Study finds ADHD affects motor skills of boys more than girls

New research published in the November 4, 2008 issue of Neurology®, the medical journal of the American Academy of Neurology, found that ADHD affects the motor skills of boys more than girls. By examining age-related improvement of motor skills in children with and without ADHD, researchers from the Kennedy Krieger Institute in Baltimore, Md. found that girls with ADHD and their typically developing peers were more likely to be able to control their movements compared to boys with ADHD. The findings are consistent with multiple MRI studies that have shown boys with ADHD have decreased activity in regions of the brain important for planning and executing movement. This study found that the motor skills of typically developing children steadily improved with age, but boys with ADHD continued to show motor skills deficits through adolescence. The motor skills of girls with ADHD improved at a rate more similar to their typically developing peers. This study's large sample size of boys and girls with ADHD distinguishes it from past research examining motor skill development in children with the disorder because it allows for direct comparison of girls and boys with ADHD. Previous research has primarily examined boys with the disorder, making this one of only a handful of studies that has explored