The genetic landscape of inherited retinal dystrophies in Arabs.

Inherited retinal dystrophies (IRDs) are a major cause of vision loss. Altogether are highly heterogeneous genotypically and phenotypically, exhibiting substantial differences worldwide. To shed more light on these conditions, we investigated the genetic and phenotypic landscape of IRDs in the Arabs globally and per country.We analyzed 1,621 affected individuals from 16 Arabic countries reported in 198 articles. At the phenotypic level, rod-cone dystrophy (RCD) and Usher syndrome were the most prevalent conditions among non-syndromic and syndromic IRDs. At the gene level, TULP1, ABCA4, RP1, CRB1, MYO7A, RPE65, KCNV2, and IMPG2 were the most mutated genes. Interestingly, all except CRB1 were highly prevalent because they harbored founder mutations, implying that consanguinity is a major determinant in Arab countries. Of note, ~ 93% of the investigated individuals carried homozygous mutations. The country analysis for the IRDs conditions and their associated genotypes revealed that whereas Leber Congenital Amaurosis, RCD, and USHER syndrome were widely distributed, bestrophinopathies and non-syndromic hearing loss were restricted to specific countries (till now).This study could be a starting point for initiating suitable health policies towards IRDs in the Arab world. The high degree of homozygosity urges the need for genetic counsellors to provide personalized information and support the affected individuals.

Novel Missense and Splice Site Mutations in USH2A, CDH23, PCDH15, and ADGRV1 Are Associated With Usher Syndrome in Lebanon.

The purpose of this study was to expand the mutation spectrum by searching the causative mutations in nine Lebanese families with Usher syndrome (USH) using whole-exome sequencing. The pathogenicity of candidate mutations was first evaluated according to their frequency, conservation, and in silico prediction tools. Then, it was confirmed via Sanger sequencing, followed by segregation analysis. Finally, a meta-analysis was conducted to calculate the prevalence of USH genes in the Lebanese population. Three missense mutations, two splice site mutations, and one insertion/deletion were detected in eight of the families. Four of these variants were novel: c.5535C > A; p.(Asn1845Lys) in exon 41 of CDH23, c.7130G > A; p.(Arg2377Gln) in exon 32 of ADGRV1, c.11390-1G > A in USH2A, and c.3999-6A > G in PCDH15. All the identified mutations were shown to be likely disease-causing through our bioinformatics analysis and co-segregated with the USH phenotype. The mutations were classified according to the ACMG standards. Finally, our meta-analysis showed that the mutations in ADGRV1, USH2A, and CLRN1 are the most prevalent and responsible for approximately 75% of USH cases in Lebanon. Of note, the frequency USH type 3 showed a relatively high incidence (23%) compared to the worldwide prevalence, which is around 2-4%. In conclusion, our study has broadened the mutational spectrum of USH and showed a high heterogeneity of this disease in the Lebanese population.

The genetics of rod-cone dystrophy in Arab countries: a systematic review.

Since a substantial difference in the prevalence of genetic causes of rod-cone dystrophy (RCD) was found among different populations, we conducted a systematic review of the genetic findings associated with RCD in Arab countries. Of the 816 articles retrieved from PubMed, 31 studies conducted on 407 participants from 11 countries were reviewed. Next-generation sequencing (NGS) was the most commonly used technique (68%). Autosomal recessive pattern was the most common pattern of inheritance (97%) and half of the known genes associated with RCD (32/63) were identified. In the Kingdom of Saudi Arabia, in addition to RP1 (20%) and TULP1 (20%), gene defects in EYS (8%) and CRB1 (7%) were also prevalently mutated. In North Africa, the main gene defects were in MERTK (18%) and RLBP1 (18%). Considering all countries, RP1 and TULP1 remained the most prevalently mutated. Variants in TULP1, RP1, EYS, MERTK, and RLBP1 were the most prevalent, possibly because of founder effects. On the other hand, only ten Individuals were found to have dominant or X-linked RCD. This is the first time a catalog of RCD genetic variations has been established in subjects from the Arabi countries. Although the last decade has seen significant interest, expertise, and an increase in RCD scientific publication, much work needs to be conducted.