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Assortative Mating and Autism Spectrum Disorder

New seed grant project headed by Judith Hellerstein investigates the causes of the rise in autism diagnoses

A research team led by MPRC Faculty Associate Judith Hellerstein has been awarded an MPRC seed grant in order begin a new project to investigate the extent to which assortative mating may help to explain substantial increases in the incidence of autism spectrum disorder (ASD) over the past few decades. Researchers have linked rising autism rates to a variety of environmental, economic, and social factors, but thus far the trend remains largely unexplained.

Dr. Hellerstein’s team will use data from the Danish psychiatric, labor, and population registries to test the hypothesis that the rising incidence of autism spectrum disorder may be partially explained by changes in assortative mating patterns. Autism can be understood as the result of an excessively systemizing personality. A person is a systemizer if he or she finds it easier to cope with situations where there are clear rules and laws, whereas situations that involve uncertainty and chaos are more difficult to handle. A typical systemizer functions relatively normally in society and will be attracted to occupations and fields of education that involve orderly systems such as engineering, information technology, computer science and natural sciences. However, an extremely systemizing individual loses the ability to cope under uncertainty, a key characteristic of autism.

A rich literature in the social sciences has documented that individuals commonly choose spouses or long-term partners with characteristics similar to themselves, a phenomenon known as assortative mating. Over time, this sorting has become stronger in developed countries, and as a result, assortative mating based on earnings, education and occupation has increased substantially through the past few decades in many countries. One potential consequence of increased assortative mating is higher incidence of rare psychological conditions. Assortative mating can increase the chances that parents with given personality traits have children with extreme realizations of those traits. If systemizing characteristics are genetically inheritable, an increasing tendency of systemizers to mate with each other will lead to an increased prevalence of extremely systemizing offspring, thereby increasing autism rates.

Previous studies have found that mothers and fathers of autistic children are more likely to score high on systemizing tests, that maternal and paternal grandfathers of autistics are disproportionately likely to be engineers, and that students in engineering, physics or math are more likely to have autistic relatives. Dr. Hellerstein’s research fills an important gap in the literature by using large samples and detailed occupational and educational information in the Danish registry data to identify the impact of assortative mating on current ASD diagnosis rates and to try to explain how much of the recent increase in ASD may be due to increased assortative mating.

This project will provide the first rigorous, large-scale, empirical test of medical theories linking assortative mating to ASD prevalence and will also investigate how changing assorative mating has changed autism rates over time. By linking a key behavioral theory with a mental health condition, it will add to a large literature in economics and sociology that studies the impacts of economic and social behaviors on health outcomes.

This project is a collaboration among researchers at the University of Southern Denmark (SDU), the University of Maryland, Michigan State University (MSU), and the London School of Economics.