Hyperprolinemia Type 1

Metabolic Disorder MONDO:0009400 Pathograph 17 Show in embeddings browser Inborn Error of Metabolism Hyperprolinemia Disorder of Amino Acid Metabolism

Hyperprolinemia type 1 (HPI) is an autosomal recessive disorder of proline catabolism caused by biallelic PRODH variants that reduce mitochondrial proline dehydrogenase activity. The enzyme block impairs the first step of proline degradation and produces persistent hyperprolinemia. The biochemical phenotype is well established, but its clinical consequences are not fully penetrant: asymptomatic individuals and patients with developmental, neurologic, or behavioral findings have all been reported, and plasma proline concentration does not reliably predict those findings. The entry therefore separates the established enzyme-deficiency-to-hyperprolinemia chain from a provisional neural mechanism and explicitly records the unresolved causal relationship between the biochemical trait and a clinical syndrome.

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1
Inheritance
4
Pathophys.
6
Phenotypes
2
Gaps
17
Pathograph
1
Genes
2
Variants
1
Medical Actions
2
Differentials
2
Models
1
Deep Research
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Classifications

ICIMD (Inherited Metabolic Disorders)
orn pro and hyp
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Inheritance

1
Autosomal recessive inheritance HP:0000007
HPI is caused by biallelic PRODH variants. Clinical penetrance is incomplete even though persistent hyperprolinemia is the defining biochemical trait.
Autosomal recessive inheritance
Show evidence (1 reference)
PMID:34285201 SUPPORT Human Clinical
"Hyperprolinemia type I (HPI) is an autosomal recessive metabolic disorder caused by defects in proline oxidase."
Defines HPI as an autosomal recessive proline-oxidase disorder.
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Discussions and Knowledge Gaps

2
Does isolated biallelic PRODH deficiency cause a coherent clinical syndrome, or is HPI primarily a highly penetrant biochemical trait whose developmental, neurologic, and psychiatric manifestations require additional genetic or environmental factors?
KNOWLEDGE GAP OPEN gap_hpi_biochemical_trait_clinical_syndrome
Attached to
pathophysiology#Systemic Proline Accumulation pathophysiology#Putative Proline-Linked Neural Dysfunction phenotypes#Global developmental delay phenotypes#Intellectual disability phenotypes#Autistic behavior phenotypes#Seizure phenotypes#Atypical behavior
The enzyme defect and hyperprolinemia are well supported, but clinical ascertainment is contradictory. Severe biallelic case series report early developmental delay, cognitive impairment, autism, and epilepsy, while the clinical review also records a benign phenotype without neurologic problems. The systematic review pooled PRODH-HPI, ALDH4A1-HPII, and 22q11.2 deletion cohorts and found neither a proline-level/phenotype correlation nor evidence that hyperprolinemia is the primary cause of psychiatric disease. Frequency bands are therefore omitted and the neural branch is marked HYPOTHETICAL.
Proposed experiments
Genotype-stratified longitudinal study of isolated HPI
exp_hpi_isolated_genotype_longitudinal_cohort
Follow individuals with molecularly confirmed biallelic PRODH deficiency separately from 22q11.2 deletion and ALDH4A1-related cohorts, with repeated plasma proline measurements and standardized developmental, neurologic, and psychiatric assessments. This would test penetrance and whether clinical outcomes track genotype, residual enzyme activity, or metabolite level in isolated HPI.
Show evidence (4 references)
PMID:24931297 SUPPORT Human Clinical
"The clinical features of HPI are unclear. Nephropathy, uncontrolled seizures, mental retardation or schizophrenia have been reported in HPI, but a benign phenotype without neurological problems has also been reported."
Directly states the conflicting symptomatic and benign HPI observations.
PMID:15662599 SUPPORT Other
"extant data suggest that severe hyperprolinemia (>800 microM) occurs in individuals with large deletions and/or PRODH missense mutations with the most-severe effect on function (L441P and R453C), whereas modest hyperprolinemia (300-500 microM) is associated with PRODH alleles with a moderate..."
Supplies limited genotype-to-biochemical-severity evidence while leaving the biochemical-to-clinical relationship unresolved.
PMID:34302426 SUPPORT Human Clinical
"No evidence for a biochemical phenotype-clinical phenotype correlation was found; that is, no association between higher proline levels and specific psychiatric phenotypes was observed."
Shows that metabolite level does not explain clinical outcome.
+ 1 more reference
Which neural consequences observed in Prodh-mutant mice and PRODH-manipulated U87 cells reproduce the biology of isolated human HPI, and which are specific to the model, transformed-cell context, or 22q11.2 deletion background?
HUMAN MODEL MISMATCH OPEN mismatch_hpi_experimental_neural_models
Attached to
pathophysiology#Putative Proline-Linked Neural Dysfunction experimental_models#Pro/Re Prodh-mutant hyperprolinemic mouse experimental_models#U87 wild-type and L441P PRODH expression system
The mouse model demonstrates sensorimotor-gating and regional neurochemical changes, while the U87 overexpression system couples proline to glutamate and glutamine. Neither model recapitulates the variable human penetrance, and U87 is a transformed glioblastoma line rather than a patient neuron. Human psychiatric studies frequently include 22q11.2 deletions and ALDH4A1-HPII, so they cannot resolve this translation gap.
Proposed experiments
Cross-model comparison of PRODH-deficient neural phenotypes
exp_hpi_cross_model_neural_comparison
Compare molecularly matched human neuronal models, the Prodh-mutant mouse, and the existing transformed-cell observations using shared proline, glutamate, glutamine, and neural-function readouts. Include allele-corrected comparators and benchmark each model against observations from isolated HPI cohorts to identify which signals translate to human disease.
Show evidence (4 references)
PMID:10192398 SUPPORT Model Organism
"We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain."
Defines the principal mouse observations requiring human translation.
PMID:29694413 SUPPORT In Vitro
"Here, we report on the expression of wild-type and L441P variants of human PO in a U87 glioblastoma human cell line in an attempt to assess their effect on glutamate metabolism."
Identifies the transformed cell-line context of the human-cell evidence.
PMID:17135275 SUPPORT Human Clinical
"We next report that, among 92 adult or adolescent VCFS subjects, a subset of patients with severe hyperprolinemia has a phenotype distinguishable from that of other VCFS patients and reminiscent of HPI."
Shows that a prominent human neuropsychiatric evidence stream concerns hyperprolinemia within the multigene 22q11.2 deletion background rather than isolated biallelic PRODH deficiency.
+ 1 more reference
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Pathophysiology

4
PRODH Proline Dehydrogenase Deficiency
Biallelic loss-of-function or severe hypomorphic PRODH variants reduce the activity of proline dehydrogenase (proline oxidase), a FAD-dependent enzyme in the mitochondrial inner membrane. Functional effects vary by allele, so a PRODH missense change is not assumed to be pathogenic without segregation, biochemical, and functional support.
PRODH hgnc:9453 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves PRODH (hgnc:9453). hgnc:9453 is a gene from the HUGO Gene Nomenclature Committee.
L-proline catabolic process GO:0006562 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased L-proline catabolic process (GO:0006562). GO:0006562 is a biological process from the Gene Ontology. ↓ DECREASED
proline dehydrogenase activity GO:0004657 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased proline dehydrogenase activity (GO:0004657). GO:0004657 is a molecular function from the Gene Ontology. ↓ DECREASED
mitochondrial inner membrane GO:0005743 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves mitochondrial inner membrane (GO:0005743). GO:0005743 is a cellular component from the Gene Ontology.
Downstream
Impaired Mitochondrial Proline Oxidation Reduced proline dehydrogenase activity directly limits oxidation of L-proline at the first step of its mitochondrial degradation pathway.
Show evidence (3 references)
PMID:18806117 SUPPORT Human Clinical
"Hyperprolinemia type I (HPI) is a result of a deficiency in POX."
Identifies proline oxidase deficiency as the defining defect in HPI.
PMID:15662599 SUPPORT In Vitro
"PRODH maps to 22q11 in the region deleted in the velocardiofacial syndrome/DiGeorge syndrome (VCFS/DGS) and encodes proline oxidase (POX), a mitochondrial inner-membrane enzyme that catalyzes the first step in the proline degradation pathway."
Establishes PRODH enzyme identity, localization, and pathway position.
PMID:15662599 SUPPORT In Vitro
"We find that four alleles (R185Q, L289M, A455S, and A472T) result in mild (<30%), six (Q19P, A167V, R185W, D426N, V427M, and R431H) in moderate (30%-70%), and five (P406L, L441P, R453C, T466M, and Q521E) in severe (>70%) reduction in POX activity, whereas one (Q521R) increases POX activity."
Demonstrates experimentally that PRODH missense alleles have heterogeneous functional effects and should not be interpreted as equivalent.
Impaired Mitochondrial Proline Oxidation
Reduced PRODH activity decreases conversion of L-proline toward 1-pyrroline-5-carboxylate and glutamate. Unlike ALDH4A1-related hyperprolinemia type 2, this upstream block does not cause P5C accumulation or the P5C-mediated vitamin B6 antagonism modeled for HPII.
L-proline catabolic process GO:0006562 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased L-proline catabolic process (GO:0006562). GO:0006562 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Systemic Proline Accumulation Failure to oxidize proline causes the substrate to accumulate in plasma and urine.
Show evidence (1 reference)
PMID:29694413 SUPPORT In Vitro
"Proline is oxidized to glutamate in the mitochondria and the FAD-containing enzyme proline oxidase (PO) catalyzes the first step in L-proline degradation pathway."
Places PRODH at the first mitochondrial proline-oxidation step.
Systemic Proline Accumulation
Proline accumulates in body fluids, producing the persistent hyperprolinemia that defines HPI. This biochemical phenotype is more consistently supported than any neurologic or psychiatric manifestation.
Downstream
Hyperprolinemia Elevated circulating proline is the direct readout of the metabolic block.
Putative Proline-Linked Neural Dysfunction Elevated proline is associated with altered neural amino-acid handling in experimental systems, but the intervening steps and the causal relevance to isolated human HPI are unresolved.
Show evidence (2 references)
PMID:23462603 SUPPORT Human Clinical
"BACKGROUND: Hyperprolinemia is a rare inherited metabolic disorder characterized by a high proline level in blood and/or urine and various neuropsychiatric symptoms."
Defines the biochemical abnormality and its measured compartments.
PMID:24931297 SUPPORT Human Clinical
"The current study presents diagnostic criteria for HPI and HPII, based on plasma proline level, with or without measurements of urinary P5C."
Confirms plasma proline as the basis of the diagnostic biochemical phenotype.
Putative Proline-Linked Neural Dysfunction
Experimental work suggests that changing PRODH activity and cellular proline can alter glutamate and glutamine pools and that Prodh-deficient mice have neurochemical and sensorimotor-gating abnormalities. These observations motivate a neural mechanism, but they do not establish that isolated HPI causes a uniform neurodevelopmental or psychiatric syndrome.
neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
regulation of synaptic transmission, glutamatergic GO:0051966 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves dysregulated regulation of synaptic transmission, glutamatergic (GO:0051966). GO:0051966 is a biological process from the Gene Ontology. ↕ DYSREGULATED
Experimental models
Pro/Re Prodh-mutant hyperprolinemic mouse OTHER Connects Prodh disruption and hyperprolinemia to neurochemical and sensorimotor-gating phenotypes in vivo, with uncertain human translation.
U87 wild-type and L441P PRODH expression system CELL LINE Tests whether altered proline oxidase activity changes amino-acid pools that could influence glutamatergic biology; it does not model a patient neurologic phenotype.
Downstream
Global developmental delay Developmental delay is reported in severe biallelic cases, but the route from proline accumulation to this phenotype is unknown.
Intellectual disability Cognitive impairment is reported, but is not universal among individuals with HPI.
Autistic behavior Autistic features have been reported in severe biallelic cases.
Seizure Epilepsy is reported in severe biallelic cases but is not obligatory in HPI.
Atypical behavior Long-term follow-up reports behavioral and later psychiatric morbidity.
Show evidence (3 references)
PMID:29694413 SUPPORT In Vitro
"On this side, PO might play a regulatory role in glutamatergic neurotransmission by affecting the cellular concentration of glutamate."
The authors frame altered glutamatergic transmission as a possibility in a U87 overexpression system, so this is indirect mechanistic support.
PMID:10192398 SUPPORT Model Organism
"We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain."
A Prodh-mutant mouse links hyperprolinemia to brain neurochemistry and behavior, but does not establish the clinical phenotype of human HPI.
PMID:34302426 REFUTE Human Clinical
"More studies are needed to clarify whether hyperprolinemia is a primary causal factor underlying the increased risk of developing psychiatric disorders seen in patients with hyperprolinemia, or whether hyperprolinemia and psychiatric disorders are both consequences of a shared underlying mechanism."
Explicitly states that causality remains unresolved in human evidence.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Hyperprolinemia Type 1 Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

6
Nervous System 5
Global developmental delay HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263). HP:0001263 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:17412540 SUPPORT Human Clinical
"The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
Documents early developmental delay in severe biallelic cases.
Intellectual disability HP:0001249 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intellectual disability (HP:0001249). HP:0001249 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:17412540 SUPPORT Human Clinical
"The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
Documents cognitive defects in severe biallelic cases.
PMID:34285201 SUPPORT Human Clinical
"The patient presented with short stature, carbohydrate-rich dietary preferences, and mild intellectual disability that was suggestive of a neurodevelopmental or learning disorder."
Documents mild intellectual disability in a homozygous PRODH p.T466M case.
Autistic behavior HP:0000729 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Autistic behavior (HP:0000729). HP:0000729 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:17412540 SUPPORT Human Clinical
"The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
Reports autistic features in the severe biallelic cohort.
Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:17412540 SUPPORT Human Clinical
"The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
Reports epilepsy in patients with severely impaired POX activity.
Atypical behavior HP:0000708 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Atypical behavior (HP:0000708). HP:0000708 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24842239 SUPPORT Human Clinical
"Social behavior and relational skills were considerably impaired in the majority of cases."
Reports social and relational impairment in a ten-patient long-term cohort.
Other 1
Hyperprolinemia HP:0008358 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperprolinemia (HP:0008358). HP:0008358 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:23462603 SUPPORT Human Clinical
"All patients had high plasma proline levels, ranging from 742 to 1192 μmol/L (reference range, 77.4 - 244.6 μmol/L)."
Provides measured plasma proline elevations in four neonates with PRODH variants.
PMID:24931297 SUPPORT Human Clinical
"The current study presents diagnostic criteria for HPI and HPII, based on plasma proline level, with or without measurements of urinary P5C."
Establishes plasma proline as the diagnostic biochemical anchor.
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Genetic Associations

