than the full-length ODC protein"
    explanation: >-
      The engineered mouse allele demonstrates that C-terminal truncation alone
      extends the half-life of the ODC protein.
  - reference: PMID:2928784
    reference_title: Prevention of rapid intracellular degradation of ODC by a carboxyl-terminal
      truncation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Ornithine decarboxylase (ODC) was converted from a protein with a short intracellular half-life in mammalian cells to a stable protein by truncating 37 residues at its carboxyl terminus."
    explanation: >-
      The founding experiment: removing the C-terminal 37 residues converts ODC
      from a short-lived to a stable protein. This is, three decades early, an
      in vitro pre-enactment of the human BABS lesion.
  - reference: PMID:2928784
    reference_title: Prevention of rapid intracellular degradation of ODC by a carboxyl-terminal
      truncation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Thus, a carboxyl-terminal domain is responsible for the rapid intracellular degradation of murine ODC."
    explanation: >-
      Localises the degradation signal to the carboxyl-terminal domain, the
      domain that BABS variants delete.
  - reference: PMID:1334232
    reference_title: Ornithine decarboxylase is degraded by the 26S proteasome without
      ubiquitination.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In addition, purified 26S proteasome complex, but not the 20S proteasome, catalyses ODC degradation in the absence of ubiquitin."
    explanation: >-
      Identifies the specific proteolytic route that the truncation escapes:
      26S-proteasomal degradation without ubiquitination.
  - reference: PMID:1334232
    reference_title: Ornithine decarboxylase is degraded by the 26S proteasome without
      ubiquitination.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We have shown that its degradation is accelerated by ODC antizyme, an inhibitory protein induced by polyamines."
    explanation: >-
      Establishes antizyme as the accelerator of ODC turnover, the regulatory
      arm that a C-terminally truncated enzyme is insensitive to.
  downstream:
  - target: ODC Protein Accumulation
    description: >-
      A protein that cannot be degraded accumulates in the cell.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:40382142
      reference_title: Monitoring ODC activity and polyamines in Bachmann-Bupp syndrome
        patient biological samples.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "These shortened ODC proteins remain enzymatically active and are not cleared by the proteasome, therefore leading to ODC protein accumulation in cells."
      explanation: >-
        Names failed proteasomal clearance as the direct cause of ODC protein
        accumulation.
- name: ODC Protein Accumulation
  biological_scale: CELLULAR
  description: >-
    Stabilised ODC protein accumulates to large excess in patient cells,
    demonstrated in primary dermal fibroblasts and in red blood cells.
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  - preferred_term: erythrocyte
    term:
      id: CL:0000232
      label: erythrocyte
  evidence:
  - reference: PMID:31249027
    reference_title: Biochemical features of primary cells from a pediatric patient with
      a gain-of-function ODC1 genetic mutation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In this study, we show that primary dermal fibroblasts derived from a skin biopsy of a 3-year-old patient contain large amounts of ODC protein and putrescine compared with primary dermal (neonatal and adult) fibroblast control cells."
    explanation: >-
      Direct measurement of accumulated ODC protein in patient-derived
      fibroblasts.
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Red blood cells obtained from our patient showed elevated ODC protein and polyamine levels compared to healthy controls."
    explanation: >-
      Confirms ODC protein accumulation in a second, circulating patient cell
      type.
  downstream:
  - target: Elevated ODC Enzyme Activity
    description: >-
      Because the accumulated protein retains catalytic competence, more enzyme
      means proportionally more activity.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31249027
      reference_title: Biochemical features of primary cells from a pediatric patient
        with a gain-of-function ODC1 genetic mutation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Importantly, the accumulated ODC protein variant remained functionally active as we detected exceptionally high ODC enzyme activity in both primary dermal fibroblasts (12-17-fold of controls) and red blood cells (RBCs) (125-137-fold of controls), using a specific 14C radioactive ODC activity assay."
      explanation: >-
        Quantifies the step from accumulated protein to elevated catalytic
        activity in two patient cell types.
- name: Elevated ODC Enzyme Activity
  biological_scale: MOLECULAR
  description: >-
    Cellular ornithine decarboxylase activity is raised by one to two orders of
    magnitude, 12-17-fold in patient fibroblasts and 125-137-fold in patient red
    blood cells. ODC is the first, rate-limiting step of polyamine biosynthesis,
    so this is the point at which pathway flux is deregulated.
  molecular_functions:
  - preferred_term: ornithine decarboxylase activity
    term:
      id: GO:0004586
      label: ornithine decarboxylase activity
    modifier: INCREASED
  biological_processes:
  - preferred_term: polyamine biosynthetic process
    term:
      id: GO:0006596
      label: polyamine biosynthetic process
    modifier: INCREASED
  evidence:
  - reference: PMID:31249027
    reference_title: Biochemical features of primary cells from a pediatric patient with
      a gain-of-function ODC1 genetic mutation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Importantly, the accumulated ODC protein variant remained functionally active as we detected exceptionally high ODC enzyme activity in both primary dermal fibroblasts (12-17-fold of controls) and red blood cells (RBCs) (125-137-fold of controls), using a specific 14C radioactive ODC activity assay."
    explanation: >-
      Quantifies the magnitude of the enzyme-activity gain in patient material.
  - reference: PMID:41410504
    reference_title: "Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome results from heterozygous gain-of-function variants in the ornithine decarboxylase 1 (ODC1) gene, resulting in increased ornithine decarboxylase enzyme activity."
    explanation: >-
      The polyaminopathy review states increased enzyme activity as the defining
      biochemical consequence.
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ornithine decarboxylase 1 (ODC1) is the rate-limiting enzyme in endogenous polyamine synthesis."
    explanation: >-
      Establishes why a change in ODC activity controls flux through the whole
      polyamine pathway.
  downstream:
  - target: Putrescine Accumulation
    description: >-
      ODC converts ornithine to putrescine; excess enzyme activity drives
      putrescine accumulation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:40382142
      reference_title: Monitoring ODC activity and polyamines in Bachmann-Bupp syndrome
        patient biological samples.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "ODC is a key enzyme of polyamine biosynthesis by converting ornithine to putrescine, and if accumulated, can lead to high putrescine levels in human cells including red blood cells (RBCs) and primary dermal fibroblasts."
      explanation: >-
        Names the reaction and the direct consequence of enzyme accumulation.
  - target: Ornithine Substrate Depletion
    description: >-
      Sustained excess flux through the decarboxylation step draws down the
      ornithine pool.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34282722
      reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
        variant disease.
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "Ornithine andN-acetylarginine were below the 2.5th percentile at start of therapy and normalized to the larger pediatric values over the course of therapy."
      explanation: >-
        Marked PARTIAL because the metabolomic study shows the ornithine deficit
        and its reversal on ODC inhibition but does not directly prove that
        substrate consumption by the overactive enzyme is the mechanism.
- name: Putrescine Accumulation
  biological_scale: MOLECULAR
  description: >-
    Putrescine, the immediate product of ODC, accumulates in patient cells. It is
    the proximate biochemical lesion of BABS and the target of eflornithine
    therapy.
  chemical_entities:
  - preferred_term: putrescine
    term:
      id: CHEBI:17148
      label: putrescine
    modifier: INCREASED
  evidence:
  - reference: PMID:31249027
    reference_title: Biochemical features of primary cells from a pediatric patient with
      a gain-of-function ODC1 genetic mutation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In this study, we show that primary dermal fibroblasts derived from a skin biopsy of a 3-year-old patient contain large amounts of ODC protein and putrescine compared with primary dermal (neonatal and adult) fibroblast control cells."
    explanation: >-
      Direct measurement of putrescine accumulation in patient-derived cells.
  - reference: PMID:40382142
    reference_title: Monitoring ODC activity and polyamines in Bachmann-Bupp syndrome
      patient biological samples.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ODC is a key enzyme of polyamine biosynthesis by converting ornithine to putrescine, and if accumulated, can lead to high putrescine levels in human cells including red blood cells (RBCs) and primary dermal fibroblasts."
    explanation: >-
      States that accumulated ODC leads to high putrescine in patient cell
      types.
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels."
    explanation: >-
      Marked PARTIAL and included as the specificity boundary on this node: the
      accumulation is putrescine-selective, and spermidine and spermine are not
      raised in plasma. A generic "polyamine excess" reading of BABS would be
      wrong.
  - reference: PMID:9563478
    reference_title: Polyamines regulate expression of the neoplastic phenotype in mouse
      skin.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The regulatory polyamine in this model appears to be putrescine, the immediate product of ornithine decarboxylase."
    explanation: >-
      In the truncated-ODC mouse, putrescine rather than spermidine or spermine
      is the effector species, matching the putrescine-selective human
      biochemical signature.
  downstream:
  - target: Elevated N-Acetylputrescine
    description: >-
      Excess putrescine is acetylated, and it is the acetylated species that is
      measurable on clinical metabolomic profiling.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30475435
      reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
        disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
        abnormalities.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels."
      explanation: >-
        Identifies N-acetylputrescine as the acetylated derivative of the
        accumulated putrescine pool.
  - target: Hair Follicle Dysfunction with Bulge Stem Cell Recruitment
    description: >-
      Elevated follicular polyamines disrupt the hair cycle and recruit bulge
      stem cells out of quiescence.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:8618048
      reference_title: Modulation of murine hair follicle function by alterations in ornithine
        decarboxylase activity.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Our results suggest that ODC is an important regulatory gene for the mouse hair follicle."
      explanation: >-
        The targeted-truncated-ODC mouse establishes ODC activity as a regulator
        of hair follicle function.
    - reference: PMID:41925768
      reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "This was the first definitive evidence that elevated epidermal polyamine levels alone can stimulate the recruitment of bulge stem cells which are then activated to give rise to a hierarchy of transit amplifying cells."
      explanation: >-
        Shows that raised polyamine levels alone suffice to recruit hair-follicle
        bulge stem cells.
  - target: Dysregulated Neural Progenitor Proliferation
    description: >-
      ODC1 expression tracks neural progenitor proliferation in fetal brain and
      cerebral organoids; gain of function is proposed to drive
      over-proliferation. The steps between the raised polyamine pool and the
      progenitor phenotype are not established.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33806076
      reference_title: Emerging Role of ODC1 in Neurodevelopmental Disorders and Brain
        Development.
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: "Further dissection of RNA-Seq during fetal brain development and within cerebral organoids showed an association of ODC1 expression with cell proliferation of neural progenitor cells, suggesting gain-of-function variants with neural over-proliferation and loss-of-function variants with neural depletion."
      explanation: >-
        Transcriptomic analysis links ODC1 level to neural progenitor
        proliferation and explicitly separates the gain-of-function from the
        loss-of-function direction.
- name: Ornithine Substrate Depletion
  biological_scale: MOLECULAR
  description: >-
    Plasma ornithine sat below the 2.5th percentile of a paediatric reference
    cohort before treatment in the first treated patient and normalised on
    eflornithine, consistent with excess consumption by the overactive enzyme.
  chemical_entities:
  - preferred_term: L-ornithine
    term:
      id: CHEBI:15729
      label: L-ornithine
    modifier: DECREASED
  evidence:
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ornithine andN-acetylarginine were below the 2.5th percentile at start of therapy and normalized to the larger pediatric values over the course of therapy."
    explanation: >-
      Documents the pre-treatment ornithine deficit and its correction on ODC
      inhibition, which is what makes substrate drawdown by the overactive
      enzyme the most parsimonious explanation. The snippet reproduces a
      missing-space text-extraction artefact present in the cached source
      ("andN-acetylarginine") and is quoted byte-exactly rather than tidied.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Urea cycle components citrulline and arginine, along with other metabolites, remained at 1 to -1 standard deviation throughout the study period"
    explanation: >-
      Shows that the metabolomic disturbance is confined to the polyamine arm
      and does not extend to the urea cycle, which bounds the scope of this
      node.
- name: Elevated N-Acetylputrescine
  biological_scale: MOLECULAR
  description: >-
    N-acetylputrescine is the clinically measurable signature of the accumulated
    putrescine pool and is the metabolite that makes metabolomic profiling
    diagnostically suggestive of BABS. Other polyamine levels may be normal.
  chemical_entities:
  - preferred_term: N-acetylputrescine
    term:
      id: CHEBI:17768
      label: N-acetylputrescine
    modifier: INCREASED
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels."
    explanation: >-
      Establishes the elevation and its selectivity within the polyamine panel.
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The finding of abnormal polyamine pathway metabolites (including increased N-acetylputrescine) on metabolomic profiling is suggestive of a diagnosis of BABS."
    explanation: >-
      GeneReviews makes this metabolite the biochemical entry point to the
      diagnosis.
- name: Hair Follicle Dysfunction with Bulge Stem Cell Recruitment
  biological_scale: TISSUE
  description: >-
    Excess ODC activity in outer root sheath keratinocytes disrupts the hair
    cycle. In the C-terminally-truncated-ODC mouse the first hair cycle is
    normal and hair is then lost completely, matching the human natural history
    of hair present at birth followed by shedding.
  cell_types:
  - preferred_term: outer root sheath cell
    term:
      id: CL:0002561
      label: outer root sheath cell
  biological_processes:
  - preferred_term: hair cycle
    term:
      id: GO:0042633
      label: hair cycle
    modifier: ABNORMAL
  evidence:
  - reference: PMID:8618048
    reference_title: Modulation of murine hair follicle function by alterations in ornithine
      decarboxylase activity.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These transgenic mice have a normal first hair cycle, but lose their hair completely beginning 2-3 wk after birth."
    explanation: >-
      Establishes the hair-cycle-specific timing of the defect in the model that
      carries the same class of lesion.
  - reference: PMID:8618048
    reference_title: Modulation of murine hair follicle function by alterations in ornithine
      decarboxylase activity.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mice that overexpress a mutated ornithine decarboxylase (ODC) transgene in outer root sheath keratinocytes of the hair follicle were used to study the role of this enzyme in regulating hair follicle structure and function."
    explanation: >-
      Identifies the outer root sheath keratinocyte as the cell type in which
      excess ODC produces the follicular phenotype.
  downstream:
  - target: Follicular Cyst Formation
    description: >-
      Hair follicles that cannot complete the cycle give rise to dermal
      follicular cysts.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:8618048
      reference_title: Modulation of murine hair follicle function by alterations in ornithine
        decarboxylase activity.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Transgene overexpression in follicular keratinocytes is first detected at day 12 after birth, coincident with the development of follicular cysts in the upper portion of the dermis."
      explanation: >-
        Ties the onset of follicular ODC overexpression to the appearance of
        dermal follicular cysts.
    - reference: PMID:41925768
      reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "These sustained high levels of polyamine biosynthesis in K6/ODC mouse skin lead to hair loss beginning at 3 weeks of age when the second cycle of hair growth begins followed by the subsequent development of follicular dermal cysts"
      explanation: >-
        Places hair loss and follicular cyst formation in sequence downstream of
        sustained polyamine excess.
- name: Follicular Cyst Formation
  biological_scale: TISSUE
  description: >-
    Recurrent follicular cysts form on the scalp, neck and back, beginning as
    small maculopapular pustules and enlarging to several centimetres, sometimes
    requiring surgical removal.
  evidence:
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Multiple lesions located on the posterior scalp and back that first were small maculopapular pustules slowly increased in size to approximately 6-7 cm in diameter"
    explanation: >-
      Describes the natural history and size of the cysts in a genotyped
      patient.
  - reference: PMID:7671221
    reference_title: Increased frequency of spontaneous skin tumors in transgenic mice
      which overexpress ornithine decarboxylase.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Effects observed include development of dermal follicular cysts, excessive skin wrinkling, enhanced nail growth, alopecia, and spontaneous tumor development."
    explanation: >-
      The original transgenic report lists dermal follicular cysts alongside
      alopecia and accelerated nail growth, the ectodermal cluster later
      recognised in BABS patients.
- name: Dysregulated Neural Progenitor Proliferation
  biological_scale: CELLULAR
  description: >-
    ODC1 expression during fetal brain development and in cerebral organoids
    associates with neural progenitor cell proliferation, and gain-of-function
    variants are proposed to produce neural over-proliferation. This node is the
    weakest link in the chain: the human neurodevelopmental phenotype is not yet
    mechanistically connected to a measured progenitor abnormality in BABS
    patient tissue.
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  biological_processes:
  - preferred_term: neural precursor cell proliferation
    term:
      id: GO:0061351
      label: neural precursor cell proliferation
    modifier: ABNORMAL
  evidence:
  - reference: PMID:33806076
    reference_title: Emerging Role of ODC1 in Neurodevelopmental Disorders and Brain Development.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "The linkage from the expression data of ODC1 in early neural progenitor proliferation to phenotypes of neurodevelopmental delay and to the connection of polyamine metabolites in brain function establish ODC1 as a bona fide neurodevelopmental disorder gene."
    explanation: >-
      States the inferential chain from progenitor proliferation to
      neurodevelopmental delay on which this node rests.
  downstream:
  - target: Abnormal Brain Development
    description: >-
      Disturbed progenitor proliferation is the proposed route to the structural
      and functional brain abnormalities, but the intermediates are unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34477286
      reference_title: "Expanding the phenotype: Four new cases and hope for treatment in Bachmann-Bupp syndrome."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "This may be related to the yet unknown impact of ODC/polyamine dysregulation on the developing brain in this syndrome."
      explanation: >-
        Marked PARTIAL because the authors explicitly describe the link between
        polyamine dysregulation and the developing brain as not yet known.
- name: Abnormal Brain Development
  biological_scale: TISSUE
  description: >-
    Structural neuroimaging findings are variable and inconsistent across
    patients, and include white matter abnormalities, prominent Virchow-Robin
    spaces, periventricular and subependymal cysts, and corpus callosum
    abnormalities. Absolute or relative macrocephaly is common.
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."
    explanation: >-
      Enumerates the structural findings that define this node.
  - reference: PMID:34477286
    reference_title: "Expanding the phenotype: Four new cases and hope for treatment in Bachmann-Bupp syndrome."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging abnormalities continue to be an inconsistent feature of the syndrome."
    explanation: >-
      Marked PARTIAL because it qualifies the finding as inconsistent rather
      than obligate, which is why no frequency band is assigned.
phenotypes:
- name: Alopecia
  category: Dermatologic
  description: >-
    The distinctive BABS alopecia is non-congenital. Hair is typically present at
    birth, may be sparse and of an unexpected colour, and is then lost in large
    clumps within the first few weeks of life. The index patient was born with a
    full head of silver-blond hair and became essentially hairless. Reported
    severity ranges up to alopecia universalis.
  phenotype_term:
    preferred_term: Alopecia
    term:
      id: HP:0001596
      label: Alopecia
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."
    explanation: >-
      GeneReviews places a distinctive alopecia first among the defining
      characteristics, which maps to the VERY_FREQUENT band under the
      GeneReviews prose-to-enum convention for a feature the disorder is
      "characterized by".
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hair is typically present at birth but may be sparse and of an unexpected color with subsequent loss of hair in large clumps within the first few weeks of life."
