Young monozygotic twin sisters with fundus albipunctatus and cone dystrophy

To describe young monozygotic twin sisters with fundus albipunctatus (a type of autosomal recessive stationary night blindness caused by mutations of the 11-cis retinol dehydrogenase gene [RDH5]) associated with cone dystrophy, previously reported in elderly men.

Ophthalmologic examinations were performed, and the RDH5 gene was analyzed by direct genomic sequencing.

Twin 23-year-old sisters with high myopic refractive errors of approximately -13 diopters were diagnosed as having fundus albipunctatus. Their photopic electroretinographic responses were markedly reduced, and cone dystrophy was diagnosed. One twin had macular degeneration with reduced best-corrected visual acuity, while the other twin had normal maculae with good visual acuity. A compound heterozygous mutation, Val132Met and Arg280His, in the RDH5 gene was found in both sisters.

Cone dystrophy can be present in patients with fundus albipunctatus, not only elderly men but also young women. The clinical severity differed between monozygotic twins with fundus albipunctatus and cone dystrophy.Clinical Relevance The patient's sex is not critical for the presence of cone dystrophy in patients with fundus albipunctatus. The discordant findings in the twins indicate that factors other than genetics influenced the phenotype.