High Heritability for ADHD, autism, and schizophrenia due in part to like-marrying-like (assortative mating)

"So, where did you meet your husband?"


"In line."


"Online? Like e-Harmony?"


"No, in line at the drug store. We were both picking up the same antipsychotic medication."

From Robert Plomin et al.'s editorial in JAMA Psychiatry (2/24/16)

"The topic of assortative (nonrandom) mating [which refers to people mating with people who share a particular trait] might seem esoteric or even salacious....Nordsletten and colleagues¹ report the first general population study to date of assortative mating for psychiatric disorders, which may help to solve 3 puzzles in psychiatric genetics: Why are psychiatric disorders so highly heritable when they are associated with reduced fecundity? Why are some psychiatric disorders so much more highly heritable than others? Why is there so much genetic comorbidity across psychiatric disorders?

The research capitalizes on the powerful population registers in Sweden, which contain diagnostic information, including psychiatric diagnoses, on all individuals admitted to Swedish hospitals since 1973. The registers yield huge samples of cases (eg, more than 70 000 individuals diagnosed as having schizophrenia). Using other registers to track couples via their children, the investigators were able to measure assortative mating levels within and between 11 psychiatric disorders.

Although you can see assortative mating for physical traits, like height and weight, with your own eyes, the correlation between spouses is only approximately 0.20 for these traits. For personality, assortative mating is even lower at approximately 0.10. In contrast, Nordsletten and colleagues¹ find an amazing amount of assortative mating within psychiatric disorders. Spouse tetrachoric correlations are greater than 0.40 for attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and schizophrenia. The next highest spouse correlation emerged for substance abuse (range, 0.36-0.39). Assortative mating was significant but far less substantial for other disorders, such as affective disorders (range, 0.14-0.19)."