Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome

Mendelian MONDO:0100247 Pathograph 16 Show in embeddings browser

Multiple congenital anomalies-hypotonia-seizures syndrome (MCAHS) is a genetically heterogeneous group of severe, early-onset neurodevelopmental disorders caused by inherited defects in the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor, the glycolipid moiety that tethers more than 150 different proteins to the outer face of the plasma membrane. The three classically delineated subtypes are defined by the affected GPI-pathway gene: MCAHS1 (PIGN), MCAHS2 (PIGA), and MCAHS3 (PIGT). All share a stereotyped clinical core of multiple congenital anomalies, profound neonatal/infantile hypotonia, early-onset drug-resistant seizures that frequently evolve into a developmental and epileptic encephalopathy, severe-to-profound global developmental delay/intellectual disability, dysmorphic features, and a high early-childhood mortality. MCAHS sits within the broader family of inherited GPI deficiencies (GPIBD) alongside the hyperphosphatasia-intellectual disability syndromes (Mabry syndrome/HPMRS); MCAHS is distinguished clinically by the predominance of congenital malformations and epileptic encephalopathy and by the absence of the persistent hyperphosphatasia that defines HPMRS (serum alkaline phosphatase in MCAHS is typically normal or, in the PIGT subtype, low). Because complete loss of GPI-anchor biosynthesis is embryonic-lethal, viable patients retain partial pathway activity from hypomorphic alleles. Note: several quantitative phenotype frequencies in this umbrella entry are drawn from the largest natural-history cohorts of inherited GPI deficiency as a whole (which also include the HPMRS/remodelling genes), not from MCAHS (PIGN/PIGA/PIGT) in isolation; they are attributed as such in the evidence explanations.

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2
Inheritance
6
Pathophys.
22
Phenotypes
1
Hypotheses
16
Pathograph
3
Genes
5
Medical Actions
3
Subtypes
2
Differentials
3
References
1
Deep Research
👪

Inheritance

2
Autosomal recessive HP:0000007
MCAHS1 (PIGN) and MCAHS3 (PIGT) are inherited in an autosomal recessive manner from biallelic hypomorphic (partial loss-of-function) variants; recurrence risk is 25% per pregnancy.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:21493957 SUPPORT Human Clinical
"This study reports on a hitherto undescribed autosomal recessive syndrome characterised by dysmorphic features and multiple congenital anomalies together with severe neurological impairment, chorea and seizures leading to early death"
Establishes MCAHS1 (PIGN) as an autosomal recessive multiple-congenital-anomaly syndrome.
PMID:23636107 SUPPORT Human Clinical
"We identified mutations in PIGT as the cause of a novel autosomal recessive intellectual disability syndrome."
Establishes MCAHS3 (PIGT) as an autosomal recessive syndrome.
X-linked recessive HP:0001419
MCAHS2 is caused by hemizygous variants in PIGA, which lies on the X chromosome (Xp22.2); affected individuals are predominantly males inheriting a hypomorphic allele from a carrier mother.
X-linked recessive inheritance
Show evidence (1 reference)
PMID:22305531 SUPPORT Human Clinical
"We report a family with an X-linked lethal disorder involving cleft palate, neonatal seizures, contractures, central nervous system (CNS) structural malformations, and other anomalies."
Establishes the X-linked inheritance and germline-PIGA basis of MCAHS2.
◆

Subtypes

3
MCAHS1 (PIGN) MONDO:0013563
PIGN hgnc:8967 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in PIGN (hgnc:8967). hgnc:8967 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal recessive subtype caused by biallelic PIGN variants. PIGN encodes the ethanolamine-phosphate transferase 1 (GPI-EtNP transferase) that adds the first ethanolamine phosphate to the first mannose of the GPI glycan in the endoplasmic reticulum. Presentations range from a lethal neonatal multiple-congenital-anomaly phenotype (including diaphragmatic hernia and cardiac and anorectal malformations) to a milder epileptic-encephalopathy phenotype with longer survival.
MCAHS2 (PIGA) MONDO:0010466
PIGA hgnc:8957 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in PIGA (hgnc:8957). hgnc:8957 is a gene from the HUGO Gene Nomenclature Committee.
X-linked recessive subtype caused by hemizygous PIGA variants (also designated developmental and epileptic encephalopathy 20, DEE20, and GPI biosynthesis defect 4, GPIBD4). PIGA encodes the catalytic subunit of the GPI-N-acetylglucosaminyl transferase complex that catalyzes the very first, committed step of GPI-anchor assembly. The phenotype spans a severe/lethal neonatal form with structural brain anomalies to an early-infantile epileptic encephalopathy; germline PIGA loss is mechanistically distinct from the somatic PIGA mutation that causes paroxysmal nocturnal hemoglobinuria.
MCAHS3 (PIGT) MONDO:0014165
PIGT hgnc:14938 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in PIGT (hgnc:14938). hgnc:14938 is a gene from the HUGO Gene Nomenclature Committee.
Autosomal recessive subtype caused by biallelic PIGT variants. PIGT encodes a subunit of the GPI transamidase complex that attaches the preassembled GPI anchor to the C-terminus of target proteins. MCAHS3 is characterized by neonatal hypotonia, infantile-onset seizures, progressive cerebral and cerebellar atrophy, skeletal abnormalities, and characteristically low (rather than elevated) serum alkaline phosphatase; some PIGT variants additionally produce an autoinflammatory phenotype.
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Mechanistic Hypotheses

1
FOLR1 Cerebral Folate Deficiency Model
folr1_cerebral_folate EMERGING
Because the folate receptor FOLR1 is itself a GPI-anchored protein, reduced cell-surface FOLR1 in GPI-anchor deficiency is proposed to impair receptor-mediated folate transport into the CNS, contributing to the neurodevelopmental/epileptic phenotype and providing a rationale for a folinic-acid trial. This mirrors the better-established TNAP/vitamin-B6 mechanism, but direct MCAHS-specific evidence for a causal cerebral-folate-deficiency arm is currently limited, so it is modeled as emerging rather than canonical.
Pathograph links
Deficient Cell-Surface GPI-Anchored Protein Expression -> Reduced Surface Folate Receptor and Cerebral Folate Delivery Loss of surface GPI-anchored folate receptor (FOLR1) may impair cerebral folate delivery.
Reduced Surface Folate Receptor and Cerebral Folate Delivery -> Neuronal Dysfunction and Epileptic Encephalopathy
⚙

Pathophysiology

6
GPI Anchor Biosynthesis Defect
Hypomorphic variants in a GPI-pathway gene (PIGA at the initiating GlcNAc-transferase step, PIGN at ethanolamine-phosphate transfer, or PIGT at the transamidase attachment step) impair the stepwise endoplasmic-reticulum assembly and protein attachment of the GPI anchor. Because the complete pathway is essential, viable disease results from partial (not total) loss of function.
GPI anchor biosynthetic process GO:0006506 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased GPI anchor biosynthetic process (GO:0006506). GO:0006506 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Deficient Cell-Surface GPI-Anchored Protein Expression
Show evidence (3 references)
PMID:22305531 SUPPORT Human Clinical
"Phosphatidylinositol glycan class A (PIGA) is involved in the first step of glycosylphosphatidylinositol (GPI) biosynthesis."
PIGA (MCAHS2) acts at the initiating, committed step of GPI-anchor biosynthesis.
PMID:21493957 SUPPORT Human Clinical
"in PIGN, which encodes glycosylphosphatidylinositol (GPI) ethanolamine phosphate transferase 1, a protein involved in GPI-anchor biosynthesis"
PIGN (MCAHS1) encodes an ethanolamine-phosphate transferase in the GPI-anchor pathway.
PMID:23636107 SUPPORT Human Clinical
"PIGT encodes phosphatidylinositol-glycan biosynthesis class T (PIG-T) protein, which is a subunit of the transamidase complex that catalyses the attachment of proteins to GPI."
PIGT (MCAHS3) is part of the transamidase that attaches the GPI anchor to protein.
Deficient Cell-Surface GPI-Anchored Protein Expression
Reduced GPI-anchor availability lowers the cell-surface expression of the >150 GPI-anchored proteins, including folate receptor, CD59, CD16, CD24, and GPI-anchored alkaline phosphatase. Loss of these surface proteins across many cell lineages underlies the multisystem, neurodevelopmental phenotype; flow-cytometric reduction of surface GPI-anchored proteins on blood cells is a diagnostic biomarker of the pathway defect.
FOLR1 Cerebral Folate Deficiency Model
neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
Downstream
Impaired TNAP-Dependent Vitamin B6 Activation Loss of surface GPI-anchored TNAP impairs vitamin B6 (PLP) activation.
Reduced Surface Folate Receptor and Cerebral Folate Delivery Loss of surface GPI-anchored folate receptor (FOLR1) may impair cerebral folate delivery. FOLR1 Cerebral Folate Deficiency Model
Neuronal Dysfunction and Epileptic Encephalopathy
Multisystem Developmental Disruption
Show evidence (3 references)
PMID:21493957 SUPPORT Human Clinical
"The expression of GPI linked protein CD59 on fibroblasts from patients as compared to that in a control individual showed a 10-fold reduction in expression, confirming the pathogenic consequences of the mutation on GPI dependent protein expression."
Demonstrates reduced surface GPI-anchored protein (CD59) as the cellular consequence of the pathway defect in MCAHS1.
PMID:23636107 SUPPORT Human Clinical
"granulocytes from the patients had reduced levels of the GPI anchored protein CD16b, supporting pathogenicity of the mutation."
Reduced surface GPI-anchored protein (CD16b) confirms the same cellular defect in MCAHS3.
PMID:22305531 SUPPORT In Vitro
"Transfection of a mutant p.Arg412(∗) PIGA construct into PIGA-null cells showed partial restoration of GPI-anchored proteins."
Functional rescue assay shows the MCAHS2 PIGA allele retains partial GPI-anchor biosynthesis, reducing surface GPI-anchored proteins rather than abolishing them.
Reduced Surface Folate Receptor and Cerebral Folate Delivery
The folate receptor (FOLR1) is itself a GPI-anchored protein. Reduced cell-surface FOLR1 may impair receptor-mediated folate transport into the CNS, a hypothesized parallel to the TNAP/vitamin-B6 mechanism and the rationale for a folinic-acid (5-formyltetrahydrofolate) trial when a cerebral folate disturbance is demonstrated. Direct MCAHS-specific evidence for this arm is currently limited, so it is modeled as an emerging/hypothesized mechanism rather than an established one.
FOLR1 Cerebral Folate Deficiency Model
Downstream
Neuronal Dysfunction and Epileptic Encephalopathy FOLR1 Cerebral Folate Deficiency Model
Show evidence (1 reference)
PMID:35058872 SUPPORT Other
"receptors (f.e. folate receptors, GDNF receptor alphas"
Confirms the folate receptor is among the GPI-anchored proteins whose surface display depends on the intact anchor (background biochemistry from a systematic review).
Impaired TNAP-Dependent Vitamin B6 Activation
Tissue-nonspecific alkaline phosphatase (TNAP) is itself a GPI-anchored protein. Reduced cell-surface TNAP impairs the extracellular dephosphorylation of pyridoxal 5'-phosphate (PLP) to pyridoxal that is required for cellular vitamin B6 uptake; intracellular re-phosphorylation to PLP then falls, reducing the activity of PLP-dependent enzymes including those of glutamate/GABA metabolism. This provides a distinctive mechanistic rationale for the vitamin B6 (pyridoxine) responsiveness observed in a subset of inherited GPI-deficiency seizures, and is mechanistically separate from the elevated serum ALP (hyperphosphatasia) seen in the HPMRS branch.
alkaline phosphatase activity GO:0004035 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased alkaline phosphatase activity (GO:0004035). GO:0004035 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Neuronal Dysfunction and Epileptic Encephalopathy
Show evidence (2 references)
PMID:39081219 SUPPORT Other
"The main active form, PLP, undergoes initial dephosphorylation by cell-surface alkaline phosphatase, particularly the tissue nonspecific alkaline phosphatase isozyme (TNAP), to yield free pyridoxal, which is then taken up by cells"
Establishes that cell-surface (GPI-anchored) TNAP mediates the extracellular step required for vitamin B6 uptake.
PMID:39081219 SUPPORT Other
"In IGD patients, the absence or reduction of cell-surface TNAP diminishes PLP uptake and subsequently affects the activities of PLP-dependent enzymes."
Links reduced surface TNAP in GPI deficiency to impaired PLP-dependent enzyme activity, the basis of B6-responsive seizures.
Neuronal Dysfunction and Epileptic Encephalopathy
Deficiency of GPI-anchored proteins critical to neuronal development and synaptic function produces cortical network hyperexcitability, drug-resistant early-onset seizures, and a developmental and epileptic encephalopathy that drives the severe cognitive impairment.
neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
Downstream
Seizures Cortical network hyperexcitability manifests as early-onset seizures.
Epileptic encephalopathy Frequent epileptiform activity drives the developmental and epileptic encephalopathy.
Profound global developmental delay The encephalopathy and neuronal dysfunction produce severe developmental impairment.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Individuals with variants in synthesis stage genes of the GPI-AP exhibited a significantly shorter time to seizure onset than individuals with variants in transamidase and remodelling stage genes of the GPI-AP"
Genotype-phenotype correlation tying the position of the defect in the GPI pathway to seizure-onset timing.
Multisystem Developmental Disruption
Deficient GPI-anchored protein function during embryogenesis and postnatal life produces the multiple congenital anomalies, dysmorphic features, hypotonia, visceral and skeletal malformations, and failure to thrive that complete the MCAHS phenotype.
Downstream
Facial dysmorphism Disrupted development produces the nonspecific dysmorphic facial gestalt.
Gastrointestinal anomalies Multisystem developmental disruption includes gastrointestinal malformations.
Cardiac anomalies Multisystem developmental disruption includes congenital cardiac malformations.
Renal anomalies Multisystem developmental disruption includes renal/urinary-tract malformations.
Hypotonia Central hypotonia is a core manifestation of the disrupted neurodevelopment.
Show evidence (2 references)
PMID:38456468 SUPPORT Human Clinical
"Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies."
Documents the multisystem congenital-anomaly burden across organ systems.
PMID:38456468 SUPPORT Human Clinical
"Though dysmorphic features were appreciated in 82%, no single dysmorphic feature had a prevalence >30%, indicating substantial phenotypic heterogeneity."
Supports the frequent but nonspecific dysmorphism of the syndrome.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

