Occurrence of a non deleterious gene conversion event in the BRCA1 gene.

The duplication in the primate lineage of a portion of the breast and ovarian cancer susceptibility gene BRCA1 has created a BRCA1 pseudogene 45 kb away. Non-allelic homologous recombination (NAHR) between BRCA1 and BRCA1P1 has generated recurrent deleterious germ-line 37-kb deletions encompassing the first two exons of BRCA1, accounting for several breast and ovarian cancer families in various populations. In principle, NAHR intermediates resolution could also lead through a non-crossover configuration to interlocus gene conversion (IGC), but none had been described as yet. Here, we report for the first time an IGC event identified in a breast and ovarian cancer family involving exactly the same segment as that involved in the 37-kb deletions. Close examination of the consequences of this IGC event showed that it does not impact BRCA1 expression. Detailed analysis of the regions of homology between BRCA1 and its pseudogene revealed the specificity of the segment where recombination systematically occurs.