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seizures-scoliosis-macrocephaly syndrome - Clinical Profile, Genes & Research | Kisho | Kisho

Rare Disease

seizures-scoliosis-macrocephaly syndrome

MONDO:0014731

Also known as:SSM syndromeSSMSseizures, scoliosis, and macrocephaly syndrome

Overview

Seizures-scoliosis-macrocephaly syndrome is a rare, genetic neurometabolic disorder characterized by seizures, macrocephaly, delayed motor milestones, moderate intellectual disability, scoliosis with no exostoses, muscular hypotonia present since birth, as well as renal dysfunction. Coarse facial features (including hypertelorism and long hypoplastic philtrum) and bilateral cryptorchidism (in males) are also commonly reported. Additional manifestations include abnormal gastrointestinal motility (resulting in constipation, diarrhea, gastroesophageal reflux and dysphagia), gait disturbances, strabismus and ventricular septal defects.

GeneticsAutosomal recessive · EXT2 (chr 11)

ResearchLimited published research (3 articles)

Clinical Presentation

Built from Human Phenotype Ontology (HPO) phenotype annotations and GeneReviews clinical descriptions. Features represent findings documented across known cases — not an exhaustive list of possible symptoms.

Features include always present findings: Moderate intellectual disability, Seizure, Low muscle tone (hypotonia), and Macrocephaly and others; and common findings: Strabismus, Ventricular septal defect, Hypertelorism, and Overlapping toe and others. 39 total HPO annotations.

Organ System	Phenotype Count	Example Features
Brain and nerves	7	Poor speech, Moderate intellectual disability, Seizure

Genetic Landscape

Assembled from HGNC gene records, ClinGen gene-disease validity evidence, and ClinVar pathogenic variant data. Validity classifications reflect the strength of published evidence linking each gene to this disease.

EXT2 encodes exostosin glycosyltransferase 2 (718 aa). Glycosyltransferase forming with EXT1 the heterodimeric heparan sulfate polymerase which catalyzes the elongation of the heparan sulfate glycan backbone. Highest expression in Cells Cultured fibroblasts (101.7 TPM) and Uterus (68.9 TPM).

Seizures-scoliosis-macrocephaly syndrome is associated with mutations in the EXT2 gene on chromosome 11.

The EXT2 protein participates in EXT2 V187Pfs*115, Defective EXT2 causes exostoses 2, and Defective EXT1 causes exostoses 1, TRPS2 and CHDS pathways.

EXT2 is classified as a druggable target (Clinically Actionable and Enzyme categories) with score 17.4.

Diagnosis

Genetic testing for EXT2 is available. Testing is considered confirmatory for diagnosis.

Prognosis

Phenotype severity distribution: 7 always present features, 8 common features.

Estimated prevalence: <1 in 1,000,000 (VERY_RARE).

Research Landscape

Sourced from ClinicalTrials.gov and PubMed. Publication types are classified using NLM-curated article metadata; research type breakdowns reflect the nature of published work for this disease.

No clinical trials have been registered for seizures-scoliosis-macrocephaly syndrome.

8 publications have been identified in PubMed for seizures-scoliosis-macrocephaly syndrome. Kisho has analyzed 3 by research type. Research spans Case Report / Case Series (67%) and Review / Meta-Analysis (33%).

Recent Publications

Diop JPD (2026). [PMID: 41839667](https://pubmed.ncbi.nlm.nih.gov/41839667/). *J Genet Eng Biotechnol*. [Case Report / Case Series]
She QY (2024). [PMID: 39027568](https://pubmed.ncbi.nlm.nih.gov/39027568/). *Heliyon*. [Case Report / Case Series]
Ouidja MO (2024). [PMID: 39630030](https://pubmed.ncbi.nlm.nih.gov/39630030/). *Essays Biochem*. [Review / Meta-Analysis]

Data assembled from 6 of 12 sources · Last updated Sep 20, 2026, 5:37 PM UTC

MONDOHPOClinicalTrials.govFDAPubMedHGNCClinVarClinGenGeneReviewsOrphanetOMIMRUSP

Medical References

External Resources

OMIM

Online Mendelian Inheritance in Man

OMIM:616682

Orphanet

European rare disease database

Orphanet:466926

GARD

Genetic and Rare Diseases Info Center

GARD:17836

Questions for Your Care Team

→Should my partner and I meet with a genetic counselor to discuss carrier status and family planning?
→Are there specialists or centers of excellence for this condition in my area?
→Is there a patient registry I should consider joining?

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seizures-scoliosis-macrocephaly syndrome

Overview

Clinical Presentation

Genetic Landscape

Diagnosis

Prognosis

Research Landscape

Recent Publications

Medical References

External Resources

OMIM

Orphanet

GARD

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Questions for Your Care Team

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