Young Parental Age May Double Child ADHD Risk

Liam Davenport

April 03, 2015

Children born to younger parents have an increased risk for attention-deficit/hyperactivity disorder (ADHD), a large, population-based study suggests.

In an analysis of data from more than 50,000 individuals in Finland, the researchers found that having one parent younger than 20 years increased the risk for childhood ADHD by approximately 50%. Children born to families in which both parents were younger than 20 years had almost twice the risk for ADHD.

"Health professionals who work with young parents should be aware of the increased risk of ADHD in offspring," investigators, led by Roshan Chudal, MBBS, MPH, Research Center for Child Psychiatry, Institute of Clinical Medicine and the University of Turku, Finland, write.

"This would improve early detection and treatment, but for the development of preventive measures and appropriate interventions, more information on the developmental pathways is needed," they add.

The study was published online March 26 by the Journal of the American Academy of Child and Adolescent Psychiatry.

Schizophrenia, Autism, Bipolar Disorder

Previous studies have demonstrated a link between older paternal age and an increased risk for schizophrenia in offspring. The risk for other conditions, such as autism and bipolar disorder, is also increased with older parental age. However, preliminary studies in ADHD showed the opposite association.

To investigate, the researchers conducted a nested case-control study using data from the Finnish Prenatal Study of ADHD. From several nationwide databases, they identified 10,409 individuals with ADHD born between 1991 and 2005; for the control group, they identified 39,125 persons who were matched for sex, date of birth, and place of birth.

The team took into account a number of factors, including parental psychiatric history, maternal socioeconomic status, marital status, maternal smoking during pregnancy, number of previous births, and birth weight for gestational age.

Compared with a reference parental age of 26 to 29 years, fathers younger than 20 years had a significantly increased risk of having offspring with ADHD, at an odds ratio (OR) of 1.55. For mothers younger than 20 years, the OR was 1.41.

Interestingly, increasing maternal age beyond 26 to 29 years was associated with a decrease in ADHD risk among offspring, at an OR of 0.79 among mothers aged ≥40 years.

In a further analysis, the researchers looked at the additive effect of both parents being younger than 20 years. Compared with children born to parents aged ≥20 years, those for whom only the mother was younger than 20 years had an OR of ADHD of 1.46. For children for whom only the father was younger than 20 years, the OR was 1.55. When both parents were younger than 20 years, the OR of ADHD was 1.94.

"Young parents are a specific group, in that they have their own problems already. They often come from parents who were already young, and then they may also have some genetic risk for ADHD. This risk could be transmitted to the offspring," Dr Chudal told Medscape Medical News.

The children of young parents are also exposed to a large number of socioeconomic risk factors.

"I think it's a mix of both," he said. "It's both the inherited genetic risk and, among those who are susceptible, additional environmental factors. That's what we believe triggers the development of ADHD."

Public Health Issue

Senior author Andre Sourander, MD, PhD, also at the University of Turku, described the findings as "a public health issue which needs to be addressed."

The team is developing programs to tackle the increased risk for behavioral problems and ADHD in the children of young parents, taking into account the stigma they face.

Dr Sourander said that they have an ongoing Strongest Family study, in collaboration with Professor Patrick McGrath and his group from Halifax, Canada, on remote parent training for children with disruptive behavior, many of whom have ADHD.

"They have, once a week, a coaching- and web-based training program, so they don't need to be stigmatized," Dr Sourander said. "They don't need to go to any services, so it's quite innovative, almost revolutionary."

He explained that they came up with the concept after analyzing the determinants of parental involvement in interventional programs for children with behavioral problems. They found that being a teenage parent was one of the factors associated with parents not getting involved with the programs.

"It's very important from that perspective to identify people at risk," Dr Sourander said.

Studies have shown that children with disruptive behavior problems are also at increased risk of committing crimes and have an increased risk of dying early.

"If we can somehow act somewhere in the pathway to prevent this, that would have a big public health impact," said Dr Chadul.

Nature vs Nurture

Commenting on the findings for Medscape Medical News, Yoko Nomura, PhD, MPH, associate professor, Department of Psychology, Queens College, City University of New York, said she believes the association is likely environmental, rather than biological or genetic.

"Being younger shouldn't really get 'under the skin.' It's about providing an environment which is suboptimal for children and having an increased risk of ADHD," she said.

"This is a population-based study. It doesn't show any mechanism. It doesn't have an ability to understand what is causing the association," Dr Nomura added.

"This study opens up a basis of discussion, and after the association has been replicated in a population study, we will be more certain that younger age is a risk factor for ADHD."

Dr Nomura said, "It's important to remember that we shouldn't really focus on the mother, we should focus on both the mother and the father. They are equally important, and when we look at the odds ratio, it's kind of similar."

"So it means it's something about young age.... [The researchers] speculated that younger people may be more impulsive or more stressed, more this, more that. But we don't know, and they are just mixing all these risks into one bag."

"Clinical studies now have an obligation to tease out what is actually making this association," she added.

Dr Nomura believes that the study points to some of the wider issues associated with ADHD.

"There is a big stigma associated with ADHD or learning disabilities, or any kind of these disorders, and I think it's time for people to really realize they are not second-class citizens."

"There is something [going on] there, and the more we can find out, the more we can intervene and modify those risks, and we can help society as a whole."

The authors and Dr Nomura report no relevant financial relationships.

J Am Acad Child Adolesc Psychiatry. Published online March 26, 2015. Abstract

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