We have identified that CFEOM1 results from heterozygous missense mutations in a kinesin motor protein, KIF21A. Eighty mutation-positive and unrelated probands of multiple ethnicities reported to date harbor only 11 unique missense mutations in KIF21A, which often arise de novo. These mutations are recurrent, specific, and alter only 7 of the 1,675 amino acids in KIF21A. Five of the seven are located in the third coiled-coil domain of the KIF21A stalk, including the 2860C>T (R954W) mutation found in 75% of probands, supporting an important role for this stalk domain in kinesin function. We are using genetic engineering, cell biological, and biochemical methods to address the pathologic consequences of the Kif21a R954W mutation as well as the normal role of Kif21a in axon growth, guidance and maintenance.