Heritability

A measure of the extent to which a disease or disorder is the result of inherited factors, as opposed to environmental influences such as diet and climate. Certain disorders (such as haemophilia or cystic fibrosis) are known to be caused entirely by hereditary factors. Others are caused by environmental factors. Between these extremes are many disorders (such as schizophrenia) in which both inheritance and environment probably play a part. A rough estimate of heritability can be obtained from the known incidence of a disorder in the first-degree relatives of affected people compared with the incidence of the disorder in a population exposed to similar environmental influences. Estimates of heritability are useful in genetic counselling. (See also genetic disorders.)