Legal and ethical principles of genetic testing - predictive testing processes

What it is

Predictive genetic testing determines whether an asymptomatic individual carries a pathogenic variant known to run in their family, before any symptoms of the condition have developed - distinct from diagnostic testing in a symptomatic patient
Most commonly performed for adult-onset conditions with a known familial pathogenic variant already identified in an affected relative (e.g. Huntington disease, hereditary cancer syndromes, some inherited cardiac conditions) - testing a family member who has not yet identified the specific variant would instead be diagnostic/exploratory testing, not predictive testing in the strict sense

Predictive testing requires the family's specific pathogenic variant to already be known (typically identified in an affected relative first) - testing an asymptomatic individual "from scratch" without a known familial variant is a fundamentally different (and generally less informative) undertaking

Structured pre-test counselling (across one or more sessions) covers the implications of both a positive and a negative result, the condition's natural history and any available interventions, psychological preparedness, and implications for reproductive planning and relatives
For conditions with no available prevention/treatment (the classic example being Huntington disease), international protocols recommend a more extended, structured process (multiple counselling sessions, psychological assessment, a mandatory waiting period) given the profound and irreversible psychological impact of a positive result with no modifying intervention available

Results should be given in person, with appropriate psychological support arranged in advance (both for a positive and, notably, sometimes for a negative result - "survivor guilt" in a family member who tests negative when others are affected is a recognised, real reaction)
Follow-up support (not just single-session disclosure) is important regardless of result, given the potential for delayed psychological impact

Huntington disease (the paradigm example of predictive testing protocol), hereditary cancer syndromes (BRCA1/2), hereditary cardiac conditions, genetic counselling

The predictive testing process is deliberately more extended and structured than most other genetic testing precisely because the result cannot be "undone" once known, and because - for conditions without an available preventive intervention - a positive result changes nothing actionable except the person's own knowledge of their future risk

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