Intronic Alterations inBRCA1andBRCA2: Effect on mRNA Splicing Fidelity and Expression

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Germline mutations in the human breast cancer susceptibility genesBRCA1andBRCA2account for the majority of hereditary breast and ovarian cancer. In spite of the large number of sequence variants identified inBRCA1andBRCA2mutation analyses, many of these genetic alterations are still classified as variants of unknown significance (VUS). In this study, we evaluated 12BRCA1/2intronic variants in order to differentiate their pathogenic or polymorphic effects on the mRNA splicing process. We detected the existence of aberrant splicing in threeBRCA1variants (c.301-2delA/IVS6-2delA, c.441+1G>A/IVS7+1G>A, and c.4986+ 6T>G/IVS16+6T>G) and twoBRCA2variants (c.8487+1G>A/IVS19+1G>A and c.8632-2A> G/IVS20-2A>G). All but one of the aberrant transcripts arise from mutations affecting the conserved splice acceptor or donor sequences and all would be predicted to result in expression of truncated BRCA1 or BRCA2 proteins. However, we demonstrated that four of these splice-site mutations (i.e., c.301-2delA, c.441+1G>A, c.4986+6T>G, and c.8632-2A>G) with premature termination codons were highly unstable and were unlikely to encode for abundant expression of a mutant protein. Three variants ofBRCA1(c.212+3A>G/IVS5+3A>G, c.593+8A>G/IVS9+8A>G, and c.4986-20A>G/IVS16-20A>G) and four variants ofBRCA2(c.516-19C>T/IVS6-19C>T, c.7976-4_7976_3delTT/IVS17-4delTT, c.8487+19A>G/IVS19+ 19A>G, and c.9256-18C>A/IVS24-18C>A) in our studies show no effects on the normal splicing process, and they are considered to be benign polymorphic alterations. Our studies help to clarify the aberrant splicing inBRCA1andBRCA2as well as provide information that can be used clinically to help counsel breast/ovarian cancer prone families. Hum Mutat 27(5), 427-435, 2006. Published 2006 Wiley-Liss, Inc.†

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