22
Cardiovascular 1
Cardiac anomalies OCCASIONAL Abnormal heart morphology HP:0001627 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal heart morphology (HP:0001627). HP:0001627 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies."
Cardiac anomalies were present in 19% of the cohort.
Digestive 2
Gastrointestinal anomalies FREQUENT Abnormality of the gastrointestinal tract HP:0011024 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormality of the gastrointestinal tract (HP:0011024). HP:0011024 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies."
Gastrointestinal anomalies were the most common systemic involvement (66%).
Feeding difficulties HP:0011968 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Feeding difficulties (HP:0011968). HP:0011968 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Individuals with a developmental epileptic encephalopathy (51%) were at greater risk of intractable epilepsy (P = 0.003), non-ambulance (P = 0.035), ongoing enteral feeds (P < 0.001) and cortical visual impairment (P = 0.007)."
Ongoing enteral feeding requirement (a marker of severe feeding difficulty) was significantly associated with the encephalopathy subgroup.
Genitourinary 1
Renal anomalies OCCASIONAL Abnormality of the kidney HP:0000077 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormality of the kidney (HP:0000077). HP:0000077 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies."
Renal anomalies were present in 14% of the cohort.
Head and Neck 1
Facial dysmorphism VERY_FREQUENT Abnormal facial shape HP:0001999 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal facial shape (HP:0001999). HP:0001999 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Though dysmorphic features were appreciated in 82%, no single dysmorphic feature had a prevalence >30%, indicating substantial phenotypic heterogeneity."
Dysmorphic features were present in 82% of the cohort but are individually nonspecific.
Musculoskeletal 2
Hypotonia FREQUENT 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:38456468 SUPPORT Human Clinical
"Core clinical features were developmental delay or intellectual disability (DD/ID, 90%), seizures (83%), hypotonia (72%) and motor symptoms (64%)."
Hypotonia was present in 72% of the largest inherited GPI-deficiency cohort (maps to FREQUENT).
Nervous System 11
Seizures VERY_FREQUENT HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (4 references)
PMID:38456468 SUPPORT Human Clinical
"Core clinical features were developmental delay or intellectual disability (DD/ID, 90%), seizures (83%), hypotonia (72%) and motor symptoms (64%)."
Seizures occurred in 83% of the largest inherited GPI-deficiency cohort (maps to VERY_FREQUENT).
PMID:38456468 SUPPORT Human Clinical
"Median age at seizure onset was 6 months."
Documents the early-infantile median seizure onset.
PMID:22305531 SUPPORT Human Clinical
"We report a family with an X-linked lethal disorder involving cleft palate, neonatal seizures, contractures, central nervous system (CNS) structural malformations, and other anomalies."
Neonatal seizures are a core feature of MCAHS2.
+ 1 more reference
Epileptic spasms HP:0011097 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Epileptic spasm (HP:0011097). HP:0011097 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35058872 SUPPORT Human Clinical
"specifically epileptic spasms (10/36), atonic (3/36), and myoclonic (2/36) seizures"
Epileptic spasms are documented among the focal seizure types in PIGA-related disease.
Profound global developmental delay FREQUENT HP:0012736 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Profound global developmental delay (HP:0012736). HP:0012736 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"The majority of individuals experienced delayed or absent speech (95%), motor delay with non-ambulance (64%), and severe-to-profound DD/ID (59%)."
Most affected individuals had severe-to-profound developmental impairment.
Intellectual disability VERY_FREQUENT 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:38456468 SUPPORT Human Clinical
"Core clinical features were developmental delay or intellectual disability (DD/ID, 90%), seizures (83%), hypotonia (72%) and motor symptoms (64%)."
Developmental delay/intellectual disability was the most common feature (90%) in the largest inherited GPI-deficiency cohort (maps to VERY_FREQUENT).
PMID:23636107 SUPPORT Human Clinical
"characterised by distinct facial features, intellectual disability, hypotonia and seizures, in combination with abnormal skeletal, endocrine, and ophthalmologic findings"
Intellectual disability is a defining feature of the GPI-deficiency (MCAHS3) phenotype.
Cerebral atrophy FREQUENT HP:0002059 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral atrophy (HP:0002059), qualified as course progressive. HP:0002059 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (2 references)
PMID:38456468 SUPPORT Human Clinical
"Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%)."
Cerebral atrophy (75%) and cerebellar atrophy (60%) were common neuroimaging findings.
PMID:38456468 SUPPORT Human Clinical
"Serial neuroimaging showed progressive cerebral volume loss in 87.5% and progressive cerebellar atrophy in 70.8%, indicating a neurodegenerative process."
Establishes the progressive/neurodegenerative course of the atrophy.
Cerebellar atrophy FREQUENT HP:0001272 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebellar atrophy (HP:0001272), qualified as course progressive. HP:0001272 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%)."
Cerebellar atrophy was present in 60% of the cohort.
Corpus callosum anomaly FREQUENT Abnormal corpus callosum morphology HP:0001273 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal corpus callosum morphology (HP:0001273). HP:0001273 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%)."
Callosal anomalies were present in 57% of the cohort.
Chorea HP:0002072 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Chorea (HP:0002072). HP:0002072 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:21493957 SUPPORT Human Clinical
"This study reports on a hitherto undescribed autosomal recessive syndrome characterised by dysmorphic features and multiple congenital anomalies together with severe neurological impairment, chorea and seizures leading to early death"
Chorea is documented as part of the neurological phenotype in MCAHS1.
Other 4
Epileptic encephalopathy HP:0200134 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Epileptic encephalopathy (HP:0200134). HP:0200134 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Individuals with a developmental epileptic encephalopathy (51%) were at greater risk of intractable epilepsy (P = 0.003), non-ambulance (P = 0.035), ongoing enteral feeds (P < 0.001) and cortical visual impairment (P = 0.007)."
About half of the cohort had a developmental and epileptic encephalopathy, which predicted worse outcomes.
Cortical visual impairment Cerebral visual impairment HP:0100704 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral visual impairment (HP:0100704). HP:0100704 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Individuals with a developmental epileptic encephalopathy (51%) were at greater risk of intractable epilepsy (P = 0.003), non-ambulance (P = 0.035), ongoing enteral feeds (P < 0.001) and cortical visual impairment (P = 0.007)."
Cortical visual impairment is enriched in the developmental-and-epileptic-encephalopathy subgroup.
Symmetric restricted diffusion of the central tegmental tracts FREQUENT
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%)."
A prognostically significant neuroimaging feature present in 60% of the cohort.
🧬

Genetic Associations

3
PIGA
Gene: PIGA hgnc:8957 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PIGA (hgnc:8957). hgnc:8957 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (1 reference)
PMID:22305531 SUPPORT Human Clinical
"An X chromosome exome next-generation sequencing screen identified a single nonsense PIGA mutation, c.1234C>T, which predicts p.Arg412(∗)."
Identifies germline PIGA as the cause of the X-linked MCAHS2 phenotype.
PIGN
Gene: PIGN hgnc:8967 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PIGN (hgnc:8967). hgnc:8967 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (1 reference)
PMID:21493957 SUPPORT Human Clinical
"Arginine at the position 709 is a highly evolutionarily conserved residue located in the PigN domain."
Supports pathogenicity of the p.Arg709Gln PIGN variant identified as the cause of MCAHS1.
PIGT
Gene: PIGT hgnc:14938 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PIGT (hgnc:14938). hgnc:14938 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (1 reference)
PMID:23636107 SUPPORT Human Clinical
"The results from WES identified a homozygous mutation, c.547A>C (p.Thr183Pro), in PIGT"
Identifies biallelic PIGT as the cause of MCAHS3.
💊

Medical Actions

5
Antiseizure medication
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: anticonvulsant agent NCIT:C264 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses anticonvulsant agent (NCIT:C264). NCIT:C264 is a therapeutic agent from the NCI Thesaurus.
Symptomatic management of the frequently drug-resistant epilepsy; the most commonly used agents in reported cohorts are valproic acid, levetiracetam, and topiramate.
Show evidence (1 reference)
PMID:35058872 SUPPORT Human Clinical
"The most commonly applied anti-epileptic drugs (AEDs) were valproic acid (N = 60), levetiracetam (N = 50), and topiramate (N = 30)."
Documents the antiseizure medications most commonly used across the pooled GPI-deficiency cohort.
Ketogenic diet
Action: Ketogenic DietNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Ketogenic Diet (NCIT:C173168). NCIT:C173168 is a clinical intervention from the NCI Thesaurus. NCIT:C173168
A ketogenic (ketone) diet has been reported effective for seizure control in some children with PIGA-related disease.
Show evidence (1 reference)
PMID:35058872 SUPPORT Human Clinical
"Based on some case reports, ketone diet is effective in children with a PIGA gene mutation"
Reports ketogenic-diet efficacy for seizures in PIGA/MCAHS2.
Folinic acid
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: folinic acid CHEBI:15640 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses folinic acid, annotated with 5-formyltetrahydrofolic acid (CHEBI:15640). CHEBI:15640 is a therapeutic agent from Chemical Entities of Biological Interest.
Folinic acid (5-formyltetrahydrofolate) may be considered when a cerebral folate disturbance is demonstrated or strongly suspected, given that the folate receptor (FOLR1) is a GPI-anchored protein; MCAHS-specific response rates are not established.
Mechanism Target:
MODULATES Reduced Surface Folate Receptor and Cerebral Folate Delivery — Folinic acid supplementation may compensate for reduced FOLR1-mediated cerebral folate delivery; the benefit in MCAHS specifically remains unproven.
Vitamin B6 (pyridoxine) supplementation
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: pyridoxine CHEBI:16709 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses pyridoxine (CHEBI:16709). CHEBI:16709 is a therapeutic agent from Chemical Entities of Biological Interest.
High-dose vitamin B6 (pyridoxine, typically 20-30 mg/kg) has shown efficacy in reducing seizure activity in a subset of individuals with inherited GPI deficiency, consistent with the impaired TNAP-dependent PLP/vitamin B6 activation mechanism.
Mechanism Target:
MODULATES Impaired TNAP-Dependent Vitamin B6 Activation — Exogenous vitamin B6 raises substrate availability to compensate for reduced TNAP-mediated PLP processing, restoring PLP-dependent enzyme activity.
Show evidence (1 reference)
PMID:39081219 SUPPORT Other
"Studies have demonstrated that vitamin B6 supplementation significantly improves outcomes in IGD by reducing seizure activity."
Supports vitamin B6 as a mechanism-directed therapy acting on the TNAP/PLP pathway.
Supportive and multidisciplinary care
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. NCIT:C15747
Supportive care including nutritional support/tube feeding, physiotherapy, and management of congenital malformations.
🔬

