In a cohort study, the likelihood of a suicide attempt (incidence rate ratio 3.96, 95% CI 3.72-4.21) and violent offending (IRR 3.62, 95% CI 3.41-3.84) was highest for children who had at least one parent diagnosed with anti-social personality disorder, Roger Webb, PhD, of the University of Manchester, and colleagues reported online in JAMA Psychiatry.
Rates were also high for offspring whose parents misused cannabis (suicide attempt IRR 3.57, 95% CI 3.25-3.92; violent offending IRR 4.05, 95% CI 3.72-4.39), and those whose parents attempted suicide (suicide attempt IRR 3.42, 95% CI 3.29-3.55; violent offending IRR 3.31, 95% CI 3.19-3.44).
Children whose parents had mood disorders, particularly bipolar disorder, also had an increased likelihood for these parameters, but to a more modest extent, the researchers said.
"This is the first study to investigate the full spectrum of parental psychiatric disease and offspring suicide attempt and violent offending in the same population," the researchers wrote.
Steven Schlozman, MD, of Massachusetts General Hospital, who was not involved in the study, said the study suggests that "we cannot, as a society, afford to simply react to what we see in the offspring of our already psychiatrically suffering parents. We must be much, much more proactive."
He added that the study "further empowers us to argue for a more cohesive and family-centric mental health system, whereby entire families are screened and monitored once risk is established. This is no different than what we do for families with strong genetic histories of other non-psychiatric illnesses. We ought to do this as well in our delivery of psychiatric care."
The study utilized data from the Danish Data Protection Agency, which captured health and demographic data of all children born in Denmark to from 1967 to 1997 who still lived in Denmark at the age of 15.
Overall, the study cohort included 1,743,525 individuals with about 48.7% being female.
The researchers also noted the number of cohort members who had their first violent offense conviction or suicide after their 15th birthday, and adjusted the relationship using log-linear Poisson regression models to estimate incidence rate ratios. They adjusted for sex, offspring age, calendar year, and parental socioeconomic status.
In addition to the previous findings, the researchers observed that a history of mental illness or suicide attempt in both parents was associated with double the risk compared with having just one affected parent.
They also found the association between violent offending in offspring and psychiatric illness in parents was stronger in females than in males, but there was little difference in risk between genders with regard to suicide attempts.
Webb and colleagues said genetic vulnerability and familial transmission contributed to the relationship between parental mental illness and risk of suicide or violent offending in their offspring. Additionally, these offspring are more likely to experience other adversities such as family violence, abuse, and neglect that increase the risk of suicide and violence, the researchers said.
"Early interventions could benefit not only the parents but also their offspring," they wrote, adding that interventions specifically focused on reducing the rate and effects of substance misuse in parents "may help reduce their offspring's future risks for suicidality and violence."
Study limitations included not controlling for confounding variables other than socio-economic status, that criminal offending data was available only from 1981 onwards, and the potential for underreporting of both childhood abuse episodes and milder cases of mental health disorders.
In an accompanying editorial, David Brent, MD, of the University of Pittsburgh, and colleagues said there is "much to commend in this study, including the assessment and control for a broad range of parental psychiatric disorders, as well as the sheer size and representativeness of this sample."
However, they noted a few drawbacks: the authors may have overestimated the impact of parental psychiatric disorder due to confounding environmental factors that contribute to suicidal behavior and violence, they said. And it would be "helpful to examine the rate and type of psychiatric disorders in offspring."
"To capitalize on these findings," they concluded, "we need further work that can more precisely define the liabilities that are being transmitted, and research to explain individual differences in trajectories of violent and suicidal behavior."
Renee Binder, MD, of the University of California San Francisco, who was not involved in the study, told MedPage Today that the findings were "somewhat surprising, especially that parental history of cannabis use was related to violent behavior in their children at age 15 and older."
"It is unclear why cannabis use, by itself, would be so important in causing violent behavior," Binder said, adding that it's also unclear as to "how much genetics affect children compared to family/environmental issues."
Edwin Williamson, MD, of Vanderbilt University Medical Center, who also wasn't involved in the study, told MedPage Today that it "helps reinforce to all mental health providers the importance of family history and the impact of family history on the risk profile of an individual."
Williamson said it reminds mental health providers to "consider the children of our adult patients, to screen for emerging symptoms, and consider offspring of our patients as 'at risk' compared to the general population."
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