    explanation: >-
      Gives the natural history that distinguishes this alopecia from congenital
      atrichia.
  - reference: PMID:37469105
    reference_title: Bachmann-Bupp syndrome and treatment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (BABS) is a neurodevelopmental disorder characterized by developmental delay, hypotonia, and varying forms of non-congenital alopecia."
    explanation: >-
      Independent review confirming the non-congenital character and variable
      form of the alopecia.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was born with a full head of silver-blond hair similar to a previously described murine phenotype (Soler et al., 1996), which fell out in early months and she remained hairless other than a few scattered, long hairs on the scalp."
    explanation: >-
      Patient-level description of the birth hair, its unusual colour and the
      subsequent loss.
- name: Absent eyebrow
  category: Dermatologic
  description: >-
    Eyebrow involvement is part of the ectodermal phenotype: eyebrows are absent
    or sparse and are the first hair to return on eflornithine, reappearing at
    one month of treatment.
  phenotype_term:
    preferred_term: Absent eyebrow
    term:
      id: HP:0002223
      label: Absent eyebrow
  evidence:
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One month into treatment, hair growth was noted, with eyebrows appearing first"
    explanation: >-
      Eyebrow regrowth on treatment implies the pre-treatment absence of
      eyebrows in this genotyped patient.
  - reference: PMID:36443247
    reference_title: Improvement of dermatological symptoms in patients with Bachmann-Bupp
      syndrome using difluoromethylornithine treatment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In both patients, treatment with difluoromethylornithine has resulted in improved dermatologic signs, including regrowth of eyebrow and scalp hair and cessation of recurrent follicular cyst development."
    explanation: >-
      Two further genotyped patients in whom eyebrow hair was absent and
      regrew on treatment.
- name: Abnormal nail growth
  category: Dermatologic
  description: >-
    Accelerated nail growth has been reported in BABS patients, mirroring the
    enhanced nail growth of the truncated-ODC transgenic mouse. HPO has no
    accelerated-nail-growth term, so the general abnormal-nail-growth term is
    used.
  phenotype_term:
    preferred_term: Accelerated nail growth
    term:
      id: HP:0030807
      label: Abnormal nail growth
  evidence:
  - reference: PMID:41925768
    reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Similar to the phenotypic abnormalities observed in K6/ODC transgenic mice, human patients with this ODC mutation also displayed alopecia, accelerated nail growth and skin cysts"
    explanation: >-
      A review states that BABS patients, like the transgenic mice, show
      accelerated nail growth.
  - reference: PMID:7671221
    reference_title: Increased frequency of spontaneous skin tumors in transgenic mice
      which overexpress ornithine decarboxylase.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Effects observed include development of dermal follicular cysts, excessive skin wrinkling, enhanced nail growth, alopecia, and spontaneous tumor development."
    explanation: >-
      The corresponding mouse observation, recorded separately so the human and
      model evidence are not conflated.
- name: Global developmental delay
  category: Neurologic
  description: >-
    Global developmental delay in the moderate to severe range is a defining
    feature. Before treatment the index patient could not stand, cruise or sit
    and had limited fine motor skills.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."
    explanation: >-
      GeneReviews names global developmental delay in the moderate to severe
      range as a defining characteristic, mapping to VERY_FREQUENT.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prior to therapy, she had delayed development which manifested with no standing, cruising, or sitting, and limited fine motor skills."
    explanation: >-
      Patient-level description of the functional severity of the delay before
      treatment.
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This disorder presents with global developmental delay, ectodermal abnormalities including alopecia, absolute or relative macrocephaly, and characteristic facial dysmorphisms."
    explanation: >-
      Independent four-patient cohort with global developmental delay as the
      leading feature.
- name: Hypotonia
  category: Neurologic
  description: >-
    Hypotonia is a defining feature and one of the manifestations that improves
    with eflornithine.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."
    explanation: >-
      GeneReviews lists hypotonia among the defining characteristics, mapping to
      VERY_FREQUENT.
  - reference: PMID:40167220
    reference_title: "Repurposing With Purpose: Treatment of Bachmann-Bupp Syndrome With Eflornithine and Implications for Other Polyaminopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "First described in 2018, Bachmann-Bupp Syndrome (BABS) is a rare neurodevelopmental disorder that is caused by gain-of-function variants in the ornithine decarboxylase (ODC1) gene and is characterized by developmental delay, hypotonia, and alopecia."
    explanation: >-
      Independent confirmation of hypotonia as one of the three core clinical
      features.
- name: Macrocephaly
  category: Growth
  description: >-
    Absolute or relative macrocephaly is characteristic and was the ultrasound
    finding that prompted prenatal suspicion in at least one reported fetus.
  phenotype_term:
    preferred_term: Macrocephaly
    term:
      id: HP:0000256
      label: Macrocephaly
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This disorder presents with global developmental delay, ectodermal abnormalities including alopecia, absolute or relative macrocephaly, and characteristic facial dysmorphisms."
    explanation: >-
      Establishes that macrocephaly may be absolute or only relative to body
      size.
  - reference: PMID:34477286
    reference_title: "Expanding the phenotype: Four new cases and hope for treatment in Bachmann-Bupp syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BABS is characterized by developmental delay, macrocephaly, macrosomia, and an unusual pattern of non-congenital alopecia."
    explanation: >-
      Independent cohort listing macrocephaly among the defining features.
- name: Macrosomia
  category: Growth
  description: >-
    Overgrowth with increased birth size and body size is reported alongside
    macrocephaly.
  phenotype_term:
    preferred_term: Overgrowth
    term:
      id: HP:0001548
      label: Overgrowth
  evidence:
  - reference: PMID:34477286
    reference_title: "Expanding the phenotype: Four new cases and hope for treatment in Bachmann-Bupp syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BABS is characterized by developmental delay, macrocephaly, macrosomia, and an unusual pattern of non-congenital alopecia."
    explanation: >-
      Names macrosomia among the four defining features of the syndrome.
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Phenotypic manifestations include macrosomia, macrocephaly, developmental delay, alopecia, spasticity, hypotonia, cutaneous vascular malformation, delayed visual maturation, and sensorineural hearing loss."
    explanation: >-
      The index case report lists macrosomia first among the phenotypic
      manifestations.
- name: Dysmorphic facial features
  category: Craniofacial
  description: >-
    Facial dysmorphism is consistently reported but nonspecific; GeneReviews
    describes the features as nonspecific while the four-patient cohort called
    them characteristic.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."
    explanation: >-
      GeneReviews lists nonspecific dysmorphic features among the defining
      characteristics.
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "This disorder presents with global developmental delay, ectodermal abnormalities including alopecia, absolute or relative macrocephaly, and characteristic facial dysmorphisms."
    explanation: >-
      Marked PARTIAL because this cohort calls the dysmorphisms characteristic
      whereas GeneReviews calls them nonspecific; the two sources disagree on
      specificity.
- name: Autistic behavior
  category: Behavioral
  description: >-
    Autism spectrum disorder is one of the behavioural abnormalities named in the
    GeneReviews clinical characteristics and is a standing surveillance item.
  phenotype_term:
    preferred_term: Autistic behavior
    term:
      id: HP:0000729
      label: Autistic behavior
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."
    explanation: >-
      GeneReviews names autism spectrum disorder explicitly among the
      behavioural abnormalities.
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Behavioral assessment for signs of autism spectrum disorder, attention, and aggressive or self-injurious behaviors annually."
    explanation: >-
      The surveillance recommendation confirms autism spectrum disorder is
      expected frequently enough to warrant annual screening.
- name: Attention deficit hyperactivity disorder
  category: Behavioral
  description: >-
    Attention-deficit/hyperactivity disorder is the second behavioural
    abnormality named in the GeneReviews clinical characteristics.
  phenotype_term:
    preferred_term: Attention deficit hyperactivity disorder
    term:
      id: HP:0007018
      label: Attention deficit hyperactivity disorder
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."
    explanation: >-
      GeneReviews names attention-deficit/hyperactivity disorder explicitly.
- name: Feeding difficulties
  category: Gastrointestinal
  description: >-
    Feeding difficulties are a defining feature and warrant a low threshold for
    formal feeding evaluation or gastrostomy tube placement. The first treated
    patient received eflornithine via a gastrostomy tube.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bachmann-Bupp syndrome (BABS) is characterized by a distinctive type of alopecia, global developmental delay in the moderate to severe range, hypotonia, nonspecific dysmorphic features, behavioral abnormalities (autism spectrum disorder, attention-deficit/hyperactivity disorder) and feeding difficulties."
    explanation: >-
      GeneReviews lists feeding difficulties among the defining characteristics.
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay / intellectual disability, refractive error, strabismus, hearing loss, follicular cysts, and congenital heart defects."
    explanation: >-
      The management recommendation reflects the clinical weight of the feeding
      problem.
- name: Seizure
  category: Neurologic
  description: >-
    Seizures are a rare finding with onset in later childhood. The oldest
    reported patient developed seizures at 23 years of age, the first report of
    this phenotype in BABS.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  frequency: VERY_RARE
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Rare findings may include seizures with onset in later childhood and conductive hearing loss."
    explanation: >-
      GeneReviews explicitly classifies seizures as a rare finding, which maps
      to the VERY_RARE band under the GeneReviews prose-to-enum convention.
  - reference: PMID:34477286
    reference_title: "Expanding the phenotype: Four new cases and hope for treatment in Bachmann-Bupp syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Recent diagnosis of four more BABS patients provides further characterization of the phenotype of this syndrome including late-onset seizures in the oldest reported patient at 23 years of age, representing the first report for this phenotype in BABS."
    explanation: >-
      Documents the single index observation of late-onset seizures in the
      published series.
- name: Conductive hearing impairment
  category: Otologic
  description: >-
    Conductive hearing loss is listed by GeneReviews as a rare finding.
  phenotype_term:
    preferred_term: Conductive hearing impairment
    term:
      id: HP:0000405
      label: Conductive hearing impairment
  frequency: VERY_RARE
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Rare findings may include seizures with onset in later childhood and conductive hearing loss."
    explanation: >-
      GeneReviews explicitly classifies conductive hearing loss as a rare
      finding, mapping to VERY_RARE.
- name: Sensorineural hearing impairment
  category: Otologic
  description: >-
    Sensorineural hearing loss was reported in the index patient. GeneReviews
    names only conductive hearing loss among the rare findings, so the two
    mechanisms are curated separately.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Phenotypic manifestations include macrosomia, macrocephaly, developmental delay, alopecia, spasticity, hypotonia, cutaneous vascular malformation, delayed visual maturation, and sensorineural hearing loss."
    explanation: >-
      The index case report documents sensorineural, not conductive, hearing
      loss.
  - reference: PMID:41925768
    reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the ODC mutation is expressed in all tissues of BABS patients resulting in macrosomia, macrocephaly, neurodevelopmental delay, spasticity, hypotonia, delayed visual maturation, and sensorineural hearing loss"
    explanation: >-
      A review restates sensorineural hearing loss among the multisystem
      consequences of ubiquitous expression of the mutant enzyme.
- name: Spasticity
  category: Neurologic
  description: >-
    Spasticity was documented in the index patient and is restated in the review
    literature as part of the multisystem phenotype.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Phenotypic manifestations include macrosomia, macrocephaly, developmental delay, alopecia, spasticity, hypotonia, cutaneous vascular malformation, delayed visual maturation, and sensorineural hearing loss."
    explanation: >-
      The index case report documents spasticity alongside hypotonia.
- name: Capillary malformation
  category: Dermatologic
  description: >-
    A cutaneous vascular malformation was documented in the index patient. This
    is a single-case observation and is not part of the GeneReviews clinical
    characteristics.
  phenotype_term:
    preferred_term: Capillary malformation
    term:
      id: HP:0025104
      label: Capillary malformation
  evidence:
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Phenotypic manifestations include macrosomia, macrocephaly, developmental delay, alopecia, spasticity, hypotonia, cutaneous vascular malformation, delayed visual maturation, and sensorineural hearing loss."
    explanation: >-
      Marked PARTIAL because the report says "cutaneous vascular malformation"
      without specifying the vessel type, so the binding to a capillary
      malformation term is the closest available rather than an exact match.
- name: Obesity
  category: Growth
  description: >-
    Obesity is a recognised management issue requiring nutritional intervention.
    Weight gain with increased muscle bulk also occurred during eflornithine
    treatment of the index patient, whose BMI rose from the 25th to the 90th
    percentile.
  phenotype_term:
    preferred_term: Obesity
    term:
      id: HP:0001513
      label: Obesity
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay / intellectual disability, refractive error, strabismus, hearing loss, follicular cysts, and congenital heart defects."
    explanation: >-
      GeneReviews management explicitly provides for nutritional intervention in
      those with obesity.
- name: Constipation
  category: Gastrointestinal
  description: >-
    Constipation is a recurrent management problem requiring stool softeners,
    prokinetics, osmotic agents or laxatives, and is a standing surveillance
    item at each visit.
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay / intellectual disability, refractive error, strabismus, hearing loss, follicular cysts, and congenital heart defects."
    explanation: >-
      GeneReviews management lists a full constipation treatment ladder,
      indicating this is an expected manifestation.
- name: Strabismus
  category: Ophthalmologic
  description: >-
    Strabismus is among the manifestations GeneReviews directs to standard
    treatment, with annual ophthalmology evaluation recommended.
  phenotype_term:
    preferred_term: Strabismus
    term:
      id: HP:0000486
      label: Strabismus
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay / intellectual disability, refractive error, strabismus, hearing loss, follicular cysts, and congenital heart defects."
    explanation: >-
      Strabismus is named among the manifestations requiring standard treatment.
- name: Abnormality of refraction
  category: Ophthalmologic
  description: >-
    Refractive error is among the manifestations GeneReviews directs to standard
    treatment, with annual ophthalmology evaluation recommended.
  phenotype_term:
    preferred_term: Abnormality of refraction
    term:
      id: HP:0000539
      label: Abnormality of refraction
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay / intellectual disability, refractive error, strabismus, hearing loss, follicular cysts, and congenital heart defects."
    explanation: >-
      Refractive error is named among the manifestations requiring standard
      treatment.
- name: Abnormal heart morphology
  category: Cardiovascular
  description: >-
    Congenital heart defects occur and are among the manifestations directed to
    standard treatment. A ventricular septal defect was one of the two prenatal
    ultrasound findings in a prenatally diagnosed fetus.
  phenotype_term:
    preferred_term: Abnormal heart morphology
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay / intellectual disability, refractive error, strabismus, hearing loss, follicular cysts, and congenital heart defects."
    explanation: >-
      Congenital heart defects are named among the manifestations requiring
      standard treatment.
- name: Epidermoid cyst
  category: Dermatologic
  description: >-
    Recurrent follicular cysts arise on the scalp, neck and back, beginning as
    small maculopapular pustules and enlarging, sometimes to 6-7 cm and to the
    point of requiring surgical removal. Complete skin evaluation for follicular
    cysts is recommended at least annually. HPO has no follicular-cyst term, so
    the nearest cutaneous cyst term is used.
  phenotype_term:
    preferred_term: Follicular cyst
    term:
      id: HP:0200040
      label: Epidermoid cyst
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complete skin evaluation for follicular cysts at least annually."
    explanation: >-
      GeneReviews makes annual follicular cyst surveillance a standing
      recommendation.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "She had a history of recurring follicular cyst formation and enlargement."
    explanation: >-
      Patient-level documentation of recurrent follicular cyst formation.
  - reference: PMID:36443247
    reference_title: Improvement of dermatological symptoms in patients with Bachmann-Bupp
      syndrome using difluoromethylornithine treatment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In both patients, treatment with difluoromethylornithine has resulted in improved dermatologic signs, including regrowth of eyebrow and scalp hair and cessation of recurrent follicular cyst development."
    explanation: >-
      Two further genotyped patients with recurrent follicular cysts.
- name: Abnormal cerebral white matter morphology
  category: Neurologic
  description: >-
    White matter abnormalities are among the variable neuroimaging findings.
    In the first treated patient the neonatal MRI showed abnormal cerebral white
    matter that normalised in signal on treatment.
  phenotype_term:
    preferred_term: Abnormal cerebral white matter morphology
    term:
      id: HP:0002500
      label: Abnormal cerebral white matter morphology
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."
    explanation: >-
      Lists white matter abnormalities first among the neuroimaging findings.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A neonatal brain MRI showed abnormal cerebral white matter and subependymal cysts"
    explanation: >-
      Patient-level neonatal MRI documentation of the white matter abnormality.
- name: Dilation of Virchow-Robin spaces
  category: Neurologic
  description: >-
    Prominent perivascular (Virchow-Robin) spaces are one of the variable
    neuroimaging findings of the syndrome.
  phenotype_term:
    preferred_term: Dilation of Virchow-Robin spaces
    term:
      id: HP:0012520
      label: Dilation of Virchow-Robin spaces
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."
    explanation: >-
      Names prominent Virchow-Robin spaces among the neuroimaging findings.
- name: Subependymal cysts
  category: Neurologic
  description: >-
    Periventricular and subependymal cysts are reported on neuroimaging. In the
    first treated patient all previously noted cysts resolved on eflornithine.
  phenotype_term:
    preferred_term: Subependymal cysts
    term:
      id: HP:0002416
      label: Subependymal cysts
  evidence:
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A neonatal brain MRI showed abnormal cerebral white matter and subependymal cysts"
    explanation: >-
      Documents subependymal cysts on the neonatal MRI of a genotyped patient.
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."
    explanation: >-
      Marked PARTIAL because this cohort describes the cysts as periventricular
      rather than specifically subependymal.
- name: Abnormal corpus callosum morphology
  category: Neurologic
  description: >-
    Corpus callosum abnormalities are among the variable neuroimaging findings.
  phenotype_term:
    preferred_term: Abnormal corpus callosum morphology
    term:
      id: HP:0001273
      label: Abnormal corpus callosum morphology
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging variably demonstrates white matter abnormalities, prominent Virchow-Robin spaces, periventricular cysts, and abnormalities of the corpus callosum."
    explanation: >-
      Names corpus callosum abnormalities among the neuroimaging findings.
biochemical:
- name: Elevated plasma N-acetylputrescine
  notes: >-
    N-acetylputrescine is the diagnostic biochemical signature of BABS. It is
    the only polyamine metabolite in the metabolomic panel meeting CAP/CLIA
    standards, so it serves as the surrogate for the putrescine pool. It falls
    on eflornithine treatment.
  biomarker_term:
    preferred_term: N-acetylputrescine
    term:
      id: CHEBI:17768
      label: N-acetylputrescine
  presence: INCREASED
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels."
    explanation: >-
      Establishes the elevation in plasma and its selectivity within the
      polyamine panel.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "N-acetylputrescine, the only polyamine that meets CAP/CLIA standards in this analysis, served as the primary indicator of putrescine levels."
    explanation: >-
      Explains why this metabolite, rather than putrescine itself, is the
      clinical readout.
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The finding of abnormal polyamine pathway metabolites (including increased N-acetylputrescine) on metabolomic profiling is suggestive of a diagnosis of BABS."
    explanation: >-
      GeneReviews uses this metabolite as the biochemical trigger for genetic
      confirmation.
- name: Elevated erythrocyte and fibroblast ODC enzyme activity
