[Genetic causes of retinal degeneration]

Premature death of rod and cone photoreceptor cells in the human retina leads to severe visual handicaps in affected patients. The two most important groups of retinal dystrophies, macular degeneration and retinitis pigmentosa, differ in primary symptoms and disease progression. Macular degeneration starts in the central retina and progresses towards the periphery. In RP, photoreceptor cell death starts in the periphery and then proceeds to the central part of the retina. Molecular studies have revealed important new findings during the last decade. There are two important results to be emphasized: 1. The very same clinical symptoms can result from mutations in different genes. RP is a prominent example for this phenomenon. 2. Mutations in the same gene can result in different phenotypes. The correlation between genotype and phenotype is not essentially straight forward. This may indicate that other factors can influence the phenotypic consequences of mutations. Different X-linked retinal dystrophies represent excellent examples for these findings.