Of 4733 individuals in the second cohort identified to have a pathogenic or likely pathogenic variant in BRCA1/2, only 12% carried 1 of the 3 mutations targeted by DTC genetic tests. Overall, variants in 19% of Ashkenazi Jewish individuals and 94% of non-Ashkenazi Jewish individuals would have gone undetected if they had only relied on DTC genetic testing.
To Dr Esplin, the results underscore the need to raise awareness that DTC genetic tests, which screen for limited variants using single-nucleotide polymorphism (SNP) microarrays, are never a substitute for comprehensive clinical-grade tests, which are primarily based on sequencing genes and detect a wide range of variants associated with disease. (Invitae provides a number of sequencing-based genetic tests which can be ordered by physicians, or also by individuals directly.)
Dr Esplin and his colleagues found striking discrepancies when they broke patients down by ethnicity. BRCA1/2 variants would have been missed in 98% of Asians, 98% of Asians, 99% of African Americans, 94% of Hispanics, and 94% of Caucasians.
Mutations in the MUTYH gene would have been missed in 100% of Asian, 75% of African-American, 46% of Hispanic, and 33% of Caucasian individuals.
“We expected there was going to be more risk of this false reassurance among those individuals that were of non-Caucasian ancestry. [But I] was somewhat surprised at how significant that difference was,” Dr Esplin remarked.
To Erica Ramos, MS, LCGC, director of clinical and product development at Geisinger National Precision Health, Washington, D.C., the research “puts some numbers around conversations that we’ve all been having in the genetics communities since the health reports began to be issued using the microarray technology,” she said.