The causes of parent-offspring transmission of drug abuse: a Swedish population-based study

Association of parental substance misuse with offspring substance misuse and criminality: a genetically informed register-based study

BACKGROUND

Genetically informed studies have provided mixed findings as to what extent parental substance misuse is associated with offspring substance misuse and antisocial behavior due to shared environmental and genetic factors.

METHODS

We linked data from nationwide registries for a cohort of 2 476 198 offspring born in Sweden 1958-1995 and their parents. Substance misuse was defined as International Classification of Diseases diagnoses of alcohol/drug use disorders or alcohol/drug-related criminal convictions. Quantitative genetic offspring-of-siblings analyses in offspring of monozygotic and dizygotic twin, full-sibling, and half-sibling parents were conducted.

RESULTS

Both maternal and paternal substance misuse were robustly associated with offspring substance misuse [maternal adjusted hazard ratio (aHR) = 1.83 (95% confidence interval (CI) 1.80-1.87); paternal aHR = 1.96 (1.94-1.98)] and criminal convictions [maternal aHR = 1.56 (1.54-1.58); paternal aHR = 1.66 (1.64-1.67)]. Additive genetic effects explained 42% (95% CI 25-56%) and 46% (36-55%) of the variance in maternal and paternal substance misuse, respectively, and between 36 and 44% of the variance in substance misuse and criminality in offspring. The associations between parental substance misuse and offspring outcomes were mostly due to additive genetic effects, which explained 54-85% of the parent-offspring covariance. However, both nuclear and extended family environmental factors also contributed to the associations, especially with offspring substance misuse.

CONCLUSIONS

Our findings from a large offspring-of-siblings study indicate that shared genetic influences mostly explain the associations between parental substance misuse and both offspring substance misuse and criminality, but we also found evidence for the contribution of environmental factors shared by members of nuclear and extended families.

Comparing Childhood Characteristics of Adopted and Non-adopted Individuals Deceased by Suicide

OBJECTIVE

Across the globe more than 35,000 children a year are adopted by non-relatives, and some studies suggest that adopted individuals may be more vulnerable to developing mental disorders. To map the differences in suicide risk factors in adopted and non-adopted individuals, this study will compare the development of mental disorders as well as life events occurring before the age of 18 for both adopted and non-adopted individuals deceased by suicide.

METHODS

This study included 13 adopted and 26 non-adopted individuals deceased by suicide as well as 26 non-adopted living control individuals. Cases were taken from a data bank created over the last decade by researchers of [our institution] comprising a mixture of 700 suicide cases and living control individuals aged from 14 to 84. Adopted and non-adopted individuals deceased by suicide; adopted individuals deceased by suicide and non-adopted living control individuals were each compared on Axis I and II disorders, early life events, and burdens of adversity.

RESULTS

Results show significant differences, with a higher rate of Attention Deficit Hyperactivity Disorder, mental health comorbidity and Cluster C personality disorders among adopted individuals. Furthermore, adopted individuals have higher adversity scores prior to the age of 15.

CONCLUSION

This study underlines the fact that adoptive families need to be supported throughout adoption. Health care professionals need specialized training on this matter, and the psychological challenges adopted individuals face need to be treated at the earliest juncture.

Parental characteristics and offspring mental health and related outcomes: a systematic review of genetically informative literature

Various parental characteristics, including psychiatric disorders and parenting behaviours, are associated with offspring mental health and related outcomes in observational studies. The application of genetically informative designs is crucial to disentangle the role of genetic and environmental factors (as well as gene-environment correlation) underlying these observations, as parents provide not only the rearing environment but also transmit 50% of their genes to their offspring. This article first provides an overview of behavioural genetics, matched-pair, and molecular genetics designs that can be applied to investigate parent-offspring associations, whilst modelling or accounting for genetic effects. We then present a systematic literature review of genetically informative studies investigating associations between parental characteristics and offspring mental health and related outcomes, published since 2014. The reviewed studies provide reliable evidence of genetic transmission of depression, criminal behaviour, educational attainment, and substance use. These results highlight that studies that do not use genetically informative designs are likely to misinterpret the mechanisms underlying these parent-offspring associations. After accounting for genetic effects, several parental characteristics, including parental psychiatric traits and parenting behaviours, were associated with offspring internalising problems, externalising problems, educational attainment, substance use, and personality through environmental pathways. Overall, genetically informative designs to study intergenerational transmission prove valuable for the understanding of individual differences in offspring mental health and related outcomes, and mechanisms of transmission within families.

