A study of possible genetic causes of inherited breast and ovarian cancer in a Norwegian cancer population

Abstract

Homologous recombination repair (HRR) is an important repair mechanism, and mutations disrupting the function of this machinery might contribute to cancer formation. Several proteins interact in this mechanism, and the two best known are BRCA1 and BRCA2. Mutations in their corresponding genes BRCA1 and BRCA2 are found in 40% of hereditary breast and ovarian cancer cases. However, there are still mutations found in these genes that are classified as variants of unknown clinical significance (VUS). Some of these variants identified in Norwegian individuals were further investigated in this study by PCR amplification of cDNA and subsequent sequencing. In addition the PALB2 gene was screened for mutations, since the encoded protein is essential in the co-localization of BRCA1 and BRCA2 in the repair machinery and mutations in PALB2 have been reported to be associated with hereditary breast and ovarian cancer. In total, 43 patients from a Norwegian cancer population were screened for mutations in PALB2 by the use of M13 tagged sequencing primers. However, no obvious pathogenic variants were detected. Nineteen individuals with BRCA1 VUS and 18 individuals with BRCA2 VUS from families with hereditary breast/ovarian cancer were investigated for the expression of both alleles in lymphocytes as well as for possible effects on RNA splicing. All possible detectable alleles were expressed in lymphocytes and three of the variants, BRCA1 c.213-5T>A, BRCA1 c.5434C>G and BRCA2 c.68-7T>A were shown to influence splicing during mRNA processing. In addition, 4 different normal alternatively spliced transcripts were identified in BRCA1 and BRCA2.