ALDH18A1-Related Spastic Paraplegia and Neurocutaneous Spectrum

Mendelian MONDO:0100126 Pathograph 36 Show in embeddings browser Hereditary Spastic Paraplegia Metabolic Disease Neurodegenerative Disease

Pathogenic variants in ALDH18A1, which encodes mitochondrial delta-1-pyrroline-5-carboxylate synthase (P5CS), cause a continuum of spastic paraplegia and neurocutaneous disease. This record curates three branches: autosomal dominant spastic paraplegia type 9A (SPG9A), autosomal recessive spastic paraplegia type 9B (SPG9B), and autosomal recessive cutis laxa type 3A (ARCL3A, De Barsy syndrome). ALDH18A1-related autosomal dominant cutis laxa (ADCL3) is a fourth branch curated separately. Disease-associated variants reduce P5CS function through variant-dependent effects on enzyme activity, oligomerization, protein abundance, or stability. Plasma proline, ornithine, citrulline, and arginine can be low in some genotypes but normal in others.

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2
Inheritance
9
Pathophys.
19
Phenotypes
3
Hypotheses
36
Pathograph
1
Genes
2
Medical Actions
3
Subtypes
12
References
1
Deep Research
👪

Inheritance

2
Autosomal Dominant (SPG9A) HP:0000006
Heterozygous ALDH18A1 pathogenic variants cause SPG9A and segregate with autosomal dominant pure or complex hereditary spastic paraplegia.
Autosomal dominant inheritance
Show evidence (1 reference)
PMID:26026163 SUPPORT Human Clinical
"identified monoallelic ALDH18A1 mutations segregating in three independent families with autosomal dominant pure or complex hereditary spastic paraplegia,"
Identifies monoallelic ALDH18A1 mutations in autosomal dominant pedigrees.
Autosomal Recessive (SPG9B / ARCL3A) HP:0000007
Biallelic ALDH18A1 pathogenic variants cause SPG9B and ARCL3A. Their functional effects are variable, ranging from hypomorphic alleles with residual P5CS activity to variants associated with absent or unstable protein. For the ARCL3A branch, when both parents are heterozygous, each sib has a 25% chance of being affected, a 50% chance of being heterozygous, and a 25% chance of being unaffected and not a carrier.
Autosomal recessive inheritance
Show evidence (3 references)
PMID:26026163 SUPPORT Human Clinical
"families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality."
Identifies biallelic ALDH18A1 mutations in autosomal recessive spastic paraplegia families.
PMID:24767728 SUPPORT Human Clinical
"Autosomal recessive cutis laxa (ARCL) is a connective tissue disorder characterized by wrinkled, inelastic skin, frequently associated with a neurologic involvement and multisystem disease."
Confirms autosomal recessive inheritance for ALDH18A1-related cutis laxa.
PMID:41570168 SUPPORT Other
"If both parents are known to be heterozygous for a pathogenic variant, each sib of an individual with PYCR1- or ALDH18A1-related ARCL has at conception a 25% chance of being affected, a 50% chance of being heterozygous, and a 25% chance of being unaffected and not a carrier."
GeneReviews supplies the recurrence-risk figures for the in-scope ALDH18A1-related ARCL3A branch; SPG9B inheritance is supported separately by its disease-specific evidence above.
◆

Subtypes

3
Spastic Paraplegia 9A (Autosomal Dominant) MONDO:0011006
Autosomal dominant hereditary spastic paraplegia caused by heterozygous ALDH18A1 pathogenic variants. Presentations range from pure to complex HSP; age at onset and additional findings, including cognitive involvement, are variable. Reduced P5CS function is established, while dominant-negative action is a proposed mechanism for dominant variants rather than a universal property of every SPG9A allele.
Show evidence (1 reference)
PMID:26026163 SUPPORT Human Clinical
"identified monoallelic ALDH18A1 mutations segregating in three independent families with autosomal dominant pure or complex hereditary spastic paraplegia, as well as in two sporadic patients."
Establishes SPG9A as an autosomal dominant form of ALDH18A1-related spastic paraplegia.
Spastic Paraplegia 9B (Autosomal Recessive) MONDO:0014702
Autosomal recessive hereditary spastic paraplegia caused by biallelic ALDH18A1 pathogenic variants. Many reported cases have earlier onset and more complex neurologic disease than SPG9A, but later-onset SPG9B without cognitive impairment is documented. Published SPG9 cohorts did not have the cutis laxa, joint laxity, or hernia phenotype that defines the cutis-laxa branches.
Show evidence (2 references)
PMID:31402623 SUPPORT Human Clinical
"conclude that both mutations are disease-causing, that SPG9B associates with partial P5CS deficiency and that it is clinically more severe than SPG9A, as reflected in onset age, disability, cognitive status, growth, and dysmorphic traits."
Early series found SPG9B generally more severe than SPG9A, without making this absolute for every genotype.
PMID:34093392 SUPPORT Human Clinical
"SPG9B patients in our cohort presented with milder symptoms, i.e., later age at onset and without cognitive impairment."
A later family establishes that SPG9B severity and cognitive involvement are variable.
Autosomal Recessive Cutis Laxa Type 3A (De Barsy Syndrome) MONDO:0009053
Biallelic ALDH18A1 pathogenic variants cause an autosomal recessive neurocutaneous disorder with thin or lax skin, joint laxity, growth and neurodevelopmental impairment, and variable cataracts, microcephaly, and pyramidal findings. Variant effects range from reduced P5CS stability or activity to absent protein.
Show evidence (1 reference)
PMID:25077174 SUPPORT Human Clinical
"Autosomal recessive cutis laxa type 3A is caused by mutations in ALDH18A1, a gene encoding the mitochondrial enzyme Δ(1)-pyrroline-5-carboxylate synthase (P5CS)."
Establishes ARCL3A as the biallelic ALDH18A1 cutis-laxa branch.
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Mechanistic Hypotheses

3
Variant-Dependent P5CS Loss-of-Function Model
variant_dependent_p5cs_loss_model CANONICAL
Evidence balance 1 support
The shared mechanism across ALDH18A1 disorders is decreased P5CS function, but different variants impair activity, oligomer incorporation, abundance, stability, or splicing to different degrees. This model does not assume that every dominant or biallelic variant has the same molecular effect.
Pathograph links
Dominant SPG9A P5CS dysfunction -> Variable P5CS-dependent amino-acid synthesis DIRECT Reduced P5CS function can alter proline- and ornithine-pathway output, but plasma amino-acid concentrations are not uniformly low across genotypes.
Dominant SPG9A P5CS dysfunction -> SPG9 corticospinal disease INDIRECT UNKNOWN INTERMEDIATES Dominant ALDH18A1 dysfunction produces pure or complex hereditary spastic paraplegia; the tissue-level bridge from P5CS dysfunction is unresolved.
Biallelic ALDH18A1 P5CS dysfunction -> Variable P5CS-dependent amino-acid synthesis DIRECT Biallelic P5CS dysfunction can reduce pathway output, although molecularly confirmed patients can have normal plasma amino-acid concentrations.
Biallelic ALDH18A1 P5CS dysfunction -> SPG9 corticospinal disease INDIRECT UNKNOWN INTERMEDIATES Some biallelic variants cause complex SPG9B without cutaneous abnormality; the intervening neural tissue mechanism is unknown.
Biallelic ALDH18A1 P5CS dysfunction -> SPG9B cognitive involvement INDIRECT UNKNOWN INTERMEDIATES Cognitive impairment is reported in complex SPG9B but is not universal; the intervening neural mechanism is unknown.
Biallelic ALDH18A1 P5CS dysfunction -> ARCL3A neurocutaneous disease INDIRECT UNKNOWN INTERMEDIATES Other biallelic ALDH18A1 variants cause ARCL3A; the tissue mechanisms separating this neurocutaneous branch from SPG9B remain unresolved.
Biallelic ALDH18A1 P5CS dysfunction -> p.Thr331Pro fibroblast metabolic and transcript changes INDIRECT UNKNOWN INTERMEDIATES In the homozygous p.Thr331Pro subgroup, impaired incorporation of P5CS monomers into oligomers accompanies measured fibroblast changes.
Biallelic ALDH18A1 P5CS dysfunction -> p.Arg749Gln/p.Arg765Gln stability and lipid-droplet phenotype INDIRECT UNKNOWN INTERMEDIATES In compound-heterozygous p.Arg749Gln/p.Arg765Gln fibroblasts, reduced P5CS stability co-occurs with a lipid-droplet phenotype; no clinical causal bridge is implied.
Biallelic ALDH18A1 P5CS dysfunction -> p.Arg84Gln-associated metabolic branch DIRECT Homozygous p.Arg84Gln markedly reduces P5CS activity and defines the reported hyperammonemic, low-amino-acid branch rather than a universal biochemical profile.
p.Arg84Gln-associated metabolic branch -> Hyperammonemia DIRECT In the p.Arg84Gln sibling pair, the genotype-specific metabolic branch manifested as hyperammonemia.
Show evidence (1 reference)
PMID:32017139 SUPPORT Other
"the four syndromes share the same pathogenic mechanisms based on decreased P5CS function."
The focused review identifies decreased P5CS function as the common mechanism across all four branches.
Proposed Dominant-Negative SPG9A Model
dominant_negative_spg9a_model EMERGING SPG9A
Evidence balance 1 support
Some heterozygous variants may impair the homooligomeric P5CS complex through a dominant-negative effect. This remains a variant-dependent proposal and is not generalized to every SPG9A allele.
Pathograph links
Dominant SPG9A P5CS dysfunction -> Variable P5CS-dependent amino-acid synthesis DIRECT Reduced P5CS function can alter proline- and ornithine-pathway output, but plasma amino-acid concentrations are not uniformly low across genotypes.
Dominant SPG9A P5CS dysfunction -> SPG9 corticospinal disease INDIRECT UNKNOWN INTERMEDIATES Dominant ALDH18A1 dysfunction produces pure or complex hereditary spastic paraplegia; the tissue-level bridge from P5CS dysfunction is unresolved.
Show evidence (1 reference)
PMID:32017139 SUPPORT Other
"the dominant mutations cause loss-of-function by dominant-negative mechanisms."
The review supports the dominant-negative model, retained here as emerging because variant-level proof is incomplete.
Downstream Neural and Connective-Tissue Consequence Model
downstream_tissue_consequence_model EMERGING
Evidence balance 1 support
Reduced P5CS function is associated with corticospinal and neurocutaneous phenotypes, but the intervening tissue mechanisms are incompletely resolved. Fibroblast metabolomic, extracellular-matrix transcript, and lipid-droplet findings are retained as genotype-specific observations rather than proven causal bridges to individual clinical features.
Pathograph links
Dominant SPG9A P5CS dysfunction -> SPG9 corticospinal disease INDIRECT UNKNOWN INTERMEDIATES Dominant ALDH18A1 dysfunction produces pure or complex hereditary spastic paraplegia; the tissue-level bridge from P5CS dysfunction is unresolved.
Biallelic ALDH18A1 P5CS dysfunction -> SPG9 corticospinal disease INDIRECT UNKNOWN INTERMEDIATES Some biallelic variants cause complex SPG9B without cutaneous abnormality; the intervening neural tissue mechanism is unknown.
Biallelic ALDH18A1 P5CS dysfunction -> SPG9B cognitive involvement INDIRECT UNKNOWN INTERMEDIATES Cognitive impairment is reported in complex SPG9B but is not universal; the intervening neural mechanism is unknown.
Biallelic ALDH18A1 P5CS dysfunction -> ARCL3A neurocutaneous disease INDIRECT UNKNOWN INTERMEDIATES Other biallelic ALDH18A1 variants cause ARCL3A; the tissue mechanisms separating this neurocutaneous branch from SPG9B remain unresolved.
SPG9 corticospinal disease -> Spastic paraplegia DIRECT Corticospinal involvement is expressed clinically as lower-limb spastic paraplegia in dominant and recessive SPG9.
SPG9B cognitive involvement -> Intellectual disability INDIRECT UNKNOWN INTERMEDIATES Intellectual disability is a reported, non-universal manifestation of complex SPG9B.
ARCL3A neurocutaneous disease -> Global developmental delay INDIRECT UNKNOWN INTERMEDIATES ARCL3A includes global developmental delay; the intervening neural mechanism is unknown.
ARCL3A neurocutaneous disease -> Cutis laxa INDIRECT UNKNOWN INTERMEDIATES ARCL3A includes lax, wrinkled, or inelastic skin. The full tissue-level mechanism remains unresolved, though patient dermal fibroblasts show reduced type I/III collagen production and altered elastin ultrastructure, a partial extracellular-matrix explanation.
ARCL3A neurocutaneous disease -> Joint hypermobility INDIRECT UNKNOWN INTERMEDIATES Joint laxity is part of ARCL3A, without a proven extracellular-matrix causal bridge.
ARCL3A neurocutaneous disease -> Prematurely aged appearance INDIRECT UNKNOWN INTERMEDIATES The triangular, progeroid facial appearance is a defining clinical characteristic of the ARCL3A/de Barsy branch; its tissue-level mechanism remains unresolved.
ARCL3A neurocutaneous disease -> Hypotonia INDIRECT UNKNOWN INTERMEDIATES Congenital hypotonia can occur in ARCL3A, although GeneReviews reports it at the grouped neurocutaneous-disorder level and the intervening mechanism is unknown.
ARCL3A neurocutaneous disease -> Corneal clouding INDIRECT UNKNOWN INTERMEDIATES Corneal clouding can occur in ARCL3A, but the grouped GeneReviews evidence does not establish its frequency or a direct corneal mechanism.
ARCL3A neurocutaneous disease -> Cataracts INDIRECT UNKNOWN INTERMEDIATES Cataracts are reported in ARCL3A, but the lens mechanism is unknown and is not attributed to the fibroblast lipid-droplet observation.
ARCL3A neurocutaneous disease -> Growth retardation INDIRECT UNKNOWN INTERMEDIATES ARCL3A growth involvement includes short stature; its intermediate mechanism is unknown.
ARCL3A neurocutaneous disease -> Microcephaly INDIRECT UNKNOWN INTERMEDIATES Microcephaly occurs in ARCL3A, with an unresolved developmental mechanism.
ARCL3A neurocutaneous disease -> Prominent superficial veins INDIRECT UNKNOWN INTERMEDIATES Visible superficial veins are reported in ARCL3A without a proven direct tissue mechanism.
ARCL3A neurocutaneous disease -> Failure to thrive INDIRECT UNKNOWN INTERMEDIATES Failure to thrive is reported in ARCL3A, while its intermediate mechanism is unresolved.
ARCL3A neurocutaneous disease -> Delayed speech and language development INDIRECT UNKNOWN INTERMEDIATES Severe speech delay accompanies developmental impairment in ARCL3A; the intervening neural mechanism is unknown.
ARCL3A neurocutaneous disease -> Dystonic posturing INDIRECT UNKNOWN INTERMEDIATES Dystonic posturing is the discriminatory ALDH18A1/PYCR1 neurocutaneous movement sign; the route from P5CS dysfunction to the basal-ganglia/motor phenotype is unresolved.
ARCL3A neurocutaneous disease -> Corpus callosum dysgenesis INDIRECT UNKNOWN INTERMEDIATES Corpus callosum dysgenesis is a CNS malformation associated with ALDH18A1 defects; the developmental mechanism from P5CS dysfunction is unresolved.
ARCL3A neurocutaneous disease -> Congenital hip dislocation INDIRECT UNKNOWN INTERMEDIATES Congenital hip dislocation is a connective-tissue/skeletal feature of the ALDH18A1-related neurocutaneous group; the extracellular-matrix bridge is not established.
ARCL3A neurocutaneous disease -> Adducted thumb INDIRECT UNKNOWN INTERMEDIATES Adducted thumbs are among the skeletal/positional features of the ALDH18A1-related neurocutaneous group; the mechanistic bridge is unknown.
Show evidence (1 reference)
PMID:36067040 SUPPORT In Vitro
"RNA sequencing of patient fibroblasts revealed transcript abundance changes in several metabolic and extracellular matrix-related genes, adding further insight into pathogenic processes associated with impaired P5CS function."
Supports downstream cellular associations while leaving tissue-level causation unresolved.
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Pathophysiology

