Risk for Substance Abuse in ADHD Relatives Due to Genetics

Liam Davenport

October 29, 2014

The increased risk for substance use disorders (SUDs) among the relatives of patients with attention-deficit/hyperactivity disorder (ADHD) is due to shared genetic factors between the disorders, new research suggests.

The researchers, led by Charlote Skoglund, MD, from Karolinska Institutet in Stockholm, Sweden, found that the first-degree relatives of ADHD probands had an increased risk for SUDs, and that the risk was lower in second-degree relatives. Crucially, the association was unaffected by coexisting psychiatric disorders.

The study was published online October 22 in Biological Psychiatry.

Improved Understanding "Crucial"

"An improved understanding of the etiologic underpinnings of SUD and ADHD is crucial and will have important clinical and public health implications," the investigators write.

"Familial history of ADHD needs to be taken into account when assessing risk for future SUD since it is not only the individual themself, but also their relatives who are at risk for SUD, should an ADHD diagnosis be established."

To explore the overlap in genetic and environmental factors between ADHD and SUD, the researchers examined data on 62,015 ADHD patients from the Swedish National Patient Register and the Swedish Prescribed Drug register.

By cross-linking with several longitudinal Swedish national registries, they were able to identify the first- and second-degree relatives of the patients, alongside 10 randomly selected unaffected control individuals for each case. Control individuals were matched by birth year, sex, and residential factors.

As expected, probands with ADHD were more likely than control persons to be diagnosed with an SUD, drug abuse, and alcohol disorder, at odds ratios (ORs) of 10.8, 19.2, and 8.3, respectively.

The first-degree relatives of ADHD patients were at increased risk for an SUD compared with control persons, at an OR of 2.2 vs 1.8. The risk for an SUD in second-degree relatives was lower in both groups, at ORs of 1.4 and 1.4, respectively.

The increased risk for an SUD remained higher in first-degree than second-degree relatives of ADHD probands even after taking into account disorders with shared genetic risk factors, such as bipolar disorder or schizophrenia, and coexisting disorders, such as depression.

"The main clinical implication is that the overlap between ADHD and SUD is likely not explained by harmful effects of stimulant medication. This is important, given that concerns around the safety of central stimulant treatment in ADHD might result in the withholding of essential and effective pharmacological treatment in affected individuals," the researchers write.

The investigators suggest that, with increased understanding of the overlap between ADHD and SUDs, individuals at high risk for an SUD could be targeted at an early stage. Furthermore, psychosocial and pharmacologic treatment could be optimized and individualized.

"Individuals with ADHD and SUD not only experience great personal suffering and functional impairment but are also exposed to a variety of misunderstandings, misinterpretations and misclassification regarding their ADHD symptoms and SUD disorders.

"Not only could a clearer understanding of the etiological overlap between ADHD and SUD increase societal acceptance for them as valid medical diagnoses, but it could also reduce the personal and psychosocial stigmatization associated with both disorders and ensure that these individuals receive effective treatment," the authors conclude.

The authors report no relevant financial relationships.

Biol Psychiatry. Published online October 22, 2014. Abstract

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