The abnormal development of axon tracts resulting in the corpus callosum hypoplasia and adducted thumbs appears to be caused by malfunction of the cytoplasmic domain of L1CAM.
X-linked hydrocephalus, HSAS (hydrocephalus due to stenosis of aqueduct of Sylvius), MASA (mental retardation, aphasia, shuffling gait, and adducted thumbs), and CRASH (corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraplegia, and hydrocephalus) syndromes are allelic disorders.