Kinesin family member 21A (KIF21A) mutation is the most common cause for congenital fibrosis of the extraocular muscles type 1 (CFEOM1) in populations worldwide. However, only 12 missense mutations have been reported to date. In this study, KIF21A screening was performed in two Chinese families with CFEOM1. Ophthalmological examinations were performed. The coding exons and adjacent intronic regions of KIF21A were analyzed with cycle sequencing. The novel mutation identified was further evaluated in 150 normal control individuals and available family members. Two heterozygous mutations in KIF21A, c.3000_3002delTGA (p.Asp1001del) and c.2861G>A (p.Arg954Gln), were detected in two families. The novel deletion involves a conserved residue in the coiled-coil domain of KIF21A and is co-segregated with the disease in the examined family, yet was absent in the 300 control chromosomes. In addition, apart from typical phenotypes for CFEOM1, optic disc hypoplasia was also observed in two patients. Deletion mutation in KIF21A has not been previously reported. Our study expands the KIF21 mutation spectrum. This study adds to the current state of knowledge about KIF21A mutations and CFEOM1, which may improve future clinical practice.

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