Biochemical Markers

1
Serum alkaline phosphatase
Show evidence (1 reference)
PMID:39081219 SUPPORT Other
"the serum level of alkaline phosphatase (ALP) serves as another biomarker and clinical evidence for IGD"
Establishes serum ALP as a biomarker of inherited GPI deficiency.
🔬

Diagnosis

1
Flow-cytometric GPI-anchored protein assay
Beyond molecular genetic confirmation, the GPI defect is validated functionally by flow cytometry of cell-surface GPI-anchored proteins (commonly CD55, CD59, and CD16, plus pan-specific FLAER) on blood cells or skin fibroblasts. Some variants reduce only a subset of GPI-anchored proteins (e.g., transamidase-stage PIGT lowers granulocyte CD16 while sparing CD55/CD59), and standard serum-transferrin CDG screening does not detect GPI-anchor defects.
Show evidence (2 references)
PMID:39081219 SUPPORT Other
"Flow cytometry analysis can detect the levels of certain GPI-APs on the cell surface, which is typically performed on blood cells and skin fibroblasts."
Establishes flow cytometry of surface GPI-anchored proteins as the functional confirmatory assay.
PMID:39081219 SUPPORT Other
"In cases with dysfunctional PIGS, PIGT, and PIGU, there is a decrease in cell-surface CD16 on granulocytes, whereas CD55 and CD59 remain unaffected"
Documents the variant-specific GPI-AP pattern (PIGT lowers granulocyte CD16 while sparing CD55/CD59) relevant to test interpretation.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
Individually ultra-rare disorders; the largest single multinational cohort of inherited GPI deficiencies to date comprised 83 individuals from 75 families.
Show evidence (1 reference)
PMID:38456468 SUPPORT Human Clinical
"we systematically analyse the molecular spectrum, phenotypic characteristics and natural history of 83 individuals from 75 unique families with IGDs, including 70 newly reported individuals; the largest single cohort to date"
Establishes the rarity and scale of the largest reported inherited GPI-deficiency cohort.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome:

Hyperphosphatasia with intellectual disability syndrome (Mabry syndrome/HPMRS)
Overlapping Features The other major branch of inherited GPI deficiency (genes PIGV, PIGO, PGAP2, PGAP3, PIGW, PIGY). HPMRS shares developmental delay, seizures, hypotonia and dysmorphism but is defined by persistently elevated serum alkaline phosphatase (hyperphosphatasia), which is characteristically absent in MCAHS.
Distinguishing Features
  • Persistently elevated serum alkaline phosphatase (normal in MCAHS; low in the PIGT/MCAHS3 subtype).
Other early-infantile developmental and epileptic encephalopathies
Overlapping Features Non-GPI genetic epileptic encephalopathies (e.g., channelopathies and synaptic-gene DEEs) overlap in the seizure and developmental phenotype but lack a GPI-anchor biosynthesis defect and the associated reduction of surface GPI-anchored proteins on flow cytometry.
Distinguishing Features
  • Normal cell-surface expression of GPI-anchored proteins (reduced in MCAHS).
{ }

Source YAML

click to show 
name: Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome
creation_date: "2026-08-14T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: multiple congenital anomalies-hypotonia-seizures syndrome
  term:
    id: MONDO:0100247
    label: multiple congenital anomalies-hypotonia-seizures syndrome
synonyms:
- MCAHS
- inherited GPI deficiency
- glycosylphosphatidylinositol biosynthesis defect
- GPI anchor deficiency
description: >-
  Multiple congenital anomalies-hypotonia-seizures syndrome (MCAHS) is a genetically
  heterogeneous group of severe, early-onset neurodevelopmental disorders caused by
  inherited defects in the biosynthesis of the glycosylphosphatidylinositol (GPI)
  anchor, the glycolipid moiety that tethers more than 150 different proteins to the
  outer face of the plasma membrane. The three classically delineated subtypes are
  defined by the affected GPI-pathway gene: MCAHS1 (PIGN), MCAHS2 (PIGA), and MCAHS3
  (PIGT). All share a stereotyped clinical core of multiple congenital anomalies,
  profound neonatal/infantile hypotonia, early-onset drug-resistant seizures that
  frequently evolve into a developmental and epileptic encephalopathy, severe-to-profound
  global developmental delay/intellectual disability, dysmorphic features, and a high
  early-childhood mortality. MCAHS sits within the broader family of inherited GPI
  deficiencies (GPIBD) alongside the hyperphosphatasia-intellectual disability
  syndromes (Mabry syndrome/HPMRS); MCAHS is distinguished clinically by the
  predominance of congenital malformations and epileptic encephalopathy and by the
  absence of the persistent hyperphosphatasia that defines HPMRS (serum alkaline
  phosphatase in MCAHS is typically normal or, in the PIGT subtype, low). Because
  complete loss of GPI-anchor biosynthesis is embryonic-lethal, viable patients retain
  partial pathway activity from hypomorphic alleles. Note: several quantitative
  phenotype frequencies in this umbrella entry are drawn from the largest natural-history
  cohorts of inherited GPI deficiency as a whole (which also include the HPMRS/remodelling
  genes), not from MCAHS (PIGN/PIGA/PIGT) in isolation; they are attributed as such in
  the evidence explanations.

inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    MCAHS1 (PIGN) and MCAHS3 (PIGT) are inherited in an autosomal recessive manner
    from biallelic hypomorphic (partial loss-of-function) variants; recurrence risk
    is 25% per pregnancy.
  evidence:
  - reference: PMID:21493957
    reference_title: "Multiple congenital anomalies-hypotonia-seizures syndrome is caused by a mutation in PIGN."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study reports on a hitherto undescribed autosomal recessive syndrome characterised by dysmorphic features and multiple congenital anomalies together with severe neurological impairment, chorea and seizures leading to early death"
    explanation: Establishes MCAHS1 (PIGN) as an autosomal recessive multiple-congenital-anomaly syndrome.
  - reference: PMID:23636107
    reference_title: "A novel intellectual disability syndrome caused by GPI anchor deficiency due to homozygous mutations in PIGT."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified mutations in PIGT as the cause of a novel autosomal recessive intellectual disability syndrome."
    explanation: Establishes MCAHS3 (PIGT) as an autosomal recessive syndrome.
- name: X-linked recessive
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  description: >-
    MCAHS2 is caused by hemizygous variants in PIGA, which lies on the X chromosome
    (Xp22.2); affected individuals are predominantly males inheriting a hypomorphic
    allele from a carrier mother.
  evidence:
  - reference: PMID:22305531
    reference_title: "The phenotype of a germline mutation in PIGA: the gene somatically mutated in paroxysmal nocturnal hemoglobinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a family with an X-linked lethal disorder involving cleft palate, neonatal seizures, contractures, central nervous system (CNS) structural malformations, and other anomalies."
    explanation: Establishes the X-linked inheritance and germline-PIGA basis of MCAHS2.

has_subtypes:
- name: MCAHS1
  display_name: MCAHS1 (PIGN)
  description: >-
    Autosomal recessive subtype caused by biallelic PIGN variants. PIGN encodes the
    ethanolamine-phosphate transferase 1 (GPI-EtNP transferase) that adds the first
    ethanolamine phosphate to the first mannose of the GPI glycan in the endoplasmic
    reticulum. Presentations range from a lethal neonatal multiple-congenital-anomaly
    phenotype (including diaphragmatic hernia and cardiac and anorectal malformations)
    to a milder epileptic-encephalopathy phenotype with longer survival.
  subtype_term:
    preferred_term: multiple congenital anomalies-hypotonia-seizures syndrome 1
    term:
      id: MONDO:0013563
      label: multiple congenital anomalies-hypotonia-seizures syndrome 1
  genes:
  - preferred_term: PIGN
    term:
      id: hgnc:8967
      label: PIGN
- name: MCAHS2
  display_name: MCAHS2 (PIGA)
  description: >-
    X-linked recessive subtype caused by hemizygous PIGA variants (also designated
    developmental and epileptic encephalopathy 20, DEE20, and GPI biosynthesis defect
    4, GPIBD4). PIGA encodes the catalytic subunit of the GPI-N-acetylglucosaminyl
    transferase complex that catalyzes the very first, committed step of GPI-anchor
    assembly. The phenotype spans a severe/lethal neonatal form with structural brain
    anomalies to an early-infantile epileptic encephalopathy; germline PIGA loss is
    mechanistically distinct from the somatic PIGA mutation that causes paroxysmal
    nocturnal hemoglobinuria.
  subtype_term:
    preferred_term: multiple congenital anomalies-hypotonia-seizures syndrome 2
    term:
      id: MONDO:0010466
      label: multiple congenital anomalies-hypotonia-seizures syndrome 2
  genes:
  - preferred_term: PIGA
    term:
      id: hgnc:8957
      label: PIGA
- name: MCAHS3
  display_name: MCAHS3 (PIGT)
  description: >-
    Autosomal recessive subtype caused by biallelic PIGT variants. PIGT encodes a
    subunit of the GPI transamidase complex that attaches the preassembled GPI anchor
    to the C-terminus of target proteins. MCAHS3 is characterized by neonatal
    hypotonia, infantile-onset seizures, progressive cerebral and cerebellar atrophy,
    skeletal abnormalities, and characteristically low (rather than elevated) serum
    alkaline phosphatase; some PIGT variants additionally produce an autoinflammatory
    phenotype.
  subtype_term:
    preferred_term: multiple congenital anomalies-hypotonia-seizures syndrome 3
    term:
      id: MONDO:0014165
      label: multiple congenital anomalies-hypotonia-seizures syndrome 3
  genes:
  - preferred_term: PIGT
    term:
      id: hgnc:14938
      label: PIGT

