This variant, which results in more of a TUBB3-CFEOM phenotype with CFEOM, facial weakness, progressive peripheral neuropathy, and intellectual disability, may simply attenuate autoinhibition to a greater degree than the substitutions that result in isolated CFEOM, or may alter KIF21A function in another way. This evidence concerns the gene KIF21A and congenital fibrosis of the extraocular muscles.