Researchers at UCL Institute of Ophthalmology and Moorfields Eye Hospital, London, UK, have reported the largest series and longitudinal study results in sector retinitis pigmentosa, that includes the identification of a genotypic spectrum of the disease being broader than previously reported. The researchers have published significant longitudinal data, expected to be valuable in informing patient prognosis and counselling, potentially leading to novel therapeutics for future treatments.
Retinitis pigmentosa (RP) is characterized by nyctalopia, visual field (VF) defects, and progressive retinal degeneration, including a sub-group of sector RP, and pericentral RP, which are atypical variants of RP. Sector RP was first reported in 1937 and describes changes in one quadrant or one half of each fundus, commonly observed in the inferior and nasal quadrants. Generally, the visual field defects are less severe than those of typical RP and may lack symptoms of defective dark adaptation but researchers also report widespread abnormalities of rod and cone function detected by ERG. Sectoral changes have been observed in autosomal dominant RP and in females heterozygous for X-linked RP. However, the current research has identified nine genes as causative for the disease, of which five (5) were not previously implicated – PRPS1, MYO7A, EYS, IMPDH1 and RP1. In addition, data for disease natural history and information is expected to inform patient counselling and prognosis for each individual genotype.
Details of the results have shown that twenty-six molecularly confirmed patients from 23 different families were identified. The mode of inheritance was autosomal recessive (AR, n=6: USH1C, n=2; MYO7A, n=2; CDH3, n=1; EYS, n=1), X-linked (XL, n=4: PRPS1, n=1; RPGR, n=3), and autosomal dominant (AD, n=16: IMPDH1, n=3; RP1, n=3; RHO, n=10), with a mean age of disease onset of 38.5, 30.5 and 39.0 years respectively. As highlighted, five of the genes had not previously been reported to cause sector RP, while inferior and nasal predilection was common across the different genotypes and patients and tended to maintain good central vision. Commenting on the study, researchers stated that, “it is difficult to draw conclusions for disease prevalence within the general population, as well as about the prevalence of each gene in patients with sector RP, since mild cases or cases with dominant inheritance may lack molecular confirmation. Our study was retrospective, and as a result not all the data were available for all the patients”.