9
Dominant SPG9A P5CS dysfunction
Heterozygous ALDH18A1 pathogenic variants decrease P5CS function in SPG9A. Dominant-negative action on the homooligomeric enzyme is proposed, but it is not assumed to be uniform across every dominant allele.
Downstream Neural and Connective-Tissue Consequence Model Proposed Dominant-Negative SPG9A Model Variant-Dependent P5CS Loss-of-Function Model
ALDH18A1 hgnc:9722 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves abnormal ALDH18A1 (hgnc:9722). hgnc:9722 is a gene from the HUGO Gene Nomenclature Committee. ⚠ ABNORMAL
Downstream
Variable P5CS-dependent amino-acid synthesis Reduced P5CS function can alter proline- and ornithine-pathway output, but plasma amino-acid concentrations are not uniformly low across genotypes. Variant-Dependent P5CS Loss-of-Function Model Proposed Dominant-Negative SPG9A Model
SPG9 corticospinal disease Dominant ALDH18A1 dysfunction produces pure or complex hereditary spastic paraplegia; the tissue-level bridge from P5CS dysfunction is unresolved. Variant-Dependent P5CS Loss-of-Function Model Proposed Dominant-Negative SPG9A Model Downstream Neural and Connective-Tissue Consequence Model
Show evidence (2 references)
PMID:32017139 SUPPORT Other
"the dominant mutations cause loss-of-function by dominant-negative mechanisms."
The focused review proposes dominant-negative loss of P5CS function for dominant variants.
PMID:26026163 SUPPORT Human Clinical
"identified monoallelic ALDH18A1 mutations segregating in three independent families with autosomal dominant pure or complex hereditary spastic paraplegia,"
Human segregation data establish heterozygous ALDH18A1 variants in SPG9A.
Biallelic ALDH18A1 P5CS dysfunction
Biallelic ALDH18A1 variants cause recessive P5CS dysfunction. Variant effects include reduced activity, oligomer incorporation, abundance, or stability with variable residual function.
Downstream Neural and Connective-Tissue Consequence Model Variant-Dependent P5CS Loss-of-Function Model
ALDH18A1 hgnc:9722 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves decreased ALDH18A1 (hgnc:9722). hgnc:9722 is a gene from the HUGO Gene Nomenclature Committee. ↓ DECREASED
Downstream
Variable P5CS-dependent amino-acid synthesis Biallelic P5CS dysfunction can reduce pathway output, although molecularly confirmed patients can have normal plasma amino-acid concentrations. Variant-Dependent P5CS Loss-of-Function Model
SPG9 corticospinal disease Some biallelic variants cause complex SPG9B without cutaneous abnormality; the intervening neural tissue mechanism is unknown. Variant-Dependent P5CS Loss-of-Function Model Downstream Neural and Connective-Tissue Consequence Model
SPG9B cognitive involvement Cognitive impairment is reported in complex SPG9B but is not universal; the intervening neural mechanism is unknown. Variant-Dependent P5CS Loss-of-Function Model Downstream Neural and Connective-Tissue Consequence Model
ARCL3A neurocutaneous disease Other biallelic ALDH18A1 variants cause ARCL3A; the tissue mechanisms separating this neurocutaneous branch from SPG9B remain unresolved. Variant-Dependent P5CS Loss-of-Function Model Downstream Neural and Connective-Tissue Consequence Model
p.Thr331Pro fibroblast metabolic and transcript changes In the homozygous p.Thr331Pro subgroup, impaired incorporation of P5CS monomers into oligomers accompanies measured fibroblast changes. Variant-Dependent P5CS Loss-of-Function Model
p.Arg749Gln/p.Arg765Gln stability and lipid-droplet phenotype In compound-heterozygous p.Arg749Gln/p.Arg765Gln fibroblasts, reduced P5CS stability co-occurs with a lipid-droplet phenotype; no clinical causal bridge is implied. Variant-Dependent P5CS Loss-of-Function Model
p.Arg84Gln-associated metabolic branch Homozygous p.Arg84Gln markedly reduces P5CS activity and defines the reported hyperammonemic, low-amino-acid branch rather than a universal biochemical profile. Variant-Dependent P5CS Loss-of-Function Model
Show evidence (2 references)
PMID:32017139 SUPPORT Other
"the four syndromes share the same pathogenic mechanisms based on decreased P5CS function."
The focused review identifies decreased P5CS function as the shared mechanism.
PMID:26026163 SUPPORT Human Clinical
"families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality."
Human segregation data establish biallelic ALDH18A1 variants in SPG9B.
Variable P5CS-dependent amino-acid synthesis
P5CS catalyzes a common step in proline and ornithine biosynthesis. Plasma proline, ornithine, citrulline, and arginine can be low in some genotypes but normal in others, so this node does not assert universal depletion.
L-proline biosynthetic process GO:0055129 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves dysregulated L-proline biosynthetic process (GO:0055129). GO:0055129 is a biological process from the Gene Ontology. ↕ DYSREGULATED Ornithine biosynthetic process GO:0006592 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves dysregulated Ornithine biosynthetic process (GO:0006592). GO:0006592 is a biological process from the Gene Ontology. ↕ DYSREGULATED L-arginine biosynthetic process GO:0006526 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves dysregulated L-arginine biosynthetic process (GO:0006526). GO:0006526 is a biological process from the Gene Ontology. ↕ DYSREGULATED
Show evidence (3 references)
PMID:11092761 SUPPORT Other
"catalyzes the reduction of glutamate to delta(1)-pyrroline-5-carboxylate, a critical step in the biosynthesis of proline, ornithine and arginine."
Defines P5CS function in amino-acid biosynthesis.
PMID:26026163 SUPPORT Human Clinical
"Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
Some ALDH18A1 families had low plasma amino acids.
PMID:29754261 SUPPORT Human Clinical
"childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
A molecularly confirmed case had normal plasma amino-acid concentrations.
SPG9 corticospinal disease
SPG9A and SPG9B are upper-motor-neuron disorders ranging from pure to complex hereditary spastic paraplegia. Cutis laxa is not part of the SPG9 branch; SPG9B-specific cognitive involvement is modeled separately.
Downstream Neural and Connective-Tissue Consequence Model
Downstream
Spastic paraplegia Corticospinal involvement is expressed clinically as lower-limb spastic paraplegia in dominant and recessive SPG9. Downstream Neural and Connective-Tissue Consequence Model
Show evidence (1 reference)
PMID:32017139 SUPPORT Other
"an upper motor neuron syndrome (spastic paraparesis/paraplegia SPG9) complicated with some traits of the neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or herniae"
The focused review distinguishes SPG9 from the cutis-laxa branches.
SPG9B cognitive involvement
Cognitive impairment is reported in complex SPG9B, while a later-onset molecularly confirmed family without cognitive impairment demonstrates that it is not universal.
Downstream Neural and Connective-Tissue Consequence Model
Downstream
Intellectual disability Intellectual disability is a reported, non-universal manifestation of complex SPG9B. Downstream Neural and Connective-Tissue Consequence Model
Show evidence (2 references)
PMID:26026163 SUPPORT Human Clinical
"families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality."
Documents cognitive impairment in recessive SPG9.
PMID:34093392 SUPPORT Human Clinical
"SPG9B patients in our cohort presented with milder symptoms, i.e., later age at onset and without cognitive impairment."
Demonstrates that cognitive impairment is not universal in SPG9B.
ARCL3A neurocutaneous disease
ARCL3A combines lax or thin skin and joint laxity with growth, ocular, and neurodevelopmental manifestations. The cellular routes from P5CS dysfunction to individual tissues remain incompletely resolved.
Downstream Neural and Connective-Tissue Consequence Model
Downstream
Global developmental delay ARCL3A includes global developmental delay; the intervening neural mechanism is unknown. Downstream Neural and Connective-Tissue Consequence Model
Cutis laxa ARCL3A includes lax, wrinkled, or inelastic skin. The full tissue-level mechanism remains unresolved, though patient dermal fibroblasts show reduced type I/III collagen production and altered elastin ultrastructure, a partial extracellular-matrix explanation. Downstream Neural and Connective-Tissue Consequence Model
Joint hypermobility Joint laxity is part of ARCL3A, without a proven extracellular-matrix causal bridge. Downstream Neural and Connective-Tissue Consequence Model
Prematurely aged appearance The triangular, progeroid facial appearance is a defining clinical characteristic of the ARCL3A/de Barsy branch; its tissue-level mechanism remains unresolved. Downstream Neural and Connective-Tissue Consequence Model
Hypotonia Congenital hypotonia can occur in ARCL3A, although GeneReviews reports it at the grouped neurocutaneous-disorder level and the intervening mechanism is unknown. Downstream Neural and Connective-Tissue Consequence Model
Corneal clouding Corneal clouding can occur in ARCL3A, but the grouped GeneReviews evidence does not establish its frequency or a direct corneal mechanism. Downstream Neural and Connective-Tissue Consequence Model
Cataracts Cataracts are reported in ARCL3A, but the lens mechanism is unknown and is not attributed to the fibroblast lipid-droplet observation. Downstream Neural and Connective-Tissue Consequence Model
Growth retardation ARCL3A growth involvement includes short stature; its intermediate mechanism is unknown. Downstream Neural and Connective-Tissue Consequence Model
Microcephaly Microcephaly occurs in ARCL3A, with an unresolved developmental mechanism. Downstream Neural and Connective-Tissue Consequence Model
Prominent superficial veins Visible superficial veins are reported in ARCL3A without a proven direct tissue mechanism. Downstream Neural and Connective-Tissue Consequence Model
Failure to thrive Failure to thrive is reported in ARCL3A, while its intermediate mechanism is unresolved. Downstream Neural and Connective-Tissue Consequence Model
Delayed speech and language development Severe speech delay accompanies developmental impairment in ARCL3A; the intervening neural mechanism is unknown. Downstream Neural and Connective-Tissue Consequence Model
Dystonic posturing Dystonic posturing is the discriminatory ALDH18A1/PYCR1 neurocutaneous movement sign; the route from P5CS dysfunction to the basal-ganglia/motor phenotype is unresolved. Downstream Neural and Connective-Tissue Consequence Model
Corpus callosum dysgenesis Corpus callosum dysgenesis is a CNS malformation associated with ALDH18A1 defects; the developmental mechanism from P5CS dysfunction is unresolved. Downstream Neural and Connective-Tissue Consequence Model
Congenital hip dislocation Congenital hip dislocation is a connective-tissue/skeletal feature of the ALDH18A1-related neurocutaneous group; the extracellular-matrix bridge is not established. Downstream Neural and Connective-Tissue Consequence Model
Adducted thumb Adducted thumbs are among the skeletal/positional features of the ALDH18A1-related neurocutaneous group; the mechanistic bridge is unknown. Downstream Neural and Connective-Tissue Consequence Model
Show evidence (1 reference)
PMID:24767728 SUPPORT Human Clinical
"Autosomal recessive cutis laxa (ARCL) is a connective tissue disorder characterized by wrinkled, inelastic skin, frequently associated with a neurologic involvement and multisystem disease."
Defines the combined connective-tissue and neurologic ARCL phenotype.
p.Thr331Pro fibroblast metabolic and transcript changes
Homozygous p.Thr331Pro reduces P5CS oligomer incorporation. Patient fibroblasts show reduced glutamate, proline, glutathione, and putrescine plus metabolic and extracellular-matrix-related transcript changes. These are genotype-specific cellular observations, not demonstrated neuronal or connective-tissue causal pathways.
fibroblast CL:0000057 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves fibroblast (CL:0000057). CL:0000057 is a cell type from the Cell Ontology.
ALDH18A1 hgnc:9722 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves abnormal ALDH18A1 (hgnc:9722). hgnc:9722 is a gene from the HUGO Gene Nomenclature Committee. ⚠ ABNORMAL
Show evidence (2 references)
PMID:36067040 SUPPORT In Vitro
"identified reduced abundance of glutamate and several metabolites derived from glutamate, including proline and glutathione. Biosynthesis of the polyamine putrescine, derived from ornithine, was also decreased in patient fibroblasts,"
Patient-fibroblast metabolomics demonstrates the genotype-specific metabolic changes.
PMID:36067040 SUPPORT In Vitro
"RNA sequencing of patient fibroblasts revealed transcript abundance changes in several metabolic and extracellular matrix-related genes, adding further insight into pathogenic processes associated with impaired P5CS function."
RNA sequencing supports the cellular transcript changes without establishing tissue-level causation.
p.Arg749Gln/p.Arg765Gln stability and lipid-droplet phenotype
Compound-heterozygous p.Arg749Gln/p.Arg765Gln variants reduce P5CS stability in patient fibroblasts, which show a lipid-droplet phenotype after oleate loading. Its relationship to ARCL3A pathology is unclear; no clinical downstream edge is modeled.
fibroblast CL:0000057 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves fibroblast (CL:0000057). CL:0000057 is a cell type from the Cell Ontology.
ALDH18A1 hgnc:9722 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves decreased ALDH18A1 (hgnc:9722). hgnc:9722 is a gene from the HUGO Gene Nomenclature Committee. ↓ DECREASED
Show evidence (2 references)
PMID:25077174 SUPPORT In Vitro
"mutations alter a conserved C-terminal domain of the encoded protein and reduce protein stability as determined through Western blot analysis of patient fibroblasts."
Patient-fibroblast Western blotting supports reduced stability.
PMID:25077174 SUPPORT In Vitro
"Patient fibroblasts exhibit a lipid droplet phenotype similar to that recently reported in Warburg Micro syndrome, a disorder with similar features but hitherto unrelated cellular etiology."
The cell study documents the lipid-droplet phenotype without proving clinical causation.
p.Arg84Gln-associated metabolic branch
Homozygous p.Arg84Gln (R84Q) markedly reduces both P5CS isoforms and was reported in siblings with hyperammonemia and low ornithine, citrulline, arginine, and proline. This branch is genotype bound, not universal.
Variant-Dependent P5CS Loss-of-Function Model
ALDH18A1 hgnc:9722 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves decreased ALDH18A1 (hgnc:9722). hgnc:9722 is a gene from the HUGO Gene Nomenclature Committee. ↓ DECREASED
Downstream
Hyperammonemia In the p.Arg84Gln sibling pair, the genotype-specific metabolic branch manifested as hyperammonemia. Variant-Dependent P5CS Loss-of-Function Model
Show evidence (1 reference)
PMID:11092761 SUPPORT Human Clinical
"Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia. Both are homozygous for the missense mutation, R84Q,"
The sibling report ties this metabolic profile to homozygous p.Arg84Gln.
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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 ALDH18A1-Related Spastic Paraplegia and Neurocutaneous Spectrum 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

19
Eye 2
Corneal clouding Corneal opacity HP:0007957 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Corneal clouding, annotated with Corneal opacity (HP:0007957). HP:0007957 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41570168 SUPPORT Other
"Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities."
GeneReviews lists corneal clouding as an additional feature across the group that includes ALDH18A1-related ARCL.
Cataracts HP:0000518 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cataract (HP:0000518). HP:0000518 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:11092761 SUPPORT Human Clinical
"two siblings with progressive neurodegeneration, joint laxity, skin hyperelasticity and bilateral subcapsular cataracts."
The original p.Arg84Gln P5CS-deficiency siblings had bilateral subcapsular cataracts.
PMID:41570168 SUPPORT Other
"Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities."
GeneReviews lists lens opacities as an additional feature across the group, represented here by the cataract term.
Head and Neck 1
Microcephaly HP:0000252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Microcephaly (HP:0000252). HP:0000252 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24767728 SUPPORT Human Clinical
"Features of our patient that have been described in literature included cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay."
The ARCL3A clinical report and review include microcephaly among the recognized features.
Integument 2
Cutis laxa HP:0000973 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cutis laxa (HP:0000973). HP:0000973 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24767728 SUPPORT Human Clinical
"Features of our patient that have been described in literature included cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay."
Cutis laxa is a recognized feature of ARCL3A with variable distribution.
Prematurely aged appearance HP:0007495 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Prematurely aged appearance (HP:0007495). HP:0007495 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41570168 SUPPORT Other
"typical facial characteristics including a triangular face with a progeroid appearance"
GeneReviews identifies the characteristic progeroid facial appearance in the neurocutaneous proline-synthesis-defect group that includes ALDH18A1-related ARCL.
Limbs 1
Congenital hip dislocation HP:0001374 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Congenital hip dislocation (HP:0001374). HP:0001374 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41570168 SUPPORT Other
"Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities."
GeneReviews lists congenital hip dislocation as an additional feature across the group that includes ALDH18A1-related ARCL.
Metabolism 1
Hyperammonemia HP:0001987 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperammonemia (HP:0001987). HP:0001987 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:11092761 SUPPORT Human Clinical
"Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia."
The original human P5CS-deficiency siblings had hyperammonemia with low amino acids.
PMID:11092761 SUPPORT Human Clinical
"Both are homozygous for the missense mutation, R84Q, which alters a conserved residue in the P5CS gamma-glutamyl kinase domain."
Binds this metabolic phenotype to the homozygous p.Arg84Gln branch rather than the full ALDH18A1 spectrum.
Musculoskeletal 3
Spastic paraplegia HP:0001258 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Spastic paraplegia (HP:0001258). HP:0001258 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:26026163 SUPPORT Human Clinical
"identified monoallelic ALDH18A1 mutations segregating in three independent families with autosomal dominant pure or complex hereditary spastic paraplegia,"
Spastic paraplegia is the defining feature of SPG9A, ranging from pure to complex forms.
PMID:26026163 SUPPORT Human Clinical
"families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality."
Biallelic ALDH18A1 variants establish the recessive SPG9B branch of spastic paraplegia.
Joint hypermobility HP:0001382 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Joint hypermobility (HP:0001382). HP:0001382 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24767728 SUPPORT Human Clinical
"Features of our patient that have been described in literature included cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay."
The clinical report and literature review include joint laxity, an exact synonym of HP:0001382 joint hypermobility.
Hypotonia HP:0001252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypotonia (HP:0001252). HP:0001252 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41570168 SUPPORT Other
"Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities."
GeneReviews lists congenital hypotonia as an additional feature across the group that includes ALDH18A1-related ARCL.
Nervous System 5
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:31402623 SUPPORT Human Clinical
"conclude that both mutations are disease-causing, that SPG9B associates with partial P5CS deficiency and that it is clinically more severe than SPG9A, as reflected in onset age, disability, cognitive status, growth, and dysmorphic traits."
Early SPG9B series documented cognitive status as one dimension of greater average clinical severity.
PMID:34093392 SUPPORT Human Clinical
"SPG9B patients in our cohort presented with milder symptoms, i.e., later age at onset and without cognitive impairment."
A later SPG9B family demonstrates that cognitive impairment is not universal.
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:36067040 SUPPORT Human Clinical
"developmental delay, neurological deficits and loose skin."
Documents developmental delay in homozygous ALDH18A1 disease with loose skin.
Delayed speech and language development HP:0000750 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Delayed speech and language development (HP:0000750). HP:0000750 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24767728 SUPPORT Human Clinical
"cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay."
The ARCL3A clinical report and literature review document severe developmental and speech delay.
Dystonic posturing Dystonia HP:0001332 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dystonic posturing, annotated with Dystonia (HP:0001332). HP:0001332 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23963297 SUPPORT Human Clinical
"Dystonic posturing was discriminatory for PYCR1 and ALDH18A1 defects."
In a prospectively evaluated neurometabolic cutis-laxa cohort, dystonic posturing specifically discriminated the ALDH18A1 (and PYCR1) neurocutaneous defects from other cutis-laxa genes.
Corpus callosum dysgenesis Abnormal corpus callosum morphology HP:0001273 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Corpus callosum dysgenesis, annotated with Abnormal corpus callosum morphology (HP:0001273). HP:0001273 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:23963297 SUPPORT Human Clinical
"Corpus callosum dysgenesis was associated with PYCR1 and ALDH18A1 mutations."
The neurometabolic cutis-laxa cohort associated corpus callosum dysgenesis with ALDH18A1 (and PYCR1) mutations.
Growth 2
Growth retardation Short stature HP:0004322 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short stature (HP:0004322). HP:0004322 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24767728 SUPPORT Human Clinical
"Features of our patient that have been described in literature included cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay."
Short stature and failure to thrive are consistent features of ARCL3A.
Failure to thrive HP:0001508 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Failure to thrive (HP:0001508). HP:0001508 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24767728 SUPPORT Human Clinical
"cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay."
The ARCL3A clinical report and literature review document failure to thrive among the recognized features.
Other 2
Prominent superficial veins HP:0001015 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Prominent superficial veins (HP:0001015). HP:0001015 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:24767728 SUPPORT Human Clinical
"cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay."
The ARCL3A clinical report and literature review document visible superficial veins on the thorax and abdomen.
Adducted thumb HP:0001181 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Adducted thumb (HP:0001181). HP:0001181 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41570168 SUPPORT Other
"Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities."
GeneReviews lists adducted thumbs as an additional feature across the group that includes ALDH18A1-related ARCL.
🧬