  notes: >-
    ODC catalytic activity measured by a 14C-ornithine radiolabelled assay is
    grossly elevated: 12-17-fold above controls in primary dermal fibroblasts
    and 125-137-fold in red blood cells. Red blood cells are the practical
    clinical specimen.
  presence: INCREASED
  evidence:
  - reference: PMID:31249027
    reference_title: Biochemical features of primary cells from a pediatric patient with
      a gain-of-function ODC1 genetic mutation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Importantly, the accumulated ODC protein variant remained functionally active as we detected exceptionally high ODC enzyme activity in both primary dermal fibroblasts (12-17-fold of controls) and red blood cells (RBCs) (125-137-fold of controls), using a specific 14C radioactive ODC activity assay."
    explanation: >-
      Supplies the quantitative fold-change and the assay used.
  - reference: PMID:40382142
    reference_title: Monitoring ODC activity and polyamines in Bachmann-Bupp syndrome
      patient biological samples.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we describe how to quantitatively measure ODC enzymatic activity and the polyamines by a radiolabeled 14C-ornithine assay and by reverse phase (RP)-HPLC, respectively."
    explanation: >-
      Documents the standardised protocol for measuring the enzyme activity and
      polyamines in BABS patient samples.
- name: Elevated erythrocyte polyamines
  notes: >-
    Red blood cells from patients contain elevated ODC protein and elevated
    polyamine levels compared with healthy controls.
  presence: INCREASED
  evidence:
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Red blood cells obtained from our patient showed elevated ODC protein and polyamine levels compared to healthy controls."
    explanation: >-
      Direct measurement of raised polyamines in a patient's circulating cells.
genetic:
- name: ODC1
  gene_term:
    preferred_term: ODC1
    term:
      id: hgnc:8109
      label: ODC1
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: DE_NOVO
  inheritance:
  - name: Autosomal dominant
    evidence:
    - reference: PMID:36007106
      reference_title: Bachmann-Bupp Syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "BABS is expressed in an autosomal dominant manner and typically caused by a de novo ODC1 pathogenic variant."
      explanation: >-
        GeneReviews states both the dominant mode and the de novo origin.
  features: >-
    Heterozygous de novo variants at the 3-prime end of ODC1 produce a
    C-terminally truncated ornithine decarboxylase. The index allele is
    c.1342A>T, a nonsense variant removing the last 14 amino acids (p.Lys448Ter).
    Reported variants cluster in the last exon. Critically, the mechanism is
    GAIN of function through protein stabilisation, not loss of function: the
    truncated enzyme retains full catalytic activity and simply escapes
    degradation. Separate, rarer ODC1 loss-of-function alleles exist (for
    example the hypomorphic G84R missense variant, present in roughly 1 percent
    of South Asian individuals and reducing enzyme function 2.5-fold) and are
    associated with a different, non-BABS neurological picture; those must not
    be conflated with the BABS allele class.
  evidence:
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The ODC1 gene mutation (c.1342 A>T) was identified by whole-exome sequencing and confirmed by Sanger sequencing."
    explanation: >-
      Names the index allele and the method by which it was identified and
      confirmed.
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this report, we present four patients with a distinct neurometabolic disorder associated with de novo heterozygous, gain-of-function variants in the ODC1 gene."
    explanation: >-
      Independent replication establishing the gene-disease relationship in four
      further patients with de novo gain-of-function alleles.
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Heterozygous pathogenic variants in ODC1 that cause BABS are typically gain-of-function variants."
    explanation: >-
      GeneReviews states the direction of effect explicitly, which is the single
      most important fact to preserve when reading ODC1 literature.
  - reference: PMID:40382142
    reference_title: Monitoring ODC activity and polyamines in Bachmann-Bupp syndrome
      patient biological samples.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ODC1 gene mutations that are linked to BABS always produce C-terminally truncated versions of the enzyme ornithine decarboxylase (ODC)."
    explanation: >-
      States that C-terminal truncation is invariant across the BABS allele
      spectrum.
  - reference: PMID:33806076
    reference_title: Emerging Role of ODC1 in Neurodevelopmental Disorders and Brain Development.
    supports: PARTIAL
    evidence_source: COMPUTATIONAL
    snippet: "An analysis of variants from ClinVar, Geno2MP, TOPMed, gnomAD, and COSMIC revealed an intellectual disability and seizure connected loss-of-function variant, ODC G84R (rs138359527, NC_000002.12:g.10444500C > T)."
    explanation: >-
      Marked PARTIAL and included deliberately as a contrast: this ODC1 allele is
      loss-of-function and is NOT a BABS allele, so it delimits the BABS allele
      class rather than supporting it.
  - reference: PMID:11533243
    reference_title: The ornithine decarboxylase gene is essential for cell survival
      during early murine development.
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "ODC-heterozygous mice were viable, normal, and fertile."
    explanation: >-
      Marked PARTIAL and included as the decisive direction-of-effect control:
      halving ODC gene dosage produces a normal mouse, so BABS cannot be a
      haploinsufficiency disorder. This is the strongest single argument against
      importing ODC1 knockout data as a model of the patient state.
  - reference: PMID:11533243
    reference_title: The ornithine decarboxylase gene is essential for cell survival
      during early murine development.
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "Therefore, ODC plays an essential role in murine development, and proper homeostasis of polyamine pools appears to be required for cell survival prior to gastrulation."
    explanation: >-
      Marked PARTIAL: complete Odc1 ablation is embryonic lethal, which is a
      constraint on how far ODC can be inhibited therapeutically but is not
      evidence about the BABS allele itself.
treatments:
- name: Eflornithine (difluoromethylornithine, DFMO)
  description: >-
    Eflornithine is an irreversible ODC inhibitor and the mechanism-matched
    targeted therapy for BABS. It was repurposed from its existing indications
    (West African trypanosomiasis, paediatric neuroblastoma maintenance, and
    hirsutism) and first given to a BABS patient under a single-patient FDA
    Investigational New Drug application, 16 months after the syndrome was first
    published. The index regimen was an oral solution given by gastrostomy tube
    at 500 mg/m2 twice daily, escalated to 750 and then 1000 mg/m2 twice daily,
    alongside a low-polyamine diet. Reported outcomes include hair regrowth
    beginning with the eyebrows at one month, immediate cessation of follicular
    cyst formation, increased muscle bulk and tone, acquisition of head control,
    unsupported sitting and self-feeding, and normalisation of cerebral white
    matter signal with resolution of subependymal cysts on MRI. Eflornithine is
    not an FDA-approved treatment for BABS and remains a compassionate-use
    therapy. Paediatric dosing and safety were taken from the neuroblastoma
    maintenance literature rather than from any BABS trial.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: eflornithine
      term:
        id: CHEBI:41948
        label: eflornithine
  target_mechanisms:
  - target: Elevated ODC Enzyme Activity
    treatment_effect: INHIBITS
    description: >-
      Eflornithine irreversibly inhibits ODC, so it suppresses the catalytic
      activity of the accumulated truncated enzyme rather than restoring its
      degradation.
    evidence:
    - reference: PMID:31249027
      reference_title: Biochemical features of primary cells from a pediatric patient
        with a gain-of-function ODC1 genetic mutation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Exposure of primary dermal fibroblasts to ODC inhibitor α-difluoromethylornithine (DFMO) reduced the ODC activity and putrescine to levels observed in controls without adversely affecting cell morphology or inducing cell death."
      explanation: >-
        Demonstrates in the patient's own cells that DFMO normalises the raised
        enzyme activity without cytotoxicity.
  - target: Putrescine Accumulation
    treatment_effect: INHIBITS
    description: >-
      Inhibiting the enzyme lowers the putrescine pool and its measurable
      acetylated derivative back toward the reference range.
    evidence:
    - reference: PMID:34282722
      reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
        variant disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Eflornithine normalized polyamine levels without disrupting other pathways."
      explanation: >-
        In-patient confirmation that the drug corrects the polyamine
        disturbance selectively.
  - target: Hair Follicle Dysfunction with Bulge Stem Cell Recruitment
    treatment_effect: INHIBITS
    description: >-
      Suppressing follicular ODC activity restores hair growth, an effect first
      shown in the truncated-ODC mouse and then reproduced in patients.
    evidence:
    - reference: PMID:8618048
      reference_title: Modulation of murine hair follicle function by alterations in ornithine
        decarboxylase activity.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "2-Difluoromethylornithine could also reactivate hair growth in animals with complete hair loss."
      explanation: >-
        The model result that motivated trying the drug in patients with
        established alopecia.
  evidence:
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Eflornithine normalized polyamine levels without disrupting other pathways. She demonstrated remarkable improvement in both neurological symptoms and cortical architecture. She gained fine motor skills with the capacity to feed herself and sit with support."
    explanation: >-
      The primary treated-patient report, giving biochemical, neurological and
      functional outcomes in the first patient treated.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At age 4 years and 8 months, we started eflornithine (Sanofi Aventis) treatment with 500 mg/m2/dose bid twice daily via a gastrostomy tube along with a low polyamine diet on November 14, 2019, for 3 months, increasing to 750 mg/m2/dose twice daily, and a final increase to 1000 mg/m2/dose twice daily after 3.5 months."
    explanation: >-
      Documents the actual regimen, route and escalation schedule used in the
      index treated case.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dosing was based on what had been demonstrated to be safe in pediatric patients in maintenance therapy for neuroblastoma treated with eflornithine (Saulnier Sholler et al., 2015)."
    explanation: >-
      Records that the paediatric dose and safety basis was borrowed from the
      neuroblastoma maintenance literature, not generated in BABS.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One month into treatment, hair growth was noted, with eyebrows appearing first"
    explanation: >-
      Timing of the first visible dermatological response.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Upon initiation of eflornithine, the formation of cysts ceased immediately"
    explanation: >-
      Documents cessation of the recurrent follicular cysts on treatment.
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Repeat MRI done at the end of the 9-month treatment trial with eflornithine demonstrated normalization of the cerebral white matter signal with decrease in volume with white matter loss and resolution of all previously noted cysts."
    explanation: >-
      Imaging outcome after nine months of therapy, including resolution of the
      cysts and normalisation of white matter signal.
  - reference: PMID:36443247
    reference_title: Improvement of dermatological symptoms in patients with Bachmann-Bupp
      syndrome using difluoromethylornithine treatment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In both patients, treatment with difluoromethylornithine has resulted in improved dermatologic signs, including regrowth of eyebrow and scalp hair and cessation of recurrent follicular cyst development."
    explanation: >-
      Two additional genotyped patients replicating the dermatological response.
  - reference: PMID:37469105
    reference_title: Bachmann-Bupp syndrome and treatment.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with BABS have been treated with DFMO and have shown improvement in hair growth, muscle tone, and development."
    explanation: >-
      Review-level summary of the three outcome domains reported across treated
      patients.
  - reference: PMID:40167220
    reference_title: "Repurposing With Purpose: Treatment of Bachmann-Bupp Syndrome With Eflornithine and Implications for Other Polyaminopathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Currently, five additional patients with BABS are being treated with DFMO."
    explanation: >-
      Establishes that the treated cohort has grown beyond the index case.
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "An experimental targeted treatment with difluoromethylornithine (DFMO) is being explored on a compassionate use basis; it is not currently an FDA-approved treatment for BABS."
    explanation: >-
      Marked PARTIAL because GeneReviews classifies DFMO as a therapy under
      investigation, not established care; the regulatory status is an important
      caveat on every outcome above.
  notes: >-
    The published treated-patient outcomes are uncontrolled single-arm
    observations in a handful of children, with the index report explicitly
    noting that COVID-19 restrictions interrupted standardised neurological
    assessment. Hair regrowth and cyst cessation are unambiguous and were
    directly observed; the developmental and imaging gains are harder to
    attribute with certainty and should be read as promising rather than proven.
- name: Low-polyamine diet
  description: >-
    Dietary restriction of polyamines was given alongside eflornithine in the
    index treated patient. It has never been tested as monotherapy in BABS, and
    the review literature raises dietary intervention and gut-flora-directed
    antibiotics only as candidate approaches to lowering putrescine.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Dietary Intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  target_mechanisms:
  - target: Putrescine Accumulation
    treatment_effect: INHIBITS
    description: >-
      Reducing dietary and gut-derived polyamine input is intended to lower the
      systemic putrescine burden.
    evidence:
    - reference: PMID:30475435
      reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
        disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
        abnormalities.
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "Therapies aimed at reducing putrescine levels, including ODC1 inhibitors, dietary interventions, and antibiotics to reduce polyamine production by gastrointestinal flora could be considered as disease-modifying therapies."
      explanation: >-
        Marked PARTIAL because this is a proposal for what could be considered,
        not a report of a tested dietary intervention.
  evidence:
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "At age 4 years and 8 months, we started eflornithine (Sanofi Aventis) treatment with 500 mg/m2/dose bid twice daily via a gastrostomy tube along with a low polyamine diet on November 14, 2019, for 3 months, increasing to 750 mg/m2/dose twice daily, and a final increase to 1000 mg/m2/dose twice daily after 3.5 months."
    explanation: >-
      Marked PARTIAL because the diet was co-administered with eflornithine, so
      no independent effect can be attributed to it.
- name: Supportive and symptom-directed management
  description: >-
    Standard multidisciplinary care for the individual manifestations: feeding
    therapy with a low threshold for gastrostomy placement, nutritional
    intervention for obesity, a constipation ladder of stool softeners,
    prokinetics, osmotic agents and laxatives, and standard treatment for
    epilepsy, developmental delay and intellectual disability, refractive error,
    strabismus, hearing loss, follicular cysts and congenital heart defects.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Feeding therapy with a low threshold for a clinical feeding evaluation and/or gastrostomy tube placement; nutritional intervention for those with obesity; stool softeners, prokinetics, osmotic agents or laxatives for constipation; standard treatment for epilepsy, developmental delay / intellectual disability, refractive error, strabismus, hearing loss, follicular cysts, and congenital heart defects."
    explanation: >-
      The GeneReviews management paragraph is the source for every element of
      this supportive-care package.
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ophthalmology and audiology evaluations annually or as clinically indicated."
    explanation: >-
      Specifies the recommended sensory surveillance cadence.
- name: Genetic counseling
  description: >-
    BABS is autosomal dominant and typically de novo, so the recurrence risk to
    other family members is presumed low. Once the familial ODC1 variant is
    known, prenatal and preimplantation genetic testing are possible.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore, the risk to other family members is presumed to be low. Once an ODC1 pathogenic variant has been identified in an affected family member, prenatal testing and preimplantation genetic testing are possible."
    explanation: >-
      GeneReviews states the recurrence-risk counselling message and the
      reproductive testing options.
diagnosis:
- name: ODC1 molecular genetic testing
  description: >-
    The diagnosis is established by identifying a heterozygous pathogenic ODC1
    variant in a proband with suggestive findings. Exome sequencing identified
    the index allele, confirmed by Sanger sequencing.
  presence: PRESENT
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis is established in a proband with suggestive findings and a heterozygous pathogenic variant in ODC1 identified by molecular genetic testing."
    explanation: >-
      GeneReviews defines the diagnostic standard.
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The ODC1 gene mutation (c.1342 A>T) was identified by whole-exome sequencing and confirmed by Sanger sequencing."
    explanation: >-
      Illustrates the two-step molecular workflow used in the index case.
- name: Plasma metabolomic profiling for polyamine metabolites
  description: >-
    Untargeted or clinical metabolomic profiling showing abnormal polyamine
    pathway metabolites, particularly increased N-acetylputrescine, is
    suggestive of BABS and typically precedes molecular confirmation.
  presence: PRESENT
  evidence:
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The finding of abnormal polyamine pathway metabolites (including increased N-acetylputrescine) on metabolomic profiling is suggestive of a diagnosis of BABS."
    explanation: >-
      GeneReviews positions metabolomic profiling as the suggestive biochemical
      test.
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels."
    explanation: >-
      Documents the specific plasma metabolomic pattern in a genotyped cohort.
- name: Erythrocyte ODC enzyme activity assay
  description: >-
    A 14C-ornithine radiolabelled assay on red blood cells, with polyamines
    measured by reverse-phase HPLC, quantifies the enzymatic gain of function
    and is used to monitor response to eflornithine.
  presence: PRESENT
  evidence:
  - reference: PMID:40382142
    reference_title: Monitoring ODC activity and polyamines in Bachmann-Bupp syndrome
      patient biological samples.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The detailed protocols of this chapter provide step-by-step guidance detailing how to measure ODC activity and polyamines in human RBCs."
    explanation: >-
      Establishes the red blood cell assay as the standardised BABS monitoring
      method.
animal_models:
- species: Mus musculus
  genotype: K6/ODC transgenic
  category: Transgenic
  description: >-
    The K6/ODC mouse expresses a mouse ODC cDNA carrying a premature stop codon
    at position 427, driven by a bovine keratin 6 promoter, in outer root sheath
    keratinocytes of the hair follicle. The lesion is the same class as the human
    BABS allele - carboxyl truncation producing a stabilised, catalytically
    active enzyme - which is why this 1995-1996 model predicted the human
    syndrome. Mice have a normal first hair cycle, lose their hair completely
    from 2-3 weeks of age, and develop dermal follicular cysts. DFMO both
    prevents the hair loss and reactivates hair growth after complete loss. The
    model is skin-restricted, so it does not model the neurodevelopmental,
    growth or sensory features of BABS, and it also develops skin tumours, which
    has no established human BABS counterpart.
  evidence:
  - reference: PMID:8618048
    reference_title: Modulation of murine hair follicle function by alterations in ornithine
      decarboxylase activity.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The ODC inhibitor 2-difluoromethylornithine could prevent hair loss and partially normalize skin histology if administered before the onset of ODC overexpression."
    explanation: >-
      Establishes the preventive arm of the DFMO effect in the model that
      motivated human treatment.
  - reference: PMID:41925768
    reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Ornithine decarboxylase (ODC), a key regulating enzyme of polyamine biosynthesis, was constitutively expressed in the outer root sheath cells of hair follicles near the bulge stem cell niche using a keratin 6 promoter in K6/ODC mice."
    explanation: >-
      Defines the transgene construct and the targeted cell population.
  - reference: PMID:41925768
    reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Remarkably, the heterozygous de novo mutation in the ODC gene of this patient and others subsequently identified as having the Bachmann-Bupp syndrome (BABS) introduces a stop codon in the ODC gene, leading to premature abrogation and deletion of the c-terminal 14 amino acids of the ODC protein, as was originally designed in the K6/ODC mouse to stabilize the ODC protein and lead to elevated ODC enzyme activity"
    explanation: >-
      States the equivalence between the engineered mouse allele and the human
      BABS allele, which is what licenses using this model.
  - reference: PMID:30239107
    reference_title: Novel de novo pathogenic variant in the ODC1 gene in a girl with
      developmental delay, alopecia, and dysmorphic features.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This is the first human case confirming similar symptoms observed in a transgenic ODC1 mouse model first described over 20 years ago."
    explanation: >-
      The index human report explicitly frames itself as the human confirmation
      of the transgenic mouse phenotype.
  - reference: PMID:41925768
    reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "Many tumors arising in K6/ODC transgenic mice are keratoacanthomas that originated from the follicular cysts in the dermis."
    explanation: >-
      Marked PARTIAL and recorded as a limitation: the model's tumour phenotype
