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  THE
BRCA1 GENEBRCA1 (BR for "breast," CA for "cancer") was the first major breast cancer gene to be isolated. The BRCA1 gene was mapped to chromosome 17 in 1990. The BRCA1 gene was fully sequenced in 1994, and specific mutations were characterized.
Larger than most previously isolated genes, BRCA1 codes for a protein 1,863 amino acids long. BRCA1 is a tumor-suppressor gene; loss of its function confers an increased risk of breast and ovarian cancer. Women and men normally possess two copies (alleles) of BRCA1, one on each copy of chromosome 17. Women who inherit one mutated copy of the BRCA1 gene from either parent are at a much greater risk of developing breast and ovarian cancer. This is because a cell with one mutated allele does not have a "backup" if the other allele is damaged or otherwise lost. Relatively few mutations have been shown to occur in multiple families. Because of this, identification of germline mutations requires the complex task of fully sequencing the DNA throughout the gene. However, two mutations, 187delAG and 5385incC are commonly seen in Ashkenazi Jewish population. THE BRCA2
GENE
About twice the size of BRCA1, this huge gene codes for a protein 3,418 amino acids long. So far, several hundred mutations have been identified throughout its 11,000 coding-region bases. As is the case with BRCA1, only a few mutations have been observed in multiple families, for example, the founder mutation in Ashkenazi Jewish individuals, 6174delT. Therefore, identification of germline mutations requires full sequencing of the DNA throughout the BRCA2 gene. BRCA2 also has a tumor-suppressor function, and loss of its function increases the risk of breast and ovarian cancer. |
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