Genetic Associations

1
ALDH18A1 (Causative)
Gene: ALDH18A1 hgnc:9722 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is ALDH18A1 (hgnc:9722). hgnc:9722 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal Dominant Autosomal Recessive
Show evidence (3 references)
PMID:29754261 SUPPORT Human Clinical
"Mutations in ALDH18A1 can cause autosomal recessive and dominant hereditary spastic paraplegia and autosomal recessive and dominant cutis laxa."
Establishes that ALDH18A1 mutations cause both dominant and recessive forms of spastic paraplegia and cutis laxa.
PMID:26026163 SUPPORT Human Clinical
"catalyses the first and common step of proline and ornithine biosynthesis from glutamate."
Defines the enzymatic function of the ALDH18A1 gene product.
CGGV:assertion_7bfbe962-beb3-4553-9909-a83a3aac2d55-2021-05-18T211134.377Z SUPPORT Other
"ALDH18A1 | HGNC:9722 | P5CS deficiency | MONDO:0100126 | SD | Definitive"
ClinGen classifies the ALDH18A1-P5CS deficiency gene-disease relationship as definitive with semidominant inheritance.
💊

Medical Actions

2
Subtype-Bounded Genetic Counseling
Category: Counseling / Informational Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Counseling should distinguish heterozygous autosomal dominant SPG9A from biallelic autosomal recessive SPG9B and ARCL3A. Recurrence assessment and family testing should be based on the identified variant(s), zygosity, and segregation rather than applying a single risk model across the spectrum.
Show evidence (1 reference)
PMID:32017139 SUPPORT Other
"In 2015 to 2016, an upper motor neuron syndrome (spastic paraparesis/paraplegia SPG9) complicated with some traits of the neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or herniae, was associated with monoallelic or biallelic ALDH18A1 mutations with, respectively,..."
The review directly distinguishes dominant monoallelic from recessive biallelic SPG9 and supports inheritance-aware counseling.
ARCL3A Multidisciplinary Supportive Care
Category: Therapeutic Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
For the ARCL3A neurocutaneous branch, care is multidisciplinary and manifestation-directed, including speech and developmental support, physical therapy and mobility assistance, orthopedic care, ophthalmologic care, and routine treatment of associated neurologic findings. Arginine supplementation has been described only in a limited number of individuals with abnormal serum amino acids, and clinical benefit remains unconfirmed; it is not established disease-modifying therapy. These GeneReviews recommendations are not extrapolated here into a formal SPG9A/SPG9B management schedule.
Show evidence (2 references)
PMID:41570168 SUPPORT Other
"MANAGEMENT: Treatment of manifestations: Prelingual speech therapy to improve swallowing and speech development; routine treatment of epilepsy; in those with abnormal serum amino acids (low ornithine, citrulline, arginine), supplementation with arginine has been described in a limited number of..."
GeneReviews supports multidisciplinary manifestation-directed care and explicitly states that arginine experience is limited and benefit unconfirmed.
PMID:22170564 SUPPORT Human Clinical
"MR spectroscopy revealed decreased brain creatine, which normalized after sustained arginine supplementation, with improvement of neurodevelopmental and metabolic parameters, suggesting a pathogenic role of brain creatine decrease and the value of arginine therapy."
A single-patient report provides a limited positive signal for arginine, while the later review states that clinical benefit remains unconfirmed.
🔬

Biochemical Markers

7
Plasma proline (NORMAL_OR_DECREASED)
Context: Plasma proline is decreased in some molecularly confirmed P5CS-deficiency families but normal in others. A low result can support the diagnosis, but a normal result does not exclude ALDH18A1-related disease.
Pathograph Readouts
Readout Of Variable P5CS-dependent amino-acid synthesis Negative Diagnostic
Low plasma proline supports impaired P5CS-dependent amino-acid synthesis, while a normal result does not exclude it.
Show evidence (2 references)
PMID:26026163 SUPPORT Human Clinical
"Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
Directly links low proline and the accompanying amino-acid profile to P5CS deficiency in a subset of affected individuals.
PMID:29754261 SUPPORT Human Clinical
"childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
Molecularly confirmed ALDH18A1 disease can have normal plasma proline, limiting sensitivity.
Show evidence (2 references)
PMID:26026163 SUPPORT Human Clinical
"as well as in two sporadic patients. Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
Plasma amino acid profiling reveals P5CS deficiency biomarkers in affected individuals.
PMID:29754261 SUPPORT Human Clinical
"childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
Demonstrates that amino acid levels may be normal when mutations affect the G5PR domain.
Plasma ornithine (NORMAL_OR_DECREASED)
Context: Plasma ornithine can be decreased as part of the P5CS-deficiency amino-acid profile, but normal values occur in molecularly confirmed disease. It is a supportive rather than universal finding.
Pathograph Readouts
Readout Of Variable P5CS-dependent amino-acid synthesis Negative Diagnostic
Low plasma ornithine supports impaired P5CS-dependent amino-acid synthesis, while a normal result does not exclude it.
Show evidence (2 references)
PMID:26026163 SUPPORT Human Clinical
"Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
Directly links low ornithine and the accompanying profile to P5CS deficiency in a subset of affected individuals.
PMID:29754261 SUPPORT Human Clinical
"childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
Molecularly confirmed ALDH18A1 disease can have normal plasma ornithine, limiting sensitivity.
Show evidence (3 references)
PMID:11092761 SUPPORT Human Clinical
"Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia."
The original P5CS deficiency report documents hypoornithinemia as part of the metabolic phenotype.
PMID:26026163 SUPPORT Human Clinical
"Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
ALDH18A1-related SPG families show reduced plasma ornithine in the diagnostic amino-acid profile.
PMID:29754261 SUPPORT Human Clinical
"childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
Demonstrates that plasma ornithine can remain normal in molecularly confirmed ALDH18A1 disease.
Plasma citrulline (NORMAL_OR_DECREASED)
Context: Plasma citrulline can be decreased with the P5CS-deficiency amino-acid profile but is not uniformly abnormal across ALDH18A1 genotypes. A low value is supportive, not required for molecular diagnosis.
Pathograph Readouts
Readout Of Variable P5CS-dependent amino-acid synthesis Negative Diagnostic
Low plasma citrulline supports impaired P5CS-dependent amino-acid synthesis, while a normal result does not exclude it.
Show evidence (2 references)
PMID:26026163 SUPPORT Human Clinical
"Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
Directly links low citrulline and the accompanying profile to P5CS deficiency in a subset of affected individuals.
PMID:29754261 SUPPORT Human Clinical
"Mutations affecting the G5K domain have previously been found to cause reduced plasma levels of proline, citrulline and arginine, whereas such effect is not seen with mutations affecting the GR5P domain."
Published ALDH18A1 genotypes need not lower citrulline, limiting this marker's sensitivity.
Show evidence (3 references)
PMID:11092761 SUPPORT Human Clinical
"Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia."
The original P5CS deficiency report documents hypocitrullinemia.
PMID:26026163 SUPPORT Human Clinical
"Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
ALDH18A1-related SPG families show reduced plasma citrulline.
PMID:29754261 SUPPORT Human Clinical
"Mutations affecting the G5K domain have previously been found to cause reduced plasma levels of proline, citrulline and arginine, whereas such effect is not seen with mutations affecting the GR5P domain."
Demonstrates genotype-dependent variability in plasma citrulline.
Plasma arginine (NORMAL_OR_DECREASED)
Context: Plasma arginine can be decreased with ornithine, citrulline, and proline in P5CS deficiency, but normal values are documented in molecularly confirmed ALDH18A1 disease. It is a supportive rather than universal finding.
Pathograph Readouts
Readout Of Variable P5CS-dependent amino-acid synthesis Negative Diagnostic
Low plasma arginine supports impaired P5CS-dependent amino-acid synthesis, while a normal result does not exclude it.
Show evidence (2 references)
PMID:26026163 SUPPORT Human Clinical
"Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
Directly links low arginine and the accompanying profile to P5CS deficiency in a subset of affected individuals.
PMID:29754261 SUPPORT Human Clinical
"childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
Molecularly confirmed ALDH18A1 disease can have normal plasma arginine, limiting sensitivity.
Show evidence (3 references)
PMID:11092761 SUPPORT Human Clinical
"Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia."
The original P5CS deficiency report documents hypoargininemia.
PMID:26026163 SUPPORT Human Clinical
"Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency."
ALDH18A1-related SPG families show reduced plasma arginine.
PMID:29754261 SUPPORT Human Clinical
"childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
Demonstrates that plasma arginine can remain normal in molecularly confirmed ALDH18A1 disease.
Blood ammonia (INCREASED)
Context: Increased blood ammonia is specific here to the original homozygous p.Arg84Gln (R84Q) branch and is not a universal biochemical feature of the ALDH18A1 spectrum.
Pathograph Readouts
Readout Of p.Arg84Gln-associated metabolic branch Positive Diagnostic
Elevated ammonia reports the p.Arg84Gln-associated metabolic branch rather than the full ALDH18A1 spectrum.
Show evidence (2 references)
PMID:11092761 SUPPORT Human Clinical
"Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia."
Directly supports hyperammonemia in the original metabolic branch.
PMID:11092761 SUPPORT Human Clinical
"Both are homozygous for the missense mutation, R84Q, which alters a conserved residue in the P5CS gamma-glutamyl kinase domain."
Binds the ammonia readout to the homozygous p.Arg84Gln branch.
Show evidence (1 reference)
PMID:11092761 SUPPORT Human Clinical
"Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia."
The original P5CS deficiency report directly documents hyperammonemia.
Cellular glutathione (DECREASED)
Context: Metabolomic profiling in patient fibroblasts shows reduced glutathione, indicating impaired glutamate-derived antioxidant metabolism.
Pathograph Readouts
Readout Of p.Thr331Pro fibroblast metabolic and transcript changes Negative
Lower cellular glutathione reports the p.Thr331Pro fibroblast metabolic phenotype and is not generalized to every ALDH18A1 variant.
Show evidence (2 references)
PMID:36067040 SUPPORT In Vitro
"Here we characterize a previously unreported homozygous ALDH18A1 variant (p.Thr331Pro) in four affected probands from two unrelated families, and demonstrate broad-based alterations in amino acid and antioxidant metabolism."
Identifies the specific p.Thr331Pro context for this cellular readout.
PMID:36067040 SUPPORT In Vitro
"identified reduced abundance of glutamate and several metabolites derived from glutamate, including proline and glutathione."
Patient-cell metabolomics directly links reduced glutathione to the p.Thr331Pro experimental branch.
Show evidence (1 reference)
PMID:36067040 SUPPORT In Vitro
"identified reduced abundance of glutamate and several metabolites derived from glutamate, including proline and glutathione."
Patient-cell metabolomics directly identifies reduced glutathione.
Cellular putrescine (DECREASED)
Context: Metabolomic profiling in patient fibroblasts shows reduced biosynthesis of putrescine from ornithine, tying the P5CS ornithine branch to antioxidant pathway dysfunction.
Pathograph Readouts
Readout Of p.Thr331Pro fibroblast metabolic and transcript changes Negative
Lower cellular putrescine reports the p.Thr331Pro fibroblast metabolic phenotype and is not generalized to every ALDH18A1 variant.
Show evidence (2 references)
PMID:36067040 SUPPORT In Vitro
"Here we characterize a previously unreported homozygous ALDH18A1 variant (p.Thr331Pro) in four affected probands from two unrelated families, and demonstrate broad-based alterations in amino acid and antioxidant metabolism."
Identifies the specific p.Thr331Pro context for this cellular readout.
PMID:36067040 SUPPORT In Vitro
"Biosynthesis of the polyamine putrescine, derived from ornithine, was also decreased in patient fibroblasts,"
Patient-cell metabolomics directly links reduced putrescine to the p.Thr331Pro experimental branch.
Show evidence (1 reference)
PMID:36067040 SUPPORT In Vitro
"Biosynthesis of the polyamine putrescine, derived from ornithine, was also decreased in patient fibroblasts,"
Patient fibroblast metabolomics directly identifies decreased putrescine biosynthesis.
🔬

Diagnosis

2
Molecular Genetic Confirmation
Confirmation centers on pathogenic ALDH18A1 variant identification, with zygosity, variant association, segregation, and phenotype interpreted together. A heterozygous HSP-associated pathogenic variant in a compatible SPG9 phenotype supports SPG9A, whereas biallelic pathogenic variants support SPG9B or ARCL3A according to clinical context. Heterozygosity alone does not distinguish SPG9A from the separately curated ADCL3 branch.
molecular genetic testing NCIT:C19770 NCI Thesaurus (NCIT)
Results: Pathogenic ALDH18A1 variant(s), variant-disease association, zygosity, segregation, and phenotype consistent with the suspected SPG9A, SPG9B, or ARCL3A branch support the molecular diagnosis.
Show evidence (2 references)
PMID:32017139 SUPPORT Other
"In 2015 to 2016, an upper motor neuron syndrome (spastic paraparesis/paraplegia SPG9) complicated with some traits of the neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or herniae, was associated with monoallelic or biallelic ALDH18A1 mutations with, respectively,..."
The focused P5CS-deficiency review ties monoallelic and biallelic ALDH18A1 variants to the dominant and recessive SPG9 branches, respectively.
PMID:41570168 SUPPORT Other
"DIAGNOSIS/TESTING: The diagnosis of a neurocutaneous disorder due a to mitochondrial proline synthesis defect can be established in a proband with characteristic clinical findings and identification of biallelic ALDH18A1 or PYCR1 pathogenic variants or a de novo ALDH18A1 pathogenic variant..."
GeneReviews establishes molecular confirmation with biallelic ALDH18A1 pathogenic variants for the autosomal recessive neurocutaneous branch.
Plasma Amino Acid Chromatography (Supportive)
Plasma amino-acid chromatography is an optional supportive test. Low ornithine, citrulline, arginine, and proline can support P5CS deficiency, particularly in some SPG9A genotypes, but sensitivity is limited and normal values do not exclude molecularly confirmed ALDH18A1 disease.
biomarker analysis NCIT:C63333 NCI Thesaurus (NCIT)
Results: A low amino-acid profile supports P5CS deficiency; a normal profile is non-exclusionary and should not stop molecular testing or variant assessment.
Show evidence (2 references)
PMID:26026163 SUPPORT Human Clinical
"we therefore suggest including amino acid chromatography in the clinico-genetic work-up of hereditary spastic paraplegia, particularly in dominant cases, as the associated phenotype is not distinct from other causative genes."
The original SPG9 study recommends amino-acid chromatography as a supportive component of the clinico-genetic work-up.
PMID:29754261 SUPPORT Human Clinical
"This young man has spastic paraplegia with onset in childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
A molecularly confirmed recessive SPG9 case had normal plasma amino acids, demonstrating that a normal result does not exclude the disorder.
{ }

