Objective: To identify the genetic causes underlying early-onset autosomal recessive retinitis pigmentosa (arRP) in the Spanish population and describe the associated phenotype. Design: Case series. Participants: A total of 244 unrelated families affected by early-onset arRP. Methods: Homozygosity mapping or exome sequencing analysis was performed in 3 families segregating arRP. A mutational screening was performed in 241 additional unrelated families for the p.Ser452Stop mutation. Haplotype analysis also was conducted. Individuals who were homozygotes, double heterozygotes, or carriers of mutations in RP1 underwent an ophthalmic evaluation to establish a genotype-phenotype correlation. Main Outcome Measures: DNA sequence variants, homozygous regions, haplotypes, best-corrected visual acuity, visual field assessments, electroretinogram responses, and optical coherence tomography images. Results: Four novel mutations in RP1 were identified. The new mutation p.Ser542Stop was present in 11 of 244 (4.5%) of the studied families. All chromosomes harboring this mutation shared the same haplotype. All patients presented a common phenotype with an early age of onset and a prompt macular degeneration, whereas the heterozygote carriers did not show any signs of retinitis pigmentosa (RP). Conclusions: p.Ser542Stop is a single founder mutation and the most prevalent described mutation in the Spanish population. It causes early-onset RP with a rapid macular degeneration and is responsible for 4.5% of all cases. Our data suggest that the implication of RP1 in arRP may be underestimated. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article.
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