Researchers have identified another factor in the development of autism spectrum disorder: body overgrowth in early childhood.

The study, published in the Journal of the American Academy of Child and Adolescent Psychiatry, found that boys with autism developed significantly larger heads and longer, heavier bodies than their normally developing peers in the first two years after birth. These effects were not significant in girls. When the autistic children were tested at four years old for verbal and nonverbal skills, large body size and overgrowth in the postnatal period correlated with lower performance. Lead author and associate professor in the Yale Child Study Center Katarzyna Chawarska said these growth patterns might help in autism diagnosis.

“I believe that somatic overgrowth might be an early marker of less optimal outcomes in ASD [Autism Spectrum Disorder], as atypical growth features in the first two years of life were associated with more severe symptoms one to two years later as well as lower levels of verbal and cognitive functioning,” she said.

The researchers performed statistical analyses of pediatric medical data from 259 boys and 88 girls recorded at frequent intervals between birth and twenty-four months, controlling for the effects of race and ethnicity, parental age, education, gestational age differences and gender sample size differences. They found that autistic boys had significantly larger head circumferences than their normally developing peers between 11 and 22 months and longer bodies after four months. They were also heavier after nine months. Meanwhile, growth patterns of autistic girls did not significantly deviate from those of their non-autistic peers.

The study also reported extreme rates of body overgrowth in 16 percent of all autistic children compared to four percent in their typically-developing peers, though the difference was only significant in boys.

Emanuel DeCicco-Bloom, a professor at Rutgers University’s Robert Wood Johnson Medical School who was not involved with the study, commended the authors for using a large sample group and contemporaneous community-based controls. He said that the study showed a “strong correlation” between early body overgrowth and more severe autism cases, but did not explain why this was the case.

“Are there factors — genetic, or environment, or both — that work on the same process of growth of body and brain?” he asked.

DeCicco-Bloom suggested that future research should examine how embryonic growth factors, genes and hormones affect body growth in autistic children. George Anderson, a senior research scientist in the Yale Child Study Center, said he would like to see more research on how the gender effects of early body growth are distributed in an even larger and more representative sample group.

Study contributor and professor at Sacred Heart University Rhea Paul agreed that further research would clarify the mechanisms underlying the correlation between body overgrowth and autism.

“It’s very easy for people to just sort of focus on the brain and say everything that’s going on with autism happens in the brain, and the brain is what we need to study,” she said. “But what this study shows is that there may be larger patterns that affect the entire organization of growth.”

Pursuing this line of research could open up new areas in early childhood intervention, which would alleviate the economic and societal burden of autism spectrum disorder, Paul said.

According to the Centers for Disease Control, autism affects approximately 1 in 68 people and five times as many boys as girls. Each year, it costs approximately $17,000 more to care for an autistic child than for a non-autistic child.