Source YAML

click to show 
name: ALDH18A1-Related Spastic Paraplegia and Neurocutaneous Spectrum
creation_date: "2026-04-04T00:00:00Z"
category: Mendelian
description: >
  Pathogenic variants in ALDH18A1, which encodes mitochondrial
  delta-1-pyrroline-5-carboxylate synthase (P5CS), cause a continuum of spastic
  paraplegia and neurocutaneous disease. This record curates three branches:
  autosomal dominant spastic paraplegia type 9A (SPG9A), autosomal recessive
  spastic paraplegia type 9B (SPG9B), and autosomal recessive cutis laxa type 3A
  (ARCL3A, De Barsy syndrome). ALDH18A1-related autosomal dominant cutis laxa
  (ADCL3) is a fourth branch curated separately. Disease-associated variants
  reduce P5CS function through variant-dependent effects on enzyme activity,
  oligomerization, protein abundance, or stability. Plasma proline, ornithine,
  citrulline, and arginine can be low in some genotypes but normal in others.
disease_term:
  preferred_term: P5CS deficiency
  term:
    id: MONDO:0100126
    label: P5CS deficiency
synonyms:
- SPG9A
- SPG9B
- Autosomal recessive cutis laxa type 3A
- ARCL3A
- De Barsy syndrome due to ALDH18A1
- P5CS deficiency
parents:
- Hereditary Spastic Paraplegia
- Metabolic Disease
- Neurodegenerative Disease
notes: >-
  This three-branch boundary is a project modeling decision, not a canonical
  external clinical grouping. The focused P5CS-deficiency review describes four
  ALDH18A1 syndromes on one continuum: SPG9A, SPG9B, ADCL3, and ARCL3A. To avoid
  duplicating the dedicated ALDH18A1_Cutis_Laxa.yaml record, this file uses the
  umbrella MONDO term P5CS deficiency (MONDO:0100126) as the entry-level
  disease_term covering SPG9A, SPG9B, and ARCL3A, while leaving ADCL3 to the
  adjacent record. Each branch is additionally grounded by its own
  subtype_term: SPG9A (MONDO:0011006), SPG9B (MONDO:0014702), and ARCL3A
  (MONDO:0009053, ALDH18A1-related de Barsy syndrome), so the subtype-level
  disease identities are machine-resolvable and not only described here.
has_subtypes:
- name: SPG9A
  display_name: Spastic Paraplegia 9A (Autosomal Dominant)
  subtype_term:
    preferred_term: Spastic paraplegia 9A, autosomal dominant
    term:
      id: MONDO:0011006
      label: hereditary spastic paraplegia 9A
  description: >
    Autosomal dominant hereditary spastic paraplegia caused by heterozygous
    ALDH18A1 pathogenic variants. Presentations range from pure to complex HSP;
    age at onset and additional findings, including cognitive involvement, are
    variable. Reduced P5CS function is established, while dominant-negative
    action is a proposed mechanism for dominant variants rather than a universal
    property of every SPG9A allele.
  evidence:
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      identified monoallelic ALDH18A1 mutations segregating in three independent
      families with autosomal dominant pure or complex hereditary spastic paraplegia,
      as well as in two sporadic patients.
    explanation: Establishes SPG9A as an autosomal dominant form of ALDH18A1-related spastic paraplegia.
- name: SPG9B
  display_name: Spastic Paraplegia 9B (Autosomal Recessive)
  subtype_term:
    preferred_term: Spastic paraplegia 9B, autosomal recessive
    term:
      id: MONDO:0014702
      label: autosomal recessive complex spastic paraplegia type 9B
  description: >
    Autosomal recessive hereditary spastic paraplegia caused by biallelic
    ALDH18A1 pathogenic variants. Many reported cases have earlier onset and
    more complex neurologic disease than SPG9A, but later-onset SPG9B without
    cognitive impairment is documented. Published SPG9 cohorts did not have the
    cutis laxa, joint laxity, or hernia phenotype that defines the cutis-laxa
    branches.
  evidence:
  - reference: PMID:31402623
    reference_title: "P5CS expression study in a new family with ALDH18A1-associated hereditary spastic paraplegia SPG9."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      conclude that both mutations are disease-causing, that SPG9B associates with
      partial P5CS deficiency and that it is clinically more severe than SPG9A, as
      reflected in onset age, disability, cognitive status, growth, and dysmorphic
      traits.
    explanation: Early series found SPG9B generally more severe than SPG9A, without making this absolute for every genotype.
  - reference: PMID:34093392
    reference_title: Novel Compound Missense and Intronic Splicing Mutation in ALDH18A1 Causes Autosomal Recessive Spastic Paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SPG9B patients in our cohort presented with milder symptoms, i.e., later age at onset and without cognitive impairment.
    explanation: A later family establishes that SPG9B severity and cognitive involvement are variable.
- name: ARCL3A
  display_name: Autosomal Recessive Cutis Laxa Type 3A (De Barsy Syndrome)
  subtype_term:
    preferred_term: ALDH18A1-related de Barsy syndrome
    term:
      id: MONDO:0009053
      label: ALDH18A1-related de Barsy syndrome
  description: >
    Biallelic ALDH18A1 pathogenic variants cause an autosomal recessive
    neurocutaneous disorder with thin or lax skin, joint laxity, growth and
    neurodevelopmental impairment, and variable cataracts, microcephaly, and
    pyramidal findings. Variant effects range from reduced P5CS stability or
    activity to absent protein.
  evidence:
  - reference: PMID:25077174
    reference_title: Loss of ALDH18A1 function is associated with a cellular lipid droplet phenotype suggesting a link between autosomal recessive cutis laxa type 3A and Warburg Micro syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autosomal recessive cutis laxa type 3A is caused by mutations in ALDH18A1, a
      gene encoding the mitochondrial enzyme Δ(1)-pyrroline-5-carboxylate synthase
      (P5CS).
    explanation: Establishes ARCL3A as the biallelic ALDH18A1 cutis-laxa branch.
inheritance:
- name: Autosomal Dominant (SPG9A)
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >
    Heterozygous ALDH18A1 pathogenic variants cause SPG9A and segregate with
    autosomal dominant pure or complex hereditary spastic paraplegia.
  evidence:
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      identified monoallelic ALDH18A1 mutations segregating in three independent
      families with autosomal dominant pure or complex hereditary spastic paraplegia,
    explanation: Identifies monoallelic ALDH18A1 mutations in autosomal dominant pedigrees.
- name: Autosomal Recessive (SPG9B / ARCL3A)
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >
    Biallelic ALDH18A1 pathogenic variants cause SPG9B and ARCL3A. Their
    functional effects are variable, ranging from hypomorphic alleles with
    residual P5CS activity to variants associated with absent or unstable
    protein. For the ARCL3A branch, when both parents are heterozygous, each sib
    has a 25% chance of being affected, a 50% chance of being heterozygous, and
    a 25% chance of being unaffected and not a carrier.
  evidence:
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      families with autosomal recessive transmission of ALDH18A1 mutations, and
      predominant complex hereditary spastic paraplegia with marked cognitive
      impairment, without any cutaneous abnormality.
    explanation: Identifies biallelic ALDH18A1 mutations in autosomal recessive spastic paraplegia families.
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Autosomal recessive cutis laxa (ARCL) is a connective tissue disorder
      characterized by wrinkled, inelastic skin, frequently associated with a
      neurologic involvement and multisystem disease.
    explanation: Confirms autosomal recessive inheritance for ALDH18A1-related cutis laxa.
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      If both parents are known to be heterozygous for a pathogenic variant, each sib
      of an individual with PYCR1- or ALDH18A1-related ARCL has at conception a 25%
      chance of being affected, a 50% chance of being heterozygous, and a 25% chance
      of being unaffected and not a carrier.
    explanation: >-
      GeneReviews supplies the recurrence-risk figures for the in-scope
      ALDH18A1-related ARCL3A branch; SPG9B inheritance is supported separately
      by its disease-specific evidence above.
genetic:
- name: ALDH18A1
  gene_term:
    preferred_term: ALDH18A1
    term:
      id: hgnc:9722
      label: ALDH18A1
  association: Causative
  features: >
    ALDH18A1 encodes the bifunctional mitochondrial enzyme P5CS (delta-1-pyrroline-
    5-carboxylate synthetase) composed of glutamate 5-kinase (G5K) and
    gamma-glutamyl phosphate reductase (G5PR) domains. Mutations in either domain
    can cause disease. Reduced P5CS function is the shared mechanism, but the
    molecular effect and residual activity are variant dependent. Dominant-negative
    action is proposed for dominant variants. Low plasma amino acids have been
    reported for some variants, whereas other molecularly confirmed cases have
    normal profiles; domain location is therefore not a reliable diagnostic rule.
  inheritance:
  - name: Autosomal Dominant
    evidence:
    - reference: PMID:26026163
      reference_title: Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        identified monoallelic ALDH18A1 mutations segregating in three independent
        families with autosomal dominant pure or complex hereditary spastic paraplegia,
      explanation: Supports dominant ALDH18A1 inheritance for SPG9A.
  - name: Autosomal Recessive
    evidence:
    - reference: PMID:26026163
      reference_title: Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        families with autosomal recessive transmission of ALDH18A1 mutations, and
        predominant complex hereditary spastic paraplegia with marked cognitive
        impairment, without any cutaneous abnormality.
      explanation: Supports recessive ALDH18A1 inheritance for SPG9B.
  evidence:
  - reference: PMID:29754261
    reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Mutations in ALDH18A1 can cause autosomal recessive and dominant hereditary
      spastic paraplegia and autosomal recessive and dominant cutis laxa.
    explanation: Establishes that ALDH18A1 mutations cause both dominant and recessive forms of spastic paraplegia and cutis laxa.
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      catalyses the first and common step of proline and ornithine biosynthesis from
      glutamate.
    explanation: Defines the enzymatic function of the ALDH18A1 gene product.
  - reference: CGGV:assertion_7bfbe962-beb3-4553-9909-a83a3aac2d55-2021-05-18T211134.377Z
    reference_title: "ALDH18A1 / P5CS deficiency (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ALDH18A1 | HGNC:9722 | P5CS deficiency | MONDO:0100126 | SD | Definitive"
    explanation: ClinGen classifies the ALDH18A1-P5CS deficiency gene-disease relationship as definitive with semidominant inheritance.
mechanistic_hypotheses:
- hypothesis_group_id: variant_dependent_p5cs_loss_model
  hypothesis_label: Variant-Dependent P5CS Loss-of-Function Model
  status: CANONICAL
  description: >-
    The shared mechanism across ALDH18A1 disorders is decreased P5CS function,
    but different variants impair activity, oligomer incorporation, abundance,
    stability, or splicing to different degrees. This model does not assume that
    every dominant or biallelic variant has the same molecular effect.
  evidence:
  - reference: PMID:32017139
    reference_title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      the four syndromes share the same pathogenic mechanisms based on decreased P5CS function.
    explanation: The focused review identifies decreased P5CS function as the common mechanism across all four branches.
- hypothesis_group_id: dominant_negative_spg9a_model
  hypothesis_label: Proposed Dominant-Negative SPG9A Model
  status: EMERGING
  applies_to_subtypes:
  - SPG9A
  description: >-
    Some heterozygous variants may impair the homooligomeric P5CS complex through
    a dominant-negative effect. This remains a variant-dependent proposal and is
    not generalized to every SPG9A allele.
  evidence:
  - reference: PMID:32017139
    reference_title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      the dominant mutations cause loss-of-function by dominant-negative mechanisms.
    explanation: The review supports the dominant-negative model, retained here as emerging because variant-level proof is incomplete.
- hypothesis_group_id: downstream_tissue_consequence_model
  hypothesis_label: Downstream Neural and Connective-Tissue Consequence Model
  status: EMERGING
  description: >-
    Reduced P5CS function is associated with corticospinal and neurocutaneous
    phenotypes, but the intervening tissue mechanisms are incompletely resolved.
    Fibroblast metabolomic, extracellular-matrix transcript, and lipid-droplet
    findings are retained as genotype-specific observations rather than proven
    causal bridges to individual clinical features.
  evidence:
  - reference: PMID:36067040
    reference_title: Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      RNA sequencing of patient fibroblasts revealed transcript abundance changes in several metabolic and extracellular matrix-related genes, adding further insight into pathogenic processes associated with impaired P5CS function.
    explanation: Supports downstream cellular associations while leaving tissue-level causation unresolved.
pathophysiology:
- name: Dominant SPG9A P5CS dysfunction
  subtypes:
  - SPG9A
  description: >-
    Heterozygous ALDH18A1 pathogenic variants decrease P5CS function in SPG9A.
    Dominant-negative action on the homooligomeric enzyme is proposed, but it is
    not assumed to be uniform across every dominant allele.
  gene:
    preferred_term: ALDH18A1
    modifier: ABNORMAL
    term:
      id: hgnc:9722
      label: ALDH18A1
  evidence:
  - reference: PMID:32017139
    reference_title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the dominant mutations cause loss-of-function by dominant-negative mechanisms."
    explanation: The focused review proposes dominant-negative loss of P5CS function for dominant variants.
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      identified monoallelic ALDH18A1 mutations segregating in three independent families with autosomal dominant pure or complex hereditary spastic paraplegia,
    explanation: Human segregation data establish heterozygous ALDH18A1 variants in SPG9A.
  downstream:
  - target: Variable P5CS-dependent amino-acid synthesis
    description: >-
      Reduced P5CS function can alter proline- and ornithine-pathway output, but
      plasma amino-acid concentrations are not uniformly low across genotypes.
    causal_link_type: DIRECT
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    - dominant_negative_spg9a_model
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency.
      explanation: Some ALDH18A1 families had low plasma amino acids, supporting altered pathway output without making it universal.
  - target: SPG9 corticospinal disease
    description: >-
      Dominant ALDH18A1 dysfunction produces pure or complex hereditary spastic
      paraplegia; the tissue-level bridge from P5CS dysfunction is unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    - dominant_negative_spg9a_model
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        identified monoallelic ALDH18A1 mutations segregating in three independent families with autosomal dominant pure or complex hereditary spastic paraplegia,
      explanation: Monoallelic ALDH18A1 variants segregate with the SPG9 phenotype.

- name: Biallelic ALDH18A1 P5CS dysfunction
  subtypes:
  - SPG9B
  - ARCL3A
  description: >-
    Biallelic ALDH18A1 variants cause recessive P5CS dysfunction. Variant effects
    include reduced activity, oligomer incorporation, abundance, or stability
    with variable residual function.
  gene:
    preferred_term: ALDH18A1
    modifier: DECREASED
    term:
      id: hgnc:9722
      label: ALDH18A1
  evidence:
  - reference: PMID:32017139
    reference_title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the four syndromes share the same pathogenic mechanisms based on decreased P5CS function."
    explanation: The focused review identifies decreased P5CS function as the shared mechanism.
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality.
    explanation: Human segregation data establish biallelic ALDH18A1 variants in SPG9B.
  downstream:
  - target: Variable P5CS-dependent amino-acid synthesis
    description: >-
      Biallelic P5CS dysfunction can reduce pathway output, although molecularly
      confirmed patients can have normal plasma amino-acid concentrations.
    causal_link_type: DIRECT
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    evidence:
    - reference: PMID:32017139
      reference_title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        They showed biochemical indications of decreased ornithine/proline synthesis, agreeing with the role of P5CS in the biosynthesis of these amino acids.
      explanation: The original biallelic sibling pair had reduced ornithine/proline synthesis.
    - reference: PMID:29754261
      reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
      explanation: A compound-heterozygous case demonstrates that plasma amino acids may remain normal.
  - target: SPG9 corticospinal disease
    description: >-
      Some biallelic variants cause complex SPG9B without cutaneous abnormality;
      the intervening neural tissue mechanism is unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality.
      explanation: Recessive families directly associate biallelic ALDH18A1 variants with complex SPG9B.
  - target: SPG9B cognitive involvement
    description: >-
      Cognitive impairment is reported in complex SPG9B but is not universal;
      the intervening neural mechanism is unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality.
      explanation: Recessive SPG9 families document cognitive impairment in the SPG9B branch.
  - target: ARCL3A neurocutaneous disease
    description: >-
      Other biallelic ALDH18A1 variants cause ARCL3A; the tissue mechanisms
      separating this neurocutaneous branch from SPG9B remain unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:25077174
      reference_title: "Loss of ALDH18A1 function is associated with a cellular lipid droplet phenotype suggesting a link between autosomal recessive cutis laxa type 3A and Warburg Micro syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Autosomal recessive cutis laxa type 3A is caused by mutations in ALDH18A1, a gene encoding the mitochondrial enzyme Δ(1)-pyrroline-5-carboxylate synthase (P5CS).
      explanation: Human evidence establishes biallelic ALDH18A1 disease as ARCL3A.
  - target: p.Thr331Pro fibroblast metabolic and transcript changes
    description: >-
      In the homozygous p.Thr331Pro subgroup, impaired incorporation of P5CS
      monomers into oligomers accompanies measured fibroblast changes.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    evidence:
    - reference: PMID:36067040
      reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Functional characterization of the p.Thr331Pro variant demonstrated a lack of any impact on the steady-state level of the P5CS monomer or mitochondrial localization of the enzyme, but reduced incorporation of the monomer into P5CS oligomers.
      explanation: Patient-cell experiments define the p.Thr331Pro oligomer-incorporation defect.
  - target: p.Arg749Gln/p.Arg765Gln stability and lipid-droplet phenotype
    description: >-
      In compound-heterozygous p.Arg749Gln/p.Arg765Gln fibroblasts, reduced P5CS
      stability co-occurs with a lipid-droplet phenotype; no clinical causal
      bridge is implied.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    evidence:
    - reference: PMID:25077174
      reference_title: "Loss of ALDH18A1 function is associated with a cellular lipid droplet phenotype suggesting a link between autosomal recessive cutis laxa type 3A and Warburg Micro syndrome."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        mutations alter a conserved C-terminal domain of the encoded protein and reduce protein stability as determined through Western blot analysis of patient fibroblasts. Patient fibroblasts exhibit a lipid droplet phenotype similar to that recently reported in Warburg Micro syndrome, a disorder with similar features but hitherto unrelated cellular etiology.
      explanation: The patient-fibroblast study reports both reduced protein stability and the lipid-droplet phenotype.
  - target: p.Arg84Gln-associated metabolic branch
    description: >-
      Homozygous p.Arg84Gln markedly reduces P5CS activity and defines the
      reported hyperammonemic, low-amino-acid branch rather than a universal
      biochemical profile.
    causal_link_type: DIRECT
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    evidence:
    - reference: PMID:11092761
      reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Both are homozygous for the missense mutation, R84Q, which alters a conserved residue in the P5CS gamma-glutamyl kinase domain. R84Q is not present in 194 control chromosomes and dramatically reduces the activity of both P5CS isoforms when expressed in mammalian cells.
      explanation: The original sibling study links homozygous p.Arg84Gln to markedly reduced P5CS activity.

- name: Variable P5CS-dependent amino-acid synthesis
  description: >-
    P5CS catalyzes a common step in proline and ornithine biosynthesis. Plasma
    proline, ornithine, citrulline, and arginine can be low in some genotypes but
    normal in others, so this node does not assert universal depletion.
  biological_processes:
  - preferred_term: L-proline biosynthetic process
    term:
      id: GO:0055129
      label: L-proline biosynthetic process
    modifier: DYSREGULATED
  - preferred_term: Ornithine biosynthetic process
    term:
      id: GO:0006592
      label: ornithine biosynthetic process
    modifier: DYSREGULATED
  - preferred_term: L-arginine biosynthetic process
    term:
      id: GO:0006526
      label: L-arginine biosynthetic process
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      catalyzes the reduction of glutamate to delta(1)-pyrroline-5-carboxylate, a critical step in the biosynthesis of proline, ornithine and arginine.
    explanation: Defines P5CS function in amino-acid biosynthesis.
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Low levels of plasma ornithine, citrulline, arginine and proline in four individuals from two families suggested P5CS deficiency.
    explanation: Some ALDH18A1 families had low plasma amino acids.
  - reference: PMID:29754261
    reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "childhood and temporal lobe epilepsy, but normal levels of proline, ornithine and arginine."
    explanation: A molecularly confirmed case had normal plasma amino-acid concentrations.

- name: SPG9 corticospinal disease
  conforms_to: "corticospinal_tract_axonopathy#Distal Length-Dependent Degeneration of Long CNS Axons"
  subtypes:
  - SPG9A
  - SPG9B
  description: >-
    SPG9A and SPG9B are upper-motor-neuron disorders ranging from pure to
    complex hereditary spastic paraplegia. Cutis laxa is not part of the SPG9
    branch; SPG9B-specific cognitive involvement is modeled separately.
  evidence:
  - reference: PMID:32017139
    reference_title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      an upper motor neuron syndrome (spastic paraparesis/paraplegia SPG9) complicated with some traits of the neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or herniae
    explanation: The focused review distinguishes SPG9 from the cutis-laxa branches.
  downstream:
  - target: Spastic paraplegia
    description: >-
      Corticospinal involvement is expressed clinically as lower-limb spastic
      paraplegia in dominant and recessive SPG9.
    causal_link_type: DIRECT
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Hereditary spastic paraplegias are heterogeneous neurological disorders characterized by a pyramidal syndrome with symptoms predominantly affecting the lower limbs.
      explanation: The human series characterizes hereditary spastic paraplegia as a lower-limb pyramidal syndrome.

- name: SPG9B cognitive involvement
  subtypes:
  - SPG9B
  description: >-
    Cognitive impairment is reported in complex SPG9B, while a later-onset
    molecularly confirmed family without cognitive impairment demonstrates that
    it is not universal.
  evidence:
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality.
    explanation: Documents cognitive impairment in recessive SPG9.
  - reference: PMID:34093392
    reference_title: "Novel Compound Missense and Intronic Splicing Mutation in ALDH18A1 Causes Autosomal Recessive Spastic Paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SPG9B patients in our cohort presented with milder symptoms, i.e., later age at onset and without cognitive impairment.
    explanation: Demonstrates that cognitive impairment is not universal in SPG9B.
  downstream:
  - target: Intellectual disability
    description: Intellectual disability is a reported, non-universal manifestation of complex SPG9B.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        families with autosomal recessive transmission of ALDH18A1 mutations, and predominant complex hereditary spastic paraplegia with marked cognitive impairment, without any cutaneous abnormality.
      explanation: Supports the SPG9B-specific cognitive phenotype edge.

