L1, also known as L1CAM, is a transmembrane protein; it is a neuronal cell adhesion molecule, member of the L1 protein family, of 200-220 kDa, and involved in axon guidance and cell migration with a strong implication in treatment-resistant cancers. L1CAM has also been designated CD171 . The protein encoded by this gene is an axonal glycoprotein belonging to the immunoglobulin superfamily of proteins. 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 three X-linked neurological syndromes known by the acronym CRASH.