pathophysiology:
- name: GPI Anchor Biosynthesis Defect
  biological_scale: MOLECULAR
  description: >-
    Hypomorphic variants in a GPI-pathway gene (PIGA at the initiating
    GlcNAc-transferase step, PIGN at ethanolamine-phosphate transfer, or PIGT at the
    transamidase attachment step) impair the stepwise endoplasmic-reticulum assembly
    and protein attachment of the GPI anchor. Because the complete pathway is
    essential, viable disease results from partial (not total) loss of function.
  biological_processes:
  - preferred_term: GPI anchor biosynthetic process
    modifier: DECREASED
    term:
      id: GO:0006506
      label: GPI anchor biosynthetic process
  evidence:
  - reference: PMID:22305531
    reference_title: "The phenotype of a germline mutation in PIGA: the gene somatically mutated in paroxysmal nocturnal hemoglobinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Phosphatidylinositol glycan class A (PIGA) is involved in the first step of glycosylphosphatidylinositol (GPI) biosynthesis."
    explanation: PIGA (MCAHS2) acts at the initiating, committed step of GPI-anchor biosynthesis.
  - reference: PMID:21493957
    reference_title: "Multiple congenital anomalies-hypotonia-seizures syndrome is caused by a mutation in PIGN."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in PIGN, which encodes glycosylphosphatidylinositol (GPI) ethanolamine phosphate transferase 1, a protein involved in GPI-anchor biosynthesis"
    explanation: PIGN (MCAHS1) encodes an ethanolamine-phosphate transferase in the GPI-anchor pathway.
  - reference: PMID:23636107
    reference_title: "A novel intellectual disability syndrome caused by GPI anchor deficiency due to homozygous mutations in PIGT."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PIGT encodes phosphatidylinositol-glycan biosynthesis class T (PIG-T) protein, which is a subunit of the transamidase complex that catalyses the attachment of proteins to GPI."
    explanation: PIGT (MCAHS3) is part of the transamidase that attaches the GPI anchor to protein.
  downstream:
  - target: Deficient Cell-Surface GPI-Anchored Protein Expression
- name: Deficient Cell-Surface GPI-Anchored Protein Expression
  biological_scale: CELLULAR
  description: >-
    Reduced GPI-anchor availability lowers the cell-surface expression of the >150
    GPI-anchored proteins, including folate receptor, CD59, CD16, CD24, and
    GPI-anchored alkaline phosphatase. Loss of these surface proteins across many cell
    lineages underlies the multisystem, neurodevelopmental phenotype; flow-cytometric
    reduction of surface GPI-anchored proteins on blood cells is a diagnostic
    biomarker of the pathway defect.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - reference: PMID:21493957
    reference_title: "Multiple congenital anomalies-hypotonia-seizures syndrome is caused by a mutation in PIGN."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The expression of GPI linked protein CD59 on fibroblasts from patients as compared to that in a control individual showed a 10-fold reduction in expression, confirming the pathogenic consequences of the mutation on GPI dependent protein expression."
    explanation: Demonstrates reduced surface GPI-anchored protein (CD59) as the cellular consequence of the pathway defect in MCAHS1.
  - reference: PMID:23636107
    reference_title: "A novel intellectual disability syndrome caused by GPI anchor deficiency due to homozygous mutations in PIGT."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "granulocytes from the patients had reduced levels of the GPI anchored protein CD16b, supporting pathogenicity of the mutation."
    explanation: Reduced surface GPI-anchored protein (CD16b) confirms the same cellular defect in MCAHS3.
  - reference: PMID:22305531
    reference_title: "The phenotype of a germline mutation in PIGA: the gene somatically mutated in paroxysmal nocturnal hemoglobinuria."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Transfection of a mutant p.Arg412(∗) PIGA construct into PIGA-null cells showed partial restoration of GPI-anchored proteins."
    explanation: Functional rescue assay shows the MCAHS2 PIGA allele retains partial GPI-anchor biosynthesis, reducing surface GPI-anchored proteins rather than abolishing them.
  downstream:
  - target: Impaired TNAP-Dependent Vitamin B6 Activation
    description: Loss of surface GPI-anchored TNAP impairs vitamin B6 (PLP) activation.
  - target: Reduced Surface Folate Receptor and Cerebral Folate Delivery
    description: Loss of surface GPI-anchored folate receptor (FOLR1) may impair cerebral folate delivery.
    hypothesis_groups:
    - folr1_cerebral_folate
  - target: Neuronal Dysfunction and Epileptic Encephalopathy
  - target: Multisystem Developmental Disruption
- name: Reduced Surface Folate Receptor and Cerebral Folate Delivery
  biological_scale: MOLECULAR
  description: >-
    The folate receptor (FOLR1) is itself a GPI-anchored protein. Reduced cell-surface
    FOLR1 may impair receptor-mediated folate transport into the CNS, a hypothesized
    parallel to the TNAP/vitamin-B6 mechanism and the rationale for a folinic-acid
    (5-formyltetrahydrofolate) trial when a cerebral folate disturbance is demonstrated.
    Direct MCAHS-specific evidence for this arm is currently limited, so it is modeled
    as an emerging/hypothesized mechanism rather than an established one.
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "receptors (f.e. folate receptors, GDNF receptor alphas"
    explanation: Confirms the folate receptor is among the GPI-anchored proteins whose surface display depends on the intact anchor (background biochemistry from a systematic review).
  downstream:
  - target: Neuronal Dysfunction and Epileptic Encephalopathy
    hypothesis_groups:
    - folr1_cerebral_folate
- name: Impaired TNAP-Dependent Vitamin B6 Activation
  biological_scale: MOLECULAR
  description: >-
    Tissue-nonspecific alkaline phosphatase (TNAP) is itself a GPI-anchored protein.
    Reduced cell-surface TNAP impairs the extracellular dephosphorylation of pyridoxal
    5'-phosphate (PLP) to pyridoxal that is required for cellular vitamin B6 uptake;
    intracellular re-phosphorylation to PLP then falls, reducing the activity of
    PLP-dependent enzymes including those of glutamate/GABA metabolism. This provides a
    distinctive mechanistic rationale for the vitamin B6 (pyridoxine) responsiveness
    observed in a subset of inherited GPI-deficiency seizures, and is mechanistically
    separate from the elevated serum ALP (hyperphosphatasia) seen in the HPMRS branch.
  molecular_functions:
  - preferred_term: alkaline phosphatase activity
    modifier: DECREASED
    term:
      id: GO:0004035
      label: alkaline phosphatase activity
  evidence:
  - reference: PMID:39081219
    reference_title: "Inherited glycosylphosphatidylinositol deficiency: a review from molecular and clinical perspectives."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The main active form, PLP, undergoes initial dephosphorylation by cell-surface alkaline phosphatase, particularly the tissue nonspecific alkaline phosphatase isozyme (TNAP), to yield free pyridoxal, which is then taken up by cells"
    explanation: Establishes that cell-surface (GPI-anchored) TNAP mediates the extracellular step required for vitamin B6 uptake.
  - reference: PMID:39081219
    reference_title: "Inherited glycosylphosphatidylinositol deficiency: a review from molecular and clinical perspectives."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "In IGD patients, the absence or reduction of cell-surface TNAP diminishes PLP uptake and subsequently affects the activities of PLP-dependent enzymes."
    explanation: Links reduced surface TNAP in GPI deficiency to impaired PLP-dependent enzyme activity, the basis of B6-responsive seizures.
  downstream:
  - target: Neuronal Dysfunction and Epileptic Encephalopathy
- name: Neuronal Dysfunction and Epileptic Encephalopathy
  biological_scale: CELLULAR
  description: >-
    Deficiency of GPI-anchored proteins critical to neuronal development and synaptic
    function produces cortical network hyperexcitability, drug-resistant early-onset
    seizures, and a developmental and epileptic encephalopathy that drives the severe
    cognitive impairment.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals with variants in synthesis stage genes of the GPI-AP exhibited a significantly shorter time to seizure onset than individuals with variants in transamidase and remodelling stage genes of the GPI-AP"
    explanation: Genotype-phenotype correlation tying the position of the defect in the GPI pathway to seizure-onset timing.
  downstream:
  - target: Seizures
    description: Cortical network hyperexcitability manifests as early-onset seizures.
  - target: Epileptic encephalopathy
    description: Frequent epileptiform activity drives the developmental and epileptic encephalopathy.
  - target: Profound global developmental delay
    description: The encephalopathy and neuronal dysfunction produce severe developmental impairment.
- name: Multisystem Developmental Disruption
  biological_scale: ORGANISM
  description: >-
    Deficient GPI-anchored protein function during embryogenesis and postnatal life
    produces the multiple congenital anomalies, dysmorphic features, hypotonia,
    visceral and skeletal malformations, and failure to thrive that complete the MCAHS
    phenotype.
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies."
    explanation: Documents the multisystem congenital-anomaly burden across organ systems.
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Though dysmorphic features were appreciated in 82%, no single dysmorphic feature had a prevalence >30%, indicating substantial phenotypic heterogeneity."
    explanation: Supports the frequent but nonspecific dysmorphism of the syndrome.
  downstream:
  - target: Facial dysmorphism
    description: Disrupted development produces the nonspecific dysmorphic facial gestalt.
  - target: Gastrointestinal anomalies
    description: Multisystem developmental disruption includes gastrointestinal malformations.
  - target: Cardiac anomalies
    description: Multisystem developmental disruption includes congenital cardiac malformations.
  - target: Renal anomalies
    description: Multisystem developmental disruption includes renal/urinary-tract malformations.
  - target: Hypotonia
    description: Central hypotonia is a core manifestation of the disrupted neurodevelopment.

mechanistic_hypotheses:
- hypothesis_group_id: folr1_cerebral_folate
  hypothesis_label: FOLR1 Cerebral Folate Deficiency Model
  status: EMERGING
  description: >-
    Because the folate receptor FOLR1 is itself a GPI-anchored protein, reduced
    cell-surface FOLR1 in GPI-anchor deficiency is proposed to impair receptor-mediated
    folate transport into the CNS, contributing to the neurodevelopmental/epileptic
    phenotype and providing a rationale for a folinic-acid trial. This mirrors the
    better-established TNAP/vitamin-B6 mechanism, but direct MCAHS-specific evidence
    for a causal cerebral-folate-deficiency arm is currently limited, so it is modeled
    as emerging rather than canonical.

