Author: Telmo Cortinhal (Portugal)
Co-authors: Sara Geada, Emmanuel Neves, Ana Luísa Carvalho, Joaquim Murta, Rufino Silva, João Pedro Marques
Purpose
Sector retinitis pigmentosa (sRP) is a rare, atypical, and milder variant of rod-cone degeneration, in which only one or two quadrants of the retina are involved. Despite being historically associated with the RHO gene, the mutational spectrum of sRP is evolving with other causative genes recently implicated. This study aimed to characterize the genotypes, phenotypes, and natural history of a Portuguese cohort with sRP.
Setting/Venue
Ophthalmology Unit, Centro Hospitalar e Universitário de Coimbra (CHUC), Coimbra, Portugal.
Methods
Retrospective, observational study. Patients with a clinical diagnosis of sRP and available genetic testing results were identified using the IRD-PT registry. Genetic testing was clinically oriented in all probands. Variants were classified according to the American College of Medical Genetics and Genomics standards and guidelines. Only class IV (Likely Pathogenic) or V (Pathogenic) variants were considered to be disease causing. The clinical diagnosis was established based on functional testing [best corrected visual acuity (BCVA) and visual field testing] and multimodal imaging [color fundus photography, fundus autofluorescence (FAF) and optical coherence tomography (OCT)]. Clinical progression was evaluated throughout follow-up.
Results
Fourteen patients from twelve families were included. Mutations in syndromic and non-syndromic RP-related genes were identified in 8 families, for a diagnostic yield of 66.7%. EYS was the most frequently implicated gene (4 families), followed by RHO (2 families), and finally MYO7A and NPHP1 (1 family each). In most unsolved cases, no clinically significant variants were found. However, for one unsolved case, a variant of uncertain significance (class III) was identified in the RHO gene. All cases were bilateral and symmetrical except for two, which were unilateral (1 unsolved and 1 solved, in association with NPHP1 variants). Inferior and/or nasal involvement of the retina on FAF was noted in all cases, with a crescent shaped hyper-autofluorescent band separating the atrophic area from the unaffected, iso-autofluorescent retina. Visual field testing revealed superior visual field defects of varying extents, always in close association with the observed FAF findings. Over a median follow-up period of 32.5 months, BCVA remained stable and ≥20/32 OU in 9/14 patients. Multimodal imaging revealed no progression over the follow-up period.
Conlusions
This study highlights the genotypic heterogeneity of sRP in a Portuguese cohort. Inferior and nasal predilection was common across the different genotypes, and a high proportion of patients maintained good central vision. The longitudinal data provided herein will help to provide patients with accurate prognoses and counseling.
Financial Disclosure
None
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