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 (Orphanet, Dec 2016).
Menkes et al. (1964) described a family with 5 males (in 4 sibships of 2 generations connected through females) with partial agenesis of the corpus callosum. Clinical features included severe intellectual retardation and intractable seizures. Postmortem studies of ... Menkes et al. (1964) described a family with 5 males (in 4 sibships of 2 generations connected through females) with partial agenesis of the corpus callosum. Clinical features included severe intellectual retardation and intractable seizures. Postmortem studies of 1 patient showed a combination of anatomic and chemical abnormalities. These patients lacked the more generalized malformations of the FG syndrome (305450). Kaplan (1983) reported a 2-year-old boy who had psychomotor retardation, weakness of the arms and Hirschsprung disease (142623) with complete agenesis of the corpus callosum and hypoplasia of the inferior vermis and cerebellum. His 24-year-old maternal uncle had severe psychomotor retardation and agenesis of the corpus callosum by CT scan, but none of the other physical features found in the nephew. Kang et al. (1992) reported dysgenesis of the corpus callosum in 4 males related as first cousins through their mothers, who were sisters. There was associated microcephaly, mental retardation, spasticity, and unusual facial appearance. Hydrocephalus and/or interhemispheric cyst was found also. Basel-Vanagaite et al. (2006) reported 2 Jewish male sibs with partial agenesis of the corpus callosum and mild mental retardation. Neither sib had hydrocephalus, adducted thumbs, or absent speech associated with X-linked hydrocephalus (307000) or MASA syndrome (303350). The older sib also had Hirschsprung disease and congenital dislocation of the radial heads bilaterally, resulting in limited extension and supination of the elbows.
In 2 Jewish sibs with X-linked partial agenesis of the corpus callosum, Basel-Vanagaite et al. (2006) identified a heterozygous mutation in the L1CAM gene (308840.0017). The authors emphasized the well-known inter- and intrafamilial phenotypic variability in patients with ... In 2 Jewish sibs with X-linked partial agenesis of the corpus callosum, Basel-Vanagaite et al. (2006) identified a heterozygous mutation in the L1CAM gene (308840.0017). The authors emphasized the well-known inter- and intrafamilial phenotypic variability in patients with L1CAM mutations.