phenotypes:
- name: Hypotonia
  description: Profound central hypotonia, typically presenting in the neonatal period.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Core clinical features were developmental delay or intellectual disability (DD/ID, 90%), seizures (83%), hypotonia (72%) and motor symptoms (64%)."
    explanation: Hypotonia was present in 72% of the largest inherited GPI-deficiency cohort (maps to FREQUENT).
- name: Seizures
  description: >-
    Early-onset, frequently drug-resistant seizures (median onset ~6 months),
    including epileptic spasms and tonic seizures, that often evolve into a
    developmental and epileptic encephalopathy.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Core clinical features were developmental delay or intellectual disability (DD/ID, 90%), seizures (83%), hypotonia (72%) and motor symptoms (64%)."
    explanation: Seizures occurred in 83% of the largest inherited GPI-deficiency cohort (maps to VERY_FREQUENT).
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Median age at seizure onset was 6 months."
    explanation: Documents the early-infantile median seizure onset.
  - reference: PMID:22305531
    reference_title: "The phenotype of a germline mutation in PIGA: the gene somatically mutated in paroxysmal nocturnal hemoglobinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a family with an X-linked lethal disorder involving cleft palate, neonatal seizures, contractures, central nervous system (CNS) structural malformations, and other anomalies."
    explanation: Neonatal seizures are a core feature of MCAHS2.
  - reference: PMID:23636107
    reference_title: "A novel intellectual disability syndrome caused by GPI anchor deficiency due to homozygous mutations in PIGT."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterised by distinct facial features, intellectual disability, hypotonia and seizures, in combination with abnormal skeletal, endocrine, and ophthalmologic findings"
    explanation: Seizures are a defining feature of MCAHS3.
- name: Epileptic encephalopathy
  description: >-
    Developmental and epileptic encephalopathy in which frequent epileptiform activity
    contributes to progressive cognitive and behavioral impairment.
  phenotype_term:
    preferred_term: Epileptic encephalopathy
    term:
      id: HP:0200134
      label: Epileptic encephalopathy
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals with a developmental epileptic encephalopathy (51%) were at greater risk of intractable epilepsy (P = 0.003), non-ambulance (P = 0.035), ongoing enteral feeds (P < 0.001) and cortical visual impairment (P = 0.007)."
    explanation: About half of the cohort had a developmental and epileptic encephalopathy, which predicted worse outcomes.
- name: Epileptic spasms
  description: Infantile/epileptic spasms are a reported seizure type in the inherited GPI deficiencies.
  phenotype_term:
    preferred_term: Epileptic spasm
    term:
      id: HP:0011097
      label: Epileptic spasm
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "specifically epileptic spasms (10/36), atonic (3/36), and myoclonic (2/36) seizures"
    explanation: Epileptic spasms are documented among the focal seizure types in PIGA-related disease.
- name: Profound global developmental delay
  description: Severe-to-profound global developmental delay in surviving children.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Profound global developmental delay
    term:
      id: HP:0012736
      label: Profound global developmental delay
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The majority of individuals experienced delayed or absent speech (95%), motor delay with non-ambulance (64%), and severe-to-profound DD/ID (59%)."
    explanation: Most affected individuals had severe-to-profound developmental impairment.
- name: Intellectual disability
  description: >-
    Developmental delay/intellectual disability is the single most common feature of
    the inherited GPI deficiencies, ranging up to severe-to-profound.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Core clinical features were developmental delay or intellectual disability (DD/ID, 90%), seizures (83%), hypotonia (72%) and motor symptoms (64%)."
    explanation: Developmental delay/intellectual disability was the most common feature (90%) in the largest inherited GPI-deficiency cohort (maps to VERY_FREQUENT).
  - reference: PMID:23636107
    reference_title: "A novel intellectual disability syndrome caused by GPI anchor deficiency due to homozygous mutations in PIGT."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterised by distinct facial features, intellectual disability, hypotonia and seizures, in combination with abnormal skeletal, endocrine, and ophthalmologic findings"
    explanation: Intellectual disability is a defining feature of the GPI-deficiency (MCAHS3) phenotype.
- name: Facial dysmorphism
  description: A frequent but nonspecific dysmorphic facial gestalt.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Though dysmorphic features were appreciated in 82%, no single dysmorphic feature had a prevalence >30%, indicating substantial phenotypic heterogeneity."
    explanation: Dysmorphic features were present in 82% of the cohort but are individually nonspecific.
- name: Cerebral atrophy
  description: >-
    Progressive cerebral (and frequently cerebellar) atrophy on serial neuroimaging,
    indicating a neurodegenerative process.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Cerebral atrophy
    clinical_course: PROGRESSIVE
    term:
      id: HP:0002059
      label: Cerebral atrophy
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%)."
    explanation: Cerebral atrophy (75%) and cerebellar atrophy (60%) were common neuroimaging findings.
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Serial neuroimaging showed progressive cerebral volume loss in 87.5% and progressive cerebellar atrophy in 70.8%, indicating a neurodegenerative process."
    explanation: Establishes the progressive/neurodegenerative course of the atrophy.
- name: Cortical visual impairment
  description: >-
    Cerebral (cortical) visual impairment, associated with the developmental and
    epileptic encephalopathy subgroup.
  phenotype_term:
    preferred_term: Cerebral visual impairment
    term:
      id: HP:0100704
      label: Cerebral visual impairment
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals with a developmental epileptic encephalopathy (51%) were at greater risk of intractable epilepsy (P = 0.003), non-ambulance (P = 0.035), ongoing enteral feeds (P < 0.001) and cortical visual impairment (P = 0.007)."
    explanation: Cortical visual impairment is enriched in the developmental-and-epileptic-encephalopathy subgroup.
- name: Cerebellar atrophy
  description: Cerebellar atrophy on neuroimaging, part of the neurodegenerative course.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Cerebellar atrophy
    clinical_course: PROGRESSIVE
    term:
      id: HP:0001272
      label: Cerebellar atrophy
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%)."
    explanation: Cerebellar atrophy was present in 60% of the cohort.
- name: Corpus callosum anomaly
  description: Callosal anomalies (e.g., thinning/hypoplasia of the corpus callosum) on neuroimaging.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Abnormal corpus callosum morphology
    term:
      id: HP:0001273
      label: Abnormal corpus callosum morphology
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%)."
    explanation: Callosal anomalies were present in 57% of the cohort.
- name: Symmetric restricted diffusion of the central tegmental tracts
  description: >-
    A characteristic neuroimaging feature of the inherited GPI deficiencies: symmetric
    restricted diffusion of the central tegmental tracts. No precise HPO term exists;
    the descriptor is left ontology-unbound rather than forced to an approximate match.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Symmetric restricted diffusion of the central tegmental tracts
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%)."
    explanation: A prognostically significant neuroimaging feature present in 60% of the cohort.
- name: Gastrointestinal anomalies
  description: Gastrointestinal congenital anomalies as part of the multisystem involvement.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Abnormality of the gastrointestinal tract
    term:
      id: HP:0011024
      label: Abnormality of the gastrointestinal tract
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies."
    explanation: Gastrointestinal anomalies were the most common systemic involvement (66%).
- name: Cardiac anomalies
  description: Congenital cardiac malformations as part of the multisystem involvement.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Abnormal heart morphology
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies."
    explanation: Cardiac anomalies were present in 19% of the cohort.
- name: Renal anomalies
  description: Congenital renal/urinary-tract anomalies as part of the multisystem involvement.
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Abnormality of the kidney
    term:
      id: HP:0000077
      label: Abnormality of the kidney
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies."
    explanation: Renal anomalies were present in 14% of the cohort.
- name: Chorea
  description: >-
    A movement disorder (chorea) reported as part of the severe neurological impairment
    in the PIGN/MCAHS1 index families.
  phenotype_term:
    preferred_term: Chorea
    term:
      id: HP:0002072
      label: Chorea
  evidence:
  - reference: PMID:21493957
    reference_title: "Multiple congenital anomalies-hypotonia-seizures syndrome is caused by a mutation in PIGN."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study reports on a hitherto undescribed autosomal recessive syndrome characterised by dysmorphic features and multiple congenital anomalies together with severe neurological impairment, chorea and seizures leading to early death"
    explanation: Chorea is documented as part of the neurological phenotype in MCAHS1.
- name: Feeding difficulties
  description: Poor sucking and feeding difficulties, often requiring enteral (tube) feeding.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Individuals with a developmental epileptic encephalopathy (51%) were at greater risk of intractable epilepsy (P = 0.003), non-ambulance (P = 0.035), ongoing enteral feeds (P < 0.001) and cortical visual impairment (P = 0.007)."
    explanation: Ongoing enteral feeding requirement (a marker of severe feeding difficulty) was significantly associated with the encephalopathy subgroup.
- name: Drug-resistant epilepsy in PIGA-related disease
  subtype: MCAHS2
  description: >-
    In the PIGA/MCAHS2 subtype, epilepsy is near-universal and frequently
    drug-resistant (76/81 with epilepsy, 52 drug-resistant in a systematic review).
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among these patients, 76 were diagnosed with epilepsy, of which 52 were drug-resistant."
    explanation: Quantifies the high epilepsy burden and drug resistance among the 81 pooled PIGA (GPIBD4/MCAHS2) cases.
- name: Intellectual disability in PIGN-related disease
  subtype: MCAHS1
  description: In the PIGN/MCAHS1 subtype, DD/ID occurs in over 80% of reported patients.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "presented a set of symptoms that each appeared in over 80% of GPIBD3 (MIM 606097; 18q21.33) patients"
    explanation: DD/ID, hypotonia and seizures each occur in over 80% of pooled PIGN (GPIBD3/MCAHS1) cases.
- name: Hypotonia in PIGN-related disease
  subtype: MCAHS1
  description: In the PIGN/MCAHS1 subtype, hypotonia occurs in over 80% of reported patients.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "presented a set of symptoms that each appeared in over 80% of GPIBD3 (MIM 606097; 18q21.33) patients"
    explanation: DD/ID, hypotonia and seizures each occur in over 80% of pooled PIGN (GPIBD3/MCAHS1) cases.
- name: Seizures in PIGN-related disease
  subtype: MCAHS1
  description: >-
    In the PIGN/MCAHS1 subtype, seizures occur in over 80% of reported patients, with a
    mean first-seizure onset around 6.9 months.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "presented a set of symptoms that each appeared in over 80% of GPIBD3 (MIM 606097; 18q21.33) patients"
    explanation: DD/ID, hypotonia and seizures each occur in over 80% of pooled PIGN (GPIBD3/MCAHS1) cases.
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean time of the first seizure was 6.9 months."
    explanation: Documents the mean first-seizure onset in pooled PIGN/MCAHS1 cases.
- name: Myoclonic seizures in PIGT-related disease
  subtype: MCAHS3
  description: >-
    In the PIGT/MCAHS3 subtype, epilepsy is a cardinal feature and the myoclonic
    seizure is the most common seizure type.
  phenotype_term:
    preferred_term: Myoclonic seizure
    term:
      id: HP:0032794
      label: Myoclonic seizure
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "epilepsy is one of the cardinal features of the disorder, with myoclonic seizure being the most common seizure type in PIGT-GPIBDs patients"
    explanation: Identifies myoclonic seizures as the predominant seizure type in PIGT/MCAHS3.

genetic:
- name: PIGA
  gene_term:
    preferred_term: PIGA
    term:
      id: hgnc:8957
      label: PIGA
  relationship_type: CAUSATIVE
  subtype: MCAHS2
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:22305531
    reference_title: "The phenotype of a germline mutation in PIGA: the gene somatically mutated in paroxysmal nocturnal hemoglobinuria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An X chromosome exome next-generation sequencing screen identified a single nonsense PIGA mutation, c.1234C>T, which predicts p.Arg412(∗)."
    explanation: Identifies germline PIGA as the cause of the X-linked MCAHS2 phenotype.
- name: PIGN
  gene_term:
    preferred_term: PIGN
    term:
      id: hgnc:8967
      label: PIGN
  relationship_type: CAUSATIVE
  subtype: MCAHS1
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:21493957
    reference_title: "Multiple congenital anomalies-hypotonia-seizures syndrome is caused by a mutation in PIGN."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Arginine at the position 709 is a highly evolutionarily conserved residue located in the PigN domain."
    explanation: Supports pathogenicity of the p.Arg709Gln PIGN variant identified as the cause of MCAHS1.
- name: PIGT
  gene_term:
    preferred_term: PIGT
    term:
      id: hgnc:14938
      label: PIGT
  relationship_type: CAUSATIVE
  subtype: MCAHS3
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:23636107
    reference_title: "A novel intellectual disability syndrome caused by GPI anchor deficiency due to homozygous mutations in PIGT."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The results from WES identified a homozygous mutation, c.547A>C (p.Thr183Pro), in PIGT"
    explanation: Identifies biallelic PIGT as the cause of MCAHS3.

biochemical:
- name: Serum alkaline phosphatase
  biomarker_term:
    preferred_term: serum alkaline phosphatase
  notes: >-
    Serum ALP is a useful biomarker across the inherited GPI deficiencies but is
    direction-dependent by branch: markedly elevated (hyperphosphatasia) in the HPMRS
    subgroup, whereas in MCAHS it is typically normal or, in the PIGT/MCAHS3 subtype,
    low. A normal ALP therefore does not exclude a GPI-anchor defect.
  evidence:
  - reference: PMID:39081219
    reference_title: "Inherited glycosylphosphatidylinositol deficiency: a review from molecular and clinical perspectives."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the serum level of alkaline phosphatase (ALP) serves as another biomarker and clinical evidence for IGD"
    explanation: Establishes serum ALP as a biomarker of inherited GPI deficiency.

diagnosis:
- name: Flow-cytometric GPI-anchored protein assay
  description: >-
    Beyond molecular genetic confirmation, the GPI defect is validated functionally by
    flow cytometry of cell-surface GPI-anchored proteins (commonly CD55, CD59, and CD16,
    plus pan-specific FLAER) on blood cells or skin fibroblasts. Some variants reduce
    only a subset of GPI-anchored proteins (e.g., transamidase-stage PIGT lowers
    granulocyte CD16 while sparing CD55/CD59), and standard serum-transferrin CDG
    screening does not detect GPI-anchor defects.
  evidence:
  - reference: PMID:39081219
    reference_title: "Inherited glycosylphosphatidylinositol deficiency: a review from molecular and clinical perspectives."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Flow cytometry analysis can detect the levels of certain GPI-APs on the cell surface, which is typically performed on blood cells and skin fibroblasts."
    explanation: Establishes flow cytometry of surface GPI-anchored proteins as the functional confirmatory assay.
  - reference: PMID:39081219
    reference_title: "Inherited glycosylphosphatidylinositol deficiency: a review from molecular and clinical perspectives."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "In cases with dysfunctional PIGS, PIGT, and PIGU, there is a decrease in cell-surface CD16 on granulocytes, whereas CD55 and CD59 remain unaffected"
    explanation: Documents the variant-specific GPI-AP pattern (PIGT lowers granulocyte CD16 while sparing CD55/CD59) relevant to test interpretation.

