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Complex mutations of USH2A gene denote ARRP

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A study of mutations associated with non-syndromic autosomal recessive retinitis pigmentosa (ARRP) in Spanish patients will ultimately help our knowledge of events leading to blindness or deafness, or both. Before then, though, the complexities of ARRP phenotypes and how these relate to genetic make up will take some unravelling.

The study found nine cases (one homozygous, eight carriers) of missense mutation of the C759F allele of the USH2A usherin gene among 196 unrelated patients. Screening family members of six cases disclosed a further 21 carriers (seven with RP, 14 unaffected) and three homozygous cases (two unaffected). Six other mutations—three of them new—emerged after complete USH2A analysis of patients and selected family members, which uncovered compound heterozygotes with nonsense, slicing, and misssense mutations.

Huge phenotypic variation existed with C759F mutation, from symptomatic homozygosity to asymptomatic homozygosity, suggesting perhaps that another mutant allele underlies the RP phenotype in asymptomatic homozygous individuals

Patients with non-syndromic ARRP and 100 blood donor controls were screened by PCR analysis for C759F mutation. Screening was extended to family members of six patients with mutations; in three no family members were available. The USH2A gene coding region was analysed in all patients with the C759F mutation and selected family members.

Only a few gene mutations have been identified so far in a small percentage of Spanish families with ARRP, but until now did not include the recently described missense mutation in the USHA2 gene (C759F), which accounts for 4.5% of non-syndromic ARRP in North Americans.

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