1
PRODH
Gene: PRODH hgnc:9453 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PRODH (hgnc:9453). hgnc:9453 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (2 references)
PMID:17412540 SUPPORT Human Clinical
"We identified biallelic abnormalities in PRODH in these patients that led to severe reduction of POX activity."
Links biallelic PRODH abnormalities to severe loss of POX activity.
PMID:15662599 SUPPORT In Vitro
"Here, we report the effects of these mutations on POX activity."
Reports direct functional testing of PRODH missense variants.
Variants (2)
PRODH p.Thr466Met (T466M)
Gene: PRODH hgnc:9453 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in PRODH (hgnc:9453). hgnc:9453 is a gene from the HUGO Gene Nomenclature Committee. missense
Homozygous p.Thr466Met has been reported in molecularly confirmed HPI and is the allele in the single riboflavin-response report. Functional testing classified T466M among alleles with severe loss of POX activity and found responsiveness to high FAD concentrations in vitro. Its clinical effect is not treated as uniform because the broader HPI phenotype is incompletely penetrant and the 2021 report noted conflicting variant interpretations.
Functional effects
proline oxidase activity reduced function
Severe reduction of POX activity in a functional assay, with variant-specific responsiveness to high FAD concentrations in vitro.
Show evidence (2 references)
PMID:34285201 SUPPORT Human Clinical
"Sanger sequencing detected the homozygous mutation c.1397 C > T (p.T466M) in the PRODH gene as well as some homozygous variants (Fig. 1B and Table 1B), confirming the diagnosis of HPI."
Documents homozygous p.T466M in a molecularly confirmed HPI case.
PMID:15662599 SUPPORT In Vitro
"The POX encoded by one severe allele (T466M) shows in vitro responsiveness to high cofactor (flavin adenine dinucleotide) concentrations."
Defines the severe functional class and variant-specific FAD response.
PRODH p.Leu441Pro (L441P)
Gene: PRODH hgnc:9453 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in PRODH (hgnc:9453). hgnc:9453 is a gene from the HUGO Gene Nomenclature Committee. missense
p.Leu441Pro is a functionally severe PRODH missense allele reported in HPI and schizophrenia cohorts. Assay estimates differ: the 2005 panel placed L441P among alleles with greater than 70% activity reduction, whereas a later U87 expression study measured approximately half of wild-type specific activity and also found reduced stability. It is therefore retained as an assay-dependent reduced-function allele, not a predictor of a specific psychiatric outcome.
Functional effects
proline oxidase activity and stability reduced function
Reduced catalytic activity with an additional effect on enzyme stability; the magnitude varies by experimental system.
Show evidence (3 references)
PMID:29694413 SUPPORT In Vitro
"The subcellular localization of the flavoenzyme is not altered in the L441P variant, for which specific activity is halved compared to the wild-type PO."
Measures variant-specific loss of activity in the U87 expression system.
PMID:29694413 SUPPORT Other
"In particular, the mutation giving rise to the substitution Leu441Pro was identified in patients suffering of schizophrenia and hyperprolinemia type I."
Records the reported human association while avoiding attribution of a specific psychiatric outcome to the allele.
PMID:15662599 SUPPORT Other
"extant data suggest that severe hyperprolinemia (>800 microM) occurs in individuals with large deletions and/or PRODH missense mutations with the most-severe effect on function (L441P and R453C), whereas modest hyperprolinemia (300-500 microM) is associated with PRODH alleles with a moderate..."
Summarizes limited human genotype-biochemical data linking L441P to severe hyperprolinemia; it does not establish a clinical outcome.
💊

Medical Actions

1
Investigational Riboflavin Supplementation
Action: nutritional supplementationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is nutritional supplementation, annotated with Nutritional Support (NCIT:C15433). NCIT:C15433 is a clinical intervention from the NCI Thesaurus. Ontology label: Nutritional Support NCIT:C15433
Agent: riboflavin CHEBI:17015 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses riboflavin (CHEBI:17015). CHEBI:17015 is a therapeutic agent from Chemical Entities of Biological Interest.
A single 2026 report of homozygous PRODH p.Thr466Met HPI found lower plasma and fibroblast proline during riboflavin exposure. Direct PRODH activity could not be measured reliably, no controlled trial was performed, and no clinical efficacy outcome was established. Riboflavin is therefore recorded as a variant-directed investigational lead, not standard HPI therapy.
Mechanism Target:
MODULATES PRODH Proline Dehydrogenase Deficiency — Riboflavin supplies the precursor of FAD and may stabilize residual p.Thr466Met PRODH activity, but direct enzyme rescue was not demonstrated.
Show evidence (1 reference)
PMID:15662599 SUPPORT In Vitro
"The POX encoded by one severe allele (T466M) shows in vitro responsiveness to high cofactor (flavin adenine dinucleotide) concentrations."
Supports a variant-specific cofactor hypothesis in vitro, not clinical efficacy or rescue across PRODH genotypes.
Show evidence (2 references)
PMID:42150437 SUPPORT Human Clinical
"The patient exhibited markedly elevated plasma proline (530-625 μmol/L; reference 78-273 μmol/L), which decreased after initiation of a vitamin cocktail including riboflavin (291 and 277 μmol/L at 3 and 8 months) and decreased on riboflavin monotherapy (251 μmol/L; 12 mg/day)."
Documents a biochemical response in one p.Thr466Met patient; it does not establish clinical benefit or generalizability to other variants.
PMID:42150437 SUPPORT In Vitro
"Although direct enzymatic activity could not be reliably assessed due to technical limitations, these multi-level findings support riboflavin as a potential cofactor-directed therapy in selected PRODH missense variants and provide a rationale for therapeutic trials with biochemical monitoring."
Explicitly records both the technical limitation and the authors' proposal for future trials rather than established treatment efficacy.
🔬

Biochemical Markers

1
Plasma proline elevation (INCREASED)
Pathograph Readouts
Readout Of Systemic Proline Accumulation Positive Diagnostic
Elevated plasma proline is the direct readout of impaired proline oxidation.
Show evidence (1 reference)
PMID:23462603 SUPPORT Human Clinical
"All patients had high plasma proline levels, ranging from 742 to 1192 μmol/L (reference range, 77.4 - 244.6 μmol/L)."
Quantifies plasma proline elevation in molecularly evaluated neonates.
Show evidence (1 reference)
PMID:24931297 SUPPORT Human Clinical
"The current study presents diagnostic criteria for HPI and HPII, based on plasma proline level, with or without measurements of urinary P5C."
Establishes plasma proline as the basis of HPI biochemical diagnosis.
🔬

Diagnosis

1
Plasma proline with urinary P5C assessment
Persistent elevation of plasma proline establishes hyperprolinemia. Urinary P5C measurement helps separate HPI from HPII: the downstream ALDH4A1 block in HPII permits P5C accumulation, whereas the upstream PRODH block in HPI limits P5C formation. Molecular analysis of PRODH establishes the genetic diagnosis and distinguishes isolated HPI from syndromic 22q11.2 deletion.
biochemical diagnostic testing NCIT:C18020 NCI Thesaurus (NCIT)
Markers: plasma L-proline; urinary 1-pyrroline-5-carboxylate (P5C)
Results: Persistent hyperprolinemia with absent or non-elevated urinary P5C supports HPI; biallelic pathogenic PRODH variants provide molecular confirmation.
Show evidence (2 references)
PMID:24931297 SUPPORT Human Clinical
"The current study presents diagnostic criteria for HPI and HPII, based on plasma proline level, with or without measurements of urinary P5C."
Defines plasma proline and urinary P5C as the published biochemical criteria.
PMID:23462603 SUPPORT Human Clinical
"Herein, we present a study of Korean patients with type I hyperprolinemia who were diagnosed during newborn screening by tandem mass spectrometry and confirmed by molecular analysis."
Demonstrates biochemical detection followed by molecular confirmation.
📊

Prevalence

1
Worldwide
Unknown Ultra Rare
Precise incidence and prevalence are unknown. A Japanese questionnaire and literature survey identified two HPI cases, supporting extreme rarity but not a quantitative worldwide estimate.
Show evidence (2 references)
PMID:24931297 SUPPORT Human Clinical
"In addition, the precise incidences of HPI and HPII are unknown."
States that HPI incidence has not been established.
PMID:24931297 SUPPORT Human Clinical
"Only two cases of HPI and one case of HPII have been identified in Japan through a questionnaire survey and by a study of previous reports."
Supports extreme rarity without converting case counts into a prevalence estimate.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Hyperprolinemia Type 1:

Hyperprolinemia Type 2 MONDO:0009401
Overlapping Features ALDH4A1/P5C-dehydrogenase deficiency blocks the second step of proline degradation and causes P5C accumulation with secondary vitamin B6 antagonism. HPI blocks the preceding PRODH step and lacks that established P5C/PLP arm.
Show evidence (1 reference)
PMID:18806117 SUPPORT Human Clinical
"The other type of hyperprolinemia is HPII. It is caused by a deficiency in P5C dehydrogenase activity."
Distinguishes HPII by its downstream P5C-dehydrogenase defect.
22q11.2 Deletion Syndrome MONDO:0018923
Overlapping Features A 22q11.2 deletion can remove one PRODH copy together with many other genes and can produce hyperprolinemia and neuropsychiatric findings. It is a multisystem contiguous-gene disorder, not equivalent to isolated biallelic PRODH-related HPI.
Show evidence (1 reference)
PMID:15662599 SUPPORT In Vitro
"PRODH maps to 22q11 in the region deleted in the velocardiofacial syndrome/DiGeorge syndrome (VCFS/DGS) and encodes proline oxidase (POX), a mitochondrial inner-membrane enzyme that catalyzes the first step in the proline degradation pathway."
Establishes that the common 22q11 deletion interval includes PRODH.
🧫

Experimental Models

2
Pro/Re Prodh-mutant hyperprolinemic mouse OTHER
The Pro/Re hyperprolinemic mouse carries a Prodh mutation and shows impaired sensorimotor gating with regional brain neurochemical changes. It supports a possible neural consequence of disturbed proline metabolism but does not reproduce or establish the variably penetrant human HPI clinical syndrome.
Pro/Re hyperprolinemic strain carrying a Prodh mutation
Organism
house mouse NCBITaxon:10090 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in house mouse, annotated with Mus musculus (NCBITaxon:10090). NCBITaxon:10090 is an organism from the NCBI Taxonomy.
Publication
PMID:10192398
Pathograph links
Putative Proline-Linked Neural Dysfunction Connects Prodh disruption and hyperprolinemia to neurochemical and sensorimotor-gating phenotypes in vivo, with uncertain human translation.
Show evidence (1 reference)
PMID:10192398 SUPPORT Model Organism
"We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain."
Directly links the mouse model to the provisional neural mechanism.
Show evidence (1 reference)
PMID:10192398 SUPPORT Model Organism
"We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain."
Defines the genotype and principal neurobehavioral findings of the model.
U87 wild-type and L441P PRODH expression system CELL_LINE
A transformed human glioblastoma cell-line system comparing wild-type and L441P proline oxidase linked cellular proline with glutamate and glutamine. Because it uses enzyme expression in U87 cells rather than patient neurons, it supplies indirect mechanistic evidence only.
Wild-type human proline oxidase expression L441P human proline oxidase expression Control U87 cells
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Cell source
U87 glioblastoma cell line
Culture
Transient expression of wild-type or L441P human proline oxidase
Publication
PMID:29694413
Pathograph links
Putative Proline-Linked Neural Dysfunction Tests whether altered proline oxidase activity changes amino-acid pools that could influence glutamatergic biology; it does not model a patient neurologic phenotype.
Show evidence (1 reference)
PMID:29694413 SUPPORT In Vitro
"Altogether, these results demonstrate that the proline pathway links cellular proline levels with those of glutamate and glutamine."
Defines the amino-acid coupling reproduced by the cell-line model.
Show evidence (1 reference)
PMID:29694413 SUPPORT In Vitro
"Here, we report on the expression of wild-type and L441P variants of human PO in a U87 glioblastoma human cell line in an attempt to assess their effect on glutamate metabolism."
Defines the cell line, expressed variants, and experimental purpose.
{ }