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Individually ultra-rare disorders; the largest single multinational cohort of
    inherited GPI deficiencies to date comprised 83 individuals from 75 families.
  evidence:
  - reference: PMID:38456468
    reference_title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we systematically analyse the molecular spectrum, phenotypic characteristics and natural history of 83 individuals from 75 unique families with IGDs, including 70 newly reported individuals; the largest single cohort to date"
    explanation: Establishes the rarity and scale of the largest reported inherited GPI-deficiency cohort.

differential_diagnoses:
- name: Hyperphosphatasia with intellectual disability syndrome (Mabry syndrome/HPMRS)
  description: >-
    The other major branch of inherited GPI deficiency (genes PIGV, PIGO, PGAP2,
    PGAP3, PIGW, PIGY). HPMRS shares developmental delay, seizures, hypotonia and
    dysmorphism but is defined by persistently elevated serum alkaline phosphatase
    (hyperphosphatasia), which is characteristically absent in MCAHS.
  distinguishing_features:
  - Persistently elevated serum alkaline phosphatase (normal in MCAHS; low in the PIGT/MCAHS3 subtype).
- name: Other early-infantile developmental and epileptic encephalopathies
  description: >-
    Non-GPI genetic epileptic encephalopathies (e.g., channelopathies and synaptic-gene
    DEEs) overlap in the seizure and developmental phenotype but lack a GPI-anchor
    biosynthesis defect and the associated reduction of surface GPI-anchored proteins
    on flow cytometry.
  distinguishing_features:
  - Normal cell-surface expression of GPI-anchored proteins (reduced in MCAHS).

treatments:
- name: Antiseizure medication
  description: >-
    Symptomatic management of the frequently drug-resistant epilepsy; the most commonly
    used agents in reported cohorts are valproic acid, levetiracetam, and topiramate.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: anticonvulsant agent
      term:
        id: NCIT:C264
        label: Anticonvulsant Agent
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most commonly applied anti-epileptic drugs (AEDs) were valproic acid (N = 60), levetiracetam (N = 50), and topiramate (N = 30)."
    explanation: Documents the antiseizure medications most commonly used across the pooled GPI-deficiency cohort.
- name: Ketogenic diet
  description: >-
    A ketogenic (ketone) diet has been reported effective for seizure control in some
    children with PIGA-related disease.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Ketogenic Diet
    term:
      id: NCIT:C173168
      label: Ketogenic Diet
  evidence:
  - reference: PMID:35058872
    reference_title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Based on some case reports, ketone diet is effective in children with a PIGA gene mutation"
    explanation: Reports ketogenic-diet efficacy for seizures in PIGA/MCAHS2.
- name: Folinic acid
  description: >-
    Folinic acid (5-formyltetrahydrofolate) may be considered when a cerebral folate
    disturbance is demonstrated or strongly suspected, given that the folate receptor
    (FOLR1) is a GPI-anchored protein; MCAHS-specific response rates are not established.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: folinic acid
      term:
        id: CHEBI:15640
        label: 5-formyltetrahydrofolic acid
  target_mechanisms:
  - target: Reduced Surface Folate Receptor and Cerebral Folate Delivery
    treatment_effect: MODULATES
    description: >-
      Folinic acid supplementation may compensate for reduced FOLR1-mediated cerebral
      folate delivery; the benefit in MCAHS specifically remains unproven.
- name: Vitamin B6 (pyridoxine) supplementation
  description: >-
    High-dose vitamin B6 (pyridoxine, typically 20-30 mg/kg) has shown efficacy in
    reducing seizure activity in a subset of individuals with inherited GPI deficiency,
    consistent with the impaired TNAP-dependent PLP/vitamin B6 activation mechanism.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: pyridoxine
      term:
        id: CHEBI:16709
        label: pyridoxine
  target_mechanisms:
  - target: Impaired TNAP-Dependent Vitamin B6 Activation
    treatment_effect: MODULATES
    description: >-
      Exogenous vitamin B6 raises substrate availability to compensate for reduced
      TNAP-mediated PLP processing, restoring PLP-dependent enzyme activity.
    evidence:
    - reference: PMID:39081219
      reference_title: "Inherited glycosylphosphatidylinositol deficiency: a review from molecular and clinical perspectives."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Studies have demonstrated that vitamin B6 supplementation significantly improves outcomes in IGD by reducing seizure activity."
      explanation: Supports vitamin B6 as a mechanism-directed therapy acting on the TNAP/PLP pathway.
- name: Supportive and multidisciplinary care
  description: >-
    Supportive care including nutritional support/tube feeding, physiotherapy, and
    management of congenital malformations.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care

references:
- reference: PMID:38456468
  title: "The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders."
- reference: PMID:39081219
  title: "Inherited glycosylphosphatidylinositol deficiency: a review from molecular and clinical perspectives."
- reference: PMID:35058872
  title: "Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review."
📚

References & Deep Research

References

3
PMID:38456468
The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders.
No top-level findings curated for this source.
PMID:39081219
Inherited glycosylphosphatidylinositol deficiency: a review from molecular and clinical perspectives.
No top-level findings curated for this source.
PMID:35058872
Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review.
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Disease Characteristics Research Template
Edison Scientific Literature 22 citations 2026-08-14T04:26:11.042014

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: Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome
  • MONDO ID: (if available)
  • Category: Mendelian

Research Objectives

Please provide a comprehensive research report on Multiple Congenital Anomalies-Hypotonia-Seizures Syndrome covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

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

1. Disease Information

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

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

2. Etiology

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

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

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

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

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

    Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

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

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

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

4. Genetic/Molecular Information

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

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

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

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

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

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

5. Environmental Information

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

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

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

    Search first: CDC databases, WHO, PubMed, NHANES

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

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

6. Mechanism / Pathophysiology

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

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

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

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

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

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

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

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

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

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

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

    Search first: PubMed, Gene Ontology, Reactome

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

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

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

    Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth

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

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

7. Anatomical Structures Affected

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

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

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

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

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

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

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

8. Temporal Development

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

    Search first: OMIM, Orphanet, HPO, PubMed

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

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

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

9. Inheritance and Population

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

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

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

10. Diagnostics

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

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

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

11. Outcome/Prognosis

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

12. Treatment

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

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

13. Prevention

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

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

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

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

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

    Search first: NSGC resources, ACMG guidelines, GeneReviews

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

    Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

  • Taxonomy: Species affected (with NCBI Taxon identifiers)

    Search first: NCBI Taxonomy

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

    Search first: VBO (Vertebrate Breed Ontology)

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

    Search first: NCBI Gene

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

15. Model Organisms

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

Citation Requirements

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

Output Format

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

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

Multiple Congenital Anomalies–Hypotonia–Seizures Syndrome (MCAHS)

Executive summary and scope

Multiple congenital anomalies–hypotonia–seizures syndrome is not a single-gene disorder but a severe subgroup of inherited glycosylphosphatidylinositol-anchor deficiencies (IGDs), themselves classified among congenital disorders of glycosylation. The umbrella term conventionally includes MCAHS1/PIGN-related disease, MCAHS2/PIGA-related disease, and MCAHS3/PIGT-related disease. These genes act at different stages of GPI-anchor synthesis or attachment, but their disruption converges on reduced or structurally abnormal GPI-anchored proteins at the cell surface. The result is a congenital, multisystem developmental disorder dominated by hypotonia, developmental impairment, and early epilepsy, often with structural malformations and progressive cerebral or cerebellar abnormalities. The umbrella identifier supported by current disease-target resources is MONDO:0100247; MCAHS1 is MONDO:0013563. (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome, murakami2024gpianchorand pages 1-2)

The evidence base remains small. Most knowledge comes from molecularly defined case reports and case series rather than registries, electronic-health-record cohorts, randomized trials, or population studies. A 2022 systematic review assembled 337 patients with all forms of GPI-biosynthesis defects from 77 publications, but subtype-specific denominators remained only 27 for PIGN, 81 for PIGA, and 38 for PIGT. Consequently, reported frequencies are subject to ascertainment and publication bias and should not be interpreted as population prevalence. (paprocka2022spectrumofneurological pages 3-5)

Subtype Umbrella/subtype MONDO where evidenced Causal gene Inheritance Molecular role Hallmark human phenotype / counts from 337-case systematic review Representative variants Diagnostic functional assay
MCAHS (umbrella) MONDO:0100247 umbrella evidenced; subtype MONDOs only partly evidenced in gathered data (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) PIGN, PIGA, PIGT (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) Mixed by subtype: AR for PIGN and PIGT; X-linked for PIGA germline disease context; umbrella-level inheritance NR (lam2015expandingtheclinical pages 1-3, paprocka2022spectrumofneurological pages 3-5) Inherited GPI-anchor biosynthesis defects causing reduced/abnormal GPI-anchored proteins on cell surfaces (murakami2024gpianchorand pages 1-2) Severe neurodevelopmental disease with seizures, hypotonia, developmental delay/intellectual disability; review states MCAHS caused by PIGA/PIGN/PIGT is among the more severe GPIBD phenotypes (paprocka2022spectrumofneurological pages 3-5) NR at umbrella level Flow-cytometric assessment of GPI-anchored proteins / FLAER-based assays in blood cells or fibroblasts are used across GPI deficiencies (johnstone2020investigationofnovel pages 44-49, murakami2024gpianchorand pages 1-2)
MCAHS1 MONDO:0013563 evidenced for “multiple congenital anomalies-hypotonia-seizures syndrome 1” (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) PIGN (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) Autosomal recessive (inherited GPI deficiency context; biallelic disease) (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) PIGN mediates ethanolamine phosphate transfer during GPI-anchor biosynthesis in the ER (murakami2024gpianchorand pages 1-2) PIGN cases in review: n=27; seizures 23; delayed motor development 7; developmental delay/intellectual disability 23; hypotonia 22 (paprocka2022spectrumofneurological pages 3-5) Specific PIGN variants NR in gathered evidence Reduced GPI-anchored protein expression by flow cytometry is the relevant functional assay class for GPIBD; subtype-specific PIGN assay details NR in gathered evidence (murakami2024gpianchorand pages 1-2)
MCAHS2 Umbrella MONDO:0100247 evidenced; subtype-specific MONDO for MCAHS2 NR in gathered evidence (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) PIGA (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) X-linked (germline PIGA disease context) (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome, paprocka2022spectrumofneurological pages 3-5) PIGA is part of the GPI-N-acetylglucosaminyltransferase complex catalyzing the first step of GPI-anchor biosynthesis in the ER (murakami2024gpianchorand pages 1-2) PIGA cases in review: n=81; seizures 76; delayed motor development 61; developmental delay/intellectual disability 70; hypotonia 55; cerebellar atrophy 19 (paprocka2022spectrumofneurological pages 3-5) Specific PIGA variants NR in gathered evidence Flow cytometry of GPI-anchored proteins / granulocyte CD16b-type screening is relevant for GPI deficiencies; subtype-specific PIGA functional assay details NR in gathered evidence (murakami2024gpianchorand pages 1-2)
MCAHS3 Umbrella MONDO:0100247 evidenced; subtype-specific MONDO for MCAHS3 NR in gathered evidence (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) PIGT (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome, lam2015expandingtheclinical pages 1-3) Autosomal recessive; affected siblings with compound heterozygous variants reported (lam2015expandingtheclinical pages 1-3) PIGT encodes a subunit of the heteropentameric GPI transamidase complex that attaches GPI anchors to proteins (lam2015expandingtheclinical pages 1-3, murakami2024gpianchorand pages 1-2) PIGT cases in review: n=38; seizures 33; delayed motor development 31; developmental delay/intellectual disability 34; hypotonia 17; cerebellar atrophy 15 (paprocka2022spectrumofneurological pages 3-5) c.918dupC (frameshift), c.1342C>T (missense) (lam2015expandingtheclinical pages 1-3) Flow cytometry showing decreased surface expression of GPI-anchored proteins on granulocytes; proposed screening approach because standard CDT/N-glycan CDG screens may miss PIGT-CDG (lam2015expandingtheclinical pages 1-3, lam2015expandingtheclinical pages 13-17)

Table: This table summarizes the MCAHS umbrella disorder and its key molecular subtypes using only gathered evidence. It highlights subtype-specific genes, inheritance, molecular function, systematic-review phenotype counts, representative variants where available, and the main functional diagnostic assays.