A Contagion Model for Within-Family Transmission of Drug Abuse

OBJECTIVE

The purpose of this study was to determine whether, controlling for genetic effects, drug abuse was transmitted within families as predicted by a contagion model.

METHODS

The authors examined 65,006 parent-offspring, sibling, and cousin pairs ascertained from Swedish population registries in which the primary case subject had a drug abuse registration. The rate of drug abuse registration among at-risk secondary case subjects ages 19-23 was studied. Utilizing matched control pairs, a difference-in-difference approach was used to infer causal effects.

RESULTS

In offspring, risk for drug abuse registration in the 3 years after an index registration of a parent residing in the same household, neighborhood, or municipality increased 5.9%, 3.4%, and 1.8%, respectively. For siblings of sibling index case subjects, parallel results were 5.9%, 3.9%, and 1.2%. For cousins of cousin index case subjects, excess risk for those in the same neighborhood or municipality was 2.9% and 0.9%, respectively. In all sets of relatives, drug abuse transmission was strongest in male-male pairs and in pairs closest in age. In sibling pairs, stronger transmission was observed in older to younger siblings compared with younger to older siblings. Transmission was stronger within than across the two drug classes with sufficient data (opiates and cannabis).

CONCLUSIONS

These results suggest that drug abuse can be transmitted within families by an environmentally mediated temporally defined model of contagion. The most important methodological limitation is that drug abuse registration is an inaccurate measure of the onset of drug abuse. Indeed, as predicted, drug abuse risk increased among potential secondary case subjects in the year before drug abuse registration of the index case subject.

Sources of Parent-Child Transmission of Drug Abuse: Path Analyses of Not-Lived-With Parental, Stepparental, Triparental, and Adoptive Families

To clarify the origins of parent-child resemblance for drug abuse (DA), using national Swedish data, we fit path models to information on DA in parents and children from six informative family types: i) not-lived-with father, ii) not-lived-with mother, iii) stepfather, iv) stepmother, v) triparental, and vi) adoptive. From these families, we estimated parent-offspring resemblance reflecting the effects of genes + rearing, genes only, and rearing only. The estimates of parent-offspring correlations were statistically homogenous across family types. The weighted estimate of the father-offspring correlation for DA for genes + rearing, genes-only, and rearing-only relationships were, respectively, +0.26, +0.19, and +0.06. Parallel figures for mother-offspring relationships were +0.19, +0.13, and +0.09. In both genes + rearing and genes-only parent-offspring relationships, DA correlations were stronger for fathers than for mothers. Both genetic and environmental factors contribute substantially to parent-offspring resemblance for DA and seem to be additive.

Changes in opiate and stimulant use through 10 years: The role of contextual factors, mental health disorders and psychosocial factors in a prospective SUD treatment cohort study

AIM

To examine temporal changes in opiate and stimulant use among patients in substance abuse treatment over a ten-year observation period and to explore the role of contextual factors, mental health disorders and psychosocial factors on these changes.

METHODS

A cohort of 481 patients was prospectively interviewed at admission to treatment and after 1, 2, 7 and 10 years. The sample was recruited from 20 facilities in the Greater Oslo region, Norway.

RESULTS

The majority of patients were poly-drug users and 80% had used both opiates and stimulants the last 30 days prior to treatment admission. Last-month use of heroin, other opiates, cocaine and amphetamines declined from 80% to 34% at the end of the observation period. The most substantial reduction was observed between baseline and one-year follow-up. Use of heroin decreased the most from 62% to 16% after 10 years (a reduction of 74%), and the reduction continued from one-year follow-up throughout the observation period. The most important multivariate risk factors for sustained use of these drugs were male gender, having one or both biological parents with severe alcohol or drug problems, having an antisocial personality disorder, and living together with a person who abuses alcohol or drugs. Employment was associated with reduced risk of drug use at 7-year follow-up.

CONCLUSIONS

There was a substantial reduction in opiate and stimulant use from baseline to all follow-up assessments, most greatly for heroin. Findings regarding sustained use could suggest familial transmission and the challenges of preventive strategies and treatment efforts in an intergenerational context. Co-occurrence between drug abuse and mental health problems highlights the need of highly specialized competence in SUD treatment.

