BCOR and microphthalmia, Lenz type: However, it is clear that Lenz microphthalmia is clinically variable and genetically heterogeneous and prior data show that phenotypes compatible with this description map both to Xp and Xq, the former caused by mutations in the BCOR gene (MIM 309800) which causes a phenotype that overlaps extensively with Lenz microphthalmia, and shares the X-linked inheritance pattern in two families [12,14].