1. Disease information and identifiers

Definition. MCAHS is a genetically heterogeneous developmental encephalopathy caused by deficient GPI-anchor biosynthesis or attachment. GPI anchors tether more than 150 functionally diverse proteins—including enzymes, receptors, adhesion molecules, protease inhibitors, and complement regulators—to the extracellular leaflet of the plasma membrane. Loss of this post-translational system explains the combination of neurologic, craniofacial, skeletal, ocular, cardiac, gastrointestinal, and other congenital abnormalities. (johnstone2020investigationofnovel pages 44-49, murakami2024gpianchorand pages 1-2, ilkovski2015mutationsinpigy pages 9-9)

Principal names and synonyms:

  • multiple congenital anomalies–hypotonia–seizures syndrome; MCAHS;
  • inherited GPI-anchor deficiency associated with MCAHS;
  • GPI-anchor biosynthesis defect/congenital disorder of glycosylation;
  • MCAHS1 / PIGN-CDG / PIGN-related GPI deficiency;
  • MCAHS2 / PIGA-CDG / germline PIGA-related developmental and epileptic encephalopathy;
  • MCAHS3 / PIGT-CDG / PIGT-related GPI deficiency.

Identifiers. MONDO:0100247 identifies the umbrella disorder and MONDO:0013563 MCAHS1. OpenTargets associates PIGN, PIGA, and PIGT with the umbrella disease and cites foundational PubMed records including PMID 21493957 for PIGN, 22305531 for PIGA, and 23636107/24906948 for PIGT. (OpenTargets Search: Multiple congenital anomalies-hypotonia-seizures syndrome) Subtype-specific OMIM, Orphanet, ICD-10/ICD-11, and MeSH identifiers were not independently verified in the retrieved evidence and should therefore be curated directly from those databases rather than inferred. ICD generally lacks a uniquely granular MCAHS code; practical coding commonly falls under congenital malformation, developmental encephalopathy, epilepsy, or congenital glycosylation-disorder categories.

2. Etiology, risk, and protective factors

Genetic causes

  • PIGN-related MCAHS1: usually biallelic germline variants; autosomal-recessive inheritance. PIGN adds an ethanolamine-phosphate side branch during ER GPI-anchor assembly.
  • PIGA-related MCAHS2: pathogenic germline variants in the X-chromosomal PIGA gene. PIGA is a catalytic component of the multisubunit GPI-N-acetylglucosaminyltransferase complex initiating GPI biosynthesis. Hemizygous males usually dominate severe presentations; female disease may reflect skewed X-inactivation or other unusual allelic circumstances. This germline disorder must not be confused with acquired somatic PIGA variants causing paroxysmal nocturnal hemoglobinuria.
  • PIGT-related MCAHS3: biallelic germline variants; autosomal-recessive inheritance. PIGT is part of the five-subunit GPI transamidase that attaches a completed GPI anchor to a protein’s C terminus. (lam2015expandingtheclinical pages 1-3, murakami2024gpianchorand pages 1-2)

Pathogenic alleles include missense, nonsense, frameshift, splice-altering, and potentially regulatory variants. In one primary PIGT-CDG family, compound heterozygous c.918dupC (p.Val307Argfs*13) and c.1342C>T alleles reduced granulocyte GPI-anchored-protein expression. (lam2015expandingtheclinical pages 1-3, lam2015expandingtheclinical pages 13-17) Variants reported in affected families are expected to be absent or extremely rare in population databases, but exact gnomAD frequencies and ACMG classifications must be checked transcript-by-transcript in ClinVar/gnomAD; they were not established by the retrieved papers.

Non-genetic risk and protection

No toxin, infection, diet, behavior, occupation, parental age, or lifestyle exposure is established as a cause of MCAHS. It is a Mendelian developmental disorder. Consanguinity increases the probability that both parents carry the same recessive PIGN or PIGT allele but is not itself a biological cause. No validated protective allele, modifier gene, epigenetic signature, or gene–environment interaction has been demonstrated. Nutrition and antiseizure management may modify complications but do not prevent the underlying molecular defect.

3. Phenotypes

The best quantitative summary is the 337-case IGD systematic review. In the relevant molecular groups:

  • PIGA (n=81): seizures 76/81 (93.8%), developmental delay/intellectual disability 70/81 (86.4%), delayed motor development 61/81 (75.3%), hypotonia 55/81 (67.9%), and cerebellar atrophy 19/81 (23.5%).
  • PIGN (n=27): seizures 23/27 (85.2%), developmental delay/intellectual disability 23/27 (85.2%), hypotonia 22/27 (81.5%), and documented delayed motor development 7/27 (25.9%). The low motor-delay count likely reflects missing reporting rather than preserved development.
  • PIGT (n=38): seizures 33/38 (86.8%), developmental delay/intellectual disability 34/38 (89.5%), delayed motor development 31/38 (81.6%), hypotonia 17/38 (44.7%), and cerebellar atrophy 15/38 (39.5%). (paprocka2022spectrumofneurological pages 3-5)

Core clinical features and suggested HPO terms

  • Congenital or infantile hypotonia — generally persistent and severe; HP:0001252.
  • Early-onset epilepsy/developmental and epileptic encephalopathy — focal, generalized, tonic, clonic, tonic-clonic, myoclonic seizures, spasms, or mixed patterns; often treatment resistant; HP:0001250, HP:0007359, HP:0002123.
  • Global developmental delay and intellectual disability — usually severe-to-profound, lifelong; HP:0001263, HP:0001249.
  • Delayed motor development/non-ambulation — HP:0001270; feeding and communication dependence are common functional consequences.
  • Microcephaly, cerebral/cerebellar atrophy, delayed myelination, thin/hypoplastic corpus callosum, and widened CSF spaces — HP:0000252, HP:0002059, HP:0001272, HP:0007370, HP:0002079. GPI-deficiency neuroimaging can show white-matter abnormalities, cerebral or cerebellar atrophy, and callosal hypoplasia. (mario2023epilepsyphenotypesof pages 4-6, murakami2024gpianchorand pages 1-2)
  • Congenital anomalies/dysmorphism — variable facial, distal-limb/nail, skeletal, cardiac, gastrointestinal, genitourinary, ocular, and auditory abnormalities. Suggested terms should be assigned at the patient level rather than treating every anomaly as universal.
  • Laboratory abnormality: serum alkaline phosphatase can be increased in some IGDs because improperly anchored ALP is released, but values can be normal or low depending on the biosynthetic step and assay. Hyperphosphatasia is therefore supportive, not required.

Seizure onset is generally neonatal or infantile, although the broader B6-responsive GPI-deficiency literature reports onset commonly after the immediate neonatal period. Across all molecularly confirmed vitamin-B6-dependent epilepsies—not MCAHS alone—67.8% began in the first month; this statistic must not be assigned directly to MCAHS. (mario2023epilepsyphenotypesof pages 4-6)

No validated MCAHS-specific EQ-5D, SF-36, PROMIS, behavioral, or caregiver-burden study was identified. Nevertheless, profound motor, cognitive, feeding, communication, and seizure burdens imply major lifelong effects on patients and caregivers.

4. Genetic and molecular information

The three proteins occupy distinct pathway positions:

  1. PIGA—upstream initiation: transfers GlcNAc to phosphatidylinositol as part of the ER GPI-N-acetylglucosaminyltransferase complex.
  2. PIGN—intermediate anchor assembly: contributes ethanolamine phosphate modification after mannose incorporation.
  3. PIGT—downstream protein attachment: acts within the PIGK–PIGT–PIGS–PIGU–GPAA1 transamidase complex to transfer completed GPI to precursor proteins. (murakami2024gpianchorand pages 1-2)

The usual disease mechanism is partial loss of function. Complete loss of essential GPI-biosynthesis activity is presumed incompatible with normal embryonic development; surviving patients generally retain residual function. Functional support includes decreased GPI-anchored proteins on patient granulocytes or fibroblasts and restoration after wild-type-gene complementation, an approach well established across IGDs. Relevant markers include CD16/CD16b, CD24, CD55, CD59, and FLAER. (johnstone2020investigationofnovel pages 44-49, nguyen2018mutationsinpigs pages 4-6, lam2015expandingtheclinical pages 1-3)

No reproducible MCAHS modifier gene, disease-specific methylation episignature, somatic driver mechanism, recurrent pathogenic chromosomal rearrangement, repeat expansion, or mitochondrial-genome cause is established. Large deletions encompassing a causal gene remain theoretically detectable by copy-number analysis but are not the canonical mechanism.

5. Environmental and infectious information

Environmental toxins, radiation, pollution, smoking, alcohol, exercise, diet, and infectious agents have no established etiologic role. MCAHS is not contagious, infectious, immune-mediated, or zoonotic. Intercurrent illness, fever, fasting, or medication nonadherence may exacerbate seizures in an affected child, but this is clinical triggering rather than disease causation.

6. Mechanism and pathophysiology

Causal chain

Germline pathogenic variant → deficient GPI biosynthesis/attachment in the ER → reduced or structurally abnormal GPI-anchored proteins at the plasma membrane → disruption of neuronal signaling, adhesion, neurogenesis, folate/B6 handling, complement regulation, and embryonic tissue patterning → congenital malformations, hypotonia, developmental impairment, epilepsy, and progressive brain abnormalities. Approximately 30 gene products participate in human GPI synthesis and remodeling. (johnstone2020investigationofnovel pages 44-49, murakami2024gpianchorand pages 1-2)

A clinically important downstream mechanism involves tissue-nonspecific alkaline phosphatase (TNSALP/ALPL), itself a GPI-anchored ectoenzyme. Reduced membrane ALP can impair extracellular dephosphorylation of pyridoxal-5′-phosphate, limiting transport of vitamin B6 species into neurons and reducing PLP-dependent neurotransmitter synthesis, including inhibitory GABA production. This provides a mechanistic rationale for B6-responsive seizures in a subset of IGD patients. Impaired localization of the GPI-anchored folate receptor FOLR1 may likewise disturb cerebral folate delivery. (murakami2024gpianchorand pages 1-2)

Suggested ontology annotations include GO:0006506 GPI-anchor biosynthetic process, GO:0016255 attachment of GPI anchor to protein, GO:0005783 endoplasmic reticulum, GO:0005886 plasma membrane, and broader terms for protein post-translational modification, neurogenesis, synaptic signaling, and embryonic morphogenesis. Candidate affected cell types include neurons (CL:0000540), neural progenitor cells, oligodendrocytes, skeletal myocytes, cardiomyocytes, and diverse embryonic epithelial/mesenchymal populations; direct cell-type-resolved human evidence is limited.

No disease-specific single-cell atlas, spatial transcriptomic study, proteome, metabolome, lipidome, or integrated multi-omics signature was identified. The strongest molecular profiling remains cell-surface GPI-AP phenotyping and gene-complementation assays.

7. Anatomical structures affected

The central nervous system is primary: cerebral cortex, white matter, corpus callosum, cerebellum, and brainstem may be involved. Suggested UBERON annotations include brain (UBERON:0000955), cerebral cortex, cerebellum (UBERON:0002037), corpus callosum, and white matter. Secondary or congenital involvement may affect eye, ear, craniofacial structures, skeleton and distal limbs, heart, diaphragm, gastrointestinal tract, kidney/urinary tract, and genital structures. PIGT-CDG case descriptions included ophthalmologic, hearing, skeletal, endocrine, and cardiac abnormalities. (lam2015expandingtheclinical pages 1-3)

At the subcellular level, the critical sites are the endoplasmic-reticulum membrane, where GPI is assembled and transferred, and the plasma membrane, where GPI-anchored proteins normally function. Lateralization is not characteristic; brain and systemic involvement is generally bilateral or diffuse.

8. Temporal development and natural history

Molecular pathology begins prenatally. Structural anomalies and fetal akinesia can occur at the severe end, whereas hypotonia, feeding problems, dysmorphism, and seizures usually become apparent at birth or in infancy. Developmental delay is chronic and typically severe. Epilepsy may remain refractory or fluctuate with treatment. Cerebral and particularly cerebellar atrophy may emerge or progress on serial MRI, showing that the phenotype is not exclusively a static malformation syndrome. (paprocka2022spectrumofneurological pages 3-5, mario2023epilepsyphenotypesof pages 4-6)

There is no validated staging system, predictable remission pattern, or quantified median progression rate. The prenatal and first-year developmental windows are critical for diagnosis, seizure control, nutrition, hearing/vision assessment, and early therapy. Lifelong surveillance is required.