      is a property of the skin-targeted transgenic and has no established
      counterpart in reported BABS patients.
  - reference: PMID:7671221
    reference_title: Increased frequency of spontaneous skin tumors in transgenic mice
      which overexpress ornithine decarboxylase.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Effects observed include development of dermal follicular cysts, excessive skin wrinkling, enhanced nail growth, alopecia, and spontaneous tumor development."
    explanation: >-
      The original description of the transgenic phenotype, three of whose four
      non-tumour elements (follicular cysts, nail growth, alopecia) were later
      recognised in BABS patients.
- species: Mus musculus
  genotype: Odc1 knockout
  category: Knockout
  description: >-
    The constitutive Odc1 knockout is included here explicitly as a NEGATIVE
    control, not as a model of BABS. Homozygous loss is lethal at
    peri-implantation because the inner cell mass fails to survive, while
    heterozygotes are viable, normal and fertile. Because halving ODC dosage
    produces no phenotype, BABS cannot be a haploinsufficiency disorder, and no
    finding from this model should be carried into the BABS mechanism graph as
    if it described the patient state.
  evidence:
  - reference: PMID:11533243
    reference_title: The ornithine decarboxylase gene is essential for cell survival
      during early murine development.
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "ODC-heterozygous mice were viable, normal, and fertile."
    explanation: >-
      Marked PARTIAL because this model describes the opposite direction of
      effect to BABS; it is curated as the control that excludes
      haploinsufficiency.
  - reference: PMID:11533243
    reference_title: The ornithine decarboxylase gene is essential for cell survival
      during early murine development.
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "Embryonic day E3.5 ODC-deficient embryos were capable of uterine implantation and induced maternal decidualization yet failed to develop substantially thereafter."
    explanation: >-
      Marked PARTIAL: documents the lethality of complete ablation, relevant as
      a theoretical bound on ODC inhibition rather than as BABS pathophysiology.
discussions:
- discussion_id: babs_k6odc_model_scope_and_cancer_risk
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    The K6/ODC mouse reproduces the alopecia and follicular cysts of BABS and
    predicted the DFMO response, but it also develops skin tumours and is
    skin-restricted. Does whole-body expression of stabilised ODC in BABS
    patients carry a tumour risk, and does the absence of a whole-body model
    mean the neurodevelopmental arm of the disease has never been modelled?
  rationale: >-
    The only well-characterised animal model of this exact lesion targets the
    transgene to hair follicle keratinocytes. Its tumour phenotype has been
    interpreted as evidence that polyamine excess promotes tumorigenesis, and
    the index human cohort report raised cancer surveillance as a consideration
    on that basis. But no BABS patient tumour series exists, GeneReviews does
    not recommend tumour surveillance, and there is no whole-body
    C-terminally-truncated-ODC model in which the neurodevelopmental phenotype
    could be studied. The mismatch matters in both directions: it risks
    over-calling a cancer risk that has not been observed in patients, and it
    leaves the central neurodevelopmental mechanism without an in vivo model.
  attaches_to:
  - pathophysiology#Dysregulated Neural Progenitor Proliferation
  proposed_experiments:
  - experiment_id: exp_babs_whole_body_truncation_knockin
    name: Whole-body or CNS-conditional Odc1 C-terminal truncation knock-in
    description: >-
      Generate a mouse carrying a knock-in of a human-equivalent C-terminally
      truncated Odc1 allele expressed ubiquitously or conditionally in neural
      lineages, rather than under a keratin 6 promoter, and characterise
      cortical progenitor proliferation, brain growth, white matter development
      and response to eflornithine started at different postnatal ages.
  - experiment_id: exp_babs_tumour_surveillance_registry
    name: Prospective tumour-surveillance registry across the BABS cohort
    description: >-
      Assemble a prospective, standardised tumour-surveillance registry across
      the international BABS cohort to establish whether the mouse skin-tumour
      phenotype has any human counterpart, and whether long-term eflornithine
      exposure modifies it.
  evidence:
  - reference: PMID:30475435
    reference_title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
      disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
      abnormalities.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "As the ODC1 gene has been implicated in neoplasia, cancer surveillance may be important in this disorder."
    explanation: >-
      The index cohort raises cancer surveillance as a hypothesis, phrased as a
      possibility rather than a recommendation.
  - reference: PMID:41925768
    reference_title: "The remarkable legacy of the K6/ODC mouse: mechanisms of polyamine-promoted tumorigenesis revealed."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "However, unlike the K6/ODC mouse where this mutation was directed to the skin, the ODC mutation is expressed in all tissues of BABS patients resulting in macrosomia, macrocephaly, neurodevelopmental delay, spasticity, hypotonia, delayed visual maturation, and sensorineural hearing loss"
    explanation: >-
      States the exact scope difference between the model and the human disease.
- discussion_id: babs_treatment_window_neonatal_initiation
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Does earlier initiation of eflornithine, for example in a neonate diagnosed
    before neurological damage accrues, change the neurodevelopmental trajectory
    of BABS?
  rationale: >-
    All reported treated patients started eflornithine after developmental delay
    was already established; the index patient was 4 years and 8 months old.
    The treating team explicitly identified neonatal initiation as the untested
    question of greatest consequence. Prenatal diagnosis of BABS has now been
    reported, which makes pre-symptomatic treatment a realistic prospect.
  attaches_to:
  - pathophysiology#Abnormal Brain Development
  proposed_experiments:
  - experiment_id: exp_babs_early_versus_late_initiation_cohort
    name: Natural-history cohort comparing early versus late eflornithine initiation
    description: >-
      Establish a prospective international natural-history cohort with
      standardised developmental assessment at fixed ages, then compare
      developmental trajectories, MRI findings and N-acetylputrescine
      normalisation between patients started on eflornithine before and after
      12 months of age.
  evidence:
  - reference: PMID:34282722
    reference_title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
      variant disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This could be especially consequential if we could initiate therapy in a neonate diagnosed early before neurological damage occurs."
    explanation: >-
      The treating team states the open question directly.
differential_diagnoses:
- name: Alopecia-intellectual disability syndrome 4 (LSS-related)
  description: >-
    The closest clinical mimic outside the polyamine pathway, and the one that
    matters most at the bedside: a recessive neuroectodermal syndrome caused by
    biallelic LSS (lanosterol synthase) variants that pairs alopecia with
    intellectual disability or developmental delay, exactly the pairing that
    defines the BABS gestalt. The discriminator is the timing of the hair loss.
    In LSS-related disease the alopecia is CONGENITAL - total alopecia with
    sparse eyelashes and eyebrows is present at birth - whereas in BABS hair is
    typically present at birth and is then shed in large clumps within the first
    weeks of life. LSS disease is also autosomal recessive, frequently
    epileptic, and often accompanied by ichthyosis or erythroderma, and it sits
    in cholesterol rather than polyamine biosynthesis, so the BABS biochemical
    signature of raised N-acetylputrescine is absent and eflornithine is not
    rational therapy.
  distinguishing_features:
  - Caused by biallelic LSS (lanosterol synthase) variants, not by ODC1
  - Autosomal recessive, not de novo autosomal dominant
  - Alopecia is CONGENITAL and total at birth, whereas BABS hair is present at birth
    and shed in clumps within weeks - this is the single most useful discriminator
  - Early-onset epilepsy is frequent, whereas seizures are a rare and typically
    late-onset finding in BABS
  - Ichthyosis and erythroderma are common; the BABS skin phenotype is recurrent
    follicular cysts
  - Cholesterol-biosynthesis rather than polyamine-pathway disorder, so ODC activity,
    putrescine and N-acetylputrescine are not elevated
  - Microcephaly is reported rather than the macrocephaly and macrosomia of BABS
  disease_term:
    preferred_term: Alopecia with intellectual disability syndrome 4
    term:
      id: MONDO:0030009
      label: alopecia-intellectual disability syndrome 4
  evidence:
  - reference: PMID:30723320
    reference_title: Biallelic pathogenic variants in the lanosterol synthase gene LSS
      involved in the cholesterol biosynthesis cause alopecia with intellectual disability,
      a rare recessive neuroectodermal syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is a rare autosomal recessive condition characterized by hypotrichosis and intellectual disability (ID) or developmental delay (DD), frequently associated with early-onset epilepsy and other dermatological features."
    explanation: >-
      Gives the inheritance mode and the alopecia-plus-developmental-delay core
      that make this the closest non-polyaminopathy mimic of BABS.
  - reference: PMID:30723320
    reference_title: Biallelic pathogenic variants in the lanosterol synthase gene LSS
      involved in the cholesterol biosynthesis cause alopecia with intellectual disability,
      a rare recessive neuroectodermal syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Total alopecia with sparse eyelashes and eyebrows was noted at birth in all affected individuals."
    explanation: >-
      Establishes the congenital timing of the alopecia, the discriminator
      against the non-congenital clump shedding of BABS.
  - reference: PMID:36007106
    reference_title: Bachmann-Bupp Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hair is typically present at birth but may be sparse and of an unexpected color with subsequent loss of hair in large clumps within the first few weeks of life."
    explanation: >-
      The BABS side of the same discriminator, stated by GeneReviews: hair is
      present at birth and lost afterwards.
- name: Snyder-Robinson syndrome
  description: >-
    The first-described and best-known polyaminopathy, and the disorder whose
    prior research the BABS team explicitly credits with accelerating BABS from
    discovery to treatment. It shares intellectual disability and hypotonia with
    BABS, and its literature uses the same polyamine-pathway vocabulary, so
    mechanism sentences are easily misattributed between the two. It is separated
    from BABS by the affected enzyme (spermine synthase, several steps
    downstream of ODC), by the direction of effect (loss of function, not gain),
    and by X-linked hemizygous rather than autosomal dominant transmission.
    Alopecia is not its presenting feature.
  distinguishing_features:
  - Caused by SMS (spermine synthase), not ODC1
  - Loss-of-function with decreased or absent enzyme activity, the opposite direction
    of effect to the ODC1 gain of function in BABS
  - X-linked, affecting hemizygous males, rather than de novo autosomal dominant
  - Osteoporosis, kyphoscoliosis, unsteady gait and facial asymmetry dominate; the
    non-congenital clump alopecia and macrocephaly/macrosomia of BABS are not its core
  - No ODC inhibitor therapy - inhibiting ODC would worsen an already spermine-deficient
    pathway
  disease_term:
    preferred_term: Snyder-Robinson syndrome
    term:
      id: MONDO:0010664
      label: syndromic X-linked intellectual disability Snyder type
  evidence:
  - reference: PMID:41410504
    reference_title: "Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Snyder-Robinson syndrome results from hemizygous loss-of-function variants in the spermine synthase (SMS) gene, resulting in decreased or complete loss of spermine synthase enzyme activity."
    explanation: >-
      Gives the gene, the zygosity and the direction of effect that separate
      Snyder-Robinson syndrome from BABS.
  - reference: PMID:37092498
    reference_title: Two New Cases of Bachmann-Bupp Syndrome Identified through the International
      Center for Polyamine Disorders.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Recent identification of four additional polyaminopathies, including Bachmann-Bupp syndrome, have benefited from previous research on Snyder-Robinson syndrome in order to advance from research to treatment more quickly."
    explanation: >-
      Documents the direct research lineage between the two disorders, which is
      precisely why their literatures are intertwined and confusable.
- name: Faundes-Banka syndrome
  description: >-
    A polyaminopathy of the hypusination arm of the pathway, caused by
    heterozygous loss-of-function variants in EIF5A. Like BABS it is a
    heterozygous, recently described neurodevelopmental polyaminopathy, so the
    two are routinely tabulated side by side and their "heterozygous variants in
    a polyamine-pathway gene" framing is easy to conflate. The discriminators are
    the gene, the direction of effect (loss, not gain), and the affected step:
    EIF5A acts on eIF5A hypusination downstream of spermidine, not on polyamine
    synthesis itself, so ODC activity and putrescine are not elevated and
    eflornithine is not rational therapy.
  distinguishing_features:
  - Caused by EIF5A, not ODC1
  - Loss-of-function impairing eIF5A protein function, not gain-of-function enzyme
    stabilisation
  - Affects the hypusination branch downstream of spermidine rather than the
    rate-limiting decarboxylation step
  - No elevated ODC activity, no putrescine or N-acetylputrescine elevation, so the
    BABS biochemical signature is absent
  - The BABS non-congenital clump alopecia is not a feature
  disease_term:
    preferred_term: Faundes-Banka syndrome
    term:
      id: MONDO:0859163
      label: Faundes-Banka syndrome
  evidence:
  - reference: PMID:41410504
    reference_title: "Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Faundes-Banka syndrome results from heterozygous loss-of-function variants in the eukaryotic translation initiation factor 5A (EIF5A) gene, impairing eIF5A protein function."
    explanation: >-
      Gives the gene and the direction of effect that separate Faundes-Banka
      syndrome from BABS.
  - reference: PMID:41410504
    reference_title: "Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The five known syndromes associated with the polyamine pathway share many similar clinical phenotypes, and yet patients with each syndrome present with distinctive syndromic features."
    explanation: >-
      Establishes that the five polyaminopathies overlap clinically, which is
      the condition under which their evidence gets mixed up.
- name: Deoxyhypusine synthase (DHPS) deficiency
  description: >-
    An autosomal recessive polyaminopathy caused by bi-allelic hypomorphic DHPS
    variants. It sits on the same hypusination branch as Faundes-Banka syndrome
    and, like BABS, presents as a Mendelian neurodevelopmental disorder with
    seizures and developmental impairment, so it appears in the same
    polyaminopathy tables. It is separated from BABS by the gene, by recessive
    rather than dominant inheritance, and by reduced rather than increased enzyme
    activity.
  distinguishing_features:
  - Caused by DHPS (deoxyhypusine synthase), not ODC1
  - Autosomal recessive with bi-allelic hypomorphic variants, not de novo heterozygous
  - Reduced enzyme activity, the opposite direction of effect to BABS
  - Acts on the spermidine-dependent hypusination of eIF5A rather than on polyamine
    synthesis, so putrescine and N-acetylputrescine are not the diagnostic signature
  - Seizures and speech and walking impairment define the phenotype; the BABS alopecia
    and macrocephaly/macrosomia combination is not its core
  disease_term:
    preferred_term: Deoxyhypusine synthase deficiency
    term:
      id: MONDO:0032775
      label: neurodevelopmental disorder with seizures and speech and walking impairment
  evidence:
  - reference: PMID:41410504
    reference_title: "Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "DHPS (deoxyhypusine synthase) deficiency is an autosomal recessive disease and results from bi-allelic hypomorphic variants in the deoxyhypusine synthase (DHPS) gene, which results in reduced deoxyhypusine synthase enzyme activity."
    explanation: >-
      Gives the gene, the inheritance mode and the direction of effect that
      separate DHPS deficiency from BABS.
- name: Deoxyhypusine hydroxylase (DOHH) disorder
  description: >-
    The fifth recognised polyaminopathy, caused by bi-allelic loss-of-function
    DOHH variants, and the second step of the hypusination branch. It is the
    newest member of the family and is grouped with BABS in every polyaminopathy
    review, which is the setting in which its findings can be misattributed. It
    is separated from BABS by the gene, by autosomal recessive inheritance, by
    decreased rather than increased enzyme activity, and by a
    microcephaly-with-cerebral-atrophy brain phenotype that is close to the
    inverse of the BABS macrocephaly.
  distinguishing_features:
  - Caused by DOHH (deoxyhypusine hydroxylase), not ODC1
  - Autosomal recessive bi-allelic loss of function, not de novo heterozygous gain of
    function
  - Decreased enzyme activity, the opposite direction of effect to BABS
  - Microcephaly with cerebral atrophy and visual impairment, the inverse of the
    absolute or relative macrocephaly and macrosomia of BABS
  - Hypusination branch, so no ODC/putrescine elevation and no rationale for an ODC
    inhibitor
  disease_term:
    preferred_term: Deoxyhypusine hydroxylase disorder
    term:
      id: MONDO:0859293
      label: neurodevelopmental disorder with microcephaly, cerebral atrophy, and visual
        impairment
  evidence:
  - reference: PMID:41410504
    reference_title: "Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Finally, DOHH (deoxyhypusine hydroxylase) disorder is an autosomal recessive disorder caused by bi-allelic loss-of-function variants in the deoxyhypusine hydroxylase (DOHH) gene, which causes decreased deoxyhypusine hydroxylase enzyme activity."
    explanation: >-
      Gives the gene, the inheritance mode and the direction of effect that
      separate DOHH disorder from BABS.
- name: ODC1 loss-of-function neurological phenotype
  description: >-
    The single most dangerous confusion for this entry, because it involves the
    same gene. Hypomorphic and loss-of-function ODC1 alleles, exemplified by the
    G84R missense variant present in roughly 1 percent of South Asian
    individuals and reducing enzyme function 2.5-fold, have been connected to
    intellectual disability and seizures. This is NOT Bachmann-Bupp syndrome: the
    direction of effect is opposite, the predicted consequence for neural
    progenitors is depletion rather than over-proliferation, the ODC-activity and
    putrescine elevations that define BABS are absent, and inhibiting ODC with
    eflornithine would be expected to aggravate rather than treat it. Importing
    ODC1 knockout or loss-of-function findings into a BABS mechanism graph is the
    specific error this differential exists to prevent.
  distinguishing_features:
  - Same gene as BABS, so gene-level literature searches return both
  - Loss of function or hypomorphic missense (for example G84R) rather than C-terminal
    truncation
  - Reduced ODC enzyme activity, so the 12-17-fold fibroblast and 125-137-fold red cell
    activity elevations of BABS are absent
  - Predicted neural progenitor depletion rather than over-proliferation
  - Not associated with the BABS alopecia, macrocephaly or macrosomia
  - Eflornithine, the BABS therapy, would be mechanistically contraindicated
  notes: >-
    Deliberately left UNBOUND. This phenotype has no OMIM entry and no MONDO
    term of its own; the only ODC1-anchored MONDO term is MONDO:0033642, which
    is this entry's own disease_term and denotes the gain-of-function disorder.
    Binding this differential to any existing MONDO term would be a fabrication,
    so the entry is recorded with distinguishing features only.
  evidence:
  - reference: PMID:33806076
    reference_title: Emerging Role of ODC1 in Neurodevelopmental Disorders and Brain Development.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "An analysis of variants from ClinVar, Geno2MP, TOPMed, gnomAD, and COSMIC revealed an intellectual disability and seizure connected loss-of-function variant, ODC G84R (rs138359527, NC_000002.12:g.10444500C > T)."
    explanation: >-
      Identifies the loss-of-function allele and the neurological phenotype
      connected to it.
  - reference: PMID:33806076
    reference_title: Emerging Role of ODC1 in Neurodevelopmental Disorders and Brain Development.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "The missense variant is found in ~1% of South Asian individuals and results in 2.5-fold decrease in enzyme function."
    explanation: >-
      Quantifies the direction and magnitude of the functional change, which is
      the opposite of the BABS gain of function.
  - reference: PMID:33806076
    reference_title: Emerging Role of ODC1 in Neurodevelopmental Disorders and Brain Development.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Further dissection of RNA-Seq during fetal brain development and within cerebral organoids showed an association of ODC1 expression with cell proliferation of neural progenitor cells, suggesting gain-of-function variants with neural over-proliferation and loss-of-function variants with neural depletion."
    explanation: >-
      States that the two allele classes have opposite predicted consequences
      for neural progenitors, which is the mechanistic reason they must not be
      merged.
references:
- reference: PMID:36007106
  title: Bachmann-Bupp Syndrome.
  tags:
  - GeneReviews
  findings: []
- reference: PMID:30239107
  title: Novel de novo pathogenic variant in the ODC1 gene in a girl with developmental
    delay, alopecia, and dysmorphic features.
  findings: []
- reference: PMID:30475435
  title: Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental
    disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging
    abnormalities.
  findings: []
- reference: PMID:34282722
  title: Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function
    variant disease.
  findings: []
- reference: PMID:37469105
  title: Bachmann-Bupp syndrome and treatment.
  findings: []
- reference: PMID:41410504
  title: "Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review."
  findings: []
- reference: PMID:31249027
  title: Biochemical features of primary cells from a pediatric patient with a gain-of-function
    ODC1 genetic mutation.
  findings: []
- reference: PMID:8618048
  title: Modulation of murine hair follicle function by alterations in ornithine decarboxylase
    activity.
  findings: []
- reference: PMID:2928784
  title: Prevention of rapid intracellular degradation of ODC by a carboxyl-terminal
    truncation.
  findings: []

