Syndromic forms of inherited retinal dystrophies: a comprehensive molecular diagnosis of consanguineous Pakistani families using capture panel sequencing.

Background: Inherited retinal dystrophies (IRDs) represent a clinically and genetically heterogeneous group of genetic disorders that involve photoreceptors and/or retinal pigment epithelium degeneration. IRDs may occur as an isolated condition or may represent an ocular manifestation of a multisystemic disorder referred as syndromic IRD. To increase the understanding of the molecular determinants of syndromic IRD-related genes in the Pakistani population, we revealed the genetic profile of 13 consanguineous Pakistani families using capture panel sequencing.

Methods: We performed comprehensive molecular testing on 72 IRD segregating Pakistani families using targeted capture panel sequencing of 344 known genes. The pathogenicity of candidate variants was assessed using American College of Medical Genetics and Genomics guidelines, followed by Sanger sequencing for segregation analysis.

Results: Causative variants in previously reported syndromic IRDs genes were detected in 13/72 (18%) IRD families, including 5/72 (6.94%), 4/72 (5.55%), 2/72 (2.8%), 1/72(1.38%) and 1/72 (1.38%) in Usher syndrome, Bardet-Biedl syndrome, Batten disease, retinitis pigmentosa with situs inversus and Stickler syndrome segregated families, respectively. Disease-causing variants included nine previously reported and six novel homozygous variants, i.e., c.1143G>C in USH2A, c.470G>A in MYO7A, c.877-2A>G in PCDH15, c.347C>T in ARL6, c.581C>T in CLN5 and c.100+1G>T in ARL2BP gene segregation with disease phenotype in eight families. Two heterozygous variants of the USH2A gene, i.e., c.12093C>A and c.9815C>T, were segregated in a compound heterozygous form in family RP243. Furthermore, RP151 showed segregation of a heterozygous variant c.247G>A in a Stickler syndrome gene, i.e., COL2A1, in an autosomal dominant manner.

Conclusions: This study reaffirms the clinical and genetic heterogeneity of syndromic IRD-associated genes and confirms the usefulness of molecular methods in advancing our understanding of these conditions in consanguineous populations. The most commonly mutated Bardet-Biedl syndrome gene was ARL6 (75%) and the most commonly mutated Usher syndrome genes were USH2A (40%) and MYO7A (40%). Our data could serve as a reference for future studies and the development of treatment modalities for affected families of Pakistani origin.