23andMe is a direct-to-consumer genetic testing service that offers insights into ancestry and health predispositions. Users submit a DNA sample, typically saliva, to receive personalized reports. Many wonder about the reliability of these results. Understanding 23andMe’s accuracy requires examining its technology and the distinct methodologies for ancestry and health information.
The Technology Behind the Test
23andMe’s genetic analysis relies on genotyping, not full genome sequencing. This process examines specific, pre-selected locations across a person’s DNA, called Single Nucleotide Polymorphisms (SNPs). These SNPs are single-letter variations that differ between individuals and populations.
Genotyping is like checking specific, highly informative words in a vast genetic library, rather than reading every single word (full genome sequencing). 23andMe analyzes approximately 600,000 to 670,000 SNPs, a small fraction (0.02% to 0.03%) of the human genome’s 3 billion DNA base pairs. This targeted approach efficiently identifies common genetic variations linked to traits and ancestries, though it does not capture every genetic difference.
Accuracy of Ancestry Reports
The accuracy of 23andMe’s ancestry reports depends on the size and diversity of its reference populations. It compares a user’s DNA to genetic profiles of over 14,000 individuals with known ancestries. This comparison helps assign ancestry percentages by identifying which global population each DNA segment most closely matches.
23andMe uses “confidence levels” to show the statistical certainty of ancestry assignments. The default is 50% confidence, offering a detailed breakdown of ancestral regions. Users can adjust to higher levels, like 90%, for broader but more certain categories. For specific country matches and genetic groups, confidence is reported as “possible” (lower confidence), “likely” (medium confidence), or “highly likely” (high confidence), based on shared DNA with individuals from those locations.
Ancestry results can evolve as 23andMe refines algorithms and expands reference databases. As more diverse DNA is contributed, the company’s ability to differentiate populations improves, potentially updating results for existing users. Broad continental assignments (e.g., European, East Asian) often show high precision (over 90%). However, accuracy for more specific regions or smaller ethnic groups can be less precise due to overlapping genetic markers or limited representation.
Accuracy of Health and Trait Reports
The accuracy of 23andMe’s health and trait reports involves two aspects: analytical validity and clinical validity. Analytical validity refers to the laboratory’s ability to correctly detect a specific genetic variant in a DNA sample. For 23andMe’s Genetic Health Risk and Carrier Status reports, this accuracy is consistently high, often over 99%. This means the test reliably identifies the presence of a specific DNA letter at the targeted marker.
Clinical validity evaluates how reliably a detected genetic variant associates with a specific health condition. 23andMe’s health reports, such as Carrier Status and Genetic Health Risk, look for specific variants linked to certain conditions. For instance, the BRCA1/BRCA2 (Selected Variants) Genetic Health Risk report examines 44 variants associated with increased cancer risks.
Many health conditions are influenced by numerous genetic variants, and 23andMe’s tests do not cover all possibilities. Therefore, a “variant not detected” result does not mean an individual is free from all genetic risk; it only means they do not have the specific variants included in the test. These reports provide information on predisposition or risk, and are not medical diagnoses.
How to Interpret Your Results
Interpreting 23andMe results requires understanding their scope and limitations. For health reports, the information indicates a genetic predisposition or carrier status, not a medical diagnosis. These reports analyze specific genetic markers that may influence risk, but they do not account for all genetic variations, lifestyle, environmental factors, or family medical history.
If a health report indicates increased risk or carrier status, discuss findings with a healthcare professional or genetic counselor. These experts can provide personalized context, recommend further testing, and offer guidance based on a comprehensive view of an individual’s health. For ancestry reports, view percentages as a general estimate of genetic heritage. These results can serve as a starting point for further genealogical research, encouraging exploration of family history beyond the DNA percentages.