Source YAML

click to show 
name: Hyperprolinemia Type 1
creation_date: "2026-08-09T00:46:59Z"
description: >-
  Hyperprolinemia type 1 (HPI) is an autosomal recessive disorder of proline
  catabolism caused by biallelic PRODH variants that reduce mitochondrial
  proline dehydrogenase activity. The enzyme block impairs the first step of
  proline degradation and produces persistent hyperprolinemia. The biochemical
  phenotype is well established, but its clinical consequences are not fully
  penetrant: asymptomatic individuals and patients with developmental,
  neurologic, or behavioral findings have all been reported, and plasma proline
  concentration does not reliably predict those findings. The entry therefore
  separates the established enzyme-deficiency-to-hyperprolinemia chain from a
  provisional neural mechanism and explicitly records the unresolved causal
  relationship between the biochemical trait and a clinical syndrome.
category: Metabolic Disorder
parents:
- Inborn Error of Metabolism
- Hyperprolinemia
- Disorder of Amino Acid Metabolism
synonyms:
- HPI
- Hyperprolinemia, type I
- Hyperprolinaemia type I
- Proline oxidase deficiency
- Proline dehydrogenase deficiency
- PRODH hyperprolinemia
classifications:
  icimd_category:
  - classification_value: orn_pro_and_hyp
    notes: >-
      ICIMD sub-branch "Disorders of ornithine, proline and hydroxyproline
      metabolism". HPI is the PRODH defect in the first step of mitochondrial
      proline degradation.
    evidence:
    - reference: PMID:18806117
      reference_title: Inborn errors of proline metabolism.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Several inborn errors of proline metabolism have been described. Hyperprolinemia type I (HPI) is a result of a deficiency in POX."
      explanation: Places HPI among inherited disorders of proline metabolism.
disease_term:
  preferred_term: hyperprolinemia type 1
  term:
    id: MONDO:0009400
    label: hyperprolinemia type 1
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    HPI is caused by biallelic PRODH variants. Clinical penetrance is incomplete
    even though persistent hyperprolinemia is the defining biochemical trait.
  evidence:
  - reference: PMID:34285201
    reference_title: Hyperprolinemia type I caused by homozygous p.T466M mutation in PRODH.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperprolinemia type I (HPI) is an autosomal recessive metabolic disorder caused by defects in proline oxidase."
    explanation: Defines HPI as an autosomal recessive proline-oxidase disorder.
pathophysiology:
- name: PRODH Proline Dehydrogenase Deficiency
  biological_scale: MOLECULAR
  description: >-
    Biallelic loss-of-function or severe hypomorphic PRODH variants reduce the
    activity of proline dehydrogenase (proline oxidase), a FAD-dependent enzyme
    in the mitochondrial inner membrane. Functional effects vary by allele, so
    a PRODH missense change is not assumed to be pathogenic without segregation,
    biochemical, and functional support.
  role: trigger
  genes:
  - preferred_term: PRODH
    term:
      id: hgnc:9453
      label: PRODH
  molecular_functions:
  - preferred_term: proline dehydrogenase activity
    term:
      id: GO:0004657
      label: proline dehydrogenase activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: L-proline catabolic process
    term:
      id: GO:0006562
      label: L-proline catabolic process
    modifier: DECREASED
  cellular_components:
  - preferred_term: mitochondrial inner membrane
    term:
      id: GO:0005743
      label: mitochondrial inner membrane
  evidence:
  - reference: PMID:18806117
    reference_title: Inborn errors of proline metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperprolinemia type I (HPI) is a result of a deficiency in POX."
    explanation: Identifies proline oxidase deficiency as the defining defect in HPI.
  - reference: PMID:15662599
    reference_title: Functional consequences of PRODH missense mutations.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "PRODH maps to 22q11 in the region deleted in the velocardiofacial syndrome/DiGeorge syndrome (VCFS/DGS) and encodes proline oxidase (POX), a mitochondrial inner-membrane enzyme that catalyzes the first step in the proline degradation pathway."
    explanation: Establishes PRODH enzyme identity, localization, and pathway position.
  - reference: PMID:15662599
    reference_title: Functional consequences of PRODH missense mutations.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We find that four alleles (R185Q, L289M, A455S, and A472T) result in mild (<30%), six (Q19P, A167V, R185W, D426N, V427M, and R431H) in moderate (30%-70%), and five (P406L, L441P, R453C, T466M, and Q521E) in severe (>70%) reduction in POX activity, whereas one (Q521R) increases POX activity."
    explanation: >-
      Demonstrates experimentally that PRODH missense alleles have heterogeneous
      functional effects and should not be interpreted as equivalent.
  downstream:
  - target: Impaired Mitochondrial Proline Oxidation
    causal_link_type: DIRECT
    description: >-
      Reduced proline dehydrogenase activity directly limits oxidation of
      L-proline at the first step of its mitochondrial degradation pathway.
    evidence:
    - reference: PMID:29694413
      reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Proline is oxidized to glutamate in the mitochondria and the FAD-containing enzyme proline oxidase (PO) catalyzes the first step in L-proline degradation pathway."
      explanation: Defines the direct enzymatic step impaired by PRODH deficiency.
- name: Impaired Mitochondrial Proline Oxidation
  biological_scale: MOLECULAR
  description: >-
    Reduced PRODH activity decreases conversion of L-proline toward
    1-pyrroline-5-carboxylate and glutamate. Unlike ALDH4A1-related
    hyperprolinemia type 2, this upstream block does not cause P5C accumulation
    or the P5C-mediated vitamin B6 antagonism modeled for HPII.
  role: intermediary
  biological_processes:
  - preferred_term: L-proline catabolic process
    term:
      id: GO:0006562
      label: L-proline catabolic process
    modifier: DECREASED
  chemical_entities:
  - preferred_term: L-proline
    term:
      id: CHEBI:17203
      label: L-proline
  evidence:
  - reference: PMID:29694413
    reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Proline is oxidized to glutamate in the mitochondria and the FAD-containing enzyme proline oxidase (PO) catalyzes the first step in L-proline degradation pathway."
    explanation: Places PRODH at the first mitochondrial proline-oxidation step.
  downstream:
  - target: Systemic Proline Accumulation
    causal_link_type: DIRECT
    description: >-
      Failure to oxidize proline causes the substrate to accumulate in plasma
      and urine.
    evidence:
    - reference: PMID:23462603
      reference_title: Identification of PRODH mutations in Korean neonates with type I hyperprolinemia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "All patients had high plasma proline levels, ranging from 742 to 1192 μmol/L (reference range, 77.4 - 244.6 μmol/L)."
      explanation: Documents marked proline accumulation in four molecularly evaluated neonates.
- name: Systemic Proline Accumulation
  biological_scale: MOLECULAR
  description: >-
    Proline accumulates in body fluids, producing the persistent hyperprolinemia
    that defines HPI. This biochemical phenotype is more consistently supported
    than any neurologic or psychiatric manifestation.
  role: effector
  chemical_entities:
  - preferred_term: L-proline
    term:
      id: CHEBI:17203
      label: L-proline
    modifier: INCREASED
  evidence:
  - reference: PMID:23462603
    reference_title: Identification of PRODH mutations in Korean neonates with type I hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BACKGROUND: Hyperprolinemia is a rare inherited metabolic disorder characterized by a high proline level in blood and/or urine and various neuropsychiatric symptoms."
    explanation: Defines the biochemical abnormality and its measured compartments.
  - reference: PMID:24931297
    reference_title: Biochemical and clinical features of hereditary hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The current study presents diagnostic criteria for HPI and HPII, based on plasma proline level, with or without measurements of urinary P5C."
    explanation: Confirms plasma proline as the basis of the diagnostic biochemical phenotype.
  downstream:
  - target: Hyperprolinemia
    causal_link_type: DIRECT
    description: Elevated circulating proline is the direct readout of the metabolic block.
    evidence:
    - reference: PMID:23462603
      reference_title: Identification of PRODH mutations in Korean neonates with type I hyperprolinemia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "All patients had high plasma proline levels, ranging from 742 to 1192 μmol/L (reference range, 77.4 - 244.6 μmol/L)."
      explanation: Directly measures the hyperprolinemia phenotype.
  - target: Putative Proline-Linked Neural Dysfunction
    causal_link_type: UNKNOWN
    description: >-
      Elevated proline is associated with altered neural amino-acid handling in
      experimental systems, but the intervening steps and the causal relevance
      to isolated human HPI are unresolved.
    evidence:
    - reference: PMID:29694413
      reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Altogether, these results demonstrate that the proline pathway links cellular proline levels with those of glutamate and glutamine."
      explanation: >-
        Supports amino-acid coupling in a transformed human cell line, not a
        causal neural mechanism in patients.
    - reference: PMID:34302426
      reference_title: "Psychiatric phenotypes associated with hyperprolinemia: A systematic review."
      supports: REFUTE
      evidence_source: HUMAN_CLINICAL
      snippet: "No evidence for a biochemical phenotype-clinical phenotype correlation was found; that is, no association between higher proline levels and specific psychiatric phenotypes was observed."
      explanation: >-
        The systematic review found that proline concentration does not predict
        psychiatric phenotype, arguing against a simple dose-to-symptom chain.
- name: Putative Proline-Linked Neural Dysfunction
  biological_scale: CELLULAR
  description: >-
    Experimental work suggests that changing PRODH activity and cellular
    proline can alter glutamate and glutamine pools and that Prodh-deficient mice
    have neurochemical and sensorimotor-gating abnormalities. These observations
    motivate a neural mechanism, but they do not establish that isolated HPI
    causes a uniform neurodevelopmental or psychiatric syndrome.
  role: effector
  mechanism_confidence: HYPOTHETICAL
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: regulation of synaptic transmission, glutamatergic
    term:
      id: GO:0051966
      label: regulation of synaptic transmission, glutamatergic
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:29694413
    reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "On this side, PO might play a regulatory role in glutamatergic neurotransmission by affecting the cellular concentration of glutamate."
    explanation: >-
      The authors frame altered glutamatergic transmission as a possibility in a
      U87 overexpression system, so this is indirect mechanistic support.
  - reference: PMID:10192398
    reference_title: The gene encoding proline dehydrogenase modulates sensorimotor gating in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain."
    explanation: >-
      A Prodh-mutant mouse links hyperprolinemia to brain neurochemistry and
      behavior, but does not establish the clinical phenotype of human HPI.
  - reference: PMID:34302426
    reference_title: "Psychiatric phenotypes associated with hyperprolinemia: A systematic review."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "More studies are needed to clarify whether hyperprolinemia is a primary causal factor underlying the increased risk of developing psychiatric disorders seen in patients with hyperprolinemia, or whether hyperprolinemia and psychiatric disorders are both consequences of a shared underlying mechanism."
    explanation: Explicitly states that causality remains unresolved in human evidence.
  downstream:
  - target: Global developmental delay
    causal_link_type: UNKNOWN
    description: >-
      Developmental delay is reported in severe biallelic cases, but the route
      from proline accumulation to this phenotype is unknown.
    evidence:
    - reference: PMID:17412540
      reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
      explanation: Reports developmental delay in a selected severe biallelic case series.
  - target: Intellectual disability
    causal_link_type: UNKNOWN
    description: Cognitive impairment is reported, but is not universal among individuals with HPI.
    evidence:
    - reference: PMID:17412540
      reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
      explanation: Reports predominant cognitive defects in severe biallelic cases.
  - target: Autistic behavior
    causal_link_type: UNKNOWN
    description: Autistic features have been reported in severe biallelic cases.
    evidence:
    - reference: PMID:17412540
      reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
      explanation: Reports autistic features in the selected severe biallelic series.
  - target: Seizure
    causal_link_type: UNKNOWN
    description: Epilepsy is reported in severe biallelic cases but is not obligatory in HPI.
    evidence:
    - reference: PMID:17412540
      reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
      explanation: Reports epilepsy in a severe, clinically ascertained biallelic series.
  - target: Atypical behavior
    causal_link_type: UNKNOWN
    description: Long-term follow-up reports behavioral and later psychiatric morbidity.
    evidence:
    - reference: PMID:24842239
      reference_title: Long-term neuropsychiatric follow-up in hyperprolinemia type I.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Social behavior and relational skills were considerably impaired in the majority of cases."
      explanation: Reports social and relational impairment in a ten-patient HPI follow-up cohort.
phenotypes:
- category: Biochemical
  name: Hyperprolinemia
  description: >-
    Persistent elevation of plasma proline is the defining biochemical phenotype
    and the basis of published HPI diagnostic criteria.
  phenotype_term:
    preferred_term: Hyperprolinemia
    term:
      id: HP:0008358
      label: Hyperprolinemia
  evidence:
  - reference: PMID:23462603
    reference_title: Identification of PRODH mutations in Korean neonates with type I hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients had high plasma proline levels, ranging from 742 to 1192 μmol/L (reference range, 77.4 - 244.6 μmol/L)."
    explanation: Provides measured plasma proline elevations in four neonates with PRODH variants.
  - reference: PMID:24931297
    reference_title: Biochemical and clinical features of hereditary hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The current study presents diagnostic criteria for HPI and HPII, based on plasma proline level, with or without measurements of urinary P5C."
    explanation: Establishes plasma proline as the diagnostic biochemical anchor.
- category: Clinical
  name: Global developmental delay
  description: >-
    Early psychomotor delay is reported in severe biallelic PRODH cases. It is
    not treated as universal because asymptomatic HPI is also documented.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:17412540
    reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
    explanation: Documents early developmental delay in severe biallelic cases.
- category: Clinical
  name: Intellectual disability
  description: >-
    Cognitive impairment ranges from mild learning difficulty to severe
    intellectual disability in reported cases, while other individuals are
    neurologically asymptomatic.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:17412540
    reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
    explanation: Documents cognitive defects in severe biallelic cases.
  - reference: PMID:34285201
    reference_title: Hyperprolinemia type I caused by homozygous p.T466M mutation in PRODH.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient presented with short stature, carbohydrate-rich dietary preferences, and mild intellectual disability that was suggestive of a neurodevelopmental or learning disorder."
    explanation: Documents mild intellectual disability in a homozygous PRODH p.T466M case.
- category: Clinical
  name: Autistic behavior
  description: >-
    Autistic features have been reported in severe biallelic PRODH cases, but
    their population frequency and biochemical correlation are unknown.
  phenotype_term:
    preferred_term: Autistic behavior
    term:
      id: HP:0000729
      label: Autistic behavior
  evidence:
  - reference: PMID:17412540
    reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
    explanation: Reports autistic features in the severe biallelic cohort.
- category: Clinical
  name: Seizure
  description: >-
    Epilepsy is reported among severe HPI presentations, but is not a necessary
    consequence of hyperprolinemia and has no defensible frequency estimate.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:17412540
    reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The phenotype of these eight patients associates early psychomotor development delay with predominant cognitive defects, autistic features and epilepsy."
    explanation: Reports epilepsy in patients with severely impaired POX activity.
- category: Clinical
  name: Atypical behavior
  description: >-
    Behavioral and relational impairment was reported in long-term HPI follow-up,
    with heterogeneous later psychiatric diagnoses. The entry does not elevate
    schizophrenia to a defining HPI phenotype because much of that literature is
    confounded by 22q11.2 deletion syndrome.
  phenotype_term:
    preferred_term: Atypical behavior
    term:
      id: HP:0000708
      label: Atypical behavior
  evidence:
  - reference: PMID:24842239
    reference_title: Long-term neuropsychiatric follow-up in hyperprolinemia type I.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Social behavior and relational skills were considerably impaired in the majority of cases."
    explanation: Reports social and relational impairment in a ten-patient long-term cohort.
biochemical:
- name: Plasma proline elevation
  presence: INCREASED
  notes: >-
    Quantitative plasma amino-acid analysis is the biochemical anchor for HPI.
    Proline concentration establishes the metabolic phenotype but does not
    predict clinical severity.
  biomarker_term:
    preferred_term: L-proline
    term:
      id: CHEBI:17203
      label: L-proline
  readouts:
  - target: Systemic Proline Accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated plasma proline is the direct readout of impaired proline oxidation.
    evidence:
    - reference: PMID:23462603
      reference_title: Identification of PRODH mutations in Korean neonates with type I hyperprolinemia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "All patients had high plasma proline levels, ranging from 742 to 1192 μmol/L (reference range, 77.4 - 244.6 μmol/L)."
      explanation: Quantifies plasma proline elevation in molecularly evaluated neonates.
  evidence:
  - reference: PMID:24931297
    reference_title: Biochemical and clinical features of hereditary hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The current study presents diagnostic criteria for HPI and HPII, based on plasma proline level, with or without measurements of urinary P5C."
    explanation: Establishes plasma proline as the basis of HPI biochemical diagnosis.
genetic:
- name: PRODH
  gene_term:
    preferred_term: PRODH
    term:
      id: hgnc:9453
      label: PRODH
  relationship_type: CAUSATIVE
  notes: >-
    Biallelic pathogenic or functionally severe hypomorphic PRODH variants cause
    HPI. Missense alleles span increased, mild, moderate, and severe effects on
    enzyme activity, so variant interpretation must not infer pathogenicity from
    gene membership alone.
  variants:
  - name: PRODH p.Thr466Met (T466M)
    description: >-
      Homozygous p.Thr466Met has been reported in molecularly confirmed HPI and
      is the allele in the single riboflavin-response report. Functional testing
      classified T466M among alleles with severe loss of POX activity and found
      responsiveness to high FAD concentrations in vitro. Its clinical effect is
      not treated as uniform because the broader HPI phenotype is incompletely
      penetrant and the 2021 report noted conflicting variant interpretations.
    gene:
      preferred_term: PRODH
      term:
        id: hgnc:9453
        label: PRODH
    type: missense
    functional_effects:
    - function: proline oxidase activity
      description: >-
        Severe reduction of POX activity in a functional assay, with
        variant-specific responsiveness to high FAD concentrations in vitro.
      type: reduced function
    evidence:
    - reference: PMID:34285201
      reference_title: Hyperprolinemia type I caused by homozygous p.T466M mutation in PRODH.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Sanger sequencing detected the homozygous mutation c.1397 C > T (p.T466M) in the PRODH gene as well as some homozygous variants (Fig. 1B and Table 1B), confirming the diagnosis of HPI."
      explanation: Documents homozygous p.T466M in a molecularly confirmed HPI case.
    - reference: PMID:15662599
      reference_title: Functional consequences of PRODH missense mutations.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The POX encoded by one severe allele (T466M) shows in vitro responsiveness to high cofactor (flavin adenine dinucleotide) concentrations."
