Consistency of Direct-to-Consumer Genetic Testing Results Among Identical Twins

Background: The purpose of this study was to evaluate the consistency of 3 commonly used direct-to-consumer genetic testing kits. Genetic testing kits are widely marketed by several companies but the consistency of their results is unclear. Because identical twins share the same DNA, their genetic testing results should provide insight into test consistency.

Methods: Forty-two identical twins (21 pairs) provided samples for 3 testing companies. Outcomes were concordance of ancestry results when twin pairs were tested by the same company and the same participant was tested by different companies. Concordance of 8 self-reported traits with 23andMe genetic analyses were also examined.

Results: Concordance of ancestry results when twin pairs were tested by the same company was high, with mean percentage agreement ranging from 94.5% to 99.2%. Concordance of ancestry results when participants were tested by 2 different companies was lower, with mean percentage agreement ranging from 52.7% to 84.1%. Concordance of trait results was variable, ranging from 34.1% for deep sleep and detached earlobes to 90.2% for cleft chin.

Conclusion: The consistency of consumer genetic testing is high for ancestry results within companies but lower and more variable for ancestry results across companies and for specific traits. These results raise questions about the usefulness of such testing.