📚

References & Deep Research

References

9

PMID:36007106

Bachmann-Bupp Syndrome.

No top-level findings curated for this source.

PMID:30239107

Novel de novo pathogenic variant in the ODC1 gene in a girl with developmental delay, alopecia, and dysmorphic features.

No top-level findings curated for this source.

PMID:30475435

Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging abnormalities.

No top-level findings curated for this source.

PMID:34282722

Repurposing eflornithine to treat a patient with a rare ODC1 gain-of-function variant disease.

No top-level findings curated for this source.

PMID:37469105

Bachmann-Bupp syndrome and treatment.

No top-level findings curated for this source.

PMID:41410504

Genetic and Phenotypic Features of the Five Known Polyaminopathies: A Critical Narrative Review.

No top-level findings curated for this source.

PMID:31249027

Biochemical features of primary cells from a pediatric patient with a gain-of-function ODC1 genetic mutation.

No top-level findings curated for this source.

PMID:8618048

Modulation of murine hair follicle function by alterations in ornithine decarboxylase activity.

No top-level findings curated for this source.

PMID:2928784

Prevention of rapid intracellular degradation of ODC by a carboxyl-terminal truncation.

No top-level findings curated for this source.

Deep Research

1

Claude Code ▸

1. Disease Information

claude-haiku-4-5-20251001, claude-opus-5[1m] 38 citations 2026-08-01T07:28:29.091479

1. Disease Information

1.1 Overview

Bachmann–Bupp syndrome (BABS) is an ultra-rare autosomal dominant neurodevelopmental disorder caused by de novo gain-of-function variants in the 3′ end of ODC1, the gene encoding ornithine decarboxylase (ODC), the first and rate-limiting enzyme of polyamine biosynthesis. It is one of five recognized "polyaminopathies."

The canonical clinical triad is global developmental delay + hypotonia + a distinctive non-congenital alopecia (hair present at birth, then shed in large clumps within the first weeks of life), usually with macrocephaly/macrosomia, dysmorphic facies, and nonspecific brain MRI abnormalities.

"Bachmann-Bupp syndrome (BABS) is a neurodevelopmental disorder characterized by developmental delay, hypotonia, and varying forms of non-congenital alopecia. The condition is caused by 3'-end mutations of the ornithine decarboxylase 1 (ODC1) gene, which produce carboxy (C)-terminally truncated variants of ODC, a pyridoxal 5'-phosphate-dependent enzyme. C-terminal truncation of ODC prevents its ubiquitin-independent proteasomal degradation and leads to cellular accumulation of ODC enzyme that remains catalytically active." — Bachmann & Bupp, Dev Med Child Neurol 2024 (PMID:37469105)

BABS is of outsized translational significance because it is the first polyaminopathy with a viable targeted treatment: the ODC suicide inhibitor eflornithine (α-difluoromethylornithine, DFMO), repurposed from oncology/trypanosomiasis, moved from disease description (2018) to first patient dosed in 16 months (PMID:40167220).

1.2 Key identifiers

Resource	Identifier
MONDO	MONDO:0033642 — "neurodevelopmental disorder with alopecia and brain abnormalities"
OMIM (phenotype)	619075 — BACHMANN-BUPP SYNDROME; BABS
OMIM (gene)	165640 — ORNITHINE DECARBOXYLASE 1; ODC1
Orphanet	ORPHA:544488
MedGen	C5436741 / UID 1775930
UMLS	C5436741
GARD	0017987
SNOMED CT	1222658006
ICD-10	E72.4 (disorders of ornithine metabolism) — via Orphanet mapping
ICD-11	Not established in retrieved sources; likely maps under 5C50.Cx (disorders of ornithine metabolism) — verify before asserting
MeSH	No dedicated MeSH descriptor found; indexed via Ornithine Decarboxylase (D009952) + Alopecia + Neurodevelopmental Disorders
Gene	ODC1 — HGNC:8109, NCBI Gene 4953, Ensembl ENSG00000115758, UniProt P11926

1.3 Synonyms

Bachmann–Bupp syndrome (BABS) — the eponymic/clinical name in wide use
Neurodevelopmental disorder with alopecia and brain abnormalities (NEDABA) — the MONDO/OMIM/MedGen preferred label
ODC1-related neurodevelopmental disorder — GeneReviews dyadic name
Global developmental delay–alopecia–macrocephaly–facial dysmorphism–structural brain anomalies syndrome — Orphanet label
Gene aliases in NCBI: ODC, BABS, NEDBA, NEDBIA

1.4 Provenance of information

Essentially all knowledge is derived from individual patient reports and small case series, not from EHR-scale or registry-scale aggregation. The aggregating structures are: - GeneReviews chapter (Bupp, VanSickle, Bachmann; PMID:36007106, NBK583220) - The International Center for Polyamine Disorders (ICPD) — a Corewell Health / Michigan State University collaboration with the Snyder-Robinson Foundation, which performs "comprehensive data generation and local as well as remote sample collection from patients with known or suspected polyamine disorders around the world" (PMID:37092498) - A 2026 systematic narrative review of all five polyaminopathies (PMID:41410504)

There is no EHR-derived cohort, no ICEES/COHD comorbidity signal, and no population registry for BABS.

2. Etiology

2.1 Primary cause

Heterozygous, almost always de novo, gain-of-function variants clustered in the 3′ end of ODC1 — specifically in exon 12 or the intron 11 splice sites immediately preceding it — that remove or disrupt the C-terminal ~37-residue degradation domain (amino acids ~425–461) of the 461-aa ODC protein.

Because these variants fall in the last exon, the transcripts escape nonsense-mediated decay; a truncated but catalytically fully active ODC protein is produced that can no longer be degraded by the antizyme/26S-proteasome route. The result is massive cellular accumulation of active ODC and putrescine overproduction.

"We hypothesized that this new mutation (c.1342 A>T) leads to a C-terminal truncation variant of the ODC protein that is resistant to normal proteasomal degradation, leading to putrescine accumulation in cells." — Schultz et al., Biochem J 2019 (PMID:31249027)

This is a true molecular gain of function (protein stabilization → enzyme over-accumulation), not haploinsufficiency. Critically, ODC1 loss-of-function produces a mechanistically opposite and phenotypically distinct picture (see §4.4).

2.2 Genetic risk factors

Causal variants: see §4.2. All reported pathogenic variants are 3′-end truncating/splice variants.
Susceptibility loci / modifier genes: None identified. No GWAS, no reported modifiers.
Parental age: Not studied. A paternal-age effect is plausible for a de novo dominant condition but has not been demonstrated for BABS.
Family history: Essentially absent — all molecularly tested probands to date have de novo variants.

2.3 Environmental risk factors

None known. BABS is a monogenic Mendelian disorder with no established environmental contribution to occurrence. Polyhydramnios (58–80% of pregnancies) is a consequence, not a cause.

One theoretical, unproven environmental modifier exists on the downstream side: dietary and gut-microbial polyamines contribute meaningfully to the body polyamine pool, and Rodan et al. explicitly proposed them as therapeutic levers:

"Therapies aimed at reducing putrescine levels, including ODC1 inhibitors, dietary interventions, and antibiotics to reduce polyamine production by gastrointestinal flora could be considered as disease-modifying therapies." — Rodan et al., Am J Med Genet A 2018 (PMID:30475435)

This makes dietary polyamine load and gut flora composition biologically plausible severity modifiers, but no human data support this in BABS.

2.4 Protective factors

Genetic protective factors: none identified.
Environmental protective factors: none validated. Polyamine-restricted diets are listed by GeneReviews under "therapies under investigation," not as established protection.

2.5 Gene–environment interactions

No documented GxE interaction. The single actionable "interaction" is pharmacological: the disease phenotype is at least partly reversible by pharmacologic ODC inhibition (eflornithine), demonstrating that the phenotype depends on ongoing polyamine flux rather than solely on fixed developmental damage — a point strongly supported by both the human treatment response (PMID:34282722) and the K6/ODC mouse (PMID:8618048, see §15).

3. Phenotypes

3.1 Frequency table — GeneReviews cohort (n=9 published individuals; primary source)

Feature	Frequency	Suggested HPO term
Alopecia (non-congenital, clumped shedding)	9/9 (100%)	HP:0001596 Alopecia; HP:0002293 Alopecia of scalp
Dysmorphic features	9/9 (100%)	HP:0001999 Abnormal facial shape
Developmental delay	8/8 (100%)	HP:0001263 Global developmental delay
Hypotonia	8/8 (100%)	HP:0001290 Generalized hypotonia
Macrocephaly	6/9 (66%)	HP:0000256 Macrocephaly
Polyhydramnios (pregnancy history)	5/9 (55.5%)	HP:0001561 Polyhydramnios
Skin findings (keratosis pilaris / follicular cysts)	4/8 (50%)	HP:0032152 Keratosis pilaris; HP:0025249 Follicular cyst (verify)
Macrosomia in infancy	2/5 (40%)	HP:0001520 Large for gestational age
Constipation	3/8 (37.5%)	HP:0002019 Constipation
Seizures	1/8 (12.5%)	HP:0001250 Seizure

Source: GeneReviews Table 2 (PMID:36007106, NBK583220).

3.2 Frequency table — 2026 systematic review (n=12 published BABS cases)

Feature	Reported	HPO
Hair abnormalities / alopecia	12/12 (100%)	HP:0001596
Brain MRI abnormalities	12/12 (100%)	HP:0012443 Abnormal brain morphology
Hypotonia	11/12	HP:0001290
Global developmental delay	11/12	HP:0001263
Dysmorphic features	10/12 (83.3%)	HP:0001999
Macrocephaly	9/12 (75%)	HP:0000256
Prenatal polyhydramnios	7/12 (58.3%)	HP:0001561
Skin abnormalities (incl. follicular cysts)	6/12 (50%)	HP:0011368 Abnormal epidermis morphology
Behavioral (ADHD/ASD)	4/12 (33.3%)	HP:0007018 / HP:0000717
Epilepsy	1/12 (8.3%)	HP:0001250

Source: VanSickle et al., Am J Med Genet A 2026 (PMID:41410504, PMC13270430, DOI 10.1002/ajmga.70029).

⚠️ Verification flag: the extracted percentages in this table were internally inconsistent for GDD (listed as "11/12 | 83.3%", where 11/12 = 91.7%). Re-verify the exact n/N against the published Table before committing frequencies from this source to the KB. The GeneReviews table (§3.1) is the safer primary frequency source.

3.3 HPO disease-annotation set (HPOA, OMIM:619075) — with explicit n/N and onset

HPO ID	Term	Frequency	Onset
HP:0002223	Absent eyebrow	5/5	—
HP:0000653	Sparse eyelashes	4/4	—
HP:0001263	Global developmental delay	4/4	—
HP:0000316	Hypertelorism	4/4	—
HP:0000348	High forehead	4/4	—
HP:0001561	Polyhydramnios	4/5	Prenatal
HP:0000750	Delayed speech and language development	3/3	—
HP:0031936	Delayed ability to walk	3/3	—
HP:0001290	Generalized hypotonia	3/3	—
HP:0012520	Dilation of Virchow-Robin spaces	3/4	—
HP:0007018	Attention deficit hyperactivity disorder	2/3	—
HP:0000028	Cryptorchidism	2/3	—
HP:0001558	Decreased fetal movement	2/5	Prenatal
HP:0001792	Small nail	2/4	—
HP:0000508	Ptosis	2/4	—
HP:0000490	Deeply set eye	2/4	—
HP:0002209	Sparse scalp hair	1/4	—
HP:0000256	Macrocephaly	1/1	—
HP:0004488	Macrocephaly at birth	1/4	Prenatal
HP:0001520	Large for gestational age	1/4	Birth
HP:0001319	Neonatal hypotonia	1/1	Neonatal
HP:0002061	Lower limb spasticity	1/1	—
HP:0008872	Feeding difficulties in infancy	1/1	Neonatal
HP:0000407	Sensorineural hearing impairment	1/1	—
HP:0000378	Cupped ear	1/1	—
HP:0000218	High palate	1/1	—
HP:0002904	Hyperbilirubinemia	1/1	Neonatal
HP:0001943	Hypoglycemia	1/1	Neonatal
HP:0007109	Periventricular cysts	1/1; 1/4	Neonatal; —
HP:0002195	Dysgenesis of the cerebellar vermis	1/4	—
HP:0032471	Focal polymicrogyria	1/4	—
HP:0002514	Cerebral calcification	1/4	—
HP:0032152	Keratosis pilaris	1/4	—
HP:0000958	Dry skin	1/4	—
HP:0004209	Clinodactyly of the 5th finger	1/4	—
HP:0000581	Blepharophimosis	1/4	—
HP:0000494	Downslanted palpebral fissures	1/4	—
HP:0000219	Thin upper lip vermilion	1/4	—
HP:0000718	Aggressive behavior	1/3	—

Source: HPO annotation network, ontology.jax.org (OMIM:619075).

Orphanet-sourced HPOA bands (via Monarch, MONDO:0033642) additionally list as Frequent (HP:0040282): HP:0000400 Macrotia, HP:0001488 Bilateral ptosis, HP:0030890 Hyperintensity of cerebral white matter on MRI; and as Occasional (HP:0040283): HP:0000023 Inguinal hernia, HP:0000278 Retrognathia, HP:0001257 Spasticity, HP:0002465 Poor speech.

3.4 Per-phenotype characterization

Alopecia (the pathognomonic sign) — HP:0001596 / HP:0002293 - Type: physical/ectodermal manifestation - Onset: non-congenital, first weeks of life. GeneReviews: hair "is sometimes sparse and sometimes has atypical color" at birth, then lost "in large clumps" within weeks. Eyebrows and eyelashes are typically congenitally absent/sparse (HP:0002223, HP:0000653). - Severity/progression: variable; often near-total scalp alopecia. Reversible on eflornithine. - Frequency: 100% - QoL impact: cosmetic and psychosocial; hair regrowth is consistently reported by families as one of the most visible and valued treatment effects.

Global developmental delay / intellectual disability — HP:0001263, HP:0001249 - Onset: infancy - Severity: "moderate to severe range" (GeneReviews). Independent walking achieved between 17 months and 4 years; three reported individuals remained nonverbal at last report. A 12-year-old (Patient 10) had "moderate developmental delay and intellectual disability, with the ability to read and write" (PMID:37092498) — demonstrating real variable expressivity. - Progression: static/non-degenerative; improvement documented with treatment. - QoL impact: the dominant driver of lifelong disability, caregiver burden, and educational need.

Hypotonia — HP:0001290 / HP:0001319 - Onset: neonatal/infantile; Frequency: ~92–100%; Progression: generally static, improves with therapy and with DFMO. - One patient developed proximal myopathy confirmed on EMG with progressive weakness and wheelchair use for distance (PMID:37092498) — HP:0003701 Proximal muscle weakness.

Macrocephaly / overgrowth — HP:0000256, HP:0001520 - Onset: prenatal to infantile; the index patient had macrosomia and macrocephaly (PMID:30239107); Patient 10 had OFC >99th centile (38 cm) at birth. - Frequency: 66–75%. Absolute or relative macrocephaly (Rodan et al.). - Overgrowth may give way to obesity risk in later childhood (GeneReviews lists caloric management).

Brain MRI abnormalities — HP:0012443 - Frequency: abnormal in essentially all imaged patients, but without a consistent pattern.

"Every patient had a brain MRI performed at some time point, and neuroimaging abnormalities are common, but not with a particular pattern or recurrence of findings." — VanSickle et al. 2021 (PMID:34477286) - Reported findings: white matter signal abnormality (HP:0002500 / HP:0030890), prominent Virchow-Robin/perivascular spaces (HP:0012520), periventricular and germinal-matrix cysts (HP:0007109), porencephalic cysts (HP:0002132), corpus callosum abnormalities incl. hypoplasia of the mid-body (HP:0002079), ventriculomegaly (HP:0002119), cerebellar vermis dysgenesis (HP:0002195), focal polymicrogyria (HP:0032471), cerebral calcification (HP:0002514), hypoplastic optic chiasm, hippocampal volume loss.

Seizures/epilepsy — HP:0001250 - Rare (1/12, 8.3%) but can be severe and late-onset. The oldest reported patient (male, 23 y) developed absence seizures at age 14, evolving to "multiple seizure types but atypical absence, atonic, and generalized tonic–clonic," refractory to ketogenic diet and multiple ASMs (PMID:34477286). This was the first epilepsy report in BABS. - Contrast: epilepsy is far more prominent in Snyder-Robinson syndrome (~63%), which is a useful discriminator (PMID:41410504).

Behavioral phenotypes - ADHD (HP:0007018, 2/3 in HPOA), autism spectrum disorder (HP:0000717), aggression (HP:0000718). Aggregate ADHD/ASD ~33%.

Dermatologic (beyond alopecia) - Follicular cysts (~50% with skin findings), keratosis pilaris (HP:0032152), dry skin (HP:0000958), hypoplastic/small nails (HP:0001792). Follicular cysts directly phenocopy the K6/ODC mouse.

"In both patients, treatment with difluoromethylornithine has resulted in improved dermatologic signs, including regrowth of eyebrow and scalp hair and cessation of recurrent follicular cyst development." — Afrin et al., Pediatr Dermatol 2023 (PMID:36443247)

Feeding / GI - Feeding difficulties in infancy (HP:0008872), aspiration (HP:0002835), constipation (HP:0002019, 37.5%). NG/G-tube may be required.

Sensory - Sensorineural hearing loss (HP:0000407) — present in index patient; refractive error and strabismus (HP:0000486) warrant annual ophthalmology.

Prenatal - Polyhydramnios (HP:0001561) 55–80%, decreased fetal movement (HP:0001558), prenatal ventriculomegaly/cerebral cysts, and — in one 2026 report — macrocephaly plus ventricular septal defect (HP:0001629) detected on second-trimester ultrasound (PMID:41931584).

Genitourinary/skeletal - Cryptorchidism (HP:0000028, 2/3), inguinal hernia (HP:0000023), fifth-finger clinodactyly (HP:0004209), joint hypermobility (HP:0001382).

3.5 Quality of life

No BABS-specific QoL instrument data (EQ-5D, PROMIS, SF-36, PedsQL) exist in the literature. QoL statements are qualitative and family-reported. Reported functionally meaningful post-treatment gains in the index patient — self-feeding with a spoon, sitting unsupported, walker use — are the closest available surrogates for QoL benefit (PMID:34282722, PMID:37469105). This is a genuine evidence gap.

4. Genetic / Molecular Information

4.1 Causal gene

Attribute	Value
Symbol / name	ODC1 / ornithine decarboxylase 1
HGNC	hgnc:8109
NCBI Gene	4953
OMIM gene	165640
Locus	2p25.1
Genomic span (GRCh38.p14)	chr2:10,439,968–10,448,327 (minus strand)
Exons	13
Canonical transcript / protein	NM_002539.3 / NP_002530.1 (461 aa)
Other RefSeqs	NM_001287188.2, NM_001287189.2, NM_001287190.2
UniProt	P11926
EC	4.1.1.17
Cofactor	pyridoxal 5′-phosphate (CHEBI:18405); binding at residues 200, 237, 274–277, 389
Quaternary structure	Homodimer; both monomers contribute residues to each of two active sites
Expression	Broad; highest in testis (RPKM 67.6) and bone marrow (54.4); strongly elevated in proliferating fetal brain ventricular zone

4.2 Pathogenic variants (compiled from all sources)

All are heterozygous, de novo, germline, and all cluster in exon 12 / intron 11 of NM_002539.3 — the 3′ region encoding the C-terminal degron.