- name: ARCL3A neurocutaneous disease
  subtypes:
  - ARCL3A
  description: >-
    ARCL3A combines lax or thin skin and joint laxity with growth, ocular, and
    neurodevelopmental manifestations. The cellular routes from P5CS dysfunction
    to individual tissues remain incompletely resolved.
  evidence:
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autosomal recessive cutis laxa (ARCL) is a connective tissue disorder characterized by wrinkled, inelastic skin, frequently associated with a neurologic involvement and multisystem disease.
    explanation: Defines the combined connective-tissue and neurologic ARCL phenotype.
  downstream:
  - target: Global developmental delay
    description: >-
      ARCL3A includes global developmental delay; the intervening neural
      mechanism is unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:36067040
      reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "developmental delay, neurological deficits and loose skin."
      explanation: Homozygous ALDH18A1 cases document developmental delay with neurologic and cutaneous findings.
  - target: Cutis laxa
    description: >-
      ARCL3A includes lax, wrinkled, or inelastic skin. The full tissue-level
      mechanism remains unresolved, though patient dermal fibroblasts show
      reduced type I/III collagen production and altered elastin
      ultrastructure, a partial extracellular-matrix explanation.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:24767728
      reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Features of our patient that have been described in literature included cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay.
      explanation: The ARCL3A report directly lists cutis laxa.
    - reference: PMID:21739576
      reference_title: "Further expansion of the phenotypic spectrum associated with mutations in ALDH18A1, encoding Δ¹-pyrroline-5-carboxylate synthase (P5CS)."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The cellular phenotype is characterized by diminished production of collagen types I and III, altered elastin ultrastructure, and diminished cell proliferation of cultured dermal fibroblasts.
      explanation: Patient dermal fibroblasts from a homozygous ALDH18A1 (P5CS) case show reduced type I/III collagen and altered elastin, a plausible extracellular-matrix route to the cutis laxa, though the full causal chain remains unproven.
  - target: Joint hypermobility
    description: >-
      Joint laxity is part of ARCL3A, without a proven extracellular-matrix
      causal bridge.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:24767728
      reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay.
      explanation: The ARCL3A report directly lists joint laxity.
  - target: Prematurely aged appearance
    description: >-
      The triangular, progeroid facial appearance is a defining clinical
      characteristic of the ARCL3A/de Barsy branch; its tissue-level mechanism
      remains unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:41570168
      reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        typical facial characteristics including a triangular face with a progeroid appearance
      explanation: GeneReviews identifies the characteristic progeroid facial appearance in the neurocutaneous proline-synthesis-defect group that includes ALDH18A1-related ARCL.
  - target: Hypotonia
    description: >-
      Congenital hypotonia can occur in ARCL3A, although GeneReviews reports it
      at the grouped neurocutaneous-disorder level and the intervening mechanism
      is unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:41570168
      reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
      explanation: GeneReviews lists congenital hypotonia as an additional feature across the group that includes ALDH18A1-related ARCL.
  - target: Corneal clouding
    description: >-
      Corneal clouding can occur in ARCL3A, but the grouped GeneReviews evidence
      does not establish its frequency or a direct corneal mechanism.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:41570168
      reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
      explanation: GeneReviews lists corneal clouding as an additional feature across the group that includes ALDH18A1-related ARCL.
  - target: Cataracts
    description: >-
      Cataracts are reported in ARCL3A, but the lens mechanism is unknown and is
      not attributed to the fibroblast lipid-droplet observation.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:11092761
      reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        P5CS in two siblings with progressive neurodegeneration, joint laxity, skin hyperelasticity and bilateral subcapsular cataracts.
      explanation: The original sibling report documents bilateral cataracts.
    - reference: PMID:41570168
      reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
      explanation: GeneReviews independently lists lens opacities as an additional grouped feature, represented here by the existing cataract phenotype.
  - target: Growth retardation
    description: >-
      ARCL3A growth involvement includes short stature; its intermediate
      mechanism is unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:24767728
      reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay.
      explanation: The ARCL3A report directly lists short stature.
  - target: Microcephaly
    description: Microcephaly occurs in ARCL3A, with an unresolved developmental mechanism.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:24767728
      reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay.
      explanation: The ARCL3A report directly lists microcephaly.
  - target: Prominent superficial veins
    description: >-
      Visible superficial veins are reported in ARCL3A without a proven direct
      tissue mechanism.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:24767728
      reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay.
      explanation: The ARCL3A report documents visible superficial veins.
  - target: Failure to thrive
    description: >-
      Failure to thrive is reported in ARCL3A, while its intermediate mechanism
      is unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:24767728
      reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay.
      explanation: The ARCL3A report directly lists failure to thrive.
  - target: Delayed speech and language development
    description: >-
      Severe speech delay accompanies developmental impairment in ARCL3A; the
      intervening neural mechanism is unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:24767728
      reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        cutis laxa on hands and feet, visible veins on thorax and abdomen, joint laxity, failure to thrive, short stature, microcephaly, and severe developmental and speech delay.
      explanation: The ARCL3A report documents severe developmental and speech delay.
  - target: Dystonic posturing
    description: >-
      Dystonic posturing is the discriminatory ALDH18A1/PYCR1 neurocutaneous
      movement sign; the route from P5CS dysfunction to the basal-ganglia/motor
      phenotype is unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:23963297
      reference_title: "Clinical and biochemical features guiding the diagnostics in neurometabolic cutis laxa."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Dystonic posturing was discriminatory for PYCR1 and ALDH18A1 defects.
      explanation: Dystonic posturing discriminated the ALDH18A1 neurocutaneous defects in the cutis-laxa cohort.
  - target: Corpus callosum dysgenesis
    description: >-
      Corpus callosum dysgenesis is a CNS malformation associated with ALDH18A1
      defects; the developmental mechanism from P5CS dysfunction is unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:23963297
      reference_title: "Clinical and biochemical features guiding the diagnostics in neurometabolic cutis laxa."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Corpus callosum dysgenesis was associated with PYCR1 and ALDH18A1 mutations.
      explanation: Corpus callosum dysgenesis was associated with ALDH18A1 (and PYCR1) mutations in the cohort.
  - target: Congenital hip dislocation
    description: >-
      Congenital hip dislocation is a connective-tissue/skeletal feature of the
      ALDH18A1-related neurocutaneous group; the extracellular-matrix bridge is
      not established.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:41570168
      reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
      explanation: GeneReviews lists congenital hip dislocation among the additional features of the group that includes ALDH18A1-related ARCL.
  - target: Adducted thumb
    description: >-
      Adducted thumbs are among the skeletal/positional features of the
      ALDH18A1-related neurocutaneous group; the mechanistic bridge is unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - downstream_tissue_consequence_model
    evidence:
    - reference: PMID:41570168
      reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
      explanation: GeneReviews lists adducted thumbs among the additional features of the group that includes ALDH18A1-related ARCL.

- name: p.Thr331Pro fibroblast metabolic and transcript changes
  subtypes:
  - ARCL3A
  description: >-
    Homozygous p.Thr331Pro reduces P5CS oligomer incorporation. Patient
    fibroblasts show reduced glutamate, proline, glutathione, and putrescine plus
    metabolic and extracellular-matrix-related transcript changes. These are
    genotype-specific cellular observations, not demonstrated neuronal or
    connective-tissue causal pathways.
  gene:
    preferred_term: ALDH18A1
    modifier: ABNORMAL
    term:
      id: hgnc:9722
      label: ALDH18A1
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  evidence:
  - reference: PMID:36067040
    reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      identified reduced abundance of glutamate and several metabolites derived from glutamate, including proline and glutathione. Biosynthesis of the polyamine putrescine, derived from ornithine, was also decreased in patient fibroblasts,
    explanation: Patient-fibroblast metabolomics demonstrates the genotype-specific metabolic changes.
  - reference: PMID:36067040
    reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      RNA sequencing of patient fibroblasts revealed transcript abundance changes in several metabolic and extracellular matrix-related genes, adding further insight into pathogenic processes associated with impaired P5CS function.
    explanation: RNA sequencing supports the cellular transcript changes without establishing tissue-level causation.

- name: p.Arg749Gln/p.Arg765Gln stability and lipid-droplet phenotype
  subtypes:
  - ARCL3A
  description: >-
    Compound-heterozygous p.Arg749Gln/p.Arg765Gln variants reduce P5CS stability
    in patient fibroblasts, which show a lipid-droplet phenotype after oleate
    loading. Its relationship to ARCL3A pathology is unclear; no clinical
    downstream edge is modeled.
  gene:
    preferred_term: ALDH18A1
    modifier: DECREASED
    term:
      id: hgnc:9722
      label: ALDH18A1
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  evidence:
  - reference: PMID:25077174
    reference_title: "Loss of ALDH18A1 function is associated with a cellular lipid droplet phenotype suggesting a link between autosomal recessive cutis laxa type 3A and Warburg Micro syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      mutations alter a conserved C-terminal domain of the encoded protein and reduce protein stability as determined through Western blot analysis of patient fibroblasts.
    explanation: Patient-fibroblast Western blotting supports reduced stability.
  - reference: PMID:25077174
    reference_title: "Loss of ALDH18A1 function is associated with a cellular lipid droplet phenotype suggesting a link between autosomal recessive cutis laxa type 3A and Warburg Micro syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Patient fibroblasts exhibit a lipid droplet phenotype similar to that recently reported in Warburg Micro syndrome, a disorder with similar features but hitherto unrelated cellular etiology.
    explanation: The cell study documents the lipid-droplet phenotype without proving clinical causation.

- name: p.Arg84Gln-associated metabolic branch
  subtypes:
  - ARCL3A
  description: >-
    Homozygous p.Arg84Gln (R84Q) markedly reduces both P5CS isoforms and was
    reported in siblings with hyperammonemia and low ornithine, citrulline,
    arginine, and proline. This branch is genotype bound, not universal.
  gene:
    preferred_term: ALDH18A1
    modifier: DECREASED
    term:
      id: hgnc:9722
      label: ALDH18A1
  evidence:
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia. Both are homozygous for the missense mutation, R84Q,
    explanation: The sibling report ties this metabolic profile to homozygous p.Arg84Gln.
  downstream:
  - target: Hyperammonemia
    description: >-
      In the p.Arg84Gln sibling pair, the genotype-specific metabolic branch
      manifested as hyperammonemia.
    causal_link_type: DIRECT
    hypothesis_groups:
    - variant_dependent_p5cs_loss_model
    evidence:
    - reference: PMID:11092761
      reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Their metabolic phenotype includes hyperammonemia, hypoornithinemia, hypocitrullinemia, hypoargininemia and hypoprolinemia.
      explanation: The original human report directly documents hyperammonemia in this genotype-specific branch.

