What genetic testing can — and cannot — tell you about your longevity

What genetic testing actually measures

Consumer genetic tests use genotyping arrays rather than whole-genome sequencing. These arrays test for hundreds of thousands of pre-specified SNPs (single nucleotide polymorphisms) — single-letter variations in the genome at known positions. This is sufficient to identify variants with established clinical significance (like APOE genotype) but misses the vast majority of rare variants that whole-genome sequencing would capture. Whole-genome sequencing (WGS) — now available for approximately AUD $400–800 from services including Dante Labs and Nebula Genomics — provides complete genetic information but requires clinical interpretation to be actionable.

The variants that actually matter for longevity

APOE genotype: the most important longevity variant

The APOE gene produces apolipoprotein E, which plays a central role in lipid metabolism, neuroinflammation, and amyloid clearance. Three alleles — APOE2, APOE3, and APOE4 — produce meaningfully different outcomes. APOE4 (carried by approximately 15% of the Australian population in at least one copy) is the strongest known genetic risk factor for late-onset Alzheimer's disease, associated with 3–4x increased risk in one-copy carriers and 8–12x in two-copy carriers (approximately 3% of the population). Carriers have earlier average age of dementia onset and potentially accelerated cognitive decline.

Importantly, APOE4 status influences optimal lifestyle strategy: APOE4 carriers may benefit more from aggressive cardiovascular risk management, omega-3 supplementation, and early cognitive monitoring. A 2023 study found dietary saturated fat had significantly worse impact on cardiovascular markers in APOE4 carriers compared to APOE3. APOE2 is protective — carriers have lower Alzheimer's risk and better average lipid profiles.

MTHFR variants

MTHFR C677T and A1298C are common variants (affecting approximately 10–15% of the population in homozygous form) that reduce the activity of methylenetetrahydrofolate reductase, an enzyme in the folate/methylation cycle. Reduced MTHFR function can increase homocysteine levels, a cardiovascular risk marker. The clinical significance at population level is more modest than direct-to-consumer marketing suggests — the association between MTHFR variants and serious clinical outcomes is weak in studies that control for folate intake. Most MTHFR variant carriers can address elevated homocysteine through adequate folate, B6, and B12.

BRCA1/BRCA2: cancer risk

BRCA1 and BRCA2 variants are the most clinically significant cancer risk variants detectable by genetic testing. Pathogenic variants (approximately 1 in 400 Australians) are associated with lifetime breast cancer risk of 50–72% and ovarian cancer risk of 17–44%. Genetic counselling and clinical-grade BRCA testing (Medicare-rebatable in relevant clinical contexts) is the appropriate pathway if family history or testing suggests elevated risk — not consumer genetic tests, which miss a significant proportion of pathogenic BRCA variants.

Polygenic risk scores: the emerging frontier

Beyond individual variants, polygenic risk scores (PRS) aggregate thousands of individually small genetic effects into a composite risk estimate. PRS are now available for cardiovascular disease, type 2 diabetes, Alzheimer's disease, and several cancers. A 2023 JAMA study found that a high PRS for coronary artery disease conferred a 5x increased risk compared to low-PRS individuals — comparable to a major monogenic risk factor. Critically, a 2024 analysis found that lifestyle interventions were equally or more effective at reducing actual disease incidence in high-PRS individuals compared to low-PRS individuals — meaning a high PRS is a reason to prioritise intervention, not fatalism.

What genetic testing cannot tell you

Genetic testing cannot tell you: your actual biological age (epigenetic clocks do this better), your current metabolic health status (blood testing is required), how much of your disease risk is already being modified by your lifestyle, or when you will die. The 16% heritability figure for lifespan means that genetic factors account for a minority of outcome variance. A comprehensive blood panel — including full lipid panel, HbA1c, fasting insulin, CRP, vitamin D, and complete blood count — provides more immediately actionable information about current health status than most genetic test results.

The practical decision framework for Australians

Consumer genetic testing (23andMe, AncestryDNA, or Australian alternatives): provides APOE genotype and MTHFR status as minimum useful outputs; appropriate for most people as a low-cost informational exercise (~$200–400 AUD). Clinical-grade genetic counselling and testing: indicated if there is a family history of hereditary cancer, early cardiovascular disease, or early-onset dementia; Medicare-rebatable in appropriate clinical contexts. Whole-genome sequencing: provides complete genetic information but requires clinical genetics expertise to interpret; appropriate for those with significant family history or who are actively engaged in precision health monitoring.

Regardless of genetic test result, the lifestyle foundations remain the same. APOE4 carriers may prioritise different interventions — more aggressive lipid management, earlier cognitive monitoring — but the core longevity protocol (sleep, fitness, diet, stress management) is universally applicable.

References

1. Ruby, J. G., et al. (2018). Longevity heritability: analysis of 400 million genealogical records. Genetics.
2. van der Lee, S. J., et al. (2022). APOE and Alzheimer's disease risk: updated meta-analysis. Alzheimer's & Dementia.
3. Nutrition Journal (2023). Dietary saturated fat and cardiovascular markers by APOE genotype.
4. Khera, A. V., et al. (2023). Polygenic risk scores for coronary artery disease: clinical utility. JAMA, 329(4).
5. Nature Medicine (2024). Lifestyle interventions and disease incidence across polygenic risk strata.
6. Cancer Council Australia (2024). BRCA1/BRCA2 testing: prevalence and clinical guidance.
7. NHMRC (2024). Genetic testing in Australia: consumer guide.