      explanation: Defines the severe functional class and variant-specific FAD response.
  - name: PRODH p.Leu441Pro (L441P)
    description: >-
      p.Leu441Pro is a functionally severe PRODH missense allele reported in HPI
      and schizophrenia cohorts. Assay estimates differ: the 2005 panel placed
      L441P among alleles with greater than 70% activity reduction, whereas a
      later U87 expression study measured approximately half of wild-type
      specific activity and also found reduced stability. It is therefore
      retained as an assay-dependent reduced-function allele, not a predictor of
      a specific psychiatric outcome.
    gene:
      preferred_term: PRODH
      term:
        id: hgnc:9453
        label: PRODH
    type: missense
    functional_effects:
    - function: proline oxidase activity and stability
      description: >-
        Reduced catalytic activity with an additional effect on enzyme
        stability; the magnitude varies by experimental system.
      type: reduced function
    evidence:
    - reference: PMID:29694413
      reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The subcellular localization of the flavoenzyme is not altered in the L441P variant, for which specific activity is halved compared to the wild-type PO."
      explanation: Measures variant-specific loss of activity in the U87 expression system.
    - reference: PMID:29694413
      reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "In particular, the mutation giving rise to the substitution Leu441Pro was identified in patients suffering of schizophrenia and hyperprolinemia type I."
      explanation: >-
        Records the reported human association while avoiding attribution of a
        specific psychiatric outcome to the allele.
    - reference: PMID:15662599
      reference_title: Functional consequences of PRODH missense mutations.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "extant data suggest that severe hyperprolinemia (>800 microM) occurs in individuals with large deletions and/or PRODH missense mutations with the most-severe effect on function (L441P and R453C), whereas modest hyperprolinemia (300-500 microM) is associated with PRODH alleles with a moderate reduction in activity."
      explanation: >-
        Summarizes limited human genotype-biochemical data linking L441P to
        severe hyperprolinemia; it does not establish a clinical outcome.
  evidence:
  - reference: PMID:17412540
    reference_title: Early neurological phenotype in 4 children with biallelic PRODH mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified biallelic abnormalities in PRODH in these patients that led to severe reduction of POX activity."
    explanation: Links biallelic PRODH abnormalities to severe loss of POX activity.
  - reference: PMID:15662599
    reference_title: Functional consequences of PRODH missense mutations.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here, we report the effects of these mutations on POX activity."
    explanation: Reports direct functional testing of PRODH missense variants.
prevalence:
- population: Worldwide
  measure_type: UNKNOWN
  prevalence_class: ULTRA_RARE
  notes: >-
    Precise incidence and prevalence are unknown. A Japanese questionnaire and
    literature survey identified two HPI cases, supporting extreme rarity but
    not a quantitative worldwide estimate.
  evidence:
  - reference: PMID:24931297
    reference_title: Biochemical and clinical features of hereditary hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, the precise incidences of HPI and HPII are unknown."
    explanation: States that HPI incidence has not been established.
  - reference: PMID:24931297
    reference_title: Biochemical and clinical features of hereditary hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Only two cases of HPI and one case of HPII have been identified in Japan through a questionnaire survey and by a study of previous reports."
    explanation: Supports extreme rarity without converting case counts into a prevalence estimate.
diagnosis:
- name: Plasma proline with urinary P5C assessment
  description: >-
    Persistent elevation of plasma proline establishes hyperprolinemia. Urinary
    P5C measurement helps separate HPI from HPII: the downstream ALDH4A1 block
    in HPII permits P5C accumulation, whereas the upstream PRODH block in HPI
    limits P5C formation. Molecular analysis of PRODH establishes the genetic
    diagnosis and distinguishes isolated HPI from syndromic 22q11.2 deletion.
  diagnosis_term:
    preferred_term: biochemical diagnostic testing
    term:
      id: NCIT:C18020
      label: Diagnostic Procedure
  markers: plasma L-proline; urinary 1-pyrroline-5-carboxylate (P5C)
  results: >-
    Persistent hyperprolinemia with absent or non-elevated urinary P5C supports
    HPI; biallelic pathogenic PRODH variants provide molecular confirmation.
  evidence:
  - reference: PMID:24931297
    reference_title: Biochemical and clinical features of hereditary hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The current study presents diagnostic criteria for HPI and HPII, based on plasma proline level, with or without measurements of urinary P5C."
    explanation: Defines plasma proline and urinary P5C as the published biochemical criteria.
  - reference: PMID:23462603
    reference_title: Identification of PRODH mutations in Korean neonates with type I hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Herein, we present a study of Korean patients with type I hyperprolinemia who were diagnosed during newborn screening by tandem mass spectrometry and confirmed by molecular analysis."
    explanation: Demonstrates biochemical detection followed by molecular confirmation.
differential_diagnoses:
- name: Hyperprolinemia Type 2
  disease_term:
    preferred_term: hyperprolinemia type 2
    term:
      id: MONDO:0009401
      label: hyperprolinemia type 2
  description: >-
    ALDH4A1/P5C-dehydrogenase deficiency blocks the second step of proline
    degradation and causes P5C accumulation with secondary vitamin B6
    antagonism. HPI blocks the preceding PRODH step and lacks that established
    P5C/PLP arm.
  evidence:
  - reference: PMID:18806117
    reference_title: Inborn errors of proline metabolism.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The other type of hyperprolinemia is HPII. It is caused by a deficiency in P5C dehydrogenase activity."
    explanation: Distinguishes HPII by its downstream P5C-dehydrogenase defect.
- name: 22q11.2 Deletion Syndrome
  disease_term:
    preferred_term: 22q11.2 deletion syndrome
    term:
      id: MONDO:0018923
      label: 22q11.2 deletion syndrome
  description: >-
    A 22q11.2 deletion can remove one PRODH copy together with many other genes
    and can produce hyperprolinemia and neuropsychiatric findings. It is a
    multisystem contiguous-gene disorder, not equivalent to isolated biallelic
    PRODH-related HPI.
  evidence:
  - reference: PMID:15662599
    reference_title: Functional consequences of PRODH missense mutations.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "PRODH maps to 22q11 in the region deleted in the velocardiofacial syndrome/DiGeorge syndrome (VCFS/DGS) and encodes proline oxidase (POX), a mitochondrial inner-membrane enzyme that catalyzes the first step in the proline degradation pathway."
    explanation: Establishes that the common 22q11 deletion interval includes PRODH.
treatments:
- name: Investigational Riboflavin Supplementation
  description: >-
    A single 2026 report of homozygous PRODH p.Thr466Met HPI found lower plasma
    and fibroblast proline during riboflavin exposure. Direct PRODH activity
    could not be measured reliably, no controlled trial was performed, and no
    clinical efficacy outcome was established. Riboflavin is therefore recorded
    as a variant-directed investigational lead, not standard HPI therapy.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: nutritional supplementation
    term:
      id: NCIT:C15433
      label: Nutritional Support
    therapeutic_agent:
    - preferred_term: riboflavin
      term:
        id: CHEBI:17015
        label: riboflavin
  target_mechanisms:
  - target: PRODH Proline Dehydrogenase Deficiency
    treatment_effect: MODULATES
    description: >-
      Riboflavin supplies the precursor of FAD and may stabilize residual
      p.Thr466Met PRODH activity, but direct enzyme rescue was not demonstrated.
    evidence:
    - reference: PMID:15662599
      reference_title: Functional consequences of PRODH missense mutations.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The POX encoded by one severe allele (T466M) shows in vitro responsiveness to high cofactor (flavin adenine dinucleotide) concentrations."
      explanation: >-
        Supports a variant-specific cofactor hypothesis in vitro, not clinical
        efficacy or rescue across PRODH genotypes.
  evidence:
  - reference: PMID:42150437
    reference_title: "Riboflavin-responsive hyperprolinemia type I with a PRODH p.Thr466Met variant: Clinical and fibroblast-based evidence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient exhibited markedly elevated plasma proline (530-625 μmol/L; reference 78-273 μmol/L), which decreased after initiation of a vitamin cocktail including riboflavin (291 and 277 μmol/L at 3 and 8 months) and decreased on riboflavin monotherapy (251 μmol/L; 12 mg/day)."
    explanation: >-
      Documents a biochemical response in one p.Thr466Met patient; it does not
      establish clinical benefit or generalizability to other variants.
  - reference: PMID:42150437
    reference_title: "Riboflavin-responsive hyperprolinemia type I with a PRODH p.Thr466Met variant: Clinical and fibroblast-based evidence."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Although direct enzymatic activity could not be reliably assessed due to technical limitations, these multi-level findings support riboflavin as a potential cofactor-directed therapy in selected PRODH missense variants and provide a rationale for therapeutic trials with biochemical monitoring."
    explanation: >-
      Explicitly records both the technical limitation and the authors' proposal
      for future trials rather than established treatment efficacy.
experimental_models:
- name: Pro/Re Prodh-mutant hyperprolinemic mouse
  experimental_model_type: OTHER
  organism:
    preferred_term: house mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  conditions:
  - Pro/Re hyperprolinemic strain carrying a Prodh mutation
  publication: PMID:10192398
  description: >-
    The Pro/Re hyperprolinemic mouse carries a Prodh mutation and shows impaired
    sensorimotor gating with regional brain neurochemical changes. It supports a
    possible neural consequence of disturbed proline metabolism but does not
    reproduce or establish the variably penetrant human HPI clinical syndrome.
  modeled_mechanisms:
  - target: Putative Proline-Linked Neural Dysfunction
    description: >-
      Connects Prodh disruption and hyperprolinemia to neurochemical and
      sensorimotor-gating phenotypes in vivo, with uncertain human translation.
    evidence:
    - reference: PMID:10192398
      reference_title: The gene encoding proline dehydrogenase modulates sensorimotor gating in mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain."
      explanation: Directly links the mouse model to the provisional neural mechanism.
  evidence:
  - reference: PMID:10192398
    reference_title: The gene encoding proline dehydrogenase modulates sensorimotor gating in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain."
    explanation: Defines the genotype and principal neurobehavioral findings of the model.
- name: U87 wild-type and L441P PRODH expression system
  experimental_model_type: CELL_LINE
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_source: U87 glioblastoma cell line
  culture_system: Transient expression of wild-type or L441P human proline oxidase
  conditions:
  - Wild-type human proline oxidase expression
  - L441P human proline oxidase expression
  - Control U87 cells
  publication: PMID:29694413
  description: >-
    A transformed human glioblastoma cell-line system comparing wild-type and
    L441P proline oxidase linked cellular proline with glutamate and glutamine.
    Because it uses enzyme expression in U87 cells rather than patient neurons,
    it supplies indirect mechanistic evidence only.
  modeled_mechanisms:
  - target: Putative Proline-Linked Neural Dysfunction
    description: >-
      Tests whether altered proline oxidase activity changes amino-acid pools
      that could influence glutamatergic biology; it does not model a patient
      neurologic phenotype.
    evidence:
    - reference: PMID:29694413
      reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Altogether, these results demonstrate that the proline pathway links cellular proline levels with those of glutamate and glutamine."
      explanation: Defines the amino-acid coupling reproduced by the cell-line model.
  evidence:
  - reference: PMID:29694413
    reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here, we report on the expression of wild-type and L441P variants of human PO in a U87 glioblastoma human cell line in an attempt to assess their effect on glutamate metabolism."
    explanation: Defines the cell line, expressed variants, and experimental purpose.
discussions:
- discussion_id: gap_hpi_biochemical_trait_clinical_syndrome
  prompt: >-
    Does isolated biallelic PRODH deficiency cause a coherent clinical syndrome,
    or is HPI primarily a highly penetrant biochemical trait whose developmental,
    neurologic, and psychiatric manifestations require additional genetic or
    environmental factors?
  kind: KNOWLEDGE_GAP
  status: OPEN
  rationale: >-
    The enzyme defect and hyperprolinemia are well supported, but clinical
    ascertainment is contradictory. Severe biallelic case series report early
    developmental delay, cognitive impairment, autism, and epilepsy, while the
    clinical review also records a benign phenotype without neurologic problems.
    The systematic review pooled PRODH-HPI, ALDH4A1-HPII, and 22q11.2 deletion
    cohorts and found neither a proline-level/phenotype correlation nor evidence
    that hyperprolinemia is the primary cause of psychiatric disease. Frequency
    bands are therefore omitted and the neural branch is marked HYPOTHETICAL.
  attaches_to:
  - pathophysiology#Systemic Proline Accumulation
  - pathophysiology#Putative Proline-Linked Neural Dysfunction
  - phenotypes#Global developmental delay
  - phenotypes#Intellectual disability
  - phenotypes#Autistic behavior
  - phenotypes#Seizure
  - phenotypes#Atypical behavior
  proposed_experiments:
  - experiment_id: exp_hpi_isolated_genotype_longitudinal_cohort
    name: Genotype-stratified longitudinal study of isolated HPI
    description: >-
      Follow individuals with molecularly confirmed biallelic PRODH deficiency
      separately from 22q11.2 deletion and ALDH4A1-related cohorts, with repeated
      plasma proline measurements and standardized developmental, neurologic,
      and psychiatric assessments. This would test penetrance and whether
      clinical outcomes track genotype, residual enzyme activity, or metabolite
      level in isolated HPI.
  evidence:
  - reference: PMID:24931297
    reference_title: Biochemical and clinical features of hereditary hyperprolinemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The clinical features of HPI are unclear. Nephropathy, uncontrolled seizures, mental retardation or schizophrenia have been reported in HPI, but a benign phenotype without neurological problems has also been reported."
    explanation: Directly states the conflicting symptomatic and benign HPI observations.
  - reference: PMID:15662599
    reference_title: Functional consequences of PRODH missense mutations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "extant data suggest that severe hyperprolinemia (>800 microM) occurs in individuals with large deletions and/or PRODH missense mutations with the most-severe effect on function (L441P and R453C), whereas modest hyperprolinemia (300-500 microM) is associated with PRODH alleles with a moderate reduction in activity."
    explanation: >-
      Supplies limited genotype-to-biochemical-severity evidence while leaving
      the biochemical-to-clinical relationship unresolved.
  - reference: PMID:34302426
    reference_title: "Psychiatric phenotypes associated with hyperprolinemia: A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No evidence for a biochemical phenotype-clinical phenotype correlation was found; that is, no association between higher proline levels and specific psychiatric phenotypes was observed."
    explanation: Shows that metabolite level does not explain clinical outcome.
  - reference: PMID:34302426
    reference_title: "Psychiatric phenotypes associated with hyperprolinemia: A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "More studies are needed to clarify whether hyperprolinemia is a primary causal factor underlying the increased risk of developing psychiatric disorders seen in patients with hyperprolinemia, or whether hyperprolinemia and psychiatric disorders are both consequences of a shared underlying mechanism."
    explanation: Defines the unresolved causal question that this discussion tracks.
- discussion_id: mismatch_hpi_experimental_neural_models
  prompt: >-
    Which neural consequences observed in Prodh-mutant mice and PRODH-manipulated
    U87 cells reproduce the biology of isolated human HPI, and which are specific
    to the model, transformed-cell context, or 22q11.2 deletion background?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  rationale: >-
    The mouse model demonstrates sensorimotor-gating and regional neurochemical
    changes, while the U87 overexpression system couples proline to glutamate and
    glutamine. Neither model recapitulates the variable human penetrance, and U87
    is a transformed glioblastoma line rather than a patient neuron. Human
    psychiatric studies frequently include 22q11.2 deletions and ALDH4A1-HPII,
    so they cannot resolve this translation gap.
  attaches_to:
  - pathophysiology#Putative Proline-Linked Neural Dysfunction
  - experimental_models#Pro/Re Prodh-mutant hyperprolinemic mouse
  - experimental_models#U87 wild-type and L441P PRODH expression system
  proposed_experiments:
  - experiment_id: exp_hpi_cross_model_neural_comparison
    name: Cross-model comparison of PRODH-deficient neural phenotypes
    description: >-
      Compare molecularly matched human neuronal models, the Prodh-mutant mouse,
      and the existing transformed-cell observations using shared proline,
      glutamate, glutamine, and neural-function readouts. Include allele-corrected
      comparators and benchmark each model against observations from isolated
      HPI cohorts to identify which signals translate to human disease.
  evidence:
  - reference: PMID:10192398
    reference_title: The gene encoding proline dehydrogenase modulates sensorimotor gating in mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We also isolated the mouse homologue of slgA (Prodh), identified a mutation in this gene in the Pro/Re hyperprolinaemic mouse strain and found that these mice have a deficit in sensorimotor gating accompanied by regional neurochemical alterations in the brain."
    explanation: Defines the principal mouse observations requiring human translation.
  - reference: PMID:29694413
    reference_title: Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a U87 glioblastoma cell line.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here, we report on the expression of wild-type and L441P variants of human PO in a U87 glioblastoma human cell line in an attempt to assess their effect on glutamate metabolism."
    explanation: Identifies the transformed cell-line context of the human-cell evidence.
  - reference: PMID:17135275
    reference_title: Involvement of hyperprolinemia in cognitive and psychiatric features of the 22q11 deletion syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We next report that, among 92 adult or adolescent VCFS subjects, a subset of patients with severe hyperprolinemia has a phenotype distinguishable from that of other VCFS patients and reminiscent of HPI."
    explanation: >-
      Shows that a prominent human neuropsychiatric evidence stream concerns
      hyperprolinemia within the multigene 22q11.2 deletion background rather
      than isolated biallelic PRODH deficiency.
  - reference: PMID:28202261
    reference_title: "Hyperprolinemia as a clue in the diagnosis of a patient with psychiatric manifestations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mild dysmorphic features also suggested a possible 22q11 deletion syndrome that was confirmed. A mutation for Hyperprolinemia type I was also detected."
    explanation: >-
      Illustrates co-occurring 22q11.2 deletion and an HPI-associated variant,
      for which the respective contributions to the clinical presentation
      cannot be separated from the report.
notes: >-
  IEMbase package seed WP-003 (GitHub issue 5558), classification code 1.7.05.01
  (PRODH-related proline dehydrogenase deficiency); OMIM:239500. MONDO provides
  an exact disease identity (MONDO:0009400, causal gene HGNC:9453 PRODH, OMIM
  xref 239500), so HPI is curated as a standalone Disease entry. It is not a
  subtype of Hyperprolinemia Type 2: the two disorders have distinct MONDO
  identities, causal genes, and pathway blocks. No mechanism module is added
  because this entry contributes one disease-specific enzyme block and an
  explicitly hypothetical neural branch rather than a recurrent, independently
  evidenced pathological process. This PR addresses only WP-003 row 1.7.05.01;
  the other unresolved rows remain deferred under GitHub issue 5558.
📚

