A Review of Secondary Photoreceptor Degenerations in Systemic Disease.

Photoreceptor neuronal degenerations are common and incurable causes of human blindness with one in 2000 affected. Approximately, half of all patients are associated with known mutations in more than 200 disease genes. Most retinal degenerations are restricted to the retina (primary retinal degeneration) but photoreceptor degeneration can also be found in a wide variety of systemic and syndromic diseases. These are called secondary retinal degenerations. We review several well-known systemic diseases with retinal degenerations (RD). We discuss RD with hearing loss, RD with brain disease, and RD with musculoskeletal disease. We then postulate which retinal degenerations may also have previously undetected systemic features. Emerging new and exciting evidence is showing that ubiquitously expressed genes associated with multitissue syndromic disorders may also harbor mutations that cause isolated primary retinal degeneration. Examples are RPGR, CEP290, CLN3, MFSD5, and HK1 mutations that cause a wide variety of primary retinal degenerations with intact systems.