#	cDNA (NM_002539.3)	Protein (NP_002530.1)	Type	ClinVar	Source
1	c.1342A>T	p.(Lys448Ter)	nonsense	VCV000983289, Pathogenic	Bupp 2018 index case (PMID:30239107)
2	c.1241+1G>T (IVS11+1G>T)	splice donor loss	splice	VCV000983285, Pathogenic	Rodan 2018 (PMID:30475435)
3	c.1240_1241dupTG	*p.(Trp414Cysfs17)**	frameshift	VCV000983286, Pathogenic	Rodan 2018
4	c.1255C>T	p.(Gln419Ter)	nonsense	VCV000983287, Pathogenic	Rodan 2018
5	c.1242_1263del22 (NC_000002.12:g.10440850_10440871del)	p.(Trp414Ter) as reported	deletion	VCV000983288, Pathogenic	Rodan 2018
6	c.1242-2A>G (IVS11-2A>G)	splice acceptor loss	splice	VCV001074405, Pathogenic (multiple submitters, no conflicts)	Recurrent — ≥3 individuals; VanSickle 2021 (PMID:34477286), Michael 2023 (PMID:37092498)
7	c.1313_1316delCTGT	p.(438Rfs9) as reported*	frameshift	—	VanSickle 2021 Patient 7
8	c.1252C>T	p.(Gln418Ter)	nonsense	—	VanSickle 2021 Patient 9
9	c.1307_1311delinsT	*p.(Thr436Ilefs11)**	indel/frameshift	—	Michael 2023 Patient 11
—	c.1217A>T	p.(Tyr406Phe)	missense	VUS	Bupp 2025 (PMID:40167220) — functionally excluded, see below

⚠️ Nomenclature verification flags for the curator: 1. One secondary source rendered the index variant as "c.1342A>G (p.Lys448*)". The primary paper and ClinVar both say c.1342A>T — use c.1342A>T. 2. Variants #5 and #7 have protein annotations that are inconsistent with their cDNA positions as extracted (c.1242_1263del22 → p.Trp414* and c.1313_1316del → p.438Rfs*9). Re-derive or re-verify from the source tables before committing HGVS protein strings. 3. c.1242-2A>G is the single recurrent variant and is the most likely candidate for a "hotspot" claim.

The instructive negative — functional testing overrides sequence intuition. Bupp et al. 2025 report a patient with the missense VUS c.1217A>T (p.Tyr406Phe) and an atypical presentation whose ODC enzyme activity was "not greater than unaffected control patients' samples," arguing against pathogenicity. This establishes that the biochemical assay, not the variant location alone, adjudicates BABS (PMID:40167220).

4.3 Variant classification, allele frequency, origin

ACMG/AMP classification: BABS variants are classified Pathogenic. Note that PVS1 (null variant) is NOT the operative criterion here — the mechanism is gain-of-function via stabilization, so PS3 (functional evidence: elevated ODC protein/activity/putrescine), PS2 (de novo with confirmed parentage), PM1 (mutational hotspot in the C-terminal degron), and PP4 (highly specific phenotype) carry the weight. Applying PVS1 to an ODC1 3′-truncating variant would be a mechanistic error.
Allele frequency: All reported BABS variants are absent from gnomAD/1000 Genomes/TOPMed (private de novo events). gnomAD constraint metrics (pLI, LOEUF, missense Z) for ODC1 could not be retrieved programmatically for this report and should be looked up directly before being asserted. Note that constraint metrics are of limited interpretive value here, since the disease mechanism is last-exon NMD-escaping GoF rather than haploinsufficiency.
Germline vs somatic: BABS variants are germline (de novo). Separately, somatic ODC1 alterations occur in sporadic tumors (colorectal, gastric, skin, breast, prostate, neuroblastoma) and are not heritable and not BABS (GeneReviews).
Functional consequence: Gain of function via loss of degradation. The truncated enzyme retains full catalytic activity; steady-state protein level rises dramatically.

4.4 Allelic disorders — the loss-of-function arm

ODC1 loss-of-function is mechanistically opposite and phenotypically distinct. Prokop et al. characterized p.Gly84Arg (NC_000002.12:g.10444500C>T, rs138359527, NP_002530.1:p.Gly84Arg):

"A functional enzyme assay…showed a 2.5-fold reduction of enzyme activity because of the variant." "The variant was found at the highest allele frequency within South Asian individuals (0.8%, specifically Gujarati Indians in Houston, TX (1.5%) and Punjabi in Lahore, Pakistan (1%)." — Prokop et al., Genes 2021 (PMID:33806076)

Overall gnomAD frequency 0.23%; TOPMed 0.18%; ~3-fold enrichment in Geno2MP, associated with intellectual disability and seizures. The authors propose a bidirectional model:

"…suggesting gain-of-function variants with neural over-proliferation and loss-of-function variants with neural depletion."

This is an important framing for the KB: ODC1 dosage is bidirectionally constrained in brain development.

4.5 Modifier genes

None validated. Mechanistically plausible but untested candidates within the pathway: OAZ1/OAZ2/OAZ3 (antizymes — the very machinery the truncation escapes), AZIN1 (antizyme inhibitor), AMD1, SRM, SMS, SAT1 (catabolic acetylation/export), and the polyamine transport system.

4.6 Epigenetics

No BABS-specific DNA methylation episignature has been published. (A DNA-methylation episignature screen would be a natural, tractable study.)
Indirect but relevant: polyamines are decarboxylated-SAM donors and chromatin-associated polycations; the K6/ODC mouse literature shows elevated polyamines "alter chromatin remodeling and cell signaling leading to metabolic reprogramming" (PMID:41925768).
Regulatory (eQTL) variation at ODC1 is extensive: Prokop et al. identified 900 variants associated with ODC1 expression across 1,414,872 bases around the locus, including rs2302615 (muscle, p=9.4×10⁻⁷) and rs77575195 (tibial nerve, p=8.3×10⁻⁹), "suggesting a high selection on ODC1 expression levels throughout human evolution" (PMID:33806076).

4.7 Chromosomal abnormalities

None reported. BABS is not caused by CNVs, translocations, or aneuploidy. GeneReviews explicitly states gene-targeted deletion/duplication analysis is "not required" given the gain-of-function mechanism — an intragenic deletion would not produce BABS.

5. Environmental Information

Environmental factors: Not applicable. No toxin, radiation, pollutant, or occupational exposure is implicated in BABS causation.
Lifestyle factors: Not applicable to causation. Post-diagnosis, caloric management matters for the overgrowth/obesity trajectory, and dietary polyamine restriction is an investigational (unproven) adjunct.
Infectious agents: Not applicable. No infectious trigger. (Note the ironic pharmacological link in the other direction: eflornithine's original indication is Trypanosoma brucei gambiense African sleeping sickness, where trypanosomal ODC's stability — it lacks the antizyme system, PMID:7730330 — is the drug's selectivity basis.)

6. Mechanism / Pathophysiology

6.1 The causal chain (upstream → downstream)

[MOLECULAR — trigger]
de novo heterozygous 3'-end ODC1 variant (exon 12 / intron 11 splice site)
↓  (last-exon location → escapes nonsense-mediated decay)
[MOLECULAR]
Production of C-terminally truncated ODC protein lacking the 37-residue
degradation domain (aa ~425–461), but retaining full catalytic activity
↓
[MOLECULAR]
Loss of antizyme-stimulated, ubiquitin-INDEPENDENT 26S proteasomal
degradation of ODC  (GO:0010499)
↓
[MOLECULAR]
Cellular accumulation of enzymatically active ODC protein
(12–17× normal activity in dermal fibroblasts; 125–137× in RBCs)
↓
[MOLECULAR / metabolic]
Excess flux: L-ornithine → putrescine  (GO:0009446 putrescine biosynthetic process;
GO:0004586 ornithine decarboxylase activity)
→ putrescine accumulation; compensatory SAT1 acetylation and cellular export
→ elevated plasma N-acetylputrescine and acisoga
↓
[CELLULAR]
Polyamine-driven dysregulation of cell proliferation and differentiation
   ├── neural progenitor over-proliferation / disturbed neurodevelopment
   └── hair follicle outer root sheath keratinocyte dysfunction
↓
[TISSUE]
   ├── Abnormal cortical/white-matter architecture, perivascular space dilation,
   │   periventricular cysts, callosal dysgenesis
   ├── Hair follicle failure → anagen disruption → clumped hair shedding;
   │   follicular cyst formation
   └── Somatic overgrowth / macrocephaly
↓
[ORGANISM]
Global developmental delay, ID, hypotonia, alopecia, dysmorphism,
± epilepsy, ± behavioral phenotypes

Therapeutic interruption point: eflornithine irreversibly inhibits the accumulated ODC enzyme at the first metabolic node, collapsing putrescine production and normalizing downstream metabolites — with demonstrable reversal of hair, tone, developmental, and even white-matter MRI phenotypes.

6.2 Molecular pathway detail

Polyamine biosynthesis (KEGG hsa00330 arginine & proline metabolism; Reactome "Metabolism of polyamines" R-HSA-351202):

L-arginine → L-ornithine (ARG1/ARG2; also LACC1 from L-citrulline)
L-ornithine --[ODC1, PLP-dependent, EC 4.1.1.17]--> putrescine + CO2   ← RATE-LIMITING; the BABS lesion
putrescine + dcSAM --[SRM]--> spermidine
spermidine + dcSAM --[SMS]--> spermine
(catabolic arm: SAT1 acetylation → PAOX/SMOX back-conversion or export)
(spermidine → hypusination of eIF5A via DHPS + DOHH)

The degradation circuit that BABS breaks (this is the mechanistic heart of the disease and is supported by classic, well-quotable primary literature):

"Ornithine decarboxylase (ODC) was converted from a protein with a short intracellular half-life in mammalian cells to a stable protein by truncating 37 residues at its carboxyl terminus. Cells expressing wild-type protein lost ODC activity with a half-life of approximately 1 hour. Cells expressing the truncated protein, however, retained full activity for at least 4 hours…Thus, a carboxyl-terminal domain is responsible for the rapid intracellular degradation of murine ODC." — Ghoda et al., Science 1989 (PMID:2928784)

"…purified 26S proteasome complex, but not the 20S proteasome, catalyses ODC degradation in the absence of ubiquitin. These results strongly suggest that the 26S proteasome, widely viewed as specific for ubiquitin-conjugated proteins, is the main enzyme responsible for ODC degradation." — Murakami et al., Nature 1992 (PMID:1334232)

And the mapping onto BABS:

"Antizyme binds to transient ODC monomer, which results in the exposure of the ODC carboxy (C)-terminal tail that is subsequently recognized by the 26S proteasome for degradation…the final 37 amino-acid residues of the ODC carboxy (C)-terminal tail constitute an ODC destabilization domain that is required for antizyme-stimulated ODC degradation…If absent/deleted, enzymatically active ODC protein is not properly degraded and consequently accumulates in cells." — Bachmann & Bupp 2024 (PMID:37469105)

Note the elegance for KB modeling: the 1989 Ghoda experiment is, in effect, an in vitro pre-enactment of the human BABS allele — the same 37-residue truncation, three decades earlier.

6.3 Cellular processes

Process	GO term	Direction	Evidence
Ornithine decarboxylase activity	GO:0004586	INCREASED	PMID:31249027
Putrescine biosynthetic process	GO:0009446	INCREASED	PMID:30239107, 31249027
Polyamine biosynthetic process	GO:0006596 (verify label)	INCREASED	PMID:37469105
Proteasomal ubiquitin-independent protein catabolic process	GO:0010499	DECREASED	PMID:1334232, 2928784
Positive regulation of cell population proliferation	GO:0008284	INCREASED	PMID:33806076
Nervous system development / neurogenesis	GO:0007399 / GO:0022008	ABNORMAL	PMID:33806076
Hair follicle development / hair cycle	GO:0001942 / GO:0042633	ABNORMAL	PMID:8618048, 7671221
Protein stabilization	GO:0050821	INCREASED (pathological)	PMID:2928784

6.4 Protein dysfunction

The wild-type ODC monomer is 461 aa; the functional enzyme is an obligate homodimer with two shared active sites (UniProt P11926). BABS variants truncate at residues ~406–448, i.e., after the catalytic core but within the C-terminal degron, which is exactly why the protein is simultaneously stable and active — the worst combination. Prokop et al. note the C-terminus is under strong evolutionary conservation, including a predicted S-farnesylation site at C454, "the most conserved site of all C-terminal amino acids" (PMID:33806076).

This is neither misfolding nor aggregation nor loss of catalysis — it is loss of a degradation signal, a comparatively uncommon disease mechanism worth flagging as such in the KB.

6.5 Metabolic changes

Measured in patients: - RBC ODC enzyme activity: 125–137× control - Primary dermal fibroblast ODC activity: 12–17× control - Putrescine (CHEBI:17148): markedly elevated in fibroblasts and RBCs - Plasma N-acetylputrescine: >97.5th percentile (Z-score vs 866-child reference cohort) - Acisoga [N-(3-acetamidopropyl)pyrrolidin-2-one]: >97.5th percentile - Ornithine (CHEBI:15729) and N-acetylarginine: BELOW the 2.5th percentile at therapy start — consistent with substrate drawdown by the hyperactive enzyme; both normalized on eflornithine (PMID:34282722) - Spermidine (CHEBI:16610) and spermine (CHEBI:15746): "otherwise normal polyamine levels" in plasma clinical metabolomics (PMID:30475435) — an important specificity point: the biochemical signature is putrescine/N-acetylputrescine-selective, not a global polyamine elevation.

"Plasma clinical metabolomics analysis demonstrates elevation of N-acetylputrescine, the acetylated form of putrescine, with otherwise normal polyamine levels." — Rodan et al. 2018 (PMID:30475435)

"…we detected exceptionally high ODC enzyme activity in both primary dermal fibroblasts (12-17-fold of controls) and red blood cells (RBCs) (125-137-fold of controls), using a specific 14C radioactive ODC activity assay." — Schultz et al. 2019 (PMID:31249027)

6.6 Immune system involvement

Not a primary feature of BABS. No immunodeficiency or autoimmunity reported. However, ODC1/polyamine metabolism is deeply embedded in myeloid immunometabolism — LACC1 converts L-citrulline to L-ornithine and "serv[es] as a bridge between proinflammatory nitric oxide synthase (NOS2) and polyamine immunometabolism," with LACC1 phenotypes requiring downstream ODC1 (PMID:35978195); and AhR-driven Odc1 transcription suppresses macrophage pyroptosis via spermine-mediated NLRP3 inhibition (PMID:39113799). These make immune phenotyping of BABS patients a reasonable unexplored question, but there is currently no evidence of clinical immune dysfunction — do not assert one.

6.7 Tissue damage mechanisms

BABS is a developmental/dysregulation disorder rather than a degeneration/necrosis disorder. There is no evidence for oxidative stress, ischemia, fibrosis, or necrosis as primary mechanisms. The tissue-level abnormalities are maldevelopmental (cortical architecture, white matter myelination, follicular structure) and — critically — at least partly reversible, which argues against fixed structural destruction:

"Repeat MRI…demonstrated normalization of the cerebral white matter signal with decrease in volume…resolution of all previously noted cysts." — Rajasekaran et al. 2021 (PMID:34282722)

6.8 Molecular profiling

Transcriptomics: Prokop et al. mined fetal-brain RNA-seq and cerebral organoid data; ODC1 expression is "markedly elevat[ed] correlating to early development, while neurons/glia progenitors are still proliferating and maturing," and elevated in ventricular zones and in SOX-marker-positive pluripotent/immature cells (PMID:33806076). No BABS patient transcriptome has been published.
Proteomics: No BABS proteomic dataset. Patient-level protein data are targeted Western blots of ODC (PMID:30239107, PMID:31249027).
Metabolomics: The best-developed omic layer. Untargeted UPLC-MS clinical metabolomics with Z-scores against an 866-child reference cohort is the established diagnostic/monitoring modality (PMID:34282722). Dansyl-chloride derivatization HPLC is the improved reference method for polyamine quantitation (PMID:40382146); the RP-HPLC + ¹⁴C-ornithine ODC activity protocol is published in detail (PMID:40382142).
Lipidomics: none.
Single-cell / spatial: none in BABS patients. Cerebral organoid single-cell data inform the neural-progenitor hypothesis (PMID:33806076).
Functional genomics screens: No BABS-specific CRISPR/RNAi screen. Extensive ODC1 dependency data exist in DepMap for cancer contexts (not disease-relevant here).

6.9 Cell types and anatomical processes — suggested ontology bindings

Entity	Term	Note
Outer root sheath cell	CL:0002561	The K6/ODC transgene's target cell; direct mouse-human correspondence
Keratinocyte	CL:0000312
Neural progenitor cell	CL:0011020	verify canonical label casing
Radial glial cell	CL:0000681	Ventricular zone
Fibroblast (skin)	CL:0002620	The accessible patient biopsy cell for ODC assay
Erythrocyte	CL:0000232	The accessible patient blood cell for ODC activity/putrescine
Hair follicle	UBERON:0002073
Hair follicle bulge	UBERON:0005975	Stem cell niche implicated in K6/ODC
Cerebral white matter	UBERON:0002316
Corpus callosum	UBERON:0002336
Lateral ventricle	UBERON:0002285
Cerebellar vermis	UBERON:0004720

7. Anatomical Structures Affected

7.1 Organ level

Primary: - Central nervous system (UBERON:0001017) — the dominant burden: cerebral cortex (UBERON:0000956), cerebral white matter (UBERON:0002316), corpus callosum (UBERON:0002336), periventricular/germinal matrix regions, lateral ventricles (UBERON:0002285), cerebellar vermis (UBERON:0004720), hippocampus (UBERON:0002421), optic chiasm (UBERON:0000959) - Skin and appendages (UBERON:0002097) — hair follicle (UBERON:0002073), scalp (UBERON:0000403), eyebrow (UBERON:0001710), eyelash (UBERON:0001711), nail (UBERON:0001705)

Secondary / systemic: - Musculoskeletal — generalized hypotonia; one case with proximal myopathy and heel/ankle contractures - Craniofacial skeleton — macrocephaly, high forehead, high palate, retrognathia, cupped/large ears - Gastrointestinal — feeding difficulty, aspiration, constipation - Special senses — cochlea/inner ear (sensorineural hearing loss), eye (ptosis, blepharophimosis, refractive error, strabismus) - Genitourinary — cryptorchidism (testis, UBERON:0000473) - Cardiovascular — one prenatal case with ventricular septal defect (PMID:41931584); the index patient had a cutaneous vascular malformation (PMID:30239107). Not established as a recurrent feature. - Hepatic — hepatic calcifications in one case (PMID:37092498); isolated finding

Body systems: nervous, integumentary, musculoskeletal, digestive, sensory; cardiovascular and hepatobiliary only anecdotally.

7.2 Tissue and cell level

Hair follicle epithelium, specifically outer root sheath keratinocytes (CL:0002561) — the cell type in which the K6 promoter drove ODC in the transgenic mouse that phenocopies BABS skin/hair
Neural progenitor cells (CL:0011020) / radial glia (CL:0000681) of the ventricular and subventricular zones
Oligodendrocytes / myelinating glia — implicated by the white-matter signal abnormalities and their normalization on treatment
Dermal fibroblasts (CL:0002620) and erythrocytes (CL:0000232) — biochemically abnormal and diagnostically accessible

7.3 Subcellular level

Cytosol (GO:0005829) — ODC is a cytosolic enzyme; this is where the pathological accumulation occurs
Proteasome complex (GO:0000502), specifically the 26S proteasome — the machinery whose substrate recognition is evaded
Nucleus (GO:0005634) — polyamines are chromatin-associated polycations

7.4 Localization / lateralization

Brain findings are predominantly bilateral (bilateral paraventricular cysts, bilateral perivascular space dilation, diffuse white matter change), though asymmetric/unilateral lesions occur (right subependymal cyst; focal polymicrogyria; porencephalic cyst). Alopecia is diffuse/generalized with occasional preserved tufts — e.g., "scalp alopecia outside of tuft of long and coarse hair on central posterior scalp" (PMID:37092498).

