CYP4V2, a relatively new member of human cytochrome P450 (P450) enzymes, is termed an "orphan" P450 because its substrate specificity and physiological roles are unknown. Mutations in the CYP4V2 gene is associated with an autosomal recessive inherited ocular disease named Bietti's crystalline dystrophy (BCD). The strong gene-disease associations provide unique opportunities for elucidating the substrate specificity of this orphan P450s and unraveling the biochemical pathways that may be impacted in patients with CYP4V2 functional deficits.