Remarkably, KIF21A missense variants that result in isolated CFEOM alter amino acid residues located precisely in the lateral aspect of the motor domain or the third coiled-coil domain of the stalk (Figure 5) and disrupt the interaction of these two domains, thus attenuating KIF21A autoinhibition (van der Vaart et al., 2013; Cheng et al., 2014). This evidence concerns the gene KIF21A and congenital fibrosis of the extraocular muscles.