KIF21A mutation in two Chinese families with congenital fibrosis of the extraocular muscles type 1 and 3.

Congenital fibrosis of the extraocular muscles (CFEOM) is a hereditary ocular disease and can be classified into three subtypes. The aim of the present study was to determine the genetic basis and describe the clinical phenotype of CFEOM type 1 and 3. Two Chinese families with CFEOM type 1 and 3 were identified. The patients and their family members were subjected to comprehensive ophthalmic examinations, including best­corrected visual acuity, slit­lamp examination, fundus examination, assessment of palpebral fissure size, levator function, ocular motility, and cover and forced duction tests. Genomic DNA was extracted from the leukocytes of venous blood samples collected from the two families and from 200 unrelated control subjects from the same population. Coding exons of the KIF21A gene were amplified using polymerase chain reaction analysis and sequenced directly in the two probands. The detected mutations were further analyzed in all available family members and the unrelated control subjects. A heterozygous mutation, c.2860C>T (p.R954W), in KIF21A was identified in the two families, and this was cosegregated with the presence of the diseases in the two families, however, it was absent in the 200 normal control subjects. Among the three affected family members with CFEOM1, differences were observed with regard to the presence of aberrant eye movement. The results indicated that, in the patients with CFEOM1 and CFEOM3, the disease was caused by the same KIF21A gene mutation. The KIF21A gene may be a major disease­causing gene for Chinese patients with CFEOM3. Phenotypic heterogeneity was observed in the patients with CFEOM1.