L1 syndrome
Findings
No curated finding names L1 syndrome yet. Everything below is reference data from Mondo, HPO and GenCC, not evidence about what affects it.
Definition
L1 syndrome is a mild to severe congenital X-linked developmental disorder characterized by hydrocephalus of varying degrees of severity, intellectual deficit, spasticity of the legs, and adducted thumbs. The syndrome represents a spectrum of disorders including: X-linked hydrocephalus with stenosis of the aqueduct of Sylvius (HSAS), MASA syndrome, X-linked complicated hereditary spastic paraplegia type 1, and X-linked complicated corpus callosum agenesis.
Definition from the Mondo Disease Ontology (MONDO:0017140), read 2026-09-29. CC BY 4.0.
Features
16 features
What the disease is reported to present with, and how often among people who have it — never how often a feature means the disease. HPO, annotations 2026-09-02.
- Aqueductal stenosisHPOHP:0002410
- Very frequent (80% to 99% of cases)
- DepressionHPOHP:0000716
- Very frequent (80% to 99% of cases)
- Gait disturbanceHPOHP:0001288
- Very frequent (80% to 99% of cases)
- Global developmental delayHPOHP:0001263
- Very frequent (80% to 99% of cases)
- HeadacheHPOHP:0002315
- Very frequent (80% to 99% of cases)
- Hemiplegia/hemiparesisHPOHP:0004374
- Very frequent (80% to 99% of cases)
- Hydrocephalus
Show the remaining 4
- Adducted thumbHPOHP:0001181
- Frequent (30% to 79% of cases)
- Aganglionic megacolonHPOHP:0002251
- Occasional (5% to 29% of cases)
- SeizureHPOHP:0001250
- Occasional (5% to 29% of cases)
- Skeletal muscle atrophyHPOHP:0003202
- Occasional (5% to 29% of cases)
Genes
1 gene
Germline variants in the gene encoding each protein, as classified by GenCC submitters, each in their own words. Limited, disputed and refuted submissions are listed too.
- L1CAMHGNC:6470
- Definitive · ClinGen · X-linked · 2026
- Strong · PanelApp Australia · X-linked · 2025
Where it sits
Other names
3 names
Resolves to: L1 syndrome
- Also called
- corpus callosum hypoplasia-retardation-adducted thumbs-spasticity-hydrocephalus syndromeCRASH syndromeL1CAM syndrome