CYP4V2 is a microsomal enzyme with ω-hydroxylase activity on both saturated and polyunsaturated medium and long-chain fatty acids [17,18,19] and is expressed in almost all body tissues, especially in the RPE and neural retina, in which alterations in lipid metabolism are proposed to be the major pathogenic mechanism of BCD. Here, CYP4V2 is linked to Bietti crystalline dystrophy.