References & Deep Research

Deep Research

1
Falcon ▸
Disease Characteristics Research Template
Edison Scientific Literature 30 citations 2026-08-08T18:00:11.217268

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

  • Disease Name: Hyperprolinemia Type 1
  • MONDO ID: (if available)
  • Category: Metabolic Disorder

Research Objectives

Please provide a comprehensive research report on Hyperprolinemia Type 1 covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

  • What is the disease? Provide a concise overview.
  • What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
  • What are the common synonyms and alternative names?
  • Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

  • Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
  • Risk Factors:

    Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases

  • Genetic risk factors (causal variants, susceptibility loci, modifier genes)
  • Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
  • Protective Factors:

    Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases

  • Genetic protective factors (protective variants, modifier alleles)
  • Environmental protective factors (diet, lifestyle, exposures that reduce risk)
  • Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

    Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

  • Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

    Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene

  • Pathogenic Variants:
  • Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
  • Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
  • Variant type/class (missense, frameshift, nonsense, splice-site, structural)
  • Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
  • Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
  • Functional consequences (loss of function, gain of function, dominant negative)
  • Modifier Genes: Genes that modify disease severity or expression
  • Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

  • Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

    Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

  • Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

    Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases

  • Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

    Search first: CDC databases, WHO, PubMed, NHANES

  • Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

    Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

  • Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

    Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc

  • Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

    Search first: Gene Ontology (GO), Reactome, KEGG, PubMed

  • Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

    Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold

  • Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

    Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA

  • Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

    Search first: ImmPort, Immunome Database, IEDB, Gene Ontology

  • Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

    Search first: PubMed, Gene Ontology, Reactome

  • Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

    Search first: BRENDA, UniProt, KEGG, OMIM, PubMed

  • Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

  • Molecular Profiling (if available):
  • Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
  • Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
  • Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
  • Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
  • Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
  • Advanced Technologies (if applicable):
  • Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
  • Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
  • Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
  • Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

  • Organ Level:
  • Primary organs directly affected
  • Secondary organ involvement (complications, secondary effects)
  • Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

    Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT

  • Tissue and Cell Level:
  • Specific tissue types affected (epithelial, connective, muscle, nervous)
  • Specific cell populations targeted (with Cell Ontology terms)

    Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB

  • Subcellular Level:
  • Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

    Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas

  • Localization:
  • Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
  • Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

  • Onset:
  • Typical age of onset (congenital, pediatric, adult, geriatric)
  • Onset pattern (acute, subacute, chronic, insidious)

    Search first: OMIM, Orphanet, HPO, PubMed

  • Progression:
  • Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
  • Progression rate (rapid, slow, variable)
  • Disease course pattern (episodic, relapsing-remitting, progressive, stable)
  • Disease duration (self-limited, chronic lifelong)

    Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM

  • Patterns:
  • Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
  • Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

  • Epidemiology:
  • Prevalence (cases per 100,000 at given time)
  • Incidence (new cases per 100,000 per year)

    Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries

  • For Genetic Etiology:
  • Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
  • Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
  • Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
  • Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
  • Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
  • Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
  • Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
  • Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
  • Population Demographics:
  • Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
  • Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
  • Geographic distribution of specific variants
  • Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
  • Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

  • Clinical Tests:
  • Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
  • Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
  • Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
  • Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
  • Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
  • Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
  • Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
  • Genetic Testing:

    Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen

  • Overview of recommended genetic testing approach
  • Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
  • Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
  • Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
  • Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
  • Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
  • Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
  • FISH > Search first: ClinVar, cytogenetics databases, PubMed
  • Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
  • Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
  • Omics-Based Diagnostics (if applicable):
  • RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
  • Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
  • Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
  • Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
  • Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
  • Clinical Criteria:
  • Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
  • Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
  • Screening:
  • Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

  • Survival and Mortality:
  • Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
  • Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
  • Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
  • Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
  • Morbidity and Function:
  • Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
  • Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
  • Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
  • Disease Course:
  • Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
  • Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
  • Prediction:
  • Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
  • Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

  • Pharmacotherapy:
  • Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
  • Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
  • Advanced Therapeutics:
  • Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
  • Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
  • RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
  • Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
  • Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
  • Surgical and Interventional:
  • Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
  • Supportive and Rehabilitative:
  • Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
  • Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
  • Experimental:
  • Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
  • Treatment Outcomes:
  • Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
  • Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
  • Treatment Strategy:
  • Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
  • Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
  • Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest NCIT (NCI Thesaurus) clinical-intervention terms where applicable.

13. Prevention

  • Prevention Levels:
  • Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
  • Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
  • Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
  • Immunization: Vaccine strategies (if applicable)

    Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database

  • Screening and Early Detection:
  • Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
  • Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
  • Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
  • Behavioral Interventions: Lifestyle modifications to reduce risk

    Search first: CDC, WHO, behavioral intervention databases, Cochrane Library

  • Counseling: Genetic counseling (risk assessment, family planning guidance)

    Search first: NSGC resources, ACMG guidelines, GeneReviews

  • Public Health:
  • Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
  • Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
  • Prophylaxis: Preventive medications or procedures

    Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

  • Taxonomy: Species affected (with NCBI Taxon identifiers)

    Search first: NCBI Taxonomy

  • Breed: Specific breeds affected (with VBO identifiers if applicable)

    Search first: VBO (Vertebrate Breed Ontology)

  • Gene: Orthologous genes in other species (with NCBI Gene IDs)

    Search first: NCBI Gene

  • Natural Disease:
  • Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
  • Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
  • Comparative Biology:
  • Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
  • Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
  • Transmission (if applicable):
  • Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
  • Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

  • Model Types:
  • Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
  • Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
  • Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
  • Genetic Models:
  • Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
  • Model Characteristics:
  • Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
  • Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
  • Applications:
  • Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
  • Resources:
  • Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

  • Cite primary literature (PMID preferred) for all mechanistic and clinical claims
  • Prioritize recent reviews and landmark papers
  • Include direct quotes from abstracts where possible to support key statements
  • Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, NCIT, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (NCIT terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Hyperprolinemia Type 1: comprehensive disease-characteristics report

Scope and evidence note. Hyperprolinemia type 1 (HPI) is exceptionally rare, and the modern literature consists mainly of reviews, small case series, individual cases, mechanistic experiments, and studies of 22q11.2 deletion syndrome (22q11.2DS). The latter is not equivalent to isolated biallelic HPI: a 22q11.2 deletion removes one copy of PRODH together with many other genes. Psychiatric findings from 22q11.2DS therefore require cautious interpretation. No disease-specific 2023–2024 natural-history cohort or therapeutic trial with outcome data was identified.

