Background：

The protein encoded by this gene is an axonal glycoprotein belonging to the immunoglobulin supergene family. The ectodomain， consisting of several immunoglobulin-like domains and fibronectin-like repeats (type III)， is linked via a single transmembrane sequence to a conserved cytoplasmic domain. This cell adhesion molecule plays an important role in nervous system development， including neuronal migration and differentiation. Mutations in the gene cause X-linked neurological syndromes known as CRASH (corpus callosum hypoplasia， retardation， aphasia， spastic paraplegia and hydrocephalus). Alternative splicing of this gene results in multiple transcript variants， some of which include an alternate exon that is considered to be specific to neurons.