8. Temporal Development

8.1 Onset

Prenatal: polyhydramnios (55–80%), decreased fetal movement, and — in the 2026 report — second-trimester macrocephaly and VSD detectable by ultrasound (PMID:41931584). Prenatal ventriculomegaly and cerebral cysts have been detected (PMID:37092498).
Birth: macrosomia/large for gestational age, macrocephaly at birth, hair present (may be sparse or atypically colored), congenitally absent/sparse eyebrows and eyelashes.
Neonatal: hypotonia, feeding difficulty, hypoglycemia, hyperbilirubinemia; respiratory distress with NICU stay in one case.
First weeks of life: the defining event — hair loss in large clumps (HP:0003623 Neonatal onset / HP:0011463 Childhood onset for later features).
Infancy onward: developmental delay becomes evident.
Adolescence/adulthood: late-onset epilepsy possible (age 14 in the one reported case).

Onset pattern: congenital/insidious, not acute. Suggested HPO onset term: HP:0003577 Congenital onset for the syndrome; HP:0003623 Neonatal onset for the alopecia.

8.2 Progression

Stages: no formal staging system exists.
Progression rate: the neurodevelopmental phenotype is static-with-slow-acquisition, not neurodegenerative. Skills are gained slowly (walking 17 months–4 years) rather than lost. One patient showed progressive motor decline with myopathy and loss of ambulation over 12 years, indicating that a subset may have a progressive motor course (PMID:37092498).
Course pattern: chronic, lifelong, generally non-progressive on the cognitive axis; epilepsy, when present, can be progressive and refractory.
Duration: lifelong.

8.3 Patterns

Remission: no spontaneous remission. Treatment-induced improvement is well documented — hair regrowth by 1–2 months of eflornithine, motor gains by 4 months, MRI normalization by ~6 months, sustained at >3 years (PMID:34282722, PMID:37469105).
Critical periods: This is the most clinically consequential open question. The mouse data are unusually informative here:

"The ODC inhibitor 2-difluoromethylornithine could prevent hair loss and partially normalize skin histology if administered before the onset of ODC overexpression. 2-Difluoromethylornithine could also reactivate hair growth in animals with complete hair loss." — Soler et al., J Invest Dermatol 1996 (PMID:8618048)

That is: for the follicular phenotype, both prevention and rescue are achievable. Whether the same holds for the neurodevelopmental phenotype — and whether there is a closing window for cortical/white-matter benefit — is unknown and is the central natural-history question for the field. The prenatal-diagnosis capability now demonstrated (PMID:41931584) makes very-early or even prenatal intervention a live question.

9. Inheritance and Population

9.1 Epidemiology

Prevalence: UNKNOWN. GeneReviews: "The prevalence of Bachmann-Bupp syndrome is unknown."
Cumulative reported cases (a moving target — cite the year):

Source (year)	Published cases	Known worldwide
GeneReviews (2022)	9	+3 unreported known to authors
Wikipedia / secondary (Nov 2022)	—	"<30 individuals"
Bachmann & Bupp, DMCN (2024)	11	<30
Bupp et al., AJMG-C (2025)	11	11 + 6 unreported = 17
VanSickle et al., AJMG-A (2026)	12	18, spanning eight countries

Best current statement: ~12 published cases; ~18–20 known worldwide across ≥8 countries as of 2026. Suggested prevalence_class: BELOW_1_IN_1000000 with measure_type: CASES_IN_LITERATURE and prevalence_class: NOT_YET_DOCUMENTED as an alternative honest encoding.
Incidence: not estimable.
Ascertainment caveat: BABS is diagnosable only by sequencing, and the phenotype (DD + alopecia) is distinctive enough that it is likely under-ascertained rather than over-ascertained. Expect the count to rise with exome/genome uptake.

9.2 Inheritance genetics

Pattern: Autosomal dominant (HP:0000006), essentially always de novo.

"All probands reported to date with BABS whose parents have also undergone molecular genetic testing have the disorder as the result of a de novo ODC1 pathogenic variant." — GeneReviews (PMID:36007106)
Penetrance: Believed complete (100%) — but note this is inferred from a tiny, ascertainment-biased de novo case series with no transmitted families; treat "100% penetrance" as provisional.
Expressivity: Variable — spanning nonverbal severe ID to a 12-year-old who reads and writes; epilepsy in only ~8%; macrocephaly in only 66–75%.
Genetic anticipation: Not applicable (not a repeat expansion).
Germline mosaicism: Not documented, but assumed possible; drives the recurrence-risk counseling figure.
Recurrence risk:
Parents test negative → ~1% sibling recurrence risk (germline mosaicism allowance)
A parent carries the variant → 50%
Offspring of an affected individual → 50% (no reported reproduction to date)
Founder effects: None. All variants are private de novo events; the only recurrence (c.1242-2A>G in ≥3 individuals) reflects a mutational hotspot at a canonical splice acceptor, not a shared haplotype.
Consanguinity: No role — dominant de novo mechanism.
Carrier frequency: Not applicable.

9.3 Population demographics

Ethnic/ancestry predilection: None known. Cases span eight countries (PMID:41410504), including the US, EU, and a Chinese prenatal case (PMID:41931584). The index case was described as Caucasian; no ancestry enrichment has been reported.
Geographic distribution: worldwide, no clustering. Apparent geographic distribution reflects where genomic sequencing and the ICPD network reach, not true biology.
Sex ratio: Reported cases include both sexes (the index case and several others are female; the 23-year-old epilepsy case is male; HPOA lists cryptorchidism in 2/3 males). No sex bias is established; the sample is far too small to estimate a ratio. Do not assert one.
Age distribution: reported ages at description range from prenatal/12 months to 23 years. No adult natural-history data beyond age 23.

10. Diagnostics

10.1 Suggestive clinical findings (GeneReviews)

Consider BABS in an individual with: 1. "An unusual pattern of noncongenital alopecia due to sudden-onset hair loss shortly after birth" — the single most specific pointer 2. Developmental delay, typically moderate to severe 3. Hypotonia 4. Supportive: "metabolomic profile showing abnormal polyamine pathway metabolites, including increased N-acetylputrescine"

10.2 Establishing the diagnosis

Requires all three of: consistent clinical/laboratory findings + a heterozygous pathogenic/likely pathogenic ODC1 variant + abnormal polyamine-pathway metabolomics. "Heterozygous pathogenic variants in ODC1 that cause BABS are typically gain-of-function variants."

10.3 Genetic testing

Modality	Utility in BABS	Notes
Exome sequencing (ES)	High — the historical diagnostic route	All index cases found by WES (PMID:30239107, PMID:34282722)
Genome sequencing (GS)	High	Better for the intron-11 splice variants
*Single-gene ODC1* sequencing**	100% detection (9/9) per GeneReviews Table 1	Appropriate when the alopecia+DD gestalt is recognized
Multigene panel	Useful if ODC1 is on the ID/alopecia panel	Confirm gene content before ordering
Deletion/duplication analysis	NOT required	GoF mechanism; CNVs do not cause BABS
Chromosomal microarray	Low yield for BABS (may be done as first-tier DD workup)	Normal in BABS
Karyotype / FISH	Not indicated
mtDNA testing	Not indicated
Repeat expansion testing	Not indicated

Reference sequence for reporting: NM_002539.3 / NP_002530.1.

10.4 Biochemical / omics diagnostics — the BABS-distinctive layer

BABS is one of the few neurodevelopmental disorders with a directly measurable, treatment-responsive enzymatic biomarker. Three assays:

Plasma untargeted clinical metabolomics (UPLC-MS) with Z-scores vs a pediatric reference cohort (n=866). Signature: ↑ N-acetylputrescine, ↑ acisoga, ↓ ornithine, ↓ N-acetylarginine — with normal spermidine/spermine. Suitable for both diagnosis and treatment monitoring (PMID:34282722).
ODC enzyme activity assay — ¹⁴C-ornithine radioassay on red blood cells (125–137× control) or primary dermal fibroblasts (12–17× control). Detailed protocol published (PMID:40382142). This is the assay that adjudicates VUSs (PMID:40167220).
Polyamine quantitation by RP-HPLC with dansyl chloride derivatization (PMID:40382146).

Also: Western blot for ODC protein in RBCs/fibroblasts (elevated).

Sample collection, shipment, consent, and biobanking protocols for international polyaminopathy patients are published (PMID:40382145) and coordinated through the ICPD.

10.5 Imaging, electrophysiology, other clinical tests

Brain MRI — abnormal in nearly all; no pathognomonic pattern. Findings listed in §3.4. MRI also serves as a treatment-response readout (white matter normalization, cyst resolution).
Prenatal ultrasound — polyhydramnios, macrocephaly, ventriculomegaly, cerebral cysts, VSD; can prompt prenatal diagnosis (PMID:41931584).
EEG — indicated only if seizures are suspected.
EMG/NCS — one patient's proximal myopathy was identified by EMG (PMID:37092498).
Audiology (sensorineural hearing loss) and ophthalmology (refractive error, strabismus, ptosis) — annually.
Skin biopsy — for fibroblast culture (research/functional assay), not for histopathology per se. No diagnostic histopathologic signature has been defined; follicular cysts are the notable dermatopathologic finding.
Echocardiogram — only if a cardiac anomaly is suspected; not routine.

10.6 Differential diagnosis (GeneReviews Table 3)

Gene	Disorder	Distinguishing from BABS
*LSS*	LSS-related neurodevelopmental disorder	Alopecia is CONGENITAL (BABS alopecia is post-natal onset)
*CHD3*	Snijders Blok-Campeau syndrome	Ventriculomegaly, joint laxity, different dysmorphic gestalt; no clumped hair loss
*DCAF17*	Woodhouse-Sakati syndrome	Hypogonadism, diabetes mellitus; later onset
*PAK1*	IDDMSSD	Ataxia; no consistent hair/skin abnormality
*PTEN*	Cowden syndrome	Facial trichilemmomas, cancer predisposition
Multiple	Ectodermal dysplasias	Congenital alopecia; dental anomalies (BABS is not associated with dental issues)

Also worth listing: other polyaminopathies — Snyder-Robinson syndrome (SMS, X-linked, ~63% epilepsy, no alopecia), Faundes-Banka syndrome (EIF5A), DHPS deficiency, DOHH disorder. Per the 2026 review, macrocephaly + non-congenital alopecia is what separates BABS from the other four:

"The majority of patients (9/12, 75%) also presented with macrocephaly, which would be considered a distinctive feature of BABS, as this was not reported in any patients with DHPS deficiency, FABAS, or DOHH disorder." (PMID:41410504)

10.7 Screening of asymptomatic individuals

Newborn screening: BABS is not on any NBS panel. It is, however, an intriguing theoretical candidate given (a) a measurable metabolite in blood and (b) an available treatment with a possible early-intervention window — but no NBS pilot exists and this should be framed as a hypothesis, not a recommendation.
Carrier screening: not applicable (de novo dominant).
Cascade screening: not applicable in practice; parental testing is done to establish de novo status and refine recurrence risk.

11. Outcome / Prognosis

11.1 Survival and mortality

No BABS-specific mortality data, survival curves, or life-expectancy estimates exist. The oldest reported patient is 23 years. No deaths have been reported in the published series. Do not assert a life expectancy.
Mortality risk, where present, would be expected to derive from aspiration/feeding complications and refractory epilepsy, not from a disease-intrinsic lethal process.

11.2 Morbidity and function

Dominant morbidity: moderate-to-severe intellectual disability, motor delay/hypotonia, communication impairment (three individuals nonverbal at last report), feeding difficulty, and — in one long-followed patient — loss of independent ambulation.
Functional range is wide: from nonverbal and wheelchair-dependent to literate with moderate ID.
Disability outcomes: lifelong need for special education, PT/OT/SLP, and in some cases assistive mobility and enteral feeding.
No validated QoL instrument data. (ICF-based functional characterization has not been done.)

11.3 Complications

Aspiration and recurrent respiratory events; refractory epilepsy (rare but severe); constipation; obesity secondary to overgrowth; recurrent follicular cysts requiring dermatologic/surgical drainage; refractive error/strabismus; sensorineural hearing loss; contractures/orthopedic sequelae of hypotonia and immobility.

11.4 Cancer risk — an unresolved, important question

ODC1 is a canonical c-Myc target and proto-oncogenic driver; K6/ODC mice develop spontaneous skin tumors (PMID:7671221) and are so tumor-prone they are used as a carcinogen-detection bioassay (PMID:10906419). Somatic ODC1/polyamine dysregulation is pervasive in human cancer.

Rodan et al. therefore raised surveillance explicitly:

"As the ODC1 gene has been implicated in neoplasia, cancer surveillance may be important in this disorder." (PMID:30475435)

However: no malignancy has been reported in any individual with BABS to date, GeneReviews' surveillance table does not include cancer screening, and the 2025 treatment review documents no cancer-monitoring protocol. With ~18 patients and a maximum reported age of 23, the cohort is far too small and young to detect an elevated cancer risk.

Recommended KB framing: encode this as an open mechanistic hypothesis / knowledge gap (kind: KNOWLEDGE_GAP, or HUMAN_MODEL_MISMATCH — strong mouse tumor phenotype, no human confirmation), not as an asserted phenotype. Note the pleasing irony that the treatment (DFMO) is itself an established chemopreventive agent (colorectal adenoma prevention, NCT00118365), so treated patients may be incidentally protected.

11.5 Recovery potential and prognostic factors

Recovery potential is genuinely favorable on treatment and this is the single most important prognostic modifier known:

"She demonstrated remarkable improvement in both neurological symptoms and cortical architecture. She gained fine motor skills with the capacity to feed herself and sit with support." (PMID:34282722) "Treated patients have consistently shown improvement in muscle tone, developmental milestones, and hair regrowth." (PMID:40167220)
Prognostic factors (all inferred, none validated): age at treatment initiation; presence of refractory epilepsy; severity of baseline structural brain abnormality; feeding/aspiration status.
Prognostic biomarkers: N-acetylputrescine Z-score and RBC ODC activity are pharmacodynamic markers with demonstrated normalization on therapy; whether they predict developmental outcome is untested.

12. Treatment

12.1 Targeted therapy — eflornithine (DFMO): the flagship

Attribute	Detail
Agent	Eflornithine / α-difluoromethylornithine (DFMO); brand Iwilfin® (oral, FDA-approved Dec 2023 for high-risk neuroblastoma maintenance)
CHEBI	CHEBI:41948 (eflornithine); CHEBI:749357 (hydrochloride)
NCIT	NCIT:C226 Eflornithine; NCIT:C1579 Eflornithine Hydrochloride
Mechanism	"DFMO is a specific, mechanism-based irreversible (suicide) inhibitor of ODC" (PMID:37469105). Directly inhibits the accumulated pathological enzyme.
Therapeutic modality	`SMALL_MOLECULE`
treatment_term	NCIT:C15986 Pharmacotherapy, with `therapeutic_agent` = CHEBI:41948
target_mechanisms	`INHIBITS` the ODC-accumulation / putrescine-overproduction node — a textbook drug-target pattern
Route/formulation	Oral. Solution (Orbus Therapeutics) and powder (ScinoPharm Taiwan) supplied for clinical use
Dosing (BABS protocol)	"Patients begin at a dose of 500 mg/m²/BID for 3 months, increase to 750 mg/m²/BID for another 3 months, and then finally increase to 1000 mg/m²/BID indefinitely" (PMID:40167220) — modeled on pediatric neuroblastoma dosing
Regulatory status for BABS	Not FDA-approved for BABS. Five US patients treated under FDA-approved single-patient Investigational New Drug (IND) protocols; ≥1 patient treated off-label outside the US. Earlier reports describe compassionate-use approval.
Number treated	6 as of the 2025 report (5 US IND + 1 ex-US); DMCN 2024 reported 4 US + 1 EU
Pharmacology	Rapid renal clearance necessitates sustained high dosing; pediatric range 1.0–6.0 g/m²/day
Safety	"DFMO has extraordinary safety and a specific long-term dosing strategy in children with neuroblastoma even if administered daily for several years." No adverse effects reported in the treated BABS patients. Known class effects to monitor (from oncology/trypanosomiasis use): reversible ototoxicity/hearing loss, myelosuppression, GI upset, and — for topical use — skin irritation. Ototoxicity monitoring is especially relevant given baseline SNHL risk in BABS.

Documented outcomes (index patient, Rajasekaran 2021 / Bachmann 2024):

Domain	Timeline & outcome
Eyebrows	Regrowth at 1 month
Scalp hair	Diffuse regrowth in normal pattern at 2 months
Motor	Self-feeding with spoon (with assistance) and unassisted sitting at 4 months; later walker use
Neuroimaging	"normalization of the cerebral white matter signal with decrease in volume…resolution of all previously noted cysts" at ~6 months
Metabolites	N-acetylputrescine and acisoga normalized at initiation and stayed reduced; ornithine and N-acetylarginine rose into normal range
Skin	"follicular cysts have not recurred for either patient" (PMID:37469105, PMID:36443247)
Durability	"just over 3 years into treatment and on maintenance dosing, the patient continues to show significant clinical improvement."

"This work highlights the strategy of repurposing drugs to treat a rare disease." — Rajasekaran et al. 2021 (PMID:34282722)

Caveats to encode honestly: all outcome data are uncontrolled single-arm case reports (n≤6) with no blinding, no comparator, and no pre-specified endpoints. Developmental gains in a young child on intensified therapy services are confounded. The MRI and metabolite changes are the most objective evidence. There is no randomized or controlled trial of DFMO in BABS, and none is registered on ClinicalTrials.gov (searches for BABS/ODC1/polyaminopathy return only oncology and chemoprevention DFMO trials: NCT00118365, NCT00086736, NCT03536728).

12.2 Other pharmacotherapy / investigational

Other ODC inhibitors and DFMO analogs — listed by GeneReviews as under investigation.
Polyamine transport inhibitors — e.g., AMXT 1501, studied with DFMO in oncology (NCT03536728); mechanistically rational for BABS (blocking uptake of dietary/microbial polyamines that could bypass ODC inhibition) but untested in BABS.
Polyamine-restricted diet — investigational (GeneReviews).
Gut-flora-directed antibiotics to reduce luminal polyamine production — proposed by Rodan et al. (PMID:30475435); never tested.
Anti-seizure medications — standard; note one reported case refractory to multiple agents and the ketogenic diet.

12.3 Advanced therapeutics

Gene therapy / gene editing: none developed. Conceptually, BABS is an allele-selective knockdown target (ASO or siRNA against the mutant allele) rather than a gene-replacement target — the pathology is a toxic stabilized protein, not absent protein. No such program exists. Note the KB's antisense_oligonucleotide_therapy module RNase-H-knockdown paradigm would be the natural conceptual fit if one were ever developed.
Cell therapy, RNA therapy, immunotherapy: none; not applicable.
Pharmacogenomics: no PharmGKB/CPIC guidance for eflornithine relevant to BABS.

