Genetic testing has become more accessible, but understanding what tests tell you and what they don't is crucial. Not all genetic abnormalities cause disease, and finding one creates obligations and anxieties you should anticipate.
Types of genetic testing
Carrier screening tests whether you carry one abnormal copy of a gene (you're healthy but could pass it to children). This is relevant if planning pregnancy, especially if you have family history of genetic disease.
Diagnostic testing confirms suspected genetic disease. If you have symptoms pointing to a genetic cause, testing identifies the specific mutation, confirming diagnosis and informing prognosis.
Predictive testing checks for mutations causing disease you don't yet have, often seen in families with strong genetic patterns (hereditary cancer, early-onset dementia). BRCA mutations causing breast cancer are commonly tested; Huntington's disease (genetic, fatal, early-onset) is another.
Pharmacogenomic testing looks at how you metabolize drugs. Some people are "poor metabolizers" of certain medications (they accumulate in your system), others are "rapid metabolizers" (normal doses don't work). This affects drug choice and dosing.
What genetic tests can and cannot tell you
Finding a mutation doesn't always predict disease. Many genetic variants are benign (normal variation in the population). Others increase risk without guaranteeing disease. A BRCA mutation means higher breast cancer risk, not certain cancer.
Penetrance (the proportion of people with a mutation who develop disease) varies. Huntington's disease has nearly 100% penetrance (nearly everyone with the mutation eventually develops it). Most variants have lower penetrance.
Expressivity (how severely disease presents) varies even among people with the same mutation. Two siblings with the same cancer gene might have dramatically different cancer risk due to environment and other genetic factors.
Getting genetic testing on the NHS
Your GP can refer you to clinical genetics if there's indication (strong family history, early-onset disease, carrier status relevant to pregnancy). Genetic counselling is provided before testing to ensure you understand results before you get them.
NHS genetic testing is free but limited to medical indications. Testing for "interesting" mutations without family history or symptoms isn't offered.
Waiting time for NHS genetics is 3-6 months depending on the complexity and your region's services.
Private genetic testing
Private genetic tests are accessible directly, without GP referral. Companies like 23andMe (£125-200) offer ancestry, health predispositions, and carrier status. These are usually less detailed than clinical genetic testing.
Clinical-grade private genetic testing costs £500-2,000 depending on the scope. A full genetic counselling session with testing (private geneticist) costs £200-400 for the consultation plus test costs.
Psychological impact of results
Finding you carry a disease gene creates lasting anxiety even if you're asymptomatic. If you have predictive test results (you will develop disease later), this affects life planning, insurance, relationships, mental health.
Before testing, particularly for predictive tests, consider psychological support (counselling helps process the information). Some people benefit from testing; others regret it.
Results can affect family members (they may carry the mutation too). This creates ethical complexity—you might discover relatives need screening, but genetic information is deeply personal.
Practical implications
BRCA mutations mean more frequent cancer screening, sometimes preventive surgery (mastectomy, oophorectomy). This requires discussion with cancer specialists about your specific risk.
Carrier status (you're healthy but could pass disease to children) affects pregnancy planning. You might seek IVF with genetic testing of embryos to avoid passing the condition. This is available privately in the UK, sometimes on NHS for specific high-risk conditions.
Always get results through clinical genetics or a qualified geneticist—not just from a direct-to-consumer company. Interpretation matters, and variants of unknown significance (mutations we don't fully understand) are common.