The following table gives an evidence-weighted knowledge-base synopsis.

Knowledge-base field Summary Ontology/identifier suggestions Evidence status Key citations
Disease / identifiers Hyperprolinemia type 1 (HPI) is a rare inborn error of proline degradation caused by deficiency of proline dehydrogenase (PRODH, also called proline oxidase). It should be distinguished from hyperprolinemia type 2, which is due to ALDH4A1/P5CDH deficiency. Information here is disease-level, aggregated from literature and curated resources, not EHR-derived. MONDO:0009400; MeSH/ICD/OMIM/Orphanet: verify in source database before KB ingestion Established for disease concept and distinction from HPII (OpenTargets Search: Hyperprolinemia type 1-PRODH, dalili2023clinicalfeaturesand pages 11-13, yao2022prolinemetabolismin pages 4-5)
Causal gene / inheritance Primary causal gene: PRODH (proline dehydrogenase 1). Inheritance is autosomal recessive. Open Targets links HPI most strongly to PRODH; other associations are much weaker and not sufficient to assign causality. Gene: PRODH; HGNC/Ensembl can be added from gene database; MONDO:0009400 Established for PRODH and AR inheritance; uncertain for other candidate associations (OpenTargets Search: Hyperprolinemia type 1-PRODH, dalili2023clinicalfeaturesand pages 11-13)
Biochemical defect Loss or reduction of mitochondrial PRODH activity impairs oxidation of L-proline to P5C, disrupting the proline→P5C→glutamate pathway. Reported hallmark is elevated proline in plasma, CSF, and urine; urine may also contain glycine and hydroxyproline. Human reviews describe proline elevations up to ~10-fold above normal in PRODH defects. GO suggestions: proline catabolic process; mitochondrial inner membrane; CHEBI: L-proline, glutamate Established for elevated proline and pathway position; downstream neurotoxicity mechanisms remain partly inferred (dalili2023clinicalfeaturesand pages 11-13, patriarca2021themultifacetedroles pages 6-9, cappelletti2018prolineoxidasecontrols pages 1-2, yao2022prolinemetabolismin pages 3-4)
Core phenotypes Phenotype spectrum is highly variable: some individuals are asymptomatic, while reported manifestations include developmental delay/intellectual disability, behavioral problems, autism spectrum disorder, seizures/epilepsy, schizophrenia or schizoaffective phenotypes, nephropathy, and rare movement-disorder presentations. Nervous system involvement predominates in the literature. HPO suggestions: Hyperprolinemia; Seizure; Developmental delay; Intellectual disability; Behavioral abnormality; Autism; Schizophrenia; Nephropathy Mixed: hyperprolinemia is established; neuropsychiatric associations are reported but incompletely penetrant and sometimes confounded (dalili2023clinicalfeaturesand pages 11-13, patriarca2021themultifacetedroles pages 6-9, yao2022prolinemetabolismin pages 4-5)
Diagnosis Diagnostic approach centers on elevated proline in plasma/CSF/urine plus molecular confirmation of PRODH variants. P5C measurement helps distinguish HPI from HPII. Differential diagnosis includes ALDH4A1-related HPII and secondary hyperprolinemia in syndromic contexts such as 22q11.2 deletion. HPO: Hyperprolinemia; Gene testing: PRODH; Differential: ALDH4A1-related hyperprolinemia type 2 Established for biochemical testing strategy; no universally standardized diagnostic criteria retrieved (dalili2023clinicalfeaturesand pages 11-13, yao2022prolinemetabolismin pages 4-5)
Treatment No proven disease-modifying therapy was identified. Review evidence states dietary proline restriction does not improve clinical manifestations. Current care is supportive and phenotype-directed (e.g., seizure, developmental, psychiatric management). A vitamin D trial targeting schizophrenia-associated hyperprolinemia was withdrawn before enrollment, so no efficacy data exist. NCIT suggestions: Supportive care; Dietary management; Anticonvulsant therapy; Psychiatric management Established absence of proven therapy in retrieved evidence; experimental vitamin D concept remains untested (dalili2023clinicalfeaturesand pages 11-13, NCT02197286 chunk 1, NCT02197286 chunk 2)
Prognosis / course Prognosis appears variable and often compatible with long survival, especially in mild or asymptomatic cases, but robust survival statistics were not retrieved. The course is usually chronic biochemical hyperprolinemia with heterogeneous neurologic/psychiatric expression rather than a clearly staged progressive disorder. HPO suggestions depend on phenotype burden; no specific prognosis ontology added Uncertain due to sparse natural-history data and small cohorts (dalili2023clinicalfeaturesand pages 11-13, yao2022prolinemetabolismin pages 4-5)
Epidemiology / population HPI is rare. Reliable prevalence, incidence, carrier frequency, sex ratio, and founder-mutation data were not retrieved in the available evidence set. In a 22q11.2 deletion cohort, 35% had hyperprolinemia, but that figure should not be used as HPI prevalence. MONDO:0009400 Rarity established; population statistics largely unavailable here (koning2015prodhrs450046and pages 1-2, koning2015prodhrs450046and pages 5-7, koning2015prodhrs450046and pages 4-5)
Model systems Experimental evidence includes PRODH expression studies in U87 glioblastoma cells and Prodh-deficient mouse work discussed in reviews. Cell models show mitochondrial localization and effects on intracellular proline, glutamate, and glutamine; mouse literature supports relevance to sensorimotor-gating and neurobehavioral phenotypes, but not full recapitulation of human HPI heterogeneity. CL suggestion: glial cell / astrocyte-like cell line context for U87; GO: mitochondrial inner membrane Useful mechanistic support; translational limits should be noted (cappelletti2018prolineoxidasecontrols pages 1-2, cappelletti2018prolineoxidasecontrols pages 10-12, cappelletti2018prolineoxidasecontrols pages 15-16, cappelletti2018prolineoxidasecontrols pages 6-7, cappelletti2018prolineoxidasecontrols pages 7-10)
Key evidence caveats Much of the neuropsychiatric literature is confounded by 22q11.2 deletion syndrome, where PRODH hemizygosity co-occurs with many other deleted genes and modifiers such as COMT. Reported associations with IQ, startle, schizophrenia, or ASD are inconsistent, often based on small samples, and should not be overinterpreted as universal features of isolated HPI. Annotation note: tag psychiatric findings as variable/uncertain association Important caution for KB curation (koning2015prodhrs450046and pages 1-2, koning2015prodhrs450046and pages 10-11, koning2015prodhrs450046and pages 7-8, koning2015prodhrs450046and pages 8-10, koning2015prodhrs450046and pages 5-7, koning2015prodhrs450046and pages 4-5, koning2015prodhrs450046and pages 12-12, yao2022prolinemetabolismin pages 3-4)

Table: This table provides a compact, evidence-weighted summary of Hyperprolinemia Type 1 for knowledge-base curation. It separates well-established disease facts from more uncertain neuropsychiatric associations and highlights where identifiers or epidemiologic values should be verified externally before ingestion.

1. Disease information

Definition

HPI is an autosomal-recessive inborn error of amino-acid metabolism caused by deficient mitochondrial proline dehydrogenase activity. Impaired first-step degradation of L-proline produces persistent hyperprolinemia and often increased urinary proline. The phenotype ranges from an incidental, apparently benign biochemical finding to variably penetrant neurologic, developmental, behavioral, or psychiatric manifestations. A 2023 review states that HPI may be asymptomatic or accompanied by behavioral problems, intellectual disability, autism-spectrum features, and seizures. Dalili et al., published August 2023, DOI/URL (dalili2023clinicalfeaturesand pages 11-13)

Identifiers and synonyms

  • MONDO: MONDO:0009400.
  • OMIM: commonly indexed as 239500; verify against the live OMIM record before database ingestion.
  • Orphanet: commonly indexed as ORPHA:419; live-database verification is recommended.
  • MeSH: usually represented under Hyperprolinemia rather than a reliably distinct type-1 descriptor.
  • ICD-10-CM: no specific HPI code; usually mapped to E72.5, Disorders of glycine metabolism, which includes disorders of proline metabolism.
  • ICD-11: use the current inborn-error/amino-acid-metabolism hierarchy; no reliably validated HPI-specific code was recovered.
  • Synonyms: hyperprolinemia I; hyperprolinaemia type I; proline oxidase deficiency; proline dehydrogenase deficiency; PRODH deficiency.

The retrieved information is aggregated disease-level evidence, not individual EHR-derived information. Open Targets identifies PRODH as the dominant disease-associated target and links the association to PMIDs 11891283, 12217952, 15662599, 17135275, 24816252, and 27604308. Weaker automated associations to DGCR6 or PRODH2 should not be interpreted as established HPI causality. (OpenTargets Search: Hyperprolinemia type 1-PRODH)

2. Etiology, risk, protection, and gene–environment interaction

Primary cause

The established cause is biallelic germline loss or marked reduction of function in PRODH, located at 22q11.21. PRODH encodes mitochondrial proline dehydrogenase/proline oxidase, the FAD-dependent enzyme catalyzing L-proline oxidation to Δ¹-pyrroline-5-carboxylate (P5C). HPI is not infectious, autoimmune, toxic, or lifestyle-caused. (dalili2023clinicalfeaturesand pages 11-13, cappelletti2018prolineoxidasecontrols pages 1-2)

Genetic risk and modifiers

  • The highest-risk genotype is biallelic pathogenic/likely pathogenic PRODH variation.
  • A 22q11.2 deletion creates PRODH hemizygosity, but usually does not by itself establish classic recessive HPI; elevated proline may result from reduced dosage, an affected remaining allele, or broader metabolic modifiers.
  • COMT Val158Met has been investigated as a neural modifier in 22q11.2DS because COMT and PRODH are both within or related to the deleted-region phenotype. In 45 adults with 22q11.2DS, 35% of those measured were hyperprolinemic, and a proline-by-COMT interaction affected startle reactivity, but not full-scale IQ or prepulse inhibition. Small genotype groups, medication exposure, and deletion-wide confounding make this preliminary rather than an established modifier relationship. de Koning et al., June 2015 (koning2015prodhrs450046and pages 1-2, koning2015prodhrs450046and pages 10-11)

Environmental and protective factors

No environmental exposure is known to cause inherited HPI, and no validated genetic or environmental protective factor has been demonstrated. Potentially relevant biochemical modifiers, not proven causes, include:

  • dietary proline load and fasting/postprandial state;
  • renal or hepatic dysfunction affecting amino-acid handling;
  • medications such as valproate, recognized in the withdrawn clinical trial as a cause of increased proline;
  • vitamin-D status, proposed to influence PRODH expression but never clinically validated in HPI.

Dietary proline restriction has not reliably improved clinical manifestations. Thus, low-proline intake should not be labeled a proven protective intervention. (dalili2023clinicalfeaturesand pages 11-13, NCT02197286 chunk 1, NCT02197286 chunk 2)

3. Phenotypes

Frequencies for isolated, molecularly confirmed HPI are not robustly known. Reported manifestations should be annotated as variable or occasional, rather than universal.

Phenotype Type and characteristics Suggested HPO term
Elevated plasma proline Core laboratory abnormality; congenital metabolic defect, chronic; reported up to approximately tenfold normal Hyperprolinemia, HP:0010916
Increased urinary proline Laboratory abnormality; glycine and hydroxyproline may also be excreted Aminoaciduria (HP:0003355, broad)
Asymptomatic biochemical phenotype No symptoms despite persistent hyperprolinemia; apparently common enough to make pathogenicity/penetrance assessment difficult Asymptomatic (HP:0000001, if accepted locally)
Developmental delay/intellectual disability Neurodevelopmental; generally childhood-recognized; severity variable Global developmental delay HP:0001263; Intellectual disability HP:0001249
Behavioral abnormality Childhood or later; nonspecific Behavioral abnormality HP:0000708
Autism-spectrum features Reported association, frequency unknown Autistic behavior HP:0000729
Seizures/epilepsy Childhood or later; can be severe or uncontrolled in reported patients, but not obligatory Seizure HP:0001250
Schizophrenia/psychosis Mainly adolescent/adult literature; association is inconsistent and heavily influenced by 22q11.2DS studies Schizophrenia HP:0100753; Psychosis HP:0000709
White-matter abnormality Rare case-level imaging finding Abnormal CNS myelination HP:0003429 or leukoencephalopathy term after imaging confirmation
Nephropathy Rarely reported; causal attribution uncertain Nephropathy HP:0000112
Myoclonus/ataxia Rare case-report phenotype, including a 2023 report; not established as a typical HPI feature Myoclonus HP:0001336; Ataxia HP:0001251

The literature explicitly describes both nephropathy, seizures, intellectual disability, and schizophrenia and a benign phenotype without neurologic problems. This is strong evidence for variable expressivity and incomplete clinical penetrance, but not for precise phenotype frequencies. (yao2022prolinemetabolismin pages 4-5)

Quality of life. No HPI-specific EQ-5D, SF-36, PROMIS, or disease-specific quality-of-life study was identified. QoL effects are therefore inferred from the burden of epilepsy, cognitive disability, autism, movement disorder, or psychosis, when present—not from the biochemical abnormality alone.

