Predisposition

Predisposition refers to an increased likelihood of developing a condition due to genetic, environmental, or lifestyle factors, without guaranteeing that the condition will occur. It describes a probability rather than a destiny, and the strength of predisposition can vary across individuals and may depend on interactions between genes and the environment.

Genetic predisposition arises from inherited variants that collectively influence risk for many diseases and traits. In complex or multifactorial conditions, multiple gene variants contribute small effects that add up with age, lifestyle, and exposures. A familial pattern of a disease can signal a genetic predisposition, but shared environment can also contribute. Environmental and lifestyle factors can modify risk through gene–environment interactions, emphasizing that predisposition is not immutable.

Assessment of predisposition often uses family history and, where appropriate, genetic testing. Risk models estimate probability rather than certainty. Important concepts include penetrance (the proportion of individuals with a variant who develop the condition) and expressivity (the range of possible manifestations). Examples of predisposition include BRCA1 and BRCA2 variants, which increase risk for breast and ovarian cancer; ApoE4, which is associated with higher risk of Alzheimer's disease; and certain HLA alleles that predispose to autoimmune diseases. Predisposition is relevant to a wide range of conditions, including allergies, metabolic disorders, and psychiatric or addictive phenotypes.

Management focuses on surveillance, screening, and preventive measures that can reduce absolute risk, even when predisposition is present. Ethical considerations include privacy, consent, and potential discrimination based on genetic information. Overall, predisposition highlights increased probability rather than determinism, guiding proactive health decisions informed by individual risk.