More than 6.4 million U.S. children have received a diagnosis of attention-deficit/hyperactivity disorder, according to the Centers for Disease Control and Prevention. Despite the prevalence of ADHD, researchers continue to search for answers about what causes the disorder, why it affects children differently, and how to best treat each individual case.

Related Story: How childhood trauma could be mistaken for ADHD

Three very different studies show the potential for scientific research to offer fresh insight into these unanswered questions.

• The first study, published in a recent issue of the Journal of Child Psychology and Psychiatry, found that the condition might be influenced by a child’s socioeconomic environment.
• Meanwhile, in 2012, scientists looked at how parenting style affected behavior in children who possessed genotypes associated with ADHD. Their findings, published in the Journal of Abnormal Child Psychology, revealed that negative parenting predicted inattention symptoms in certain children.
• Finally, in the third study, which is currently unpublished, U.C. Berkeley researchers tracked and analyzed long-term outcomes for girls who were both diagnosed with ADHD and experienced severe abuse or neglect. The results indicate that experiencing ADHD and trauma may put some youth at an increased risk for eating disorders, depression and suicide later in life.

Study #1: Dr. Ginny Russell and her colleagues at the University of Exeter set out to better understand how a child’s socioeconomic standing might play a role in the development of ADHD. Russell firmly believes that ADHD is indeed a brain disorder with genetic underpinnings, but she also worries that it has been characterized as a “context-free condition.” Time and again, studies have shown that poor or disadvantaged children are more likely to have ADHD, and this fact struck Russell.

Some researchers have argued that this increased likelihood could be the result of reverse causality, or in other words, that the difficulty of parenting a child with behavioral problems might lead to economic hardship and divorce. In Russell’s study, which used data from a longitudinal study of more than 19,000 children in the United Kingdom, low-income families were more likely to have a child with ADHD – but that couldn’t be traced back to reverse causality. In fact, household income for families with an ADHD-diagnosed child didn’t decline over a period of several years compared to families without a diagnosis. Both sets of families had matching earnings at the start.

Rather, parenting involvement and family conflict appeared to play a role in the link between socioeconomic status and ADHD. Families that reported higher levels of household tension as well as a strained connection between a parent and child were more likely to experience social or economic disadvantage. The quality of the family relationship, including the bond between parent and child, was also associated with an ADHD diagnosis. These dynamics may partly explain the higher prevalence of ADHD in low-income families.

“The aetiology of ADHD is likely to be a complex interplay of genetic and environmental factors, some linked to socioeconomic disadvantage,” the authors wrote.

Russell told ACEsTooHigh that it’s important to understand the social and economic factors that may influence the development of ADHD, particularly as clinicians look to effectively treat the disorder. For example, focusing on medication alone without considering behavioral or psychosocial therapy might distract the provider and parents from other ways of improving not only a child’s behavior, but also the household environment. “It makes the problem within the child rather than within the family,” Russell said.

Study available at the Journal of Child Psychology and Psychiatry: The association of attention deficit hyperactivity disorder with socioeconomic disadvantage: alternative explanations and evidence

Study #2: In the search for the genetic origins of ADHD, researchers have considered the role of a gene known as monoamine oxidase A (MAO-A). This gene affects the breakdown of mood-related neurotransmitters in the brain and has been linked to psychiatric disorders, including anti-social behavior and depression. Scientists have found that the variations in the way that MAO-A is expressed may influence behavior, though the research on this has yielded inconsistent results. It is possible that those with a low-activity MAO-A genotype are more prone to aggression. The high-activity genotype, on the other hand, may decrease levels of neurotransmitters widely implicated in ADHD. Variations in MAO-A expression could make children more sensitive to different styles of parenting, and thus more likely to exhibit symptoms of the disorder.

James J. Li, a researcher at the Virginia Institute for Psychiatric and Behavioral Genetics, and Steve S. Lee, a researcher at the University of California at Los Angeles, explored this premise in their 2012 paper for the Journal of Abnormal Child Psychology. Their study included 150 boys between the ages of six and nine with and without an ADHD diagnosis. Li and Lee collected saliva for DNA testing to determine the MAO-A genotype of each subject. They also assessed factors like family income, parental depression, ADHD symptoms, and parenting style.

Boys with the high-activity MAO-A genotype showed more symptoms of inattention with higher levels of negative parenting, according to the study’s findings. These same children showed fewer symptoms with low levels of negative parenting. The researchers did not detect any influence of positive parenting on the MAO-A genotype. Li and Lee concluded that parenting practices play an important role in moderating the expression of genetic predisposition to ADHD symptoms.

Abstract available at Journal of Abnormal Child Psychology: Association of Positive and Negative Parenting Behavior with Childhood ADHD: Interactions with Offspring Monoamine Oxidase A (MAO-A) Genotype

Study #3: For more than a decade, Dr. Stephen P. Hinshaw, a researcher and psychology professor at U.C. Berkeley, has followed 140 girls diagnosed with ADHD. He and his colleagues have produced several studies using data from this sample. One paper looked at the role of peer influence in ADHD symptoms and risky driving behavior. Another study considered how childhood ADHD led to impairment in adulthood and an increased risk for suicide and self-harm. The team’s latest research, which is currently unpublished, evaluates an overlooked population of ADHD patients: those who experienced trauma or maltreatment as children and adolescents.

The results showed that the girls with ADHD who experienced maltreatment were at greater risk for depression, poor self-esteem, eating disorders and suicide attempts than their peers who had not been maltreated.

Maya Guendelman, a doctoral candidate and researcher who works with Hinshaw, said she wanted to focus on the role of trauma in ADHD outcomes after spending time at U.C. San Francisco where young patients are routinely screened for childhood adversity. While it’s not clear whether subjects experienced trauma or were given a diagnosis of ADHD first, Guendelman hopes her research, once published, convinces clinicians to stop and consider the possibility that their patients may also have a history of childhood adversity. “It’s so important to do a through screening of their early life experiences because that you can’t assume all the symptoms are directly the result of ADHD,” Guendelman said.

Guendelman expects the paper will be published in a peer-reviewed journal this year.