Substance abuse can be inherited. Mental illness can be inherited. But can both? According to various sources, the answer is yes. The caveat: the heredity line from parent to child is not always discernible.
Shared risk factors
On its Drug Facts website, the National Institute on Drug Abuse notes an individual with a substance abuse disorder (SUD) is twice as likely to experience mood and anxiety disorders as a person without an SUD – and vice versa. In classic chicken-or-egg fashion, researchers are not united on which condition is responsible. They do agree individuals with mental health disorders and SUDs share certain risk factors. These are:
- Predisposing genetic vulnerabilities
- Overlapping environmental triggers (physical/sexual abuse, early exposure to drugs)
- The same affected brain regions (reward and stress centers)
- Both mental health disorders and SUDs are developmental disorders; they impact a developing, immature brain in many of the same ways
What the institute fails to provide is a definitive genetic link between mental health disorders and SUDs. Nowhere on the site is there data identifying a specific gene responsible for comorbidity. But an article published in Child & Adolescent Psychiatric Clinics of North America (available on the National Institutes of Health Public Access website) makes a stronger argument for a genetic link between mental illness and SUDs.
Looking for a genetic link
Researchers used the Virginia Twin Registry to determine whether twins shared underlying genetic similarities with respect to the major class of psychiatric and SUDs. They found a common factor for SUDs and externalizing psychopathologies. Dubbed the latent genetic externalizing factor, scientists conclude this genetic element accounts for a large portion of alcohol and drug dependence as well as conduct disorders and personality disorders, such as antisocial personality disorder.
Two factors mitigate the conclusiveness of these findings. First, twins are distinct from the normal population with respect to chromosomal similarities. Even if some of these individuals are genetically predisposed to mental health disorders and SUDs, there is no concrete evidence to suggest the general population is so predisposed. Second, the authors write that “much of the genetic predisposition to alcohol and other drug dependence is not specific to that disorder.” Meaning, an individual with depression may be at greater risk for developing a dependence on alcohol, but there is nothing peculiar to genetics driving that dependence.
The role of the environment
The authors note a better barometer for assessing the likelihood of comorbidity occurrences is gene-environment interaction. They cite the growing body of research identifying childhood stressors (physical/emotional/sexual abuse), availability and access to substances, peer group anti- and prosocial behaviors, parental neglect and attitudes toward substances and socioeconomic conditions. Citing the FinnTwin studies, researchers found among that group of siblings, in neighborhoods without parental monitoring or community involvement, there was greater genetic influence on the risk factor for developing mental health problems and SUDs.
Conversely, researchers found the opposite in communities where parents exerted stricter control over their children. Again, researchers are quick to point out their analyses only suggest a relationship, but what they suggest is that a child who lives in an environment where there are rules and parental involvement has less opportunity to express genetic predispositions as well as environmental factors influencing mental illness and SUDs.
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About the author:
Darren Fraser, worked two and half years as reporter and researcher for The Yomiuri Shimbun until they realized he did not read, speak or write Japanese and fired him. Undeterred, he channels his love of research into unearthing stories that provide hope to those dealing with addiction and mental illness. Darren loves the Montreal Canadiens hockey club and horror films and would prefer to enjoy these from the comforts of his family’s farm in Quebec.