The authors of mainstream psychiatric and psychiatric genetic publications believe that the major psychiatric disorders are “moderately to highly heritable.”
Are DSM Psychiatric Disorders “Heritable”?
By JAY JOSEPH
A key psychiatric genetic concept is heritability. The concept was originally developed as a tool to help predict the results of selective breeding programs of farm animals,1 but has been extended in the past few decades as an indicator of the strength or magnitude of genetic influences on various psychiatric disorders and behavioral characteristics. Numerical heritability estimates have been a mainstay of the field of behavioral genetics, but here I would like to focus on problems with the heritability concept in psychiatry, while keeping in mind that most of the points made here and by previous critics apply to the use of heritability estimates in all areas of human behavior, including other controversial areas such as IQ and personality. In this brief discussion I will try to explain the main issues surrounding heritability as clearly as possible, while recognizing that for many people this “extraordinarily misunderstood” concept is difficult to comprehend and to articulate.2
Kenneth Kendler, a leading psychiatric genetic researcher, defined heritability as “the proportion of variation due to genetic factors.”3 The key word here is “variation,” which in this context refers to how psychiatric disorders and characteristics are distributed in the population. In human genetic research, heritability is said to measure the extent to which variation among people is explained (accounted for) by genetic influences. A group of leading behavioral geneticists argued that assessing the causes of variation allows researchers to estimate “how much genetics contributes to a trait,” and allows them to quantify the “relative importance” of genetic and environmental influences.4 According to Michael Rutter, a prominent genetically oriented researcher and author, within certain “constraints,” it “is possible, and meaningful, to quantify the strength of genetic influences on individual differences with respect to psychological characteristics or mental disorder as they occur in the populations studied.”5
Heritability estimates are derived from correlations among relatives, which include twins, adoptees, siblings, and other types of family relationships. Although heritability assesses the causes of variation in a population, it does not address developmental processes that cause individuals to develop various characteristics and abilities.6