Novel Mutations in the PRPC8 Gene, Encoding a Pre-mRNA Splicing Factor in Patients with Autosomal Dominant Retinitis Pigmentosa

Abstract

Abstract: : Purpose: To screen patients with autosomal dominant retinitis pigmentosa (RP) for mutations in the PRPC8 gene, located on chromosome 17p13.3. Missense mutations in this gene were recently described as the cause of dominant RP in seven patients (Inglehearn et al., Hum.Mol.Genet.10:1555,2001). Although the entire gene had been screened, all reported mutations were located within a 42-bp sequence (14 codons) in the last exon (exon 42). Methods: We are screening exons 41 and 42 by designing oligonucleotide primers based on the flanking intron sequences and the 3’ untranslated region. Using these primers, we separately amplify the two exons in 190 unrelated patients with autosomal dominant RP. Amplified fragments are examined by single-strand conformation (SSCP) analysis. DNA samples with an SSCP variant are directly sequenced. Results: We have identified four patients each with a different mutation in the PRPC8 gene. All four patients are heterozygotes. Three mutations are novel: a frameshift due to a 1-bp deletion (Glu2331, 1-bp del, GAG≷-AG), a nonsense mutation (Gln2321End, CAG≷TAG), and a missense mutation (Tyr2334Asn, TAT≷AAT). Segregation analysis was performed on 23 family members of the index patient with the mutation Tyr2334Asn. Twelve relatives of this patient were heterozygous for the mutation: eleven of these were affected and one; was asymptomatic by history but has yet to be clinically examined. No segregation analysis has yet been performed on the families with the novel mutations (Glu2331, 1-bp del) and (Gln2321TER). The fourth mutation, Arg2310Gly (AGG≷GGG), has been previously described. Conclusion: Our frameshift and nonsense mutations are the first mutations of these types discovered so far in this gene, and they support the idea that the carboxyl-terminal region of the encoded protein is essential to retinal function. With the majority of the screening of the PRPC8 gene complete, we are currently evaluating whether the other novel mutations cosegregate with RP.

Keywords: 420 genetics • 480 mutations • 562 retinal degenerations: hereditary