phenotypes:
- category: Neurological
  name: Spastic paraplegia
  subtypes:
  - SPG9A
  - SPG9B
  description: >
    Progressive lower-limb spasticity is the shared hallmark of SPG9A and
    SPG9B. SPG9A may be pure or complex, whereas reported SPG9B presentations
    are often complex but vary in onset and associated cognitive findings.
  phenotype_term:
    preferred_term: Spastic paraplegia
    term:
      id: HP:0001258
      label: Spastic paraplegia
  evidence:
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      identified monoallelic ALDH18A1 mutations segregating in three independent
      families with autosomal dominant pure or complex hereditary spastic paraplegia,
    explanation: Spastic paraplegia is the defining feature of SPG9A, ranging from pure to complex forms.
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      families with autosomal recessive transmission of ALDH18A1 mutations, and
      predominant complex hereditary spastic paraplegia with marked cognitive
      impairment, without any cutaneous abnormality.
    explanation: Biallelic ALDH18A1 variants establish the recessive SPG9B branch of spastic paraplegia.
- category: Neurological
  name: Intellectual disability
  subtype: SPG9B
  description: >
    Intellectual disability is reported in SPG9B but is not universal; a
    later-onset molecularly confirmed family without cognitive impairment is
    documented.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:31402623
    reference_title: "P5CS expression study in a new family with ALDH18A1-associated hereditary spastic paraplegia SPG9."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      conclude that both mutations are disease-causing, that SPG9B associates with
      partial P5CS deficiency and that it is clinically more severe than SPG9A, as
      reflected in onset age, disability, cognitive status, growth, and dysmorphic
      traits.
    explanation: Early SPG9B series documented cognitive status as one dimension of greater average clinical severity.
  - reference: PMID:34093392
    reference_title: Novel Compound Missense and Intronic Splicing Mutation in ALDH18A1 Causes Autosomal Recessive Spastic Paraplegia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SPG9B patients in our cohort presented with milder symptoms, i.e., later age at onset and without cognitive impairment.
    explanation: A later SPG9B family demonstrates that cognitive impairment is not universal.
- category: Neurological
  name: Global developmental delay
  subtype: ARCL3A
  description: >
    Developmental delay is reported in the ARCL3A neurocutaneous phenotype.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:36067040
    reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "developmental delay, neurological deficits and loose skin."
    explanation: Documents developmental delay in homozygous ALDH18A1 disease with loose skin.
- category: Dermatological
  name: Cutis laxa
  subtype: ARCL3A
  description: >
    Wrinkled or inelastic skin with visible veins is a defining feature of the
    ARCL3A neurocutaneous branch. Published SPG9B cohorts are kept separate
    because cutaneous abnormalities were absent in the defining SPG9B series.
  phenotype_term:
    preferred_term: Cutis laxa
    term:
      id: HP:0000973
      label: Cutis laxa
  evidence:
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Features of our patient that
      have been described in literature included cutis laxa on hands and feet, visible
      veins on thorax and abdomen, joint laxity, failure to thrive, short stature,
      microcephaly, and severe developmental and speech delay.
    explanation: Cutis laxa is a recognized feature of ARCL3A with variable distribution.
- category: Musculoskeletal
  name: Joint hypermobility
  subtype: ARCL3A
  description: >
    Joint laxity or hypermobility is part of the connective-tissue phenotype in
    ALDH18A1-related ARCL3A/de Barsy-spectrum disease, occurring with cutis laxa,
    visible veins, growth failure, microcephaly, and developmental delay.
  phenotype_term:
    preferred_term: Joint hypermobility
    term:
      id: HP:0001382
      label: Joint hypermobility
  evidence:
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Features of our patient that
      have been described in literature included cutis laxa on hands and feet, visible
      veins on thorax and abdomen, joint laxity, failure to thrive, short stature,
      microcephaly, and severe developmental and speech delay.
    explanation: The clinical report and literature review include joint laxity, an exact synonym of HP:0001382 joint hypermobility.
- category: Craniofacial
  name: Prematurely aged appearance
  subtype: ARCL3A
  description: >
    A triangular face with a progeroid or prematurely aged appearance is a
    defining facial characteristic of the ARCL3A/de Barsy phenotype.
  phenotype_term:
    preferred_term: Prematurely aged appearance
    term:
      id: HP:0007495
      label: Prematurely aged appearance
  evidence:
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      typical facial characteristics including a triangular face with a progeroid appearance
    explanation: >-
      GeneReviews identifies the characteristic progeroid facial appearance in
      the neurocutaneous proline-synthesis-defect group that includes
      ALDH18A1-related ARCL.
- category: Neurological
  name: Hypotonia
  subtype: ARCL3A
  description: >
    Congenital hypotonia can occur in the ARCL3A neurocutaneous branch; the
    grouped GeneReviews evidence does not establish its frequency.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
    explanation: GeneReviews lists congenital hypotonia as an additional feature across the group that includes ALDH18A1-related ARCL.
- category: Ophthalmological
  name: Corneal clouding
  subtype: ARCL3A
  description: >
    Corneal clouding can occur in the ARCL3A neurocutaneous branch; the grouped
    GeneReviews evidence does not establish its frequency.
  phenotype_term:
    preferred_term: Corneal clouding
    term:
      id: HP:0007957
      label: Corneal opacity
  evidence:
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
    explanation: GeneReviews lists corneal clouding as an additional feature across the group that includes ALDH18A1-related ARCL.
- category: Ophthalmological
  name: Cataracts
  subtype: ARCL3A
  description: >
    Bilateral cataracts are reported in ARCL3A. The historic early case count is
    retained only as study context, not as a current spectrum-wide frequency
    estimate.
  phenotype_term:
    preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
  evidence:
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      two siblings with progressive
      neurodegeneration, joint laxity, skin hyperelasticity and bilateral subcapsular
      cataracts.
    explanation: The original p.Arg84Gln P5CS-deficiency siblings had bilateral subcapsular cataracts.
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
    explanation: GeneReviews lists lens opacities as an additional feature across the group, represented here by the cataract term.
- category: Growth
  name: Growth retardation
  subtype: ARCL3A
  description: >
    Short stature is part of the ARCL3A growth phenotype and often accompanies
    failure to thrive.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Features of our patient that
      have been described in literature included cutis laxa on hands and feet, visible
      veins on thorax and abdomen, joint laxity, failure to thrive, short stature,
      microcephaly, and severe developmental and speech delay.
    explanation: Short stature and failure to thrive are consistent features of ARCL3A.
- category: Neurological
  name: Microcephaly
  subtype: ARCL3A
  description: >
    Microcephaly is reported in ARCL3A. The small historic case series is not
    treated as a current spectrum-wide frequency estimate.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Features of our patient that
      have been described in literature included cutis laxa on hands and feet, visible
      veins on thorax and abdomen, joint laxity, failure to thrive, short stature,
      microcephaly, and severe developmental and speech delay.
    explanation: The ARCL3A clinical report and review include microcephaly among the recognized features.
- category: Metabolic
  name: Hyperammonemia
  subtype: ARCL3A
  description: >
    Hyperammonemia is bound here to the original homozygous p.Arg84Gln (R84Q)
    ARCL3A branch, in which it accompanied reduced ornithine, citrulline,
    arginine, and proline. It is not modeled as a universal ALDH18A1 finding.
  phenotype_term:
    preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  evidence:
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Their metabolic phenotype includes hyperammonemia, hypoornithinemia,
      hypocitrullinemia, hypoargininemia and hypoprolinemia.
    explanation: The original human P5CS-deficiency siblings had hyperammonemia with low amino acids.
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both are homozygous for the missense mutation, R84Q, which alters a conserved residue in the P5CS gamma-glutamyl kinase domain.
    explanation: Binds this metabolic phenotype to the homozygous p.Arg84Gln branch rather than the full ALDH18A1 spectrum.
- category: Dermatological
  name: Prominent superficial veins
  subtype: ARCL3A
  description: >
    Visible superficial veins through the thin, inelastic skin are part of the
    connective-tissue phenotype of ALDH18A1-related cutis laxa.
  phenotype_term:
    preferred_term: Prominent superficial veins
    term:
      id: HP:0001015
      label: Prominent superficial veins
  evidence:
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      cutis laxa on hands and feet, visible
      veins on thorax and abdomen, joint laxity, failure to thrive, short stature,
      microcephaly, and severe developmental and speech delay.
    explanation: The ARCL3A clinical report and literature review document visible superficial veins on the thorax and abdomen.
- category: Growth
  name: Failure to thrive
  subtype: ARCL3A
  description: >
    Failure to thrive occurs in ARCL3A/de Barsy-spectrum disease alongside short
    stature and the broader growth-failure phenotype.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      cutis laxa on hands and feet, visible
      veins on thorax and abdomen, joint laxity, failure to thrive, short stature,
      microcephaly, and severe developmental and speech delay.
    explanation: The ARCL3A clinical report and literature review document failure to thrive among the recognized features.
- category: Neurological
  name: Delayed speech and language development
  subtype: ARCL3A
  description: >
    Severe speech and language delay accompanies the global developmental delay
    in ALDH18A1-related cutis laxa.
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:24767728
    reference_title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      cutis laxa on hands and feet, visible
      veins on thorax and abdomen, joint laxity, failure to thrive, short stature,
      microcephaly, and severe developmental and speech delay.
    explanation: The ARCL3A clinical report and literature review document severe developmental and speech delay.
- category: Neurological
  name: Dystonic posturing
  subtype: ARCL3A
  description: >
    Dystonic posturing is a discriminatory neurologic sign of the ALDH18A1
    (and PYCR1) mitochondrial proline-synthesis neurocutaneous disorders, and
    the classic De Barsy-syndrome movement phenotype, distinguishing them from
    other genetic cutis-laxa subtypes.
  phenotype_term:
    preferred_term: Dystonic posturing
    term:
      id: HP:0001332
      label: Dystonia
  evidence:
  - reference: PMID:23963297
    reference_title: "Clinical and biochemical features guiding the diagnostics in neurometabolic cutis laxa."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dystonic posturing was discriminatory for PYCR1 and ALDH18A1 defects.
    explanation: In a prospectively evaluated neurometabolic cutis-laxa cohort, dystonic posturing specifically discriminated the ALDH18A1 (and PYCR1) neurocutaneous defects from other cutis-laxa genes.
- category: Neurological
  name: Corpus callosum dysgenesis
  subtype: ARCL3A
  description: >
    Corpus callosum dysgenesis (abnormal corpus callosum morphology) is a
    recognized central-nervous-system malformation of ALDH18A1-related
    neurocutaneous cutis laxa.
  phenotype_term:
    preferred_term: Corpus callosum dysgenesis
    term:
      id: HP:0001273
      label: Abnormal corpus callosum morphology
  evidence:
  - reference: PMID:23963297
    reference_title: "Clinical and biochemical features guiding the diagnostics in neurometabolic cutis laxa."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Corpus callosum dysgenesis was associated with PYCR1 and ALDH18A1 mutations.
    explanation: The neurometabolic cutis-laxa cohort associated corpus callosum dysgenesis with ALDH18A1 (and PYCR1) mutations.
- category: Musculoskeletal
  name: Congenital hip dislocation
  subtype: ARCL3A
  description: >
    Congenital hip dislocation is among the additional connective-tissue and
    skeletal features reported across the ALDH18A1-related neurocutaneous
    proline-synthesis disorders.
  phenotype_term:
    preferred_term: Congenital hip dislocation
    term:
      id: HP:0001374
      label: Congenital hip dislocation
  evidence:
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
    explanation: GeneReviews lists congenital hip dislocation as an additional feature across the group that includes ALDH18A1-related ARCL.
- category: Musculoskeletal
  name: Adducted thumb
  subtype: ARCL3A
  description: >
    Adducted thumbs are among the additional skeletal and positional features
    reported across the ALDH18A1-related neurocutaneous proline-synthesis
    disorders.
  phenotype_term:
    preferred_term: Adducted thumb
    term:
      id: HP:0001181
      label: Adducted thumb
  evidence:
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Additional features can include joint laxity, congenital hypotonia, progressive increased lower limb reflexes/spasticity, congenital hip dislocation, adducted thumbs, corneal clouding, and lens opacities.
    explanation: GeneReviews lists adducted thumbs as an additional feature across the group that includes ALDH18A1-related ARCL.
biochemical:
- name: Plasma proline
  presence: NORMAL_OR_DECREASED
  context: >-
    Plasma proline is decreased in some molecularly confirmed P5CS-deficiency
    families but normal in others. A low result can support the diagnosis, but
    a normal result does not exclude ALDH18A1-related disease.
  biomarker_term:
    preferred_term: L-proline
    term:
      id: CHEBI:17203
      label: L-proline
  readouts:
  - target: Variable P5CS-dependent amino-acid synthesis
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Low plasma proline supports impaired P5CS-dependent amino-acid synthesis, while a normal result does not exclude it.
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: |-
        Low levels of plasma ornithine, citrulline,
        arginine and proline in four individuals from two families suggested P5CS
        deficiency.
      explanation: Directly links low proline and the accompanying amino-acid profile to P5CS deficiency in a subset of affected individuals.
    - reference: PMID:29754261
      reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: |-
        childhood and temporal lobe epilepsy, but normal levels of proline, ornithine
        and arginine.
      explanation: Molecularly confirmed ALDH18A1 disease can have normal plasma proline, limiting sensitivity.
  evidence:
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      as well as in two sporadic patients. Low levels of plasma ornithine, citrulline,
      arginine and proline in four individuals from two families suggested P5CS
      deficiency.
    explanation: Plasma amino acid profiling reveals P5CS deficiency biomarkers in affected individuals.
  - reference: PMID:29754261
    reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      childhood and temporal lobe epilepsy, but normal levels of proline, ornithine
      and arginine.
    explanation: Demonstrates that amino acid levels may be normal when mutations affect the G5PR domain.
- name: Plasma ornithine
  presence: NORMAL_OR_DECREASED
  context: >-
    Plasma ornithine can be decreased as part of the P5CS-deficiency amino-acid
    profile, but normal values occur in molecularly confirmed disease. It is a
    supportive rather than universal finding.
  biomarker_term:
    preferred_term: L-ornithine
    term:
      id: CHEBI:15729
      label: L-ornithine
  readouts:
  - target: Variable P5CS-dependent amino-acid synthesis
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Low plasma ornithine supports impaired P5CS-dependent amino-acid synthesis, while a normal result does not exclude it.
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: |-
        Low levels of plasma ornithine, citrulline,
        arginine and proline in four individuals from two families suggested P5CS
        deficiency.
      explanation: Directly links low ornithine and the accompanying profile to P5CS deficiency in a subset of affected individuals.
    - reference: PMID:29754261
      reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: |-
        childhood and temporal lobe epilepsy, but normal levels of proline, ornithine
        and arginine.
      explanation: Molecularly confirmed ALDH18A1 disease can have normal plasma ornithine, limiting sensitivity.
  evidence:
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Their metabolic phenotype includes hyperammonemia, hypoornithinemia,
      hypocitrullinemia, hypoargininemia and hypoprolinemia.
    explanation: The original P5CS deficiency report documents hypoornithinemia as part of the metabolic phenotype.
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Low levels of plasma ornithine, citrulline,
      arginine and proline in four individuals from two families suggested P5CS
      deficiency.
    explanation: ALDH18A1-related SPG families show reduced plasma ornithine in the diagnostic amino-acid profile.
  - reference: PMID:29754261
    reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      childhood and temporal lobe epilepsy, but normal levels of proline, ornithine
      and arginine.
    explanation: Demonstrates that plasma ornithine can remain normal in molecularly confirmed ALDH18A1 disease.
- name: Plasma citrulline
  presence: NORMAL_OR_DECREASED
  context: >-
    Plasma citrulline can be decreased with the P5CS-deficiency amino-acid
    profile but is not uniformly abnormal across ALDH18A1 genotypes. A low value
    is supportive, not required for molecular diagnosis.
  biomarker_term:
    preferred_term: L-citrulline
    term:
      id: CHEBI:16349
      label: L-citrulline
  readouts:
  - target: Variable P5CS-dependent amino-acid synthesis
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Low plasma citrulline supports impaired P5CS-dependent amino-acid synthesis, while a normal result does not exclude it.
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: |-
        Low levels of plasma ornithine, citrulline,
        arginine and proline in four individuals from two families suggested P5CS
        deficiency.
      explanation: Directly links low citrulline and the accompanying profile to P5CS deficiency in a subset of affected individuals.
    - reference: PMID:29754261
      reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Mutations affecting the G5K domain have previously been found to cause reduced plasma levels of proline, citrulline and arginine, whereas such effect is not seen with mutations affecting the GR5P domain.
      explanation: Published ALDH18A1 genotypes need not lower citrulline, limiting this marker's sensitivity.
  evidence:
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Their metabolic phenotype includes hyperammonemia, hypoornithinemia,
      hypocitrullinemia, hypoargininemia and hypoprolinemia.
    explanation: The original P5CS deficiency report documents hypocitrullinemia.
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Low levels of plasma ornithine, citrulline,
      arginine and proline in four individuals from two families suggested P5CS
      deficiency.
    explanation: ALDH18A1-related SPG families show reduced plasma citrulline.
  - reference: PMID:29754261
    reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutations affecting the G5K domain have previously been found to cause reduced plasma levels of proline, citrulline and arginine, whereas such effect is not seen with mutations affecting the GR5P domain.
    explanation: Demonstrates genotype-dependent variability in plasma citrulline.
- name: Plasma arginine
  presence: NORMAL_OR_DECREASED
  context: >-
    Plasma arginine can be decreased with ornithine, citrulline, and proline in
    P5CS deficiency, but normal values are documented in molecularly confirmed
    ALDH18A1 disease. It is a supportive rather than universal finding.
  biomarker_term:
    preferred_term: L-arginine
    term:
      id: CHEBI:16467
      label: L-arginine
  readouts:
  - target: Variable P5CS-dependent amino-acid synthesis
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Low plasma arginine supports impaired P5CS-dependent amino-acid synthesis, while a normal result does not exclude it.
    evidence:
    - reference: PMID:26026163
      reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: |-
        Low levels of plasma ornithine, citrulline,
        arginine and proline in four individuals from two families suggested P5CS
        deficiency.
      explanation: Directly links low arginine and the accompanying profile to P5CS deficiency in a subset of affected individuals.
    - reference: PMID:29754261
      reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: |-
        childhood and temporal lobe epilepsy, but normal levels of proline, ornithine
        and arginine.
      explanation: Molecularly confirmed ALDH18A1 disease can have normal plasma arginine, limiting sensitivity.
  evidence:
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Their metabolic phenotype includes hyperammonemia, hypoornithinemia,
      hypocitrullinemia, hypoargininemia and hypoprolinemia.
    explanation: The original P5CS deficiency report documents hypoargininemia.
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Low levels of plasma ornithine, citrulline,
      arginine and proline in four individuals from two families suggested P5CS
      deficiency.
    explanation: ALDH18A1-related SPG families show reduced plasma arginine.
  - reference: PMID:29754261
    reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      childhood and temporal lobe epilepsy, but normal levels of proline, ornithine
      and arginine.
    explanation: Demonstrates that plasma arginine can remain normal in molecularly confirmed ALDH18A1 disease.
- name: Blood ammonia
  subtype: ARCL3A
  presence: INCREASED
  context: >-
    Increased blood ammonia is specific here to the original homozygous
    p.Arg84Gln (R84Q) branch and is not a universal biochemical feature of the
    ALDH18A1 spectrum.
  biomarker_term:
    preferred_term: ammonia
    term:
      id: CHEBI:16134
      label: ammonia
  readouts:
  - target: p.Arg84Gln-associated metabolic branch
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated ammonia reports the p.Arg84Gln-associated metabolic branch rather than the full ALDH18A1 spectrum.
    evidence:
    - reference: PMID:11092761
      reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: |-
        Their metabolic phenotype includes hyperammonemia, hypoornithinemia,
        hypocitrullinemia, hypoargininemia and hypoprolinemia.
      explanation: Directly supports hyperammonemia in the original metabolic branch.
    - reference: PMID:11092761
      reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Both are homozygous for the missense mutation, R84Q, which alters a conserved residue in the P5CS gamma-glutamyl kinase domain.
      explanation: Binds the ammonia readout to the homozygous p.Arg84Gln branch.
  evidence:
  - reference: PMID:11092761
    reference_title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: |-
      Their metabolic phenotype includes hyperammonemia, hypoornithinemia,
      hypocitrullinemia, hypoargininemia and hypoprolinemia.
    explanation: The original P5CS deficiency report directly documents hyperammonemia.
- name: Cellular glutathione
  subtype: ARCL3A
  presence: DECREASED
  context: >-
    Metabolomic profiling in patient fibroblasts shows reduced glutathione,
    indicating impaired glutamate-derived antioxidant metabolism.
  biomarker_term:
    preferred_term: glutathione
    term:
      id: CHEBI:16856
      label: glutathione
  readouts:
  - target: p.Thr331Pro fibroblast metabolic and transcript changes
    relationship: READOUT_OF
    direction: NEGATIVE
    interpretation: Lower cellular glutathione reports the p.Thr331Pro fibroblast metabolic phenotype and is not generalized to every ALDH18A1 variant.
    evidence:
    - reference: PMID:36067040
      reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Here we characterize a previously unreported homozygous ALDH18A1 variant (p.Thr331Pro) in four affected probands from two unrelated families, and demonstrate broad-based alterations in amino acid and antioxidant metabolism.
      explanation: Identifies the specific p.Thr331Pro context for this cellular readout.
    - reference: PMID:36067040
      reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: |-
        identified reduced abundance of glutamate and several metabolites derived from
        glutamate, including proline and glutathione.
      explanation: Patient-cell metabolomics directly links reduced glutathione to the p.Thr331Pro experimental branch.
  evidence:
  - reference: PMID:36067040
    reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: |-
      identified reduced abundance of glutamate and several metabolites derived from
      glutamate, including proline and glutathione.
    explanation: Patient-cell metabolomics directly identifies reduced glutathione.
- name: Cellular putrescine
  subtype: ARCL3A
  presence: DECREASED
  context: >-
    Metabolomic profiling in patient fibroblasts shows reduced biosynthesis of
    putrescine from ornithine, tying the P5CS ornithine branch to antioxidant
    pathway dysfunction.
  biomarker_term:
    preferred_term: putrescine
    term:
      id: CHEBI:17148
      label: putrescine
  readouts:
  - target: p.Thr331Pro fibroblast metabolic and transcript changes
    relationship: READOUT_OF
    direction: NEGATIVE
    interpretation: Lower cellular putrescine reports the p.Thr331Pro fibroblast metabolic phenotype and is not generalized to every ALDH18A1 variant.
    evidence:
    - reference: PMID:36067040
      reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Here we characterize a previously unreported homozygous ALDH18A1 variant (p.Thr331Pro) in four affected probands from two unrelated families, and demonstrate broad-based alterations in amino acid and antioxidant metabolism.
      explanation: Identifies the specific p.Thr331Pro context for this cellular readout.
    - reference: PMID:36067040
      reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: |-
        Biosynthesis of the polyamine
        putrescine, derived from ornithine, was also decreased in patient fibroblasts,
      explanation: Patient-cell metabolomics directly links reduced putrescine to the p.Thr331Pro experimental branch.
  evidence:
  - reference: PMID:36067040
    reference_title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: |-
      Biosynthesis of the polyamine
      putrescine, derived from ornithine, was also decreased in patient fibroblasts,
    explanation: Patient fibroblast metabolomics directly identifies decreased putrescine biosynthesis.
diagnosis:
- name: Molecular Genetic Confirmation
  description: >-
    Confirmation centers on pathogenic ALDH18A1 variant identification, with
    zygosity, variant association, segregation, and phenotype interpreted
    together. A heterozygous HSP-associated pathogenic variant in a compatible
    SPG9 phenotype supports SPG9A, whereas biallelic pathogenic variants support
    SPG9B or ARCL3A according to clinical context. Heterozygosity alone does not
    distinguish SPG9A from the separately curated ADCL3 branch.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  results: >-
    Pathogenic ALDH18A1 variant(s), variant-disease association, zygosity,
    segregation, and phenotype consistent with the suspected SPG9A, SPG9B, or
    ARCL3A branch support the molecular diagnosis.
  evidence:
  - reference: PMID:32017139
    reference_title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      In 2015 to 2016, an upper motor neuron syndrome (spastic
      paraparesis/paraplegia SPG9) complicated with some traits of the
      neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or
      herniae, was associated with monoallelic or biallelic ALDH18A1 mutations with,
      respectively, dominant and recessive inheritance.
    explanation: >-
      The focused P5CS-deficiency review ties monoallelic and biallelic ALDH18A1
      variants to the dominant and recessive SPG9 branches, respectively.
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      DIAGNOSIS/TESTING: The diagnosis of a neurocutaneous disorder due a to
      mitochondrial proline synthesis defect can be established in a proband with
      characteristic clinical findings and identification of biallelic ALDH18A1 or
      PYCR1 pathogenic variants or a de novo ALDH18A1 pathogenic variant associated
      with ALDH18A1-related ADCL.
    explanation: >-
      GeneReviews establishes molecular confirmation with biallelic ALDH18A1
      pathogenic variants for the autosomal recessive neurocutaneous branch.
- name: Plasma Amino Acid Chromatography (Supportive)
  description: >-
    Plasma amino-acid chromatography is an optional supportive test. Low
    ornithine, citrulline, arginine, and proline can support P5CS deficiency,
    particularly in some SPG9A genotypes, but sensitivity is limited and normal
    values do not exclude molecularly confirmed ALDH18A1 disease.
  diagnosis_term:
    preferred_term: biomarker analysis
    term:
      id: NCIT:C63333
      label: Biomarker Analysis
  results: >-
    A low amino-acid profile supports P5CS deficiency; a normal profile is
    non-exclusionary and should not stop molecular testing or variant assessment.
  evidence:
  - reference: PMID:26026163
    reference_title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we therefore suggest including
      amino acid chromatography in the clinico-genetic work-up of hereditary spastic
      paraplegia, particularly in dominant cases, as the associated phenotype is not
      distinct from other causative genes.
    explanation: >-
      The original SPG9 study recommends amino-acid chromatography as a
      supportive component of the clinico-genetic work-up.
  - reference: PMID:29754261
    reference_title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This young man has spastic paraplegia with onset in
      childhood and temporal lobe epilepsy, but normal levels of proline, ornithine
      and arginine.
    explanation: >-
      A molecularly confirmed recessive SPG9 case had normal plasma amino acids,
      demonstrating that a normal result does not exclude the disorder.
treatments:
- name: Subtype-Bounded Genetic Counseling
  description: >-
    Counseling should distinguish heterozygous autosomal dominant SPG9A from
    biallelic autosomal recessive SPG9B and ARCL3A. Recurrence assessment and
    family testing should be based on the identified variant(s), zygosity, and
    segregation rather than applying a single risk model across the spectrum.
  action_category: COUNSELING_INFORMATIONAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:32017139
    reference_title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      In 2015 to 2016, an upper motor neuron syndrome
      (spastic paraparesis/paraplegia SPG9) complicated with some traits of the
      neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or
      herniae, was associated with monoallelic or biallelic ALDH18A1 mutations with,
      respectively, dominant and recessive inheritance.
    explanation: >-
      The review directly distinguishes dominant monoallelic from recessive
      biallelic SPG9 and supports inheritance-aware counseling.
- name: ARCL3A Multidisciplinary Supportive Care
  description: >-
    For the ARCL3A neurocutaneous branch, care is multidisciplinary and
    manifestation-directed, including speech and developmental support, physical
    therapy and mobility assistance, orthopedic care, ophthalmologic care, and
    routine treatment of associated neurologic findings. Arginine supplementation
    has been described only in a limited number of individuals with abnormal serum
    amino acids, and clinical benefit remains unconfirmed; it is not established
    disease-modifying therapy. These GeneReviews recommendations are not
    extrapolated here into a formal SPG9A/SPG9B management schedule.
  context: ARCL3A neurocutaneous branch
  action_category: THERAPEUTIC
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:41570168
    reference_title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      MANAGEMENT: Treatment of manifestations: Prelingual speech therapy to improve
      swallowing and speech development; routine treatment of epilepsy; in those with
      abnormal serum amino acids (low ornithine, citrulline, arginine),
      supplementation with arginine has been described in a limited number of
      individuals, but clinical benefit remains to be confirmed; physical therapy for
      motor delays and spastic diplegia; mobility devices for spastic diplegia;
      treatment of hip dislocation, scoliosis, and joint contractures per orthopedist;
    explanation: >-
      GeneReviews supports multidisciplinary manifestation-directed care and
      explicitly states that arginine experience is limited and benefit unconfirmed.
  - reference: PMID:22170564
    reference_title: "Understanding pyrroline-5-carboxylate synthetase deficiency: clinical, molecular, functional, and expression studies, structure-based analysis, and novel therapy with arginine."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MR spectroscopy revealed decreased brain creatine, which normalized after sustained
      arginine supplementation, with improvement of neurodevelopmental and metabolic
      parameters, suggesting a pathogenic role of brain creatine decrease and the
      value of arginine therapy.
    explanation: >-
      A single-patient report provides a limited positive signal for arginine,
      while the later review states that clinical benefit remains unconfirmed.
references:
- reference: PMID:11092761
  title: "Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase."
  findings: []
- reference: PMID:22170564
  title: "Understanding pyrroline-5-carboxylate synthetase deficiency: clinical, molecular, functional, and expression studies, structure-based analysis, and novel therapy with arginine."
  findings: []
- reference: PMID:24767728
  title: "Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature."
  findings: []
- reference: PMID:25077174
  title: "Loss of ALDH18A1 function is associated with a cellular lipid droplet phenotype suggesting a link between autosomal recessive cutis laxa type 3A and Warburg Micro syndrome."
  findings: []
- reference: PMID:26026163
  title: "Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia."
  findings: []
- reference: PMID:29754261
  title: "Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia."
  findings: []
- reference: PMID:31402623
  title: "P5CS expression study in a new family with ALDH18A1-associated hereditary spastic paraplegia SPG9."
  findings: []
- reference: PMID:32017139
  title: "Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder."
  findings: []
- reference: PMID:34093392
  title: "Novel Compound Missense and Intronic Splicing Mutation in ALDH18A1 Causes Autosomal Recessive Spastic Paraplegia."
  findings: []
- reference: PMID:36067040
  title: "Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism."
  findings: []
- reference: PMID:41570168
  title: "Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects."
  tags:
  - GeneReviews
  findings: []
- reference: CGGV:assertion_7bfbe962-beb3-4553-9909-a83a3aac2d55-2021-05-18T211134.377Z
  title: "ALDH18A1 / P5CS deficiency (Definitive)"
  findings: []
📚

