Autism spectrum disorders (ASD) and attention-deficit hyperactivity disorder (ADHD) have been growing in prevalence in recent years as two of the most commonly diagnosed behavioral and psychosocial disorders. While both bear distinct genetic and physical differences, a new study has revealed common traits among the two, which support prior findings on the pair’s genetic risk factors.

Findings Amid A Controversy

ASD and ADHD diagnoses have growing prevalence — ASD is now diagnosed in one in 88 children under eight years old, ADHD nearly one in 10 — and so the debate surrounding psychosocial diagnoses grows in magnitude. Rife with unclear causes and uncorroborated evidence, many find themselves becoming more polarized because of too little information. A new study suggests a link between the two disorders and pushes the debate further toward ASD and ADHD having similar roots.

Researchers from Massachusetts General Hospital in Boston, led by ADHD researcher Amelia Kotte, analyzed behavior patterns from 240 children with ADHD and 227 without it. They looked for autistic traits (ATs) among both groups, ultimately finding less than one percent of non-ADHD children exhibiting ATs and some 18 percent of kids with ADHD scoring highly for ATs. Measures of autistic traits included levels of withdrawal and social and thought problems, as reported by the children’s parents.

“A substantial minority of ADHD children manifests ATs,” the researchers concluded, “and those exhibiting ATs have greater severity of illness and dysfunction.”

Among the children tested, those with ADHD were more likely to exhibit behaviors closer to ASD symptoms, such as getting into fights, being rejected by peers, having problems with their siblings, and experiencing difficulty in school. Other traits were present as well, pointing toward a deeper genetic underpinning. These included psychiatric conditions such as disruptive behavior, mood disorders, language disorders, and anxiety problems.

Common Ground Among The Disorders

ASD has received much of its attention in recent months because of its tenuous relationship with vaccines. While a growing body of evidence suggests no link exists between heavy vaccinations in infancy and growing rates of autism, skeptics point to flawed methodology in the studies’ approach. Nearly one in 54 boys is diagnosed with a form of autism, according to the Centers for Disease Control and Prevention, ranging from severe speech and social problems to high-functioning cases of Asperger syndrome. ADHD, meanwhile, has its own controversy concerning growing rates of diagnosis. Advocates cite genetic risk factors, while skeptics heap responsibility on parents and means of socialization.

"These disorders that we thought of as quite different may not have such sharp boundaries," said Dr. Jordan Smoller of Massachusetts General Hospital, one of the lead researchers for a recent international study appearing in The Lancet that found genetic links among autism, ADHD, and other psychiatric disorders.

These blurred lines can have deep implications for how the medical community diagnoses psychiatric disorders, said Dr. Bruce Cuthbert of the National Institute on Mental Health (NIMH), which funded the research. In the same way that chest pains may not always signal a heart attack, mental illness may have varied symptoms as well. Learning the root cause of one, and not the other, may help doctors specialize their treatment.

The NIMH study included analysis of five disorders: schizophrenia, bipolar disorder, autism, ADHD, and depression. Researchers examined the genomes of 33,332 patients with all five disorders and 27,888 controls. For the first time, they found overlap between all genetic risk factors. More precisely, one genetic factor accounted for a 17 to 28 percent risk of having any of the disorders.

Researchers concluded that their findings make sense, as the behavioral effects of the five disorders tend to bear resemblance to one another. More importantly, the findings highlight the importance of genetic similarity in treating the disorders themselves. Mere behavioral observation tends to fall short.

"If we really want to diagnose and treat people effectively,” Cuthbert told the Huffington Post, “we have to get to these more fine-grained understandings of what's actually going wrong biologically."

Source: Kotte A, Joshi G, Fried R. Autistic Traits in Children With and Without ADHD. Pediatrics. 2013.