An amazing amount of assortative mating within psychiatric disorders

A suggestive piece from Assortative Mating—A Missing Piece in the Jigsaw of Psychiatric Genetics by Robert Plomin, Eva Krapohl, and Paul F. O’Reilly. Can only be taken as indicative at this point without further and more robust testing.

The topic of assortative (nonrandom) mating might seem esoteric or even salacious. For example, in lectures you have to point out to students that random mating is not about promiscuity. In this issue of JAMA Psychiatry, 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?

Those are three interesting questions. They map to three general puzzles as well: Why are there always dysfunctional poor regardless of societal averages, why is there higher fecundity among the poor, and why do familial dysfunctions propagate across generations?

Addressing their posed questions:

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 colleagues 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).

The article then goes on to explore the implications of these findings.

Helping the poor usually entails some complex variety of solutions to address a large portfolio of dysfunctions and incapabilities (behavioral and otherwise). That is why it is so hard to address. If the answer was a simple as transferring resources for a given time, we'd be in good shape. Instead, many solutions have to work together to tackle the entirety of the pathologies that cause the poverty in the first place. A challenge reflected in the final observation from the paper.

Beyond genetics and genomics, assortative mating matters because it means that the person closest to an individual with a psychiatric disorder is also likely to have psychiatric problems, which could exacerbate problems for both spouses and their offspring.

Not just the spouse and off-spring. If you are trying to assist an individual in addressing their multitude of issues, if those in their relational networking are similarly afflicted, then it is yet harder to create the conditions to make the necessary changes likely to help them break free from the behaviors and capabilities causing their problems.