Genetic tests: what APOE4, MTHFR and others really tell you — and where the limits lie

Consumer-friendly genetic tests promise insight into your own DNA. What they actually show, which variants are genuinely relevant, and how to interpret results without being unsettled by risk percentages.

What a genetic test measures — and what it doesn't

Consumer-friendly genetic tests, available today for a few hundred francs or euros, typically analyse several hundred thousand single-nucleotide variations in the genome (SNPs — Single Nucleotide Polymorphisms). They do not provide a complete sequence of your genome, but rather a profile of known variants associated with certain traits or disease risks.

For most complex conditions such as type 2 diabetes, heart attack or Alzheimer's, there is no single responsible gene — instead, dozens or hundreds of variants collectively influence the risk. Environmental factors, lifestyle and epigenetic processes that can alter gene activity add to this. A genetic test therefore always shows only part of the picture.

APOE4: A risk factor for Alzheimer's, but not a verdict

The APOE gene comes in three variants: ε2, ε3 and ε4. The most common variant is ε3, which is considered neutral. Carrying one copy of APOE4 is associated with an approximately threefold increased risk of developing Alzheimer's over a lifetime compared to ε3 homozygotes. Carrying two copies — which affects around 2 to 3 percent of the population — is associated with up to a twelvefold increased risk.

At the same time: around 60 to 70 percent of APOE4 homozygotes do not develop Alzheimer's. A positive result is not a verdict, but information. The evidence suggests that lifestyle measures such as aerobic physical activity, sleep quality and blood pressure control may favourably influence risk even in APOE4 carriers. Knowing the result allows you to approach these measures more deliberately.

MTHFR: A common variant, often overstated

MTHFR (methylenetetrahydrofolate reductase) is an enzyme responsible for folate metabolism and the breakdown of homocysteine. The variants C677T and A1298C are very common in the population: an estimated up to 50 percent of people carry at least one of these variants. In certain combinations, enzyme activity may be reduced, which could theoretically lead to elevated homocysteine levels.

In practice, the effect is often not clinically relevant when folate and vitamin B12 intake is adequate through a balanced diet. Studies examining MTHFR variants in isolation from other factors rarely show strong clinical impacts. If you see an MTHFR variant in your test, a direct homocysteine blood test is far more informative than the genotype information alone.

Other gene variants: What else is worth checking

BRCA1 and BRCA2 variants substantially increase the risk of breast and ovarian cancer. These findings require a genetic counselling consultation with a doctor or genetic specialist — they should not simply be taken from a consumer kit. PCSK9 variants influence LDL cholesterol levels and may indicate genetically caused hypercholesterolaemia. TCF7L2 variants are among the strongest genetic risk factors for type 2 diabetes.

CYP genes (cytochrome P450 enzymes) affect drug metabolism and are relevant in pharmacogenomics. Knowing whether you metabolise certain medications quickly or slowly can be valuable to discuss with your doctor — especially for painkillers, antidepressants or blood pressure medications. This information is useful, but always requires expert interpretation.

Know the limits: What genetic tests cannot do

Genetic risk scores are population-based and were often developed using people of European descent. For other ethnic backgrounds, precision is currently lower. Additionally, a genetic test captures a static picture — it never changes. Lifestyle, environment and epigenetic processes can strongly influence gene expression without changing the genotype.

A result indicating elevated risks can be emotionally burdensome. Genetic testing providers often recommend, for good reason, not automatically displaying results for certain risk genes such as APOE4. You can choose which information you want to see. If you are unsure whether you can process certain findings, speaking with a genetic counselling service before taking the test is a good idea.

Anchoring genetic findings in your health picture with the YUTHI app

In the YUTHI app, you can record information from your genetic test and view it alongside other measurements — blood markers, body composition, lifestyle indicators. This way, an APOE4 finding doesn't stand in isolation, but becomes part of an overall picture that you can actively shape.

Sources

• Corder EH et al. Gene dose of apolipoprotein E type 4 allele and the risk of Alzheimer's disease in late onset families. Science, 1993;261(5123):921–923.
• Frosst P et al. A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nature Genetics, 1995;10(1):111–113.
• Lambert JC et al. Meta-analysis of 74,046 individuals identifies 11 new susceptibility loci for Alzheimer's disease. Nature Genetics, 2013;45(12):1452–1458.
• Kraft P, Hunter DJ. Genetic risk prediction — are we there yet? New England Journal of Medicine, 2009;360(17):1701–1703.