12.4 Supportive, rehabilitative, and surgical management (GeneReviews Table 5)

Manifestation	Intervention	NCIT suggestion
Developmental delay / ID	Early intervention (0–3), developmental preschool (3–5), IEP, ABA and behavioral interventions	NCIT:C15315 Rehabilitation
Motor delay / hypotonia	Physical therapy; occupational therapy	NCIT:C15302 Physical Therapy; NCIT:C121351 Occupational Therapy
Speech delay / nonverbal	Speech-language pathology, AAC	NCIT:C159273 Speech Therapy
Feeding difficulties	Feeding therapy; NG/G-tube if needed	NCIT:C15433 Nutritional Support
Obesity / overgrowth	Nutritional intervention, caloric restriction	NCIT:C15447 Dietary Intervention
Constipation	Stool softeners, prokinetics, laxatives	NCIT:C15986 Pharmacotherapy
Epilepsy	Standard ASMs (one case refractory)	NCIT:C15986 Pharmacotherapy
Refractive error / strabismus	Standard ophthalmologic care	NCIT:C49236 Therapeutic Procedure
Hearing loss	Audiologic management / amplification	NCIT:C49236
Follicular cysts	Dermatologic treatment, surgical drainage	NCIT:C15329 Surgical Procedure
Family support	Social work	NCIT:C15747 Supportive Care
Reproductive counseling	Genetic counseling	NCIT:C15240 Genetic Counseling

12.5 Surveillance (GeneReviews Table 6)

Item	Frequency
Growth parameters	Each visit
Nutritional status / safety of oral intake	Each visit
Constipation assessment	Each visit
Mobility & self-help skills (OT/PT)	Each visit
Developmental progress / educational needs	Each visit
Behavioral assessment (ASD, attention, aggression)	Annually
Ophthalmology	Annually or as indicated
Audiology	Annually or as indicated
Complete skin examination for follicular cysts	At least annually
Seizure assessment	As clinically indicated
Family/social work support needs	Each visit

Notably absent from GeneReviews surveillance: cancer screening (see §11.4).

12.6 Treatment strategy

No formal algorithm exists. In practice: 1. Confirm diagnosis (variant + metabolomics + ODC activity — the latter is decisive for VUSs). 2. Institute full multidisciplinary supportive/rehabilitative care immediately. 3. Refer to the ICPD for biochemical characterization and biobanking. 4. Pursue eflornithine via single-patient IND (US) or off-label pathway; escalate 500 → 750 → 1000 mg/m² BID. 5. Monitor pharmacodynamically (N-acetylputrescine Z-score, RBC ODC activity) and clinically (hair, tone, milestones, MRI); monitor for DFMO class toxicity including audiometry and CBC.

Personalized-medicine framing: BABS is a genuine N-of-1-to-N-of-6 precision medicine exemplar — genotype-directed, biomarker-monitored, mechanism-matched.

13. Prevention

13.1 Primary prevention

Not possible. BABS arises from de novo germline variants with no known modifiable determinant. There is no vaccination, no risk-factor modification, and no environmental lever.

13.2 Secondary prevention (early detection)

Genomic: early ES/GS in an infant with the DD + post-natal clumped alopecia gestalt is the practical early-detection route.
Biochemical: plasma N-acetixputrescine on clinical metabolomics can flag the diagnosis; hypothetically a newborn-screening analyte, but no NBS program or pilot exists — this is speculation, not policy.
Prenatal: the 2026 report demonstrates that second-trimester ultrasound findings (macrocephaly, VSD) can trigger prenatal molecular diagnosis (PMID:41931584), and polyhydramnios/ventriculomegaly/cerebral cysts are recurrent prenatal signals.
Rationale for early detection is unusually strong here because a mechanism-matched treatment exists and mouse data show pre-onset DFMO prevents the follicular phenotype (PMID:8618048).

13.3 Tertiary prevention

This is where the actionable prevention lives: eflornithine to prevent progression/persistence of alopecia, hypotonia, follicular cysts, and possibly white-matter injury; aspiration precautions and feeding management; seizure control; caloric management to prevent obesity; annual skin/eye/ear surveillance.

13.4 Genetic screening and counseling

Genetic counseling (NCIT:C15240) is indicated for every family: confirm de novo status by parental testing; counsel ~1% sibling recurrence if parents are negative (germline mosaicism), 50% if a parent carries the variant, 50% for offspring of an affected individual.
Prenatal diagnosis and preimplantation genetic testing (PGT-M) are technically available once the familial variant is known: "Given this risk, prenatal and preimplantation genetic testing may be considered." (GeneReviews)
Carrier screening / population genetic screening: not applicable.

13.5 Immunization, public health, environmental interventions, prophylaxis

Immunization: routine childhood immunizations only; no disease-specific vaccine strategy. No contraindication known.
Public health / environmental interventions: not applicable.
Prophylaxis: no antimicrobial or other prophylaxis indicated. (Prophylactic antibiotics to suppress gut polyamine production is a mechanistic proposal, not a recommendation.)

14. Other Species / Natural Disease

14.1 Taxonomy and orthology

Species	NCBI Taxon	Gene	Notes
Homo sapiens	NCBITaxon:9606	ODC1 (Gene 4953)	The disease species
Mus musculus	NCBITaxon:10090	Odc1	The workhorse model; MGI ID MGI:97402 — verify
Rattus norvegicus	NCBITaxon:10116	Odc1	Antizyme biology largely worked out in rat systems
Danio rerio	NCBITaxon:7955	odc1	Used for other polyaminopathies (DHPS zebrafish model, PMID:39297975/PMC11429087); no BABS zebrafish model published
Trypanosoma brucei	NCBITaxon:5691	ODC	Pharmacologically pivotal — trypanosomal ODC lacks the antizyme degradation system and is thus constitutively stable, the basis for DFMO's selectivity (PMID:7730330)

The C-terminal degron is highly evolutionarily conserved — the predicted farnesylation site C454 is conserved in 215/220 sequences analyzed (PMID:33806076).

14.2 Natural disease in other species

None reported. There is no OMIA entry for a naturally occurring ODC1 disorder in companion animals, livestock, or wildlife found in this search. BABS-equivalent disease in animals exists only as engineered models. Veterinary relevance: nil.

14.3 Comparative biology

The comparative story is unusually clean and is the strongest cross-species evidence in the file: - The K6/ODC transgenic mouse (constitutive ODC in hair-follicle outer root sheath keratinocytes near the bulge stem cell niche) develops alopecia, dermal follicular cysts, excessive skin wrinkling, and enhanced nail growth — i.e., the exact dermatologic tetrad of BABS, including the follicular cysts and nail changes. - Bupp et al. framed the index human case explicitly against this:

"This is the first human case confirming similar symptoms observed in a transgenic ODC1 mouse model first described over 20 years ago." (PMID:30239107) - Evolutionary conservation of the mechanism is complete: the 37-residue C-terminal degron, antizyme-stimulated ubiquitin-independent 26S degradation, and DFMO sensitivity are all conserved mouse↔human. - Divergence: Trypanosoma brucei lacks antizyme-mediated ODC degradation entirely, which is why DFMO is a trypanocide — a natural "phenocopy" of the BABS lesion at the organismal level.

14.4 Transmission

Not applicable. BABS has no zoonotic potential and no cross-species transmissibility.

15. Model Organisms

15.1 The K6/ODC transgenic mouse — the phenocopy model

Construct: bovine keratin 6 promoter driving a mutated ODC transgene in outer root sheath keratinocytes (CL:0002561) of the hair follicle near the bulge stem cell niche. Model type: mammalian, transgenic (gain-of-function overexpression).

Phenotype recapitulation — excellent for the ectodermal arm:

"Effects observed include development of dermal follicular cysts, excessive skin wrinkling, enhanced nail growth, alopecia, and spontaneous tumor development. These results indicate that up-regulation of polyamine biosynthesis can profoundly disturb skin homeostasis and alter susceptibility to neoplastic development." — Megosh et al., Cancer Res 1995 (PMID:7671221)

"These transgenic mice have a normal first hair cycle, but lose their hair completely beginning 2-3 wk after birth… The ODC inhibitor 2-difluoromethylornithine could prevent hair loss and partially normalize skin histology if administered before the onset of ODC overexpression. 2-Difluoromethylornithine could also reactivate hair growth in animals with complete hair loss. Our results suggest that ODC is an important regulatory gene for the mouse hair follicle." — Soler et al., J Invest Dermatol 1996 (PMID:8618048)

Note the striking temporal parallel: mice have a normal first hair cycle then lose hair at 2–3 weeks; BABS infants have hair at birth then shed it in clumps within weeks.

Putrescine — not spermidine/spermine — is the effector, matching the human metabolomic signature:

"The regulatory polyamine in this model appears to be putrescine, the immediate product of ornithine decarboxylase." — Peralta Soler et al., Cancer Res 1998 (PMID:9563478)

Model limitations: (a) expression is skin/follicle-restricted (K6 promoter), so the model does not recapitulate the neurodevelopmental, macrocephaly, hypotonia, or brain-imaging phenotypes — the dominant human morbidity; (b) it is an overexpression model, not a knock-in of the human degron truncation, so the stoichiometry and cell-type distribution differ; (c) the tumor phenotype is prominent in mice but has not been observed in humans with BABS, a genuine human-model mismatch that should be recorded as such rather than translated forward.

Applications: hair-cycle biology; DFMO prevention-vs-rescue timing (directly informs the human critical-period question); skin carcinogenesis; and — as a 30-year retrospective published in 2026 — mechanisms of polyamine-promoted tumorigenesis including stem-cell recruitment, chromatin remodeling, metabolic reprogramming, angiogenesis, and immune modulation (PMID:41925768). Also validated as a sensitive carcinogen-identification bioassay (PMID:10906419).

15.2 The Odc1 knockout mouse — the loss-of-function arm

"Embryonic day E3.5 ODC-deficient embryos were capable of uterine implantation and induced maternal decidualization yet failed to develop substantially thereafter… loss of ODC does not affect cell growth per se but rather is required for survival of the pluripotent cells of the inner cell mass. Therefore, ODC plays an essential role in murine development." — Pendeville et al., Mol Cell Biol 2001 (PMID:11533243)

Odc1^-/-^ is embryonic lethal (peri-implantation); Odc1^+/-^ heterozygotes are "viable, normal, and fertile." This is directly relevant: it shows that (a) ODC1 haploinsufficiency does not produce BABS, reinforcing that BABS is GoF; and (b) complete ODC ablation is not survivable — which sets a theoretical floor on how aggressively ODC can be inhibited therapeutically (though DFMO's clinical safety record indicates a wide window).

15.3 Cellular and in vitro models

Patient-derived primary dermal fibroblasts — the best-characterized BABS cell model. Show 12–17× ODC activity, elevated ODC protein and putrescine; DFMO exposure "reduced the ODC activity and putrescine to levels observed in controls without adversely affecting cell morphology or inducing cell death" (PMID:31249027). This is the in vitro proof-of-concept that directly justified the human trial-of-one — an exemplary bench-to-bedside chain.
Patient RBCs — 125–137× ODC activity; a non-invasive biomarker source.
Cerebral organoids (not patient-derived) — used to link ODC1 expression to neural progenitor proliferation (PMID:33806076).
The 1989 Ghoda C-terminal truncation construct (PMID:2928784) is, retrospectively, the founding in vitro model of the BABS lesion.

15.4 Models that do NOT exist (gaps)

No knock-in mouse carrying a human BABS ODC1 C-terminal truncation allele — this is the most conspicuous missing model, and the only one that could address the neurodevelopmental phenotype and treatment-window question.
No BABS zebrafish model (in contrast to DHPS deficiency, which has one).
No patient-derived iPSC or iPSC-derived neuron/organoid model.
No conditional/neural-specific ODC overexpression model.
No MorPhiC ODC1 null-allele dataset identified.

15.5 Model resources

MGI (mouse), IMPC/KOMP (for Odc1 alleles), Alliance of Genome Resources, ZFIN, IMSR/JAX for strain availability. The ICPD (Corewell Health / Michigan State University / Snyder-Robinson Foundation) is the primary human-sample and biobanking resource (PMID:37092498, PMID:40382145).

Curation Notes: Evidence Classification and Verification Flags

Evidence-source tagging for KB items

Source type	PMIDs
HUMAN_CLINICAL	30239107, 30475435, 34477286, 34282722, 36443247, 37092498, 36007106, 37469105, 40167220, 41410504, 41931584
IN_VITRO	31249027, 2928784, 1334232, 40382142, 40382146
MODEL_ORGANISM	7671221, 8618048, 9563478, 11533243, 10906419, 9688139, 7730330, 41925768
COMPUTATIONAL	33806076 (molecular dynamics, eQTL mining, organoid RNA-seq reanalysis — mixed; split evidence items by claim)
OTHER	36007106 (GeneReviews — expert consensus review)

Do not let model-organism evidence stand alone for human phenotypes. The K6/ODC skin-tumor phenotype in particular must not be carried into the human entry as a phenotype; encode it as a HUMAN_MODEL_MISMATCH discussion.

Items requiring verification before commit

c.1342A>T vs c.1342A>G for the index variant — use A>T (primary source + ClinVar VCV000983289).
Protein HGVS for c.1242_1263del22 and c.1313_1316delCTGT — the extracted protein annotations do not reconcile with the cDNA positions. Re-derive from the source tables.
VanSickle 2026 frequency percentages — internally inconsistent as extracted (11/12 rendered as 83.3%). Prefer GeneReviews Table 2 as the frequency source; re-verify the 2026 table directly.
gnomAD constraint metrics for ODC1 — not retrieved; look up directly if needed (and note their limited relevance to a last-exon GoF mechanism).
ICD-11 code — not confirmed; do not assert.
MGI:97402 for mouse Odc1 — not verified in this session.
HP:0025249 "Follicular cyst" — term ID not verified via OAK; run just validate-terms before commit.
CL:0011020 label casing — OLS returned "Neural progenitor cell"; confirm canonical label with OAK.
Sex ratio — do not assert; the sample is too small.
Cancer risk — encode as knowledge gap, not phenotype.

Suggested module conformance

BABS does not map cleanly onto an existing kb/modules/ entry. The closest conceptual neighbors are metabolic_intoxication_decompensation (an enzymatic block in intermediary metabolism) — but BABS is a chronic overproduction, not an episodic catabolic-stress decompensation, so conformance would be a poor fit. Consider instead that BABS, Snyder-Robinson syndrome, Faundes-Banka syndrome, DHPS deficiency, and DOHH disorder together justify a new polyamine_pathway_dysregulation module and/or a Polyaminopathies Grouping (grouping_basis: SHARED_PATHWAY, with a NECESSARY HAS_BIOLOGICAL_PROCESS criterion on polyamine metabolic process) — the 2026 systematic review (PMID:41410504) is purpose-built as the curated rationale for exactly such a grouping.

Sources

Primary literature (PubMed): - Bupp CP et al. Am J Med Genet A 2018 — PMID:30239107 - Rodan LH et al. Am J Med Genet A 2018 — PMID:30475435 - Schultz CR et al. Biochem J 2019 — PMID:31249027 - Prokop JW et al. Genes (Basel) 2021 — PMID:33806076 - Rajasekaran S et al. eLife 2021 — PMID:34282722 - VanSickle EA et al. Am J Med Genet A 2021 — PMID:34477286 (correction: PMID:37078542) - Bupp C, VanSickle E, Bachmann AS. GeneReviews 2022 — PMID:36007106 / NBK583220 - Afrin A et al. Pediatr Dermatol 2023 — PMID:36443247 - Michael J et al. Med Sci (Basel) 2023 — PMID:37092498 - Bachmann AS, Bupp CP. Dev Med Child Neurol 2024 — PMID:37469105 - Wu B et al. Int J Mol Sci 2024 — PMID:38928047 - Bupp CP et al. Am J Med Genet C 2025 — PMID:40167220 - Schultz CR et al. Methods Enzymol 2025 — PMID:40382142 - VanSickle EA et al. Methods Enzymol 2025 — PMID:40382145 - Nwafor A et al. Methods Enzymol 2025 — PMID:40382146 - VanSickle EA et al. Am J Med Genet A 2026 — PMID:41410504 - Li R et al. Prenat Diagn 2026 — PMID:41931584 - Gilmour SK et al. Amino Acids 2026 — PMID:41925768

Mechanism / model organism: - Ghoda L et al. Science 1989 — PMID:2928784 - Murakami Y et al. Nature 1992 — PMID:1334232 - Megosh L et al. Cancer Res 1995 — PMID:7671221 - Hua SB et al. J Biol Chem 1995 — PMID:7730330 - Soler AP et al. J Invest Dermatol 1996 — PMID:8618048 - Peralta Soler A et al. Cancer Res 1998 — PMID:9563478 - Chen Y et al. Toxicol Lett 2000 — PMID:10906419 - Pendeville H et al. Mol Cell Biol 2001 — PMID:11533243 - Wei Z et al. Nature 2022 (LACC1–NOS2–ODC1) — PMID:35978195

Databases: - OMIM 619075 / 165640 · MONDO:0033642 (Monarch) · MedGen C5436741 · Orphanet 544488 · NCBI Gene 4953 (ODC1) · UniProt P11926 · HPO annotations, OMIM:619075 · ClinVar VCV000983285–983289, VCV001074405 · NORD · Wikipedia · ClinicalTrials.gov (NCT00118365, NCT00086736, NCT03536728 — DFMO oncology/chemoprevention only; no BABS trial registered)

PubMed metadata and abstracts in this report were retrieved via NCBI E-utilities and PubMed Central; DOIs are listed where retrieved.

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Classifications

Inheritance

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Biochemical Markers

Differential Diagnoses

Source YAML

References & Deep Research

References

Deep Research

1. Disease Information

1.1 Overview

1.2 Key identifiers

1.3 Synonyms

1.4 Provenance of information

2. Etiology

2.1 Primary cause

2.2 Genetic risk factors

2.3 Environmental risk factors

2.4 Protective factors

2.5 Gene–environment interactions

3. Phenotypes

3.1 Frequency table — GeneReviews cohort (n=9 published individuals; primary source)

3.2 Frequency table — 2026 systematic review (n=12 published BABS cases)

3.3 HPO disease-annotation set (HPOA, OMIM:619075) — with explicit n/N and onset

3.4 Per-phenotype characterization

3.5 Quality of life

4. Genetic / Molecular Information

4.1 Causal gene

4.2 Pathogenic variants (compiled from all sources)

4.3 Variant classification, allele frequency, origin

4.4 Allelic disorders — the loss-of-function arm

4.5 Modifier genes

4.6 Epigenetics

4.7 Chromosomal abnormalities

5. Environmental Information

6. Mechanism / Pathophysiology

6.1 The causal chain (upstream → downstream)

6.2 Molecular pathway detail

6.3 Cellular processes

6.4 Protein dysfunction

6.5 Metabolic changes

6.6 Immune system involvement

6.7 Tissue damage mechanisms

6.8 Molecular profiling

6.9 Cell types and anatomical processes — suggested ontology bindings

7. Anatomical Structures Affected

7.1 Organ level

7.2 Tissue and cell level

7.3 Subcellular level

7.4 Localization / lateralization

8. Temporal Development

8.1 Onset

8.2 Progression

8.3 Patterns

9. Inheritance and Population

9.1 Epidemiology

9.2 Inheritance genetics

9.3 Population demographics

10. Diagnostics

10.1 Suggestive clinical findings (GeneReviews)

10.2 Establishing the diagnosis

10.3 Genetic testing

10.4 Biochemical / omics diagnostics — the BABS-distinctive layer

10.5 Imaging, electrophysiology, other clinical tests

10.6 Differential diagnosis (GeneReviews Table 3)

10.7 Screening of asymptomatic individuals

11. Outcome / Prognosis

11.1 Survival and mortality

11.2 Morbidity and function

11.3 Complications

11.4 Cancer risk — an unresolved, important question

11.5 Recovery potential and prognostic factors

12. Treatment