9. Inheritance and population

PIGN- and PIGT-related disease are autosomal recessive: each pregnancy of two confirmed heterozygous parents has a 25% probability of an affected child, 50% probability of a carrier child, and 25% probability of a child inheriting neither familial allele. PIGA-related MCAHS is X-linked; recurrence depends on maternal carrier status, X-inactivation, and whether the variant is inherited or de novo.

Penetrance for clearly damaging biallelic/hemizygous variants appears high, but expressivity is broad and residual activity likely influences severity. No anticipation is expected. Parental germline mosaicism is possible, particularly after an apparently de novo event, but its frequency is unknown. No robust carrier frequency, founder effect, prevalence, incidence, sex ratio, ethnic enrichment, or geographic distribution has been established. The disorder is ultra-rare and reported internationally. Apparent male enrichment in PIGA disease follows X-linked biology; PIGN and PIGT should affect both sexes comparably.

10. Diagnostics

Recommended approach

  1. Clinical recognition: congenital anomalies plus hypotonia, severe developmental delay, and infantile epilepsy; obtain three-generation pedigree and detailed dysmorphology examination.
  2. Routine assessment: EEG; brain MRI; serum alkaline phosphatase with age-specific reference range; CBC, metabolic profile, liver tests, calcium/phosphate, vitamin D, and nutrition assessment. Add echocardiography, renal ultrasound, hearing, ophthalmologic, orthopedic, and feeding/swallowing evaluations according to phenotype.
  3. Genomic testing: trio exome or genome sequencing is preferred because IGDs are genetically heterogeneous. An epilepsy/congenital-anomaly/CDG panel should include PIGN, PIGA, PIGT and other PIG/PGAP genes. WGS is useful when WES is negative because it better captures noncoding, structural, and poorly covered variants. A separate mitochondrial or repeat-expansion test is not routinely indicated unless the phenotype suggests another diagnosis.
  4. Variant confirmation: Sanger confirmation and segregation; deletion/duplication analysis if read-depth suggests copy-number change.
  5. Functional confirmation: flow cytometry of granulocytes or fibroblasts for GPI-APs—especially CD16b, CD55, CD59 and/or FLAER—with specialist-laboratory complementation when needed. Standard carbohydrate-deficient transferrin or N-glycan screening may be normal and cannot exclude PIGT-CDG or other anchor defects. (lam2015expandingtheclinical pages 1-3, lam2015expandingtheclinical pages 13-17, murakami2024gpianchorand pages 1-2)

There are no universally accepted clinical diagnostic criteria; molecular confirmation is central. Differential diagnoses include other inherited GPI deficiencies, non-GPI congenital disorders of glycosylation, pyridoxine-dependent epilepsy (ALDH7A1), PNPO or PLPBP deficiency, hypophosphatasia, mitochondrial disease, chromosomal syndromes, and other developmental and epileptic encephalopathies.

Population newborn screening is unavailable. Cascade testing of relatives and targeted prenatal or preimplantation testing are feasible after familial variants are known.

11. Outcomes and prognosis

Severity ranges from fetal/neonatal lethality to survival into childhood or adulthood with profound disability. Poor prognostic indicators plausibly include major congenital malformations, fetal akinesia, early refractory seizures, severe feeding/respiratory dysfunction, and progressive brain atrophy, but no validated prognostic model exists. Long-term morbidity includes severe intellectual and motor disability, communication impairment, aspiration and undernutrition, orthopedic complications, sensory impairment, and medication-related adverse effects.

No reliable 5- or 10-year survival, life-expectancy, disease-specific mortality, recovery rate, or standardized quality-of-life statistic is available. Early death has been documented in severe IGDs, but extrapolation across genes is unsafe. (ilkovski2015mutationsinpigy pages 1-2)

12. Treatment and current implementation

There is no approved therapy that repairs PIGN, PIGA, or PIGT function. Management is multidisciplinary and phenotype directed:

  • Epilepsy: individualized antiseizure medication based on seizure type and EEG; rescue plan for prolonged seizures; ketogenic diet may be considered for drug-resistant epilepsy under specialist supervision, although MCAHS evidence is limited to reports rather than controlled trials.
  • Vitamin B6 trial: because some GPI-anchor defects reduce neuronal PLP availability, a monitored pyridoxine or pyridoxal-5′-phosphate trial is biologically justified in refractory early epilepsy. The broader B6-dependent epilepsy literature describes acute 100 mg IV pyridoxine and maintenance 100–400 mg/day or approximately 20–30 mg/kg/day, but these are class-level data, not an MCAHS-specific dosing guideline. IV administration can cause apnea and must occur with cardiorespiratory monitoring; chronic high doses require neuropathy surveillance. (mario2023epilepsyphenotypesof pages 4-6)
  • Folinic acid: may be considered when cerebral folate disturbance is demonstrated or strongly suspected, but MCAHS-specific response rates are unavailable.
  • Support: gastrostomy or feeding therapy when necessary; aspiration precautions; physical, occupational, speech/augmentative-communication and respiratory therapy; orthopedic management; hearing and vision aids; cardiac, renal, endocrine, and skeletal surveillance.
  • Surgery: anomaly-specific procedures or gastrostomy; epilepsy surgery is rarely appropriate for diffuse genetic encephalopathy unless a clearly resectable focus exists.

Suggested NCIt intervention concepts include anticonvulsant therapy, ketogenic diet, pyridoxine, pyridoxal phosphate, folinic acid, physical therapy, occupational therapy, speech therapy, nutritional support, gastrostomy, genetic counseling, prenatal diagnosis, and preimplantation genetic testing. Suggested chemical annotations include pyridoxine (CHEBI:16709), pyridoxal 5′-phosphate, and folinic acid; database identifiers should be validated during curation.

No relevant disease-specific interventional ClinicalTrials.gov study, gene therapy, CRISPR therapy, ASO, siRNA, cell therapy, immunotherapy, or approved targeted molecule was identified. Therefore, treatment-response percentages and comparative adverse-event rates cannot presently be supplied.

13. Prevention

Primary lifestyle or environmental prevention is not possible. The meaningful preventive measures are reproductive: carrier testing, cascade testing, genetic counseling, targeted prenatal diagnosis by chorionic-villus sampling/amniocentesis, and preimplantation genetic testing for a known familial variant. Secondary prevention consists of rapid genomic diagnosis, EEG surveillance, specialist-supervised B6 testing when appropriate, and early nutrition/hearing/vision/cardiac assessment. Tertiary prevention addresses status epilepticus, aspiration, contractures, malnutrition, scoliosis, respiratory infection, and caregiver burden. Vaccination follows routine schedules unless an individual contraindication exists; no MCAHS-specific vaccine or prophylactic drug applies.

14. Other species and natural disease

PIGN, PIGA, and PIGT and the broader GPI pathway are evolutionarily conserved in vertebrates. However, no well-established naturally occurring veterinary syndrome demonstrably equivalent to human MCAHS was identified in the retrieved literature. There is no zoonotic potential or cross-species transmission because this is a germline genetic disorder. NCBI Taxon and ortholog Gene IDs should be retrieved directly for each intended species rather than inferred.

15. Model organisms and experimental systems

The most directly informative models are patient-derived fibroblasts or blood granulocytes, gene-deficient cultured cells, and complementation assays. Flow cytometry quantifies CD16, CD24, CD55, CD59, or FLAER binding; rescue by wild-type cDNA supports variant causality. Related IGD experiments show that mutant constructs may only partially restore cell-surface GPI-APs, linking residual biochemical activity to phenotypic severity. (johnstone2020investigationofnovel pages 44-49, nguyen2018mutationsinpigs pages 4-6, ilkovski2015mutationsinpigy pages 9-9)

Whole-animal GPI-pathway knockouts often face embryonic lethality or phenotypes more severe than surviving human hypomorphic disease, limiting direct translation. No sufficiently characterized MCAHS1/2/3-specific mouse, rat, zebrafish, Drosophila, organoid, or iPSC model with quantitative human-phenotype recapitulation was available in the retrieved corpus. Priorities include conditional neural Pign/Piga/Pigt models, patient iPSC-derived neurons and cerebral organoids, and rescue studies measuring GPI-AP localization, PLP-dependent neurotransmission, network excitability, myelination, and cerebellar development.

Recent developments and evidence assessment

The most important recent advances are conceptual rather than therapeutic. A 2023 genotype–phenotype study broadened PIGN-related disease from lethal Fryns-like presentations through classic MCAHS to milder neurologic phenotypes, reinforcing a residual-function continuum. A 2024 expert review formalized the positions of PIGA, PIGN, and PIGT within the approximately 30-component GPI pathway and highlighted CD16b flow cytometry and ALP/B6 biology. Recent 2023–2024 vitamin-metabolism research also treats GPI-anchor deficiency as a potentially B6-responsive epilepsy subgroup, while emphasizing that biomarker-guided, monitored trials are preferable to assuming universal responsiveness. (mario2023epilepsyphenotypesof pages 4-6, murakami2024gpianchorand pages 1-2)

The systematic review’s central conclusion is that GPI defects should be considered in children with early seizures and developmental delay; its abstract reports that 337 cases from 77 articles met inclusion criteria. (paprocka2022spectrumofneurological pages 3-5) A primary PIGT study further demonstrates why biochemical screening alone is insufficient: decreased granulocyte GPI-AP expression was detectable by flow cytometry even though conventional CDG screening may miss the disorder. (lam2015expandingtheclinical pages 1-3, lam2015expandingtheclinical pages 13-17)

Key evidence gaps

Reliable epidemiology, prospective natural history, standardized seizure and developmental outcomes, patient-reported quality of life, variant-level penetrance, population allele frequencies, pharmacogenomics, validated prognostic biomarkers, subtype-specific treatment response, and disease-specific interventional trials are absent. Likewise, there are no established immune, epigenetic, transcriptomic, single-cell, spatial, proteomic, metabolomic, or lipidomic signatures. These omissions should be encoded as unknown/not available, not as negative findings.

Selected source details

  • Paprocka J, et al. Spectrum of Neurological Symptoms in Glycosylphosphatidylinositol Biosynthesis Defects: Systematic Review. Frontiers in Neurology, published January 2022. DOI/URL: https://doi.org/10.3389/fneur.2021.758899. (paprocka2022spectrumofneurological pages 3-5)
  • Lam C, et al. Expanding the clinical and molecular characteristics of PIGT-CDG, a disorder of glycosylphosphatidylinositol anchors. Molecular Genetics and Metabolism, June 2015. DOI/URL: https://doi.org/10.1016/j.ymgme.2015.04.007. (lam2015expandingtheclinical pages 1-3)
  • Murakami Y, Kinoshita T. GPI Anchor and Its Deficiency. Trends in Glycoscience and Glycotechnology, January 2024. DOI/URL: https://doi.org/10.4052/tigg.2331.1e. (murakami2024gpianchorand pages 1-2)
  • Mastrangelo M, et al. Epilepsy Phenotypes of Vitamin B6-Dependent Diseases: An Updated Systematic Review. Children, March 2023. DOI/URL: https://doi.org/10.3390/children10030553. (mario2023epilepsyphenotypesof pages 4-6)
  • Nguyen TTM, et al. Mutations in PIGS, Encoding a GPI Transamidase, Cause a Neurological Syndrome Ranging from Fetal Akinesia to Epileptic Encephalopathy. American Journal of Human Genetics, October 2018. DOI/URL: https://doi.org/10.1016/j.ajhg.2018.08.014. This is supporting pathway/comparator evidence rather than MCAHS-subtype evidence. (nguyen2018mutationsinpigs pages 4-6)
  • Ilkovski B, et al. Mutations in PIGY: expanding the phenotype of inherited glycosylphosphatidylinositol deficiencies. Human Molecular Genetics, August 2015. DOI/URL: https://doi.org/10.1093/hmg/ddv331. This is supporting residual-function and cellular-assay evidence rather than a canonical MCAHS subtype. (ilkovski2015mutationsinpigy pages 1-2, ilkovski2015mutationsinpigy pages 9-9)

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