Purpose.: To identify the genetic basis of a large consanguineous Spanish pedigree affected with autosomal recessive retinitis pigmentosa (arRP) with premature macular atrophy and myopia. Methods.: After a high-throughput cosegregation gene chip was used to exclude all known RP and Leber congenital amaurosis (LCA) candidates, genome-wide screening and linkage analysis were performed. Direct mutational screening identified the pathogenic mutation, and primers were designed to obtain the RT-PCR products for isoform characterization. Results.: Mutational analysis detected a novel homozygous PROM1 mutation, c.869delG in exon 8 cosegregating with the disease. This variant causes a frameshift that introduces a premature stop codon, producing truncation of approximately two-thirds of the protein. Analysis of PROM1 expression in the lymphocytes of patients, carriers, and control subjects revealed an aberrant transcript that is degraded by the nonsense-mediated decay pathway, suggesting that the disease is caused by the absence of the PROM1 protein. Three (s2, s11 and s12) of the seven alternatively spliced isoforms reported in humans, accounted for 98% of the transcripts in the retina. Given that these three contained exon 8, no PROM1 isoform is expected in the affected retinas. Conclusions.: A remarkable clinical finding in the affected family is early macular atrophy with concentric spared areas. The authors propose that the hallmark of PROM1 truncating mutations is early and severe progressive degeneration of both rods and cones and highlight this gene as a candidate of choice to prioritize in the molecular genetic study of patients with noncanonical clinical peripheral and macular affectation.

NGS-based genetic diagnosis has completely revolutionized the human genetics field. In this study, we have aimed to identify new genes and mutations by Whole Exome Sequencing (WES) responsible for inherited retinal dystrophies (IRD). A cohort of 33 pedigrees affected with a variety of retinal disorders was analysed by WES. Initial prioritization analysis included around 300 IRD-associated genes. In non-diagnosed families a search for pathogenic mutations in novel genes was undertaken. Genetic diagnosis was attained in 18 families. Moreover, a plausible candidate is proposed for 10 more cases. Two thirds of the mutations were novel, including 4 chromosomal rearrangements, which expand the IRD allelic heterogeneity and highlight the contribution of private mutations. Our results prompted clinical re-evaluation of some patients resulting in assignment to a syndromic instead of non-syndromic IRD. Notably, WES unveiled four new candidates for non-syndromic IRD: SEMA6B, CEP78, CEP250, SCLT1, the two latter previously associated to syndromic disorders. We provide functional data supporting that missense mutations in CEP250 alter cilia formation. The diagnostic efficiency of WES, and strictly following the ACMG/AMP criteria is 55% in reported causative genes or functionally supported new candidates, plus 30% families in which likely pathogenic or VGUS/VUS variants were identified in plausible candidates. Our results highlight the clinical utility of WES for molecular diagnosis of IRD, provide a wider spectrum of mutations and concomitant genetic variants, and challenge our view on syndromic vs non-syndromic, and causative vs modifier genes.