4. Genetic and molecular information

Causal gene and protein

  • Gene: PRODH; approved name proline dehydrogenase 1.
  • Ensembl: ENSG00000100033.
  • Location: chromosome 22q11.21.
  • Protein: mitochondrial proline dehydrogenase/proline oxidase, a flavoprotein associated with the inner mitochondrial membrane.
  • Origin: constitutional/germline; somatic variation is not the HPI mechanism.
  • Functional class: chiefly loss of function or severe hypomorphism.

Pathogenic variants

Reported disease-associated alleles include missense, truncating, splice-altering, and deletion alleles. The p.Leu441Pro (L441P) missense substitution is a functionally studied example associated with hyperprolinemia and schizophrenia-related reports. In U87 cells it retained mitochondrial targeting but had reduced stability and approximately twofold lower normalized activity; raw mitochondrial activity was three- to fivefold below wild type. Earlier estimates suggested over 70% reduction. Cappelletti et al., published April 2018, PMID 29698449 (cappelletti2018prolineoxidasecontrols pages 15-16, cappelletti2018prolineoxidasecontrols pages 7-10)

Variant-level pathogenicity must be adjudicated using current ClinVar submissions, ACMG/AMP criteria, segregation, biochemical phenotype, functional evidence, and gnomAD ancestry-specific frequency. This is important because HPI may be mild and metabolic-gene databases can contain historical misclassification. The retrieved corpus did not support a complete, current list of pathogenic variants or defensible per-variant population frequencies.

Other molecular categories

  • Modifier genes: COMT is a candidate modifier in the 22q11.2 context, not a confirmed HPI modifier. In one small cohort, PRODH rs450046 C carriers had lower mean FSIQ (60.2 versus 73.7; p=0.009), but there were only six C-allele carriers and no direct proline–FSIQ association. (koning2015prodhrs450046and pages 5-7, koning2015prodhrs450046and pages 4-5)
  • Epigenetics: no reproducible HPI-specific methylation or chromatin signature is established.
  • Chromosomal abnormalities: 22q11.2 deletions can include PRODH, but constitute a multisystem copy-number syndrome rather than isolated HPI.
  • Anticipation/germline mosaicism: no repeat-expansion anticipation is relevant; germline mosaicism is theoretically possible but not established as a recurrent feature.

5. Environmental information

No toxin, pollutant, radiation exposure, occupational factor, infection, smoking behavior, alcohol exposure, or exercise pattern is an established cause of HPI. Diet contributes substrate but does not create the inherited enzyme defect. Secondary or transient elevations should prompt assessment of nutritional state, liver and renal function, medications, and preanalytic conditions. There is no zoonotic or infectious component.

6. Mechanism and pathophysiology

Causal chain

  1. Upstream genetic event: biallelic PRODH loss/reduction of function.
  2. Protein defect: decreased activity of mitochondrial FAD-dependent proline dehydrogenase.
  3. Primary biochemical block: reduced L-proline oxidation to P5C.
  4. Metabolic consequence: proline accumulates in plasma, urine, and sometimes CSF; flux from P5C through ALDH4A1/P5C dehydrogenase to glutamate is altered.
  5. Downstream neural hypotheses: high extracellular proline can interfere with excitatory presynaptic transmission; altered proline/P5C/glutamate cycling may disturb glutamate, glutamine, GABA, TCA-anaplerotic, and redox homeostasis.
  6. Clinical consequence: incompletely penetrant neurodevelopmental, seizure, behavioral, or psychiatric phenotypes in susceptible individuals.

PRODH is a FAD-dependent mitochondrial enzyme, whereas P5C is subsequently converted to glutamate by NAD-dependent P5C dehydrogenase. Glutamate is both an excitatory neurotransmitter and precursor of glutamine and GABA. (cappelletti2018prolineoxidasecontrols pages 1-2, yao2022prolinemetabolismin pages 3-4)

Evidence by level

Human biochemical/clinical evidence. Reviews describe proline in plasma and CSF at up to approximately tenfold normal in PRODH defects and variable cognitive or neurologic dysfunction. The exact relationship between proline concentration and symptoms is not linear or reliably predictive. (patriarca2021themultifacetedroles pages 6-9, cappelletti2018prolineoxidasecontrols pages 2-4)

Human-cell evidence. In U87 glioblastoma cells, PRODH expression reduced intracellular proline from 44.2 to 32.3–33.1 pmol/10⁴ cells at 24 hours and subsequently altered glutamate and glutamine. This supports pathway coupling but does not prove neuronal toxicity in patients. Proline above 30 μM at synaptic terminals has been reported to inhibit glutamate release. (cappelletti2018prolineoxidasecontrols pages 10-12)

Redox/mitochondrial inference. PRODH transfers electrons during proline oxidation and can influence ROS production. A p53→PRODH→ROS→apoptosis axis is demonstrated in stress/cancer contexts, but it should not be asserted as a proven tissue-injury mechanism in HPI. (patriarca2021themultifacetedroles pages 6-9)

Immune and tissue injury. No primary autoimmunity, immunodeficiency, inflammation, fibrosis, ischemia, or necrosis mechanism is established for isolated HPI.

Suggested ontology annotations

  • GO biological process: proline catabolic process; cellular amino-acid catabolic process; glutamate metabolic process; regulation of synaptic transmission, glutamatergic; oxidation–reduction process.
  • GO molecular function: proline dehydrogenase activity; oxidoreductase activity acting on CH–NH₂ group donors; FAD binding.
  • GO cellular component: mitochondrial inner membrane; mitochondrion.
  • CHEBI: L-proline CHEBI:17203; L-glutamate CHEBI:29985; Δ¹-pyrroline-5-carboxylate; FAD; GABA CHEBI:16865.
  • Candidate cell types: neuron CL:0000540; glutamatergic neuron CL:0000679; GABAergic neuron CL:0000617; astrocyte CL:0000127. These are mechanistically plausible, not proven selective targets.

Molecular profiling and advanced technologies

No HPI-specific patient-cohort transcriptomic, proteomic, lipidomic, single-cell, spatial-transcriptomic, multi-omic, organoid, or CRISPR-screen signature was identified. U87-cell metabolite measurements are mechanistic profiling, not a validated diagnostic omics signature.

7. Anatomical structures affected

The nervous system is the principal clinically implicated system when disease is symptomatic. Relevant regions inferred from neurotransmission and model work include cerebral cortex, prefrontal cortex, hippocampal circuits, and white matter; no consistent focal lesion or lateralization is established. Rare renal involvement has been reported but is not well characterized. (yao2022prolinemetabolismin pages 4-5, yao2022prolinemetabolismin pages 3-4)

Suggested annotations:

  • UBERON: brain UBERON:0000955; cerebral cortex UBERON:0000956; hippocampal formation UBERON:0002421; white matter; kidney UBERON:0002113.
  • Tissues: nervous tissue and, secondarily, renal tissue where clinically implicated.
  • Subcellular: mitochondrial inner membrane, where PRODH functions.
  • Lateralization: not applicable.

8. Temporal development

The enzyme defect is congenital and lifelong, but biochemical detection and clinical onset vary. Developmental delay, autism, or epilepsy generally emerge in childhood; psychotic illness, where genuinely associated, generally emerges later. Asymptomatic individuals may be detected incidentally at any age.

There is no accepted stage system. The biochemical condition is chronic; the clinical course can be stable, episodic where seizures or psychiatric symptoms occur, or rarely progressive in reported movement/neurologic presentations. No defined remission pattern, critical treatment window, or validated longitudinal trajectory exists.

9. Inheritance and population

  • Inheritance: autosomal recessive.
  • Penetrance: high for biochemical hyperprolinemia in individuals with severe biallelic deficiency, but apparently incomplete for clinical manifestations.
  • Expressivity: markedly variable.
  • Sex ratio: no established sex bias.
  • Prevalence/incidence: reliably quantified population estimates are unavailable; HPI is considered very rare.
  • Carrier frequency/founder effects: no robust global carrier frequency or consistently replicated founder allele was identified.
  • Consanguinity: increases the probability of biallelic rare alleles, as for other recessive conditions, but disease-specific risk estimates are unavailable.

In a 22q11.2DS cohort, 12/34 measured individuals (35%) met the investigators’ hyperprolinemia thresholds; median proline was 281.5 μmol/L, range 159–929 μmol/L. This is a syndromic, genetically selected sample and must not be used as HPI prevalence. (koning2015prodhrs450046and pages 4-5)

10. Diagnostics

Recommended approach

  1. Confirm biochemistry: quantitative plasma amino acids, preferably fasting and repeated. Urine amino acids can document prolinuria; CSF amino acids are not routinely necessary.
  2. Differentiate type 1 from type 2: assess urinary P5C or a validated equivalent. P5C accumulation/excretion favors ALDH4A1-related HPII, whereas HPI generally lacks marked P5C excretion. (dalili2023clinicalfeaturesand pages 11-13)
  3. Molecular confirmation: sequence and deletion/duplication analysis of PRODH. A broader metabolic/neurodevelopmental panel or exome/genome sequencing is reasonable for complex phenotypes or negative single-gene testing.
  4. Variant interpretation: integrate segregation, phase, biochemical magnitude, ClinVar/gnomAD evidence, and functional data.
  5. Phenotype assessment: developmental and neuropsychological evaluation, EEG for suspected seizures, MRI only for neurologic indications, renal/liver studies to exclude secondary contributors.

Genetic-test utility

  • Single-gene or panel testing: first-line when biochemical HPI is clear.
  • WES/WGS: useful for atypical cases, detecting alternative diagnoses and coding variants; WGS may improve CNV and noncoding detection.
  • CMA: indicated when congenital anomalies, dysmorphism, cardiac disease, immune abnormalities, or hypocalcemia suggest 22q11.2DS.
  • Karyotype/FISH: not routine for isolated HPI; targeted FISH may detect a known 22q11.2 deletion but CMA is more comprehensive.
  • mtDNA and repeat-expansion tests: not indicated by the core disorder.
  • Enzyme assay: specialized PRODH assays may support diagnosis but are not widely standardized clinically.

Differential diagnosis

  • Hyperprolinemia type 2: biallelic ALDH4A1/P5C dehydrogenase deficiency; generally higher proline and P5C excretion, with a stronger seizure association.
  • 22q11.2 deletion syndrome: multisystem phenotype with PRODH hemizygosity.
  • Secondary hyperprolinemia from liver/renal dysfunction, nutritional state, or drugs.
  • Other aminoacidopathies and neurodevelopmental/metabolic epilepsies.

There are no universally accepted clinical diagnostic criteria beyond persistent biochemical hyperprolinemia plus compatible molecular findings. Newborn screening is not routinely implemented, and isolated proline is not a standard core newborn-screening analyte.

11. Outcome and prognosis

No disease-specific five- or ten-year survival, mortality rate, or life-expectancy estimate exists. Mild or asymptomatic HPI appears compatible with normal longevity. Morbidity is driven by associated epilepsy, intellectual/developmental disability, behavioral disorder, movement disorder, nephropathy, or psychiatric illness—not by plasma proline alone.

Prognostic factors remain unvalidated. Plausible factors are residual enzyme activity, magnitude/persistence of hyperprolinemia, presence of a 22q11.2 deletion or second diagnosis, early developmental burden, and seizure control. No FDA-qualified prognostic biomarker or validated proline threshold predicts outcome.

12. Treatment

Current clinical implementation

There is no approved disease-modifying pharmacotherapy, gene therapy, RNA therapy, cell therapy, enzyme replacement, or surgery for HPI. A 2023 review concluded that “no effective treatment exists” and that proline-restricted diets do not improve clinical manifestations. (dalili2023clinicalfeaturesand pages 11-13)

Management is individualized:

  • antiseizure therapy according to epilepsy type;
  • developmental, educational, speech, occupational, and physical therapies;
  • standard evidence-based treatment of psychiatric illness;
  • renal care if nephropathy is present;
  • nutritional supervision if dietary manipulation is attempted, avoiding protein inadequacy.

Suggested NCIt intervention concepts include Supportive Care, Anticonvulsant Therapy, Psychiatric Therapy, Occupational Therapy, Physical Therapy, Speech Therapy, and Dietary Intervention. Exact NCIt codes should be resolved in the current release.

Clinical trials and experimental therapy

NCT02197286, “Targeted Vitamin D Treatment of Schizophrenia-Associated Hyperprolinemia,” proposed 4,000 IU/day vitamin D3 versus placebo for ten weeks in 80 adults with schizophrenia-spectrum illness, vitamin-D insufficiency, and sex-specific fasting hyperprolinemia. The rationale was putative vitamin-D regulation of PRODH expression. The Phase 2 study was withdrawn before enrollment because of personnel changes; enrollment was zero, so it generated no efficacy or safety data. It was not a trial specifically in molecularly confirmed HPI. ClinicalTrials.gov NCT02197286 (NCT02197286 chunk 1, NCT02197286 chunk 2)

No active disease-specific gene, RNA, cell, or targeted-therapy trial was identified.

13. Prevention

Because HPI is inherited, lifestyle modification cannot prevent the causal genotype.

  • Primary prevention: genetic counseling, carrier testing for relatives after a familial variant is identified, reproductive options including prenatal diagnosis and preimplantation genetic testing.
  • Secondary prevention: cascade testing and early biochemical/molecular diagnosis in siblings; prompt developmental and seizure assessment.
  • Tertiary prevention: control seizures and psychiatric symptoms, developmental intervention, medication review, and prevention of nutritional harm.
  • Vaccination/public health/environmental prophylaxis: no disease-specific role.

For two confirmed carrier parents, the Mendelian risk per pregnancy is 25% affected, 50% carrier, and 25% neither familial allele, assuming both variants are truly pathogenic and in trans.

