Identification of pathogenic retrotransposon insertions in cancer predisposition genes.

Cancer risks have been previously reported for some retrotransposon element (RE) insertions; however, detection of these insertions is technically challenging and very few oncogenic RE insertions have been reported. Here we evaluate RE insertions identified during hereditary cancer genetic testing using a comprehensive testing strategy. Individuals who had single-syndrome or pan-cancer hereditary cancer genetic testing from February 2004 to March 2017 were included. RE insertions were identified using Sanger sequencing, Next Generation Sequencing, or multiplex quantitative PCR, and further characterized using targeted PCR and sequencing analysis. Personal cancer history, ancestry, and haplotype were evaluated. A total of 37 unique RE insertions were identified in 10 genes, affecting 211 individuals. BRCA2 accounted for 45.9% (17/37) of all unique RE insertions. Several RE insertions were detected with high frequency in populations of conserved ancestry wherein up to 100% of carriers shared a high degree of haplotype conservation, suggesting founder effects. Our comprehensive testing strategy resulted in a substantial increase in the number of reported oncogenic RE insertions, several of which may have possible founder effects. Collectively, these data show that the detection of RE insertions is an important component of hereditary cancer genetic testing and may be more prevalent than previously reported.