The disorder CFEOM1 is inherited as an autosomal dominant trait, and if all affected members of a CFEOM family meet CFEOM1 criteria, the family is classified as a CFEOM1 pedigree. In most pedigrees, CFEOM1 maps to the FEOM1 locus at the centromeric region of chromosome 1231 and results from heterozygous mutations in KIF21A.30 In addition, rare CFEOM1 probands likely harbor mutations in the FEOM3 gene.32KIF21A has 3 domains and is a member of the kinesin family of molecular motors that transport cargo along microtubules and, in neurons, are responsible for anterograde axonal transport.33 The motor domain contains the microtubule binding site. The tail domain is where cargo is loaded and carried,often via an adaptor or scaffolding protein or protein complex.34 The stalk domain is a flexible connector between the motor and tail that typically contains α-helical coiled-coil repeats through which kinesin can homodimerize or heterodimerize, permitting 2 kinesin motors to “walk” down the microtubule. In some instances, the distal stalk also interacts with cargo.35,36 Mouse Kif21a is expressed abundantly in the brain, including neuronal cell bodies, axons, and dendrites33; its cargo is not known. Other kinesin family members regulate many aspects of neuronal differentiation, including neurite extension,37,38 collateral branching,39 and growth cone and cytoskeleton dynamics,39- 41 supporting the hypothesis that CFEOM1 results from a defect in neuronal differentiation.