References & Deep Research

References

12
PMID:11092761
Hyperammonemia with reduced ornithine, citrulline, arginine and proline: a new inborn error caused by a mutation in the gene encoding delta(1)-pyrroline-5-carboxylate synthase.
No top-level findings curated for this source.
PMID:22170564
Understanding pyrroline-5-carboxylate synthetase deficiency: clinical, molecular, functional, and expression studies, structure-based analysis, and novel therapy with arginine.
No top-level findings curated for this source.
PMID:24767728
Cutis laxa, fat pads and retinopathy due to ALDH18A1 mutation and review of the literature.
No top-level findings curated for this source.
PMID:25077174
Loss of ALDH18A1 function is associated with a cellular lipid droplet phenotype suggesting a link between autosomal recessive cutis laxa type 3A and Warburg Micro syndrome.
No top-level findings curated for this source.
PMID:26026163
Alteration of ornithine metabolism leads to dominant and recessive hereditary spastic paraplegia.
No top-level findings curated for this source.
PMID:29754261
Compound heterozygous mutations in two different domains of ALDH18A1 do not affect the amino acid levels in a patient with hereditary spastic paraplegia.
No top-level findings curated for this source.
PMID:31402623
P5CS expression study in a new family with ALDH18A1-associated hereditary spastic paraplegia SPG9.
No top-level findings curated for this source.
PMID:32017139
Δ(1) -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder.
No top-level findings curated for this source.
PMID:34093392
Novel Compound Missense and Intronic Splicing Mutation in ALDH18A1 Causes Autosomal Recessive Spastic Paraplegia.
No top-level findings curated for this source.
PMID:36067040
Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism.
No top-level findings curated for this source.
PMID:41570168
Neurocutaneous Disorders due to Mitochondrial Proline Synthesis Defects.
No top-level findings curated for this source.
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Disease Characteristics Research Template
Edison Scientific Literature 36 citations 2026-05-08T07:51:27.206605

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: ALDH18A1-Related Spastic Paraplegia and Neurocutaneous Spectrum
  • MONDO ID: (if available)
  • Category: Mendelian

Research Objectives

Please provide a comprehensive research report on ALDH18A1-Related Spastic Paraplegia and Neurocutaneous Spectrum 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
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For each treatment, suggest MAXO (Medical Action Ontology) terms where applicable.

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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, MAXO, 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 (MAXO terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

Comprehensive research report: ALDH18A1‑Related Spastic Paraplegia and Neurocutaneous Spectrum (P5CS deficiency continuum)

Executive summary

ALDH18A1 encodes the mitochondrial bifunctional enzyme Δ1‑pyrroline‑5‑carboxylate synthase (P5CS), which catalyzes conversion of glutamate to pyrroline‑5‑carboxylate (P5C), a branch point for proline and ornithine/arginine‑urea‑cycle–linked metabolism. Pathogenic ALDH18A1 variants produce a continuous clinicogenetic spectrum spanning neurocutaneous cutis laxa / de Barsy–like presentations and hereditary spastic paraplegia (HSP) type 9 (SPG9), with dominant forms frequently proposed to act by dominant‑negative loss‑of‑function and recessive forms by partial/marked deficiency. A widely cited synthesis proposes severity ordering SPG9A < SPG9B < ADCL3 ≤ ARCL3A as a single disease entity (“P5CS deficiency”). (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

Recent (2023) multi‑omics work in patient fibroblasts with a homozygous ALDH18A1 variant demonstrates broad alterations in amino‑acid and antioxidant metabolism, including reduced glutamate‑derived metabolites (proline, glutathione) and decreased ornithine‑derived putrescine, providing a modern mechanistic and biomarker framework for this Mendelian spectrum. (colonna2023functionalassessmentof pages 1-1)

1. Disease information (definitions, identifiers, synonyms)

1.1 Disease concept

ALDH18A1‑related spastic paraplegia and neurocutaneous spectrum refers to Mendelian disorders caused by mono‑ or biallelic pathogenic variants in ALDH18A1, producing a phenotype continuum that includes: - Hereditary spastic paraplegia type 9: SPG9A (AD) and SPG9B (AR). - Cutis laxa 3: autosomal dominant cutis laxa 3 (ADCL3) and autosomal recessive cutis laxa type IIIA (ARCL3A). - ALDH18A1‑related de Barsy syndrome as a neurocutaneous entity overlapping the cutis laxa/progeroid spectrum.

A central definition from a 2020 expert review states that ALDH18A1 mutations cause “two neurocutaneous syndromes … and two SPG9 syndromes” and that they “represent a continuum of increasing severity … of the same disease, P5CS deficiency.” (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

1.2 Key identifiers

  • Gene: ALDH18A1 at 10q24.1 (OMIM gene entry cited as OMIM 138250 in a SPG9B case report). (kalmar2021tremorasan pages 1-2)
  • SPG9A: OMIM/MIM 601162. (kalmar2021tremorasan pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • SPG9B: OMIM/MIM 616586. (kalmar2021tremorasan pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, chen2021novelcompoundmissense pages 1-2)
  • ADCL3: OMIM/MIM 616603. (kalmar2021tremorasan pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • ARCL3A: OMIM/MIM 219150. (kalmar2021tremorasan pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • De Barsy syndrome (DBS): discussed within ARCL3 / ARCL3A spectrum; DBS listed with MIM 219150 within a cutis laxa diagnostic/nosology paper. (gardeitchik2014clinicalandbiochemical pages 1-2)

MONDO (via Open Targets association evidence): - MONDO:0009053 “ALDH18A1‑related de Barsy syndrome” - MONDO:0014702 “autosomal recessive complex spastic paraplegia type 9B” - MONDO:0014706 “cutis laxa, autosomal dominant 3” - MONDO:0015091 “autosomal dominant spastic paraplegia type 9” (OpenTargets Search: -ALDH18A1)

1.3 Synonyms and alternative names

  • P5CS deficiency / Δ1‑pyrroline‑5‑carboxylate synthetase deficiency (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • ALDH18A1‑related cutis laxa (dominant or recessive) (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • ALDH18A1‑associated HSP / spastic paraplegia 9 (chen2021novelcompoundmissense pages 1-2)
  • De Barsy‑like progeroid cutis laxa phenotype (fischerzirnsak2015recurrentdenovo pages 1-2)

1.4 Evidence source types

Most information in the available corpus is derived from aggregated disease‑level resources and literature synthesis (e.g., JIMD review) (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) and primary case series (e.g., Am J Hum Genet Arg138 de novo cohort) (fischerzirnsak2015recurrentdenovo pages 1-2, fischerzirnsak2015recurrentdenovo media 44a36465), complemented by functional studies in patient cells (colonna2023functionalassessmentof pages 1-1) and clinical cohort sequencing studies (mahungu2023themutationalprofile pages 1-2).

2. Etiology

2.1 Disease causal factors

Primary cause is genetic: pathogenic variants in ALDH18A1. The encoded enzyme P5CS catalyzes the first and common step of proline and ornithine biosynthesis from glutamate, linking glutamate metabolism to urea cycle and broader amino‑acid/polyamine metabolism. (coutelier2015alterationofornithine pages 1-2, colonna2023functionalassessmentof pages 1-2)

2.2 Risk factors

  • Genetic: Monoallelic variants (dominant) or biallelic variants (recessive) in ALDH18A1. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, chen2021novelcompoundmissense pages 1-2)
  • Environmental/lifestyle risk factors are not established in the retrieved disease‑specific literature.

2.3 Protective factors / gene–environment interactions

The initial ARCL3A description included “paradoxical hyperammonemia (alleviated by protein),” indicating dietary protein intake can acutely modify a biochemical phenotype in severe P5CS deficiency. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

3. Phenotypes (clinical spectrum)

3.1 Overarching phenotype architecture

A key modern framing is that ALDH18A1 disorders encompass at least two named syndromic groupings—SPG9A/B and cutis laxa 3 (ADCL3/ARCL3A)—with overlapping neurological and cutaneous findings. (colonna2023functionalassessmentof pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

Entity/synonym Inheritance Typical onset Core neuro features Core cutaneous/connective-tissue features Key biochemical clues Notes/quantitative stats Key references
SPG9A / autosomal dominant spastic paraplegia type 9 / dominant ALDH18A1-related HSP Autosomal dominant; monoallelic ALDH18A1 variants, with dominant-negative loss-of-function proposed (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, panza2016aldh18a1genemutations pages 8-8) Generally later-onset than recessive/neurocutaneous forms; upper motor neuron syndrome with progressive course (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) Progressive spastic paraparesis/paraplegia; can be pure or complex HSP; corticospinal tract involvement; tremor can occur in ALDH18A1-related HSP spectrum (coutelier2015alterationofornithine pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, kalmar2021tremorasan pages 1-2) Typically lacks overt cutis laxa/joint hypermobility seen in neurocutaneous forms (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) Plasma ornithine, citrulline, arginine, and proline may be low or low-normal; amino-acid chromatography suggested as a trait biomarker in ALDH18A1 HSP (coutelier2015alterationofornithine pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) Review cited 50 total SPG9 patients, of whom 36 were monoallelic; SPG9A framed as the mildest end of the ALDH18A1/P5CS deficiency continuum (SPG9A < SPG9B < ADCL3 ≤ ARCL3A) (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) Coutelier et al., 2015, Brain, https://doi.org/10.1093/brain/awv143; Panza et al., 2016, Brain, https://doi.org/10.1093/brain/awv247; Marco-Marín et al., 2020, JIMD, https://doi.org/10.1002/jimd.12220
SPG9B / autosomal recessive complex spastic paraplegia type 9B / recessive ALDH18A1-related HSP Autosomal recessive; biallelic ALDH18A1 variants (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, chen2021novelcompoundmissense pages 1-2, kalmar2021tremorasan pages 1-2) Usually childhood onset; clinically more severe than SPG9A, but milder than cutis laxa neurocutaneous forms overall (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, chen2021novelcompoundmissense pages 1-2, kalmar2021tremorasan pages 1-2) Complex HSP with spasticity, developmental delay/intellectual impairment in some cases, tremor as early sign in at least one child, white-matter reduction/corpus callosum hypoplasia reported, variable cognitive involvement (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, chen2021novelcompoundmissense pages 1-2, kalmar2021tremorasan pages 1-2) Usually no frank cutis laxa; may have growth issues/dysmorphic traits in more severe cases (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, kalmar2021tremorasan pages 1-2) P5CS concentration can be significantly decreased in plasma; amino-acid abnormalities may include low or low-normal ornithine/citrulline/arginine/proline, but can also be normal except mild hypocitrullinemia; RNA splicing analysis can clarify intronic variants (coutelier2015alterationofornithine pages 1-2, chen2021novelcompoundmissense pages 1-2, kalmar2021tremorasan pages 1-2) Review cited 50 total SPG9 patients, 14 biallelic; Chen 2021 reported novel c.880T>C (p.S294P) plus c.-28-13A>G in one AR family; Kalmár 2021 detailed early tremor (~2 months), DQ 45 at 2 years, MRI abnormalities, normal fasting ammonia, normal proline/ornithine/arginine, slightly decreased citrulline (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, chen2021novelcompoundmissense pages 1-2, kalmar2021tremorasan pages 1-2) Magini et al., 2019, Ann Clin Transl Neurol, https://doi.org/10.1002/acn3.50821; Chen et al., 2021, Front Neurol, https://doi.org/10.3389/fneur.2021.627531; Kalmár et al., 2021, Brain Dev, https://doi.org/10.1016/j.braindev.2020.07.015
ADCL3 / cutis laxa, autosomal dominant 3 / progeroid autosomal-dominant cutis laxa due to ALDH18A1 Autosomal dominant, typically de novo heterozygous ALDH18A1 variants; recurrent Arg138 substitutions highlighted (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, fischerzirnsak2015recurrentdenovo pages 1-2) Congenital/prenatal to early infancy; growth restriction often prenatal and postnatal (fischerzirnsak2015recurrentdenovo pages 1-2) Developmental/psychomotor delay common; neurodevelopmental impairment; vascular tortuosity reported in some; overlaps with De Barsy-like neurocutaneous phenotype (fischerzirnsak2015recurrentdenovo pages 1-2) Lax thin skin, progeroid appearance, joint hyperlaxity; cataracts frequent; adducted thumbs in many patients (fischerzirnsak2015recurrentdenovo pages 1-2) Reduced P5CS enzymatic activity; delayed proline accumulation; altered sub-mitochondrial distribution of mutant P5CS (fischerzirnsak2015recurrentdenovo pages 1-2) In a cohort of 8 unrelated individuals, all had lax thin skin and joint hyperlaxity; all had prenatal growth restriction and 7/8 postnatal growth restriction; 6/8 had cataracts; 5/8 adducted thumbs; 4/8 cranial vessel tortuosity; de novo origin confirmed in all 6 probands with parental DNA available (fischerzirnsak2015recurrentdenovo pages 1-2, fischerzirnsak2015recurrentdenovo media 44a36465) Fischer-Zirnsak et al., 2015, Am J Hum Genet, https://doi.org/10.1016/j.ajhg.2015.08.001; Marco-Marín et al., 2020, JIMD, https://doi.org/10.1002/jimd.12220
ARCL3A / cutis laxa, autosomal recessive type IIIA / recessive neurocutaneous P5CS deficiency Autosomal recessive; homozygous or compound heterozygous ALDH18A1 variants (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, lugli2022autosomalrecessivecutis pages 6-6, gardeitchik2014clinicalandbiochemical pages 1-2) Usually congenital/infantile; often severe, including fetal presentations in some reports (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, lugli2022autosomalrecessivecutis pages 6-6) Developmental disability/intellectual disability, severe neurologic involvement in many cases, growth restriction, cataracts; corpus callosum agenesis/dysgenesis and dystonic posturing associated in broader cutis laxa diagnostic series (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, lugli2022autosomalrecessivecutis pages 6-6, gardeitchik2014clinicalandbiochemical pages 1-2) Cutis laxa, connective-tissue laxity, joint laxity, hernias; systemic involvement typical (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, lugli2022autosomalrecessivecutis pages 6-6) Plasma proline, arginine, citrulline, and ornithine can be decreased or low-normal; hyperammonemia reported in classic P5CS deficiency; considered a multifaceted urea-cycle-related disorder (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, lugli2022autosomalrecessivecutis pages 6-6) Review cited 32 neurocutaneous patients: 21 familial with homozygous/compound heterozygous variants and 11 sporadic with de novo heterozygous variants across the broader neurocutaneous spectrum; ARCL3A considered among the most severe manifestations (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) Gardeitchik et al., 2014, Eur J Hum Genet, https://doi.org/10.1038/ejhg.2013.154; Angelini et al., 2020, Neuropediatrics, https://doi.org/10.1055/s-0040-1701671; Lugli et al., 2022, Eur J Med Genet, https://doi.org/10.1016/j.ejmg.2022.104568
ALDH18A1-related de Barsy syndrome / De Barsy-like neurocutaneous syndrome / P5CS deficiency spectrum Usually autosomal recessive in classic de Barsy-like presentations, but ALDH18A1-related disease spans recessive neurocutaneous forms and de novo dominant cutis laxa phenotypes (lugli2022autosomalrecessivecutis pages 6-6, fischerzirnsak2015recurrentdenovo pages 1-2, OpenTargets Search: -ALDH18A1) Congenital to infantile in classic neurocutaneous presentations (lugli2022autosomalrecessivecutis pages 6-6, fischerzirnsak2015recurrentdenovo pages 1-2) Neurodevelopmental delay, cataracts, neurodegeneration/neurologic deficits; overlap with spastic paraplegia and broader ALDH18A1 neurocutaneous disease (OpenTargets Search: -ALDH18A1, lugli2022autosomalrecessivecutis pages 6-6, fischerzirnsak2015recurrentdenovo pages 1-2) Cutis laxa/progeroid appearance, joint laxity, connective-tissue manifestations; fat pads/retinopathy and cardiovascular involvement reported in broader ALDH18A1 literature (lugli2022autosomalrecessivecutis pages 6-6, panza2016aldh18a1genemutations pages 8-8) Hyperammonemia with reduced ornithine, citrulline, arginine, and proline described in classic P5CS deficiency; recent work also shows altered amino-acid and antioxidant metabolism, including reduced glutamate, proline, glutathione, and putrescine (fischerzirnsak2026neurocutaneousdisordersduea pages 20-22, colonna2023functionalassessmentof pages 1-1) Open Targets links ALDH18A1 to MONDO:0009053 “ALDH18A1-related de Barsy syndrome”; named disease concept overlaps substantially with ARCL3A/ADCL3 and is best understood as part of a continuous ALDH18A1/P5CS deficiency spectrum rather than a sharply separate entity (OpenTargets Search: -ALDH18A1, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) Colonna et al., 2023, Hum Mol Genet, https://doi.org/10.1093/hmg/ddac226; Fischer-Zirnsak et al., 2015, Am J Hum Genet, https://doi.org/10.1016/j.ajhg.2015.08.001; Open Targets disease association (OpenTargets Search: -ALDH18A1)

Table: This table summarizes the named ALDH18A1/P5CS deficiency entities across the spastic paraplegia and neurocutaneous spectrum, including inheritance, onset, core features, biochemical clues, and available quantitative cohort data. It is useful for comparing how SPG9 and cutis laxa/de Barsy-like presentations fit into a single mechanistic disease continuum.

