2011). Our results suggest that CYP4V2 mutations in our patients may reside in genomic locations that were not studied in our gene sequencing protocol, that is, in promoter, untranslated region, or deep intronic regions. Alternatively our data suggests locus heterogeneity and a second Bietti's gene. We were able to re-examine five CYP4V2-negative crystalline retinal dystrophy patients and found that their phenotypes (Figs. S1, S2) are indistinguishable from our BCD patients. Here, CYP4V2 is linked to Bietti crystalline dystrophy.