A new examination of spousal similarity for alcohol consumption and AD risk reveals that while one type of association, assortative mating, results in an increased frequency of AD in partners, another type, spousal interaction, may diminish AD risk for spouses.

Results are published in the May issue of Alcoholism: Clinical & Experimental Research.

"We know that AD runs in families, and that genetic influences explain about 50 percent of the variation in risk for AD," explained Julia D. Grant, research assistant professor in the department of psychiatry at Washington University School of Medicine. "Not surprisingly, spouses are positively correlated for AD. Our goal was to better understand the processes that may explain this association."

Grant, who is also the study's corresponding author, explained that the commonly used phrase, "like marries like," describes assortative mating, a type of behavioral similarity by which individuals seek partners with whom they share certain characteristics. Another process that she and her colleagues examined is called spousal interaction, in which an individual's drinking behavior has an impact on his or her partner's drinking behavior.

"Phenotypic assortment for alcoholism risk is part of a much larger phenomenon, having deep evolutionary roots," commented Michael Vanyukov, associate professor of pharmaceutical sciences, psychiatry and human genetics at the University of Pittsburgh. "Selecting a phenotypically similar spouse increases the chances that offspring will inherit one's genes related to AD risk inasmuch as the spouse shares them. A closer phenotypic and genetic similarity may translate into higher social cohesion and thus benefit the group, and perhaps the whole species. Similar mechanisms likely work with peer affiliation, such as selection of friends. Unfortunately, as with many other benefits, there is a downside to that, the price paid by our species when these mechanisms extend to those traits considered antisocial."

Researchers used telephone interviews to assess AD-related criteria of 5,974 twin participants in the Australian Twin Register who were born in the years 1902 through to 1964, as well as 3,814 spouses of the twins. Statistical modeling was used to determine the extent to which variability in risk for AD was influenced by genetic factors, the extent of spousal association for AD, and whether any association was attributable to assortative mating, reciprocal spousal interaction, or both.

Results revealed that, when examined separately, both assortative mating and spousal interaction effects were "positive," meaning that those with an AD partner appear to be at increased risk of developing AD themselves. However, when examined simultaneously, only assortative mating remained positive while spousal interaction effects appeared to be protective.

"This means that after controlling for assortative mating," said Grant, "having an AD spouse reduces the likelihood of an individual developing AD. This is consistent with a scenario in which an individual with an AD partner reduces his or her consumption in reaction to the other's excess. The suggestion of a protective spousal interaction effect after accounting for assortative mating highlights the importance of examining both processes simultaneously, as it was missed when we analyzed spousal interactions separately."

Grant and her colleagues also assessed potential gender differences in the direction and magnitude of spousal influence, but found none. "This is quite interesting," noted Grant, "because it suggests that men and women are equally susceptible to the influences of their partner."

Both Grant and Vanyukov noted that assortative mating is likely to result in an increased proportion of offspring who will be exposed to the genetic liability of two alcoholic parents. "The offspring will have a greater chance to inherit such genes than in the case of random or non-assortative mating," said Vanyukov, "and on the population level, this would lead to an increased frequency of genotypes associated with extreme phenotypes, such as those related to an increased risk for alcoholism."

Furthermore, added Grant, clinicians need to be aware that in addition to an increased genetic risk, children with AD parents are more likely to be exposed to a high-risk environment and less likely to experience protective environmental influences.

"Detrimental environmental characteristics associated with AD include reduced educational attainment and income, fewer social and neighborhood support networks, higher rates of divorce and single parenthood, and exposure to other psychiatric disorders," she said. "These environmental factors not only increase the risk of AD for the partner of an AD individual, but also for any children in the household." She added that education is key: incorporating parental monitoring and involvement, providing coping mechanisms for when alcohol is available, educating offspring about specific risks, and discussing guidelines about responsible alcohol consumption.

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