Genetic Testing Detects Uncommon Variants Incorrectly by Angela Mohan on February 16, 2021 at 3:03 PM BMJ. After hearing of cases where women had surgery scheduled after wrongly being told they had very rare genetic variations in the gene BRCA1 that could significantly increase risk of breast cancer, a team at the University of Exeter conducted a large-scale analysis of the technology using data from nearly 50,000 people. They found that the technology wrongly identified the presence of very rare genetic variants in the majority of cases. The team analyzed SNP chips, which test genetic variation at hundreds-of-thousands of specific locations across the genome.