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. RETINAL DEGENERATION AND SYSTEMIC DISEASEP hotoreceptor degeneration leads to blind- ness in millions of people and is thought to have a worldwide prevalence of one in 2000.Photoreceptor death and pigmentary retinal degeneration is the final common outcome in many retinal disorders (such as retinitis pigmentosa, RP) and many choroidal disorders (such as choroideremia), but it is also a common and serious manifestation of numerous metabolic, neuro-degenerative and other systemic diseases.The evaluation of patients with pigmentary retinal degeneration is especially challenging for various reasons.First, the retinal degenerations can be found in babies and infants, and dominate the phenotype early in the disease process, whereas life threatening systemic disease follows