Retinitis pigmentosa (RP) is a group of genetic disorders with extremely high heterogeneity, characterized by pigment deposits predominant in the peripheral retina and by a relative sparing of the central retina, which leads to blindness. RP patients show a wide variation in severity, mode of inheritance, age of onset, progression, and clinical manifestation. RP is usually non-syndromic (isolated), but also it can be associated with systemic disease, such as Usher syndrome and other conditions. The prevalence of non-syndromic forms of retinitis pigmentosa is approximately 1/4,000. There are autosomal dominant, autosomal recessive, X-linked, and rare mitochondrial and digenic forms of retinitis pigmentosa. The autosomal dominant and the autosomal recessive forms each account for 20% of the cases, the X-linked is about 10%, while the rest (50%) are still unidentified types of retinitis pigmentosa.
Diagnosis of retinitis pigmentosa is based on the presence of night blindness and peripheral visual field defects, lesions in the fundus, hypovolted electroretinogram traces, and progressive worsening of these signs. Molecular diagnosis can be performed, but it is difficult because of the genetic heterogeneity of the disease. Therapies of retinitis pigmentosa are limited and there is no therapy to stop the progression of the disease or restores the vision; it is only restricted to slowing down the degenerative process by sunlight protection and vitamin therapy.
Retinitis pigmentosa 20 (RP20) is inherited as an autosomal recessive pattern caused by mutations in the RPE65 gene.