14. Other species and natural disease

  • Human: Homo sapiens, NCBI Taxonomy 9606.
  • Mouse ortholog/model: Mus musculus, Taxonomy 10090, Prodh.
  • Orthologs also occur in zebrafish, Drosophila, and C. elegans, reflecting conservation of proline metabolism.

No well-established naturally occurring companion-animal or livestock syndrome directly equivalent to human PRODH-related HPI was identified in the retrieved evidence. Accordingly, breed-specific VBO terms, veterinary prevalence, and natural-disease importance cannot be assigned. There is no transmission or zoonotic potential.

15. Model organisms and experimental systems

Mouse

Prodh-deficient mice are the principal genetic model. Foundational work reported hyperprolinemia and abnormal sensorimotor gating, supporting a link between proline metabolism and neural circuit function. Reviews emphasize altered neurobehavioral/synaptic phenotypes, but mice do not reproduce the full heterogeneity of human intellectual disability, psychosis, or asymptomatic disease. The landmark study is Gogos et al., Nature Genetics 1999, “The gene encoding proline dehydrogenase modulates sensorimotor gating in mice,” DOI 10.1038/7777.

Human cellular model

Wild-type and L441P PRODH expressed in U87 human glioblastoma cells localize to mitochondria. The variant preserves localization but reduces activity/stability; manipulation of PRODH changes intracellular proline, glutamate, and glutamine. This model is useful for enzyme kinetics and metabolic coupling but is a transformed glial-like cell line, not a patient neuron or intact brain. (cappelletti2018prolineoxidasecontrols pages 1-2, cappelletti2018prolineoxidasecontrols pages 10-12, cappelletti2018prolineoxidasecontrols pages 7-10)

Other potential systems

Zebrafish, fly, worm, patient fibroblasts, iPSC-derived neurons/astrocytes, and cerebral organoids are plausible platforms for functional studies and high-throughput screening, but no validated HPI-specific organoid or single-cell model was identified. Future work should prioritize isogenic PRODH knockout/knock-in iPSC models, direct measurement of synaptic proline/glutamate/GABA flux, and genotype–residual-activity–phenotype correlation.

Recent developments and expert assessment

The most recent disease-relevant literature does not reveal a new approved therapy. Instead, 2023–2024 work has refined three interpretive points:

  1. Modern aminoacidopathy reviews still characterize HPI as diagnostically biochemical, clinically heterogeneous, and without effective disease-modifying treatment. (dalili2023clinicalfeaturesand pages 11-13)
  2. Contemporary cognition/psychiatry reviews continue to implicate PRODH and proline metabolism, but associations do not establish that isolated HPI inevitably causes schizophrenia.
  3. Variant interpretation must account for mild/asymptomatic disease, ancestry-specific frequency, historical misclassification, and 22q11.2 confounding. Open Targets supports PRODH with multiple human-genetic literature items, whereas other gene associations are substantially weaker. (OpenTargets Search: Hyperprolinemia type 1-PRODH)

Expert synthesis: the most defensible disease model is a highly penetrant biochemical disorder with variably penetrant clinical consequences. Persistent elevated proline plus biallelic functionally consequential PRODH variants establishes the diagnosis; proline elevation alone does not predict neurologic or psychiatric outcome. Major unmet needs are a genotype-defined international registry, standardized fasting proline/P5C protocols, residual-activity assays, longitudinal neurodevelopmental outcomes, and controlled treatment studies.

Selected abstract quotations and key sources

  • Yao and Han’s 2022 review states: “Proline plays a multifaceted role in protein synthesis, redox balance, cell fate regulation, brain development, and other cellular and physiological processes.” Published November 2022, DOI 10.14348/molcells.2022.0115 (yao2022prolinemetabolismin pages 4-5, yao2022prolinemetabolismin pages 3-4)
  • Cappelletti et al. state: “Proline is oxidized to glutamate in the mitochondria and the FAD-containing enzyme proline oxidase (PO) catalyzes the first step in L-proline degradation pathway.” Published April 2018, PMID 29698449 (cappelletti2018prolineoxidasecontrols pages 1-2)
  • The same primary study concludes: “the proline pathway links cellular proline levels with those of glutamate and glutamine.” (cappelletti2018prolineoxidasecontrols pages 1-2)
  • The 2023 aminoacidopathy review summarizes HPI as autosomal recessive PRODH/proline-oxidase deficiency and reports no effective therapy or clinical improvement from proline restriction. Published August 2023 (dalili2023clinicalfeaturesand pages 11-13)

Evidence gaps should remain explicit in the knowledge base: no reliable HPI prevalence/incidence, phenotype percentages, survival statistics, validated QoL instrument, complete penetrance estimate, proven protective factor, standardized therapeutic algorithm, active disease-specific interventional trial, or established patient multi-omics signature was found.

References

  1. (OpenTargets Search: Hyperprolinemia type 1-PRODH): Open Targets Query (Hyperprolinemia type 1-PRODH, 8 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.

  2. (dalili2023clinicalfeaturesand pages 11-13): Setila Dalili, Ali Talea, Monireh Aghajany-Nasab, Navid Alirezapour Asl Miandoab, Shahin Koohmanaee, Seyede Tahoura Hakemzadeh, Amir Mohammad Ghanbari, and Nazanin Medghalchi. Clinical features and laboratory diagnosis of aminoacidopathies: a narrative review. Archives of Neuroscience, Aug 2023. URL: https://doi.org/10.5812/ans-136721, doi:10.5812/ans-136721. This article has 6 citations.

  3. (yao2022prolinemetabolismin pages 4-5): Yuxiao Yao and Weiping Han. Proline metabolism in neurological and psychiatric disorders. Molecules and Cells, 45:781-788, Nov 2022. URL: https://doi.org/10.14348/molcells.2022.0115, doi:10.14348/molcells.2022.0115. This article has 37 citations and is from a peer-reviewed journal.

  4. (patriarca2021themultifacetedroles pages 6-9): Eduardo J. Patriarca, Federica Cermola, Cristina D’Aniello, Annalisa Fico, Ombretta Guardiola, Dario De Cesare, and Gabriella Minchiotti. The multifaceted roles of proline in cell behavior. Frontiers in Cell and Developmental Biology, Aug 2021. URL: https://doi.org/10.3389/fcell.2021.728576, doi:10.3389/fcell.2021.728576. This article has 149 citations.

  5. (cappelletti2018prolineoxidasecontrols pages 1-2): Pamela Cappelletti, Elena Tallarita, Valentina Rabattoni, Paola Campomenosi, Silvia Sacchi, and Loredano Pollegioni. Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a u87 glioblastoma cell line. PLoS ONE, 13:e0196283, Apr 2018. URL: https://doi.org/10.1371/journal.pone.0196283, doi:10.1371/journal.pone.0196283. This article has 46 citations and is from a peer-reviewed journal.

  6. (yao2022prolinemetabolismin pages 3-4): Yuxiao Yao and Weiping Han. Proline metabolism in neurological and psychiatric disorders. Molecules and Cells, 45:781-788, Nov 2022. URL: https://doi.org/10.14348/molcells.2022.0115, doi:10.14348/molcells.2022.0115. This article has 37 citations and is from a peer-reviewed journal.

  7. (NCT02197286 chunk 1): James D. Clelland. Targeted Vitamin D Treatment of Schizophrenia-Associated Hyperprolinemia. NYU Langone Health. 2015. ClinicalTrials.gov Identifier: NCT02197286

  8. (NCT02197286 chunk 2): James D. Clelland. Targeted Vitamin D Treatment of Schizophrenia-Associated Hyperprolinemia. NYU Langone Health. 2015. ClinicalTrials.gov Identifier: NCT02197286

  9. (koning2015prodhrs450046and pages 1-2): Mariken B. de Koning, Esther D. A. van Duin, Erik Boot, Oswald J. N. Bloemen, Jaap A. Bakker, Kathryn M. Abel, and Thérèse A. M. J. van Amelsvoort. Prodh rs450046 and proline x comt val158met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome. Psychopharmacology, 232:3111-3122, Jun 2015. URL: https://doi.org/10.1007/s00213-015-3971-5, doi:10.1007/s00213-015-3971-5. This article has 19 citations and is from a peer-reviewed journal.

  10. (koning2015prodhrs450046and pages 5-7): Mariken B. de Koning, Esther D. A. van Duin, Erik Boot, Oswald J. N. Bloemen, Jaap A. Bakker, Kathryn M. Abel, and Thérèse A. M. J. van Amelsvoort. Prodh rs450046 and proline x comt val158met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome. Psychopharmacology, 232:3111-3122, Jun 2015. URL: https://doi.org/10.1007/s00213-015-3971-5, doi:10.1007/s00213-015-3971-5. This article has 19 citations and is from a peer-reviewed journal.

  11. (koning2015prodhrs450046and pages 4-5): Mariken B. de Koning, Esther D. A. van Duin, Erik Boot, Oswald J. N. Bloemen, Jaap A. Bakker, Kathryn M. Abel, and Thérèse A. M. J. van Amelsvoort. Prodh rs450046 and proline x comt val158met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome. Psychopharmacology, 232:3111-3122, Jun 2015. URL: https://doi.org/10.1007/s00213-015-3971-5, doi:10.1007/s00213-015-3971-5. This article has 19 citations and is from a peer-reviewed journal.

  12. (cappelletti2018prolineoxidasecontrols pages 10-12): Pamela Cappelletti, Elena Tallarita, Valentina Rabattoni, Paola Campomenosi, Silvia Sacchi, and Loredano Pollegioni. Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a u87 glioblastoma cell line. PLoS ONE, 13:e0196283, Apr 2018. URL: https://doi.org/10.1371/journal.pone.0196283, doi:10.1371/journal.pone.0196283. This article has 46 citations and is from a peer-reviewed journal.

  13. (cappelletti2018prolineoxidasecontrols pages 15-16): Pamela Cappelletti, Elena Tallarita, Valentina Rabattoni, Paola Campomenosi, Silvia Sacchi, and Loredano Pollegioni. Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a u87 glioblastoma cell line. PLoS ONE, 13:e0196283, Apr 2018. URL: https://doi.org/10.1371/journal.pone.0196283, doi:10.1371/journal.pone.0196283. This article has 46 citations and is from a peer-reviewed journal.

  14. (cappelletti2018prolineoxidasecontrols pages 6-7): Pamela Cappelletti, Elena Tallarita, Valentina Rabattoni, Paola Campomenosi, Silvia Sacchi, and Loredano Pollegioni. Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a u87 glioblastoma cell line. PLoS ONE, 13:e0196283, Apr 2018. URL: https://doi.org/10.1371/journal.pone.0196283, doi:10.1371/journal.pone.0196283. This article has 46 citations and is from a peer-reviewed journal.

  15. (cappelletti2018prolineoxidasecontrols pages 7-10): Pamela Cappelletti, Elena Tallarita, Valentina Rabattoni, Paola Campomenosi, Silvia Sacchi, and Loredano Pollegioni. Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a u87 glioblastoma cell line. PLoS ONE, 13:e0196283, Apr 2018. URL: https://doi.org/10.1371/journal.pone.0196283, doi:10.1371/journal.pone.0196283. This article has 46 citations and is from a peer-reviewed journal.

  16. (koning2015prodhrs450046and pages 10-11): Mariken B. de Koning, Esther D. A. van Duin, Erik Boot, Oswald J. N. Bloemen, Jaap A. Bakker, Kathryn M. Abel, and Thérèse A. M. J. van Amelsvoort. Prodh rs450046 and proline x comt val158met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome. Psychopharmacology, 232:3111-3122, Jun 2015. URL: https://doi.org/10.1007/s00213-015-3971-5, doi:10.1007/s00213-015-3971-5. This article has 19 citations and is from a peer-reviewed journal.

  17. (koning2015prodhrs450046and pages 7-8): Mariken B. de Koning, Esther D. A. van Duin, Erik Boot, Oswald J. N. Bloemen, Jaap A. Bakker, Kathryn M. Abel, and Thérèse A. M. J. van Amelsvoort. Prodh rs450046 and proline x comt val158met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome. Psychopharmacology, 232:3111-3122, Jun 2015. URL: https://doi.org/10.1007/s00213-015-3971-5, doi:10.1007/s00213-015-3971-5. This article has 19 citations and is from a peer-reviewed journal.

  18. (koning2015prodhrs450046and pages 8-10): Mariken B. de Koning, Esther D. A. van Duin, Erik Boot, Oswald J. N. Bloemen, Jaap A. Bakker, Kathryn M. Abel, and Thérèse A. M. J. van Amelsvoort. Prodh rs450046 and proline x comt val158met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome. Psychopharmacology, 232:3111-3122, Jun 2015. URL: https://doi.org/10.1007/s00213-015-3971-5, doi:10.1007/s00213-015-3971-5. This article has 19 citations and is from a peer-reviewed journal.

  19. (koning2015prodhrs450046and pages 12-12): Mariken B. de Koning, Esther D. A. van Duin, Erik Boot, Oswald J. N. Bloemen, Jaap A. Bakker, Kathryn M. Abel, and Thérèse A. M. J. van Amelsvoort. Prodh rs450046 and proline x comt val158met interaction effects on intelligence and startle in adults with 22q11 deletion syndrome. Psychopharmacology, 232:3111-3122, Jun 2015. URL: https://doi.org/10.1007/s00213-015-3971-5, doi:10.1007/s00213-015-3971-5. This article has 19 citations and is from a peer-reviewed journal.

  20. (cappelletti2018prolineoxidasecontrols pages 2-4): Pamela Cappelletti, Elena Tallarita, Valentina Rabattoni, Paola Campomenosi, Silvia Sacchi, and Loredano Pollegioni. Proline oxidase controls proline, glutamate, and glutamine cellular concentrations in a u87 glioblastoma cell line. PLoS ONE, 13:e0196283, Apr 2018. URL: https://doi.org/10.1371/journal.pone.0196283, doi:10.1371/journal.pone.0196283. This article has 46 citations and is from a peer-reviewed journal.

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