CYP4V2 and Bietti crystalline corneoretinal dystrophy: Nearly 80% of BCD patients carry mutations in exons 7 to 11 of CYP4V2 gene, and three variants c.802-8_810del17insGC/GT, c.992A>C and c.1091-2A>G can account for more than 70% of the mutations identified26.