The rearing environment and risk for drug abuse: a Swedish national high-risk adopted and not adopted co-sibling control study

BACKGROUND

Although drug abuse (DA) is strongly familial, with important genetic influences, we need to know more about the role of rearing environment in the risk for DA. To address this question, we utilized a high-risk adopted and non-adopted co-sibling control design.

METHOD

High-risk offspring had one or more biological parents registered for DA, alcohol use disorders or criminal behavior. Using Swedish registries, we identified 1161 high-risk full-sibships and 3085 high-risk half-sibships containing at least one member who was adopted-away and one member who was not. Registration for DA was via national criminal, medical and pharmacy registers. In Sweden, adoptive families are screened to provide high-quality rearing environment for adoptees.

RESULTS

Controlling for parental age at birth and gender (and, in half-siblings, high-risk status of the other parent), risk for DA was substantially lower in the full- and half-siblings who were adopted v. not adopted [hazard ratios and 95% confidence intervals: 0.55 (0.45-0·69) and 0.55 (95% CI 0.48-0.63), respectively]. The protective effect of adoption on risk for DA was significantly stronger in the full- and half-sibling pairs with very high familial liability (two high-risk parents) and significantly weaker when the adoptive family was broken by death or divorce, or contained a high-risk parent.

CONCLUSIONS

In both full- and half-sibling pairs, we found replicated evidence that rearing environment strongly impacts on risk for DA. High-quality rearing environments can substantively reduce risk for DA in those at high genetic risk.

Cross-generational transmission from drug abuse in parents to attention-deficit/hyperactivity disorder in children

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) predisposes to drug abuse (DA) and twin studies suggest shared genetic effects. We here seek to determine, using adoption and adoption-like samples, the magnitude of the cross-generational transmission from DA in parents to ADHD in their children and clarify the degree to which this arises from genetic v. rearing effects.

METHOD

We ascertained ADHD and DA from multiple Swedish registries. Statistical analysis was performed by Cox and path models.

RESULTS

Risk for ADHD was significantly and similarly increased in the offspring of biological mothers and fathers with DA who did v. did not rear their offspring. Risk for ADHD was not elevated in the offspring of adoptive or step-parents with DA.

CONCLUSIONS

Cross-generational transmission was observed from DA in parents to ADHD in their children. An analysis of adoptive and adoptive-like parent-offspring relationships suggested that this transmission results from genetic and not from rearing effects.

Triparental families: a new genetic-epidemiological design applied to drug abuse, alcohol use disorders, and criminal behavior in a Swedish national sample

OBJECTIVE

The authors sought to clarify the sources of parent-offspring resemblance for drug abuse, alcohol use disorders, and criminal behavior, using a novel genetic-epidemiological design.

METHOD

Using national registries, the authors identified rates of drug abuse, alcohol use disorders, and criminal behavior in 41,360 Swedish individuals born between 1960 and 1990 and raised in triparental families comprising a biological mother who reared them, a "not-lived-with" biological father, and a stepfather.

RESULTS

When each syndrome was examined individually, hazard rates for drug abuse in offspring of parents with drug abuse were highest for mothers (2.80, 95% CI=2.23-3.38), intermediate for not-lived-with fathers (2.45, 95% CI=2.14-2.79), and lowest for stepfathers (1.99, 95% CI=1.55-2.56). The same pattern was seen for alcohol use disorders (2.23, 95% CI=1.93-2.58; 1.84, 95% CI=1.69-2.00; and 1.27, 95% CI=1.12-1.43) and criminal behavior (1.55, 95% CI=1.44-1.66; 1.46, 95% CI=1.40-1.52; and 1.30, 95% CI=1.23-1.37). When all three syndromes were examined together, specificity of cross-generational transmission was highest for mothers, intermediate for not-lived-with fathers, and lowest for stepfathers. Analyses of intact families and other not-lived-with parents and stepparents showed similar cross-generation transmission for these syndromes in mothers and fathers, supporting the representativeness of results from triparental families.

CONCLUSIONS

A major strength of the triparental design is its inclusion, within a single family, of parents who provide, to a first approximation, their offspring with genes plus rearing, genes only, and rearing only. For drug abuse, alcohol use disorders, and criminal behavior, the results of this study suggest that parent-offspring transmission involves both genetic and environmental processes, with genetic factors being somewhat more important. These results should be interpreted in the context of the strengths and limitations of national registry data.