KIF21A and congenital fibrosis of extraocular muscles: Eight of the CFEOM1 probands harbor previously reported KIF21A mutations: 5 harbor the most common CFEOM1 mutation, 2860C>T, which alters the first nucleotide of the triplet codon encoding amino acid residue 954 (R954W); 2 harbor the second most common mutation, 2861G>A, which alters the second nucleotide of the same triplet codon (R954Q); while 1 harbors the 1067T>C mutation which alters a residue located at the end of the kinesin motor domain (M356T), and is the third proband with this mutation we have identified.