3.2 Neurocutaneous / cutis laxa / de Barsy‑like phenotypes (ADCL3; ARCL3A; ALDH18A1‑related de Barsy)

Core clinical features in an autosomal‑dominant progeroid cutis laxa cohort (8 unrelated individuals) include: - Lax thin skin with visible veins and joint hyperlaxity in all individuals - Prenatal growth restriction in all; postnatal growth restriction in 7/8 - Cataracts in 6/8 - Adducted thumbs in 5/8 - Cranial vessel tortuosity in 4/8 - Psychomotor development delayed in all probands These individuals carried heterozygous de novo ALDH18A1 variants affecting Arg138 of P5CS. (fischerzirnsak2015recurrentdenovo pages 1-2, fischerzirnsak2015recurrentdenovo media 44a36465)

The same paper provides a concise abstract statement (useful for knowledge‑base evidence quoting): it reports “eight unrelated individuals … clinically diagnosed with DBS or wrinkly skin syndrome” with “three heterozygous mutations in ALDH18A1 … Arg138,” and notes reduced enzymatic activity and delayed proline accumulation, concluding that these recurrent de novo variants “cause an autosomal‑dominant form of cutis laxa with progeroid features” and “will have immediate impact on diagnostics and genetic counseling.” (fischerzirnsak2015recurrentdenovo pages 1-2)

Suggested HPO terms (examples): - Cutis laxa (HP:0000973) - Joint hypermobility (HP:0001382) - Cataract (HP:0000518) - Prenatal growth restriction / IUGR (HP:0001511) - Postnatal growth retardation (HP:0008897) - Developmental delay (HP:0001263) - Arterial/cerebral vessel tortuosity (HP:0005116)

3.3 Spastic paraplegia phenotypes (SPG9A/B)

SPG9 clinical definition and spectrum: HSP due to ALDH18A1 can be pure (lower‑limb spasticity with mild urinary symptoms and distal vibration impairment) or complicated (cognitive impairment, seizures, neuropathy, amyotrophy, short stature, vision abnormalities, etc.). (chen2021novelcompoundmissense pages 1-2)

Primary HSP series evidence: In 2015, ALDH18A1 variants were found to cause both recessive and dominant HSP; low plasma ornithine/citrulline/arginine/proline suggested P5CS deficiency, and fibroblast glutamine‑loading tests confirmed a metabolic block at P5CS. The authors propose amino‑acid chromatography in the clinico‑genetic work‑up. (coutelier2015alterationofornithine pages 1-2)

Example SPG9B natural history (case report): a child with compound heterozygous ALDH18A1 variants had tremor onset at ~2 months, developmental delay (unable to sit at 10 months, stand at 12 months), DQ 45 at age 2 years, MRI showing reduced white matter and corpus callosum hypoplasia, and slightly decreased citrulline with otherwise normal proline/ornithine/arginine and normal fasting ammonia. (kalmar2021tremorasan pages 1-2)

Suggested HPO terms (examples): - Spastic paraplegia (HP:0001258) - Hyperreflexia (HP:0001347) - Urinary urgency (HP:0000012) - Tremor (HP:0001337) - Corpus callosum hypoplasia/dysgenesis (HP:0002079) - White matter abnormality / hypomyelination (HP:0002500) - Intellectual disability / developmental delay (HP:0001249, HP:0001263)

3.4 Quality of life impact

Disease‑specific QoL instruments were not present in the retrieved ALDH18A1‑specific sources. For HSP broadly, the disease “significantly impairs … quality of life” and worsens with severity/age. (awuah2024hereditaryspasticparaplegia pages 1-2)

4. Genetic/molecular information

4.1 Causal gene

  • ALDH18A1 encodes P5CS (Δ1‑pyrroline‑5‑carboxylate synthetase), a bifunctional mitochondrial enzyme. (colonna2023functionalassessmentof pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

4.2 Pathogenic variants and variant classes (examples)

  • Autosomal dominant progeroid cutis laxa (ADCL3): recurrent heterozygous de novo missense variants affecting Arg138 (amino‑acid substitutions of the same conserved residue). (fischerzirnsak2015recurrentdenovo pages 1-2)
  • Autosomal recessive SPG9B: compound missense plus intronic splicing variants (e.g., c.880T>C p.S294P and c.-28-13A>G) with reduced P5CS concentration in plasma by ELISA. (chen2021novelcompoundmissense pages 1-2)
  • Biallelic ARCL3A / neurocutaneous: early reports include biallelic variants and biochemical evidence of impaired ornithine/proline synthesis and paradoxical hyperammonemia. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

4.3 Functional consequences and inheritance mechanisms

A 2020 review concludes that dominant mutations “cause loss‑of‑function by dominant‑negative mechanisms,” and that decreased P5CS function underlies all four named syndromes. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

A primary study of Arg138 de novo variants shows the mutant protein can interact with wild‑type P5CS but has altered sub‑mitochondrial distribution and reduced enzymatic activity, consistent with a dominant negative/complex destabilization model. (fischerzirnsak2015recurrentdenovo pages 1-2)

4.4 Population frequencies, modifier genes, epigenetics

No gnomAD‑style allele frequencies, established modifier genes, or disease‑specific epigenetic mechanisms were available in the retrieved sources.

5. Environmental information

No specific environmental toxins/lifestyle exposures were implicated in the retrieved ALDH18A1‑specific literature. Diet can modulate biochemical expression in severe cases (protein alleviating paradoxical hyperammonemia). (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

6. Mechanism / pathophysiology

6.1 Core metabolic pathway and causal chain

ALDH18A1/P5CS converts glutamate → P5C, which then supports: - Proline synthesis via PYCR1 - Ornithine synthesis via OAT, connecting to urea‑cycle amino acids (citrulline, arginine) This connects P5CS to the urea cycle and TCA cycle and to synthesis of polyamines and glutathione (redox). (colonna2023functionalassessmentof pages 1-2)

Causal chain (simplified): 1) Pathogenic ALDH18A1 variant → reduced P5CS function/complex formation (fischerzirnsak2015recurrentdenovo pages 1-2, colonna2023functionalassessmentof pages 1-1) 2) Reduced de novo proline/ornithine production → low/low‑normal plasma proline/ornithine/citrulline/arginine (trait biomarker) and, in severe cases, paradoxical hyperammonemia (coutelier2015alterationofornithine pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 5-9) 3) Downstream consequences: - Connective tissue/skin: impaired proline availability plausibly limits collagen/elastin production → cutis laxa/progeroid appearance (colonna2023functionalassessmentof pages 1-2) - Neurodevelopment/neurodegeneration: not fully understood mechanistically, but may relate to metabolic/redox stress and selective neuronal vulnerability (colonna2023functionalassessmentof pages 1-2) - Antioxidant pathway: reduced glutathione and polyamine metabolism → impaired cellular antioxidant responses (colonna2023functionalassessmentof pages 1-1)

6.2 Recent mechanistic developments (2023)

A 2023 Human Molecular Genetics functional study of a homozygous ALDH18A1 variant (p.Thr331Pro) used NMR metabolomics and showed reduced glutamate and glutamate‑derived metabolites “including proline and glutathione,” and decreased biosynthesis of putrescine (ornithine‑derived), with RNA‑seq changes in metabolic and ECM‑related genes. (colonna2023functionalassessmentof pages 1-1)

6.3 Suggested ontology terms

  • GO biological process (examples): proline biosynthetic process; ornithine biosynthetic process; glutathione metabolic process; polyamine biosynthetic process.
  • GO cellular component: mitochondrion.
  • CHEBI (examples): L‑proline, L‑ornithine, L‑arginine, L‑citrulline, glutamate, glutathione, putrescine.
  • Cell types (CL): upper motor neuron (for HSP manifestations; specific CL mapping not provided in retrieved texts).

7. Anatomical structures affected

  • Nervous system: corticospinal tract degeneration/upper motor neuron syndrome in SPG9; brain structural abnormalities (white matter, corpus callosum) in some complex cases. (awuah2024hereditaryspasticparaplegia pages 1-2, kalmar2021tremorasan pages 1-2)
  • Skin/connective tissue: cutis laxa, joint hyperlaxity. (fischerzirnsak2015recurrentdenovo pages 1-2)
  • Eye: cataracts/corneal clouding common in neurocutaneous and some SPG9 cases. (fischerzirnsak2015recurrentdenovo pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • Vasculature: cranial vessel tortuosity in a subset of ADCL3 Arg138 cases. (fischerzirnsak2015recurrentdenovo pages 1-2, fischerzirnsak2015recurrentdenovo media 44a36465)

Suggested UBERON (examples): skin; brain; corpus callosum; corticospinal tract; eye lens; arteries.

8. Temporal development

  • ARCL3A / severe neurocutaneous: typically congenital/early onset; can be very severe; associated with growth restriction and early systemic involvement. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • ADCL3 Arg138: prenatal growth restriction and early postnatal manifestations; psychomotor delay. (fischerzirnsak2015recurrentdenovo pages 1-2)
  • SPG9A/SPG9B: generally later onset upper motor neuron syndrome, with SPG9B typically more severe than SPG9A in growth/cognitive features per review synthesis. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

9. Inheritance and population

9.1 Inheritance

  • Autosomal dominant: SPG9A; ADCL3 (often de novo). (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, fischerzirnsak2015recurrentdenovo pages 1-2)
  • Autosomal recessive: SPG9B; ARCL3A. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5, chen2021novelcompoundmissense pages 1-2)

9.2 Epidemiology and statistics

ALDH18A1‑specific prevalence is not established in the retrieved sources. Available proxy statistics: - Cutis laxa (overall) estimated incidence: 1:2–400,000. (gardeitchik2014clinicalandbiochemical pages 1-2) - HSP (overall): global incidence reported as 3.6 per 100,000 in a 2024 review; HSP “does not reduce a person’s lifespan.” (awuah2024hereditaryspasticparaplegia pages 1-2) - Literature case counts compiled in a 2020 review: 32 neurocutaneous patients (21 familial biallelic; 11 sporadic de novo heterozygous) and 50 SPG9 patients (14 biallelic; 36 monoallelic). (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) - Detection benchmarking in cohorts: ALDH18A1 heterozygous variants in 2/530 screened HSP patients in one 2015 study. (coutelier2015alterationofornithine pages 5-5)

10. Diagnostics

10.1 Clinical and biochemical testing

  • Plasma amino acids: low ornithine/citrulline/arginine/proline may suggest P5CS deficiency. (coutelier2015alterationofornithine pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • Functional confirmation: glutamine loading tests in patient fibroblasts can show a metabolic block at P5CS. (coutelier2015alterationofornithine pages 1-2)
  • Protein quantification: ELISA can show significantly decreased plasma P5CS concentration in SPG9B (used to support variant pathogenicity). (chen2021novelcompoundmissense pages 1-2)

10.2 Imaging

  • Corpus callosum dysgenesis/hypoplasia and white‑matter reduction are reported in PYCR1/ALDH18A1‑related cutis laxa spectrum and in an SPG9B child. (gardeitchik2014clinicalandbiochemical pages 1-2, kalmar2021tremorasan pages 1-2)

10.3 Genetic testing and real‑world implementation

  • Whole‑exome sequencing with RNA splicing analysis was used to diagnose SPG9B and characterize intronic splice variants; splicing prediction and RNA assays were emphasized as informative. (chen2021novelcompoundmissense pages 1-2)
  • Large HSP screening approach (2015): ALDH18A1 evaluated across 530 HSP patients (435 WES; 95 panel). (coutelier2015alterationofornithine pages 5-5)
  • 2023 real‑world cohort (South Africa; 61 probands total): after initial targeted tests, remaining cases underwent WES or WGS; among 29 HSP probands, 48% were solved genetically, with ALDH18A1 represented among solved genes (single case). Variant curation used internal African‑ancestry control genomes (n=537) and ClinGen SVI guidance. (mahungu2023themutationalprofile pages 1-2)

10.4 Differential diagnosis

Within “neurometabolic cutis laxa,” strong overlap exists early in life; diagnostic discrimination can depend on metabolic testing and imaging. In a 26‑child cohort referred for suspected ARCL, mutations were found in 16 children (14 probands), and corpus callosum dysgenesis/dystonic posturing were associated with PYCR1 and ALDH18A1. (gardeitchik2014clinicalandbiochemical pages 1-2)

11. Outcomes / prognosis

  • The ALDH18A1 spectrum ranges from severe early neurocutaneous disease (including growth restriction and multisystem involvement) to later‑onset spastic paraplegia. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • HSP broadly does not reduce lifespan, but impairs quality of life. (awuah2024hereditaryspasticparaplegia pages 1-2)
  • No ALDH18A1‑specific survival curves, life expectancy estimates, or validated prognostic biomarkers were present in the retrieved sources.

12. Treatment

12.1 Metabolic interventions (evidence and rationale)

  • Early ARCL3A cases included paradoxical hyperammonemia “alleviated by protein,” suggesting dietary intake can modulate metabolic phenotype. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)
  • A 2020 review cites literature describing a “novel therapy with arginine” (full primary report not retrievable here), consistent with the pathway logic of replenishing urea‑cycle amino acids. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 18-22)

12.2 Supportive management

Disease‑specific management guidelines were not present in the retrieved corpus. For HSP broadly, there is “no disease‑modifying treatment,” implying management is symptomatic/supportive. (awuah2024hereditaryspasticparaplegia pages 1-2)

12.3 Experimental directions

A review of amino‑acid synthesis deficiencies summarizes attempted and hypothesized treatments in P5CS deficiency, including L‑glutamine escalation (minimal clinical change despite biochemical/EEG improvement) and potential therapeutic interest in nicotinamide due to NAD rescue in cellular models. (koning2017aminoacidsynthesis pages 6-7)

12.4 Clinical trials

A ClinicalTrials.gov search for ALDH18A1/P5CS did not surface any clearly ALDH18A1‑specific interventional trials in the retrieved set; returned trials were unrelated. (clinical‑trial tool output; no trial context IDs were provided for ALDH18A1‑specific disease trials).

Suggested MAXO terms (examples): - Amino acid supplementation therapy (arginine/proline/ornithine) (conceptual; limited primary evidence in retrieved texts) (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 18-22) - Physical therapy / rehabilitation therapy for spasticity (general HSP supportive care; not ALDH18A1‑specific in evidence) (awuah2024hereditaryspasticparaplegia pages 1-2)

13. Prevention

Primary prevention is not available (genetic disorder). Secondary/tertiary prevention centers on: - Early molecular diagnosis enabling anticipatory care and family counseling (fischerzirnsak2015recurrentdenovo pages 1-2) - Genetic counseling given de novo dominant cases and recessive inheritance patterns (fischerzirnsak2015recurrentdenovo pages 1-2, marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5)

14. Other species / natural disease

No naturally occurring veterinary ALDH18A1‑related analogs were identified in the retrieved sources.

15. Model organisms

The retrieved sources did not include specific ALDH18A1 animal models. The 2023 functional study used patient fibroblasts and an ALDH18A1‑null human embryonic kidney cell system expressing variant P5CS for mechanistic validation. (colonna2023functionalassessmentof pages 1-1)

Expert opinion / analysis (synthesis across authoritative sources)

1) Nosology: Multiple expert sources argue ALDH18A1 disorders should be conceptualized as a single P5CS deficiency continuum, with “essentially different spectra of ALDH18A1 mutations” producing dominant/recessive and neurocutaneous/motor presentations but sharing decreased P5CS function. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 1-5) 2) Diagnostics: ALDH18A1 is unusual among HSP genes in having a plausible trait biomarker (low urea‑cycle amino acids/proline) and functional confirmation tests in fibroblasts; therefore adding plasma amino‑acid chromatography can be rational in the diagnostic work‑up, especially when genetic results are uncertain. (coutelier2015alterationofornithine pages 1-2) 3) Current research direction: The 2023 multi‑omics study shifts the field from single‑metabolite thinking to system‑level metabolic and redox pathway disruption (glutathione/putrescine), suggesting new biomarker candidates and therapeutic hypotheses (antioxidant/NAD‑related interventions) that need clinical validation. (colonna2023functionalassessmentof pages 1-1, koning2017aminoacidsynthesis pages 6-7)

Key figure/table evidence

A key table summarizing frequency of clinical findings in the eight‑person Arg138 de novo cohort is available and should be consulted for structured phenotyping. (fischerzirnsak2015recurrentdenovo media 44a36465)

Limitations of this report (evidence gaps)

  • Orphanet/ICD‑10/ICD‑11/MeSH identifiers and ALDH18A1‑specific prevalence/incidence were not retrievable via the provided tools in this run.
  • The primary 2012 “novel therapy with arginine” study was not obtainable, so arginine treatment details (dose/outcomes) cannot be stated beyond citation‑level mention in a review. (marco‐marin2020δ1‐pyrroline‐5‐carboxylatesynthetasedeficiency pages 18-22)
  • No ALDH18A1‑specific interventional clinical trials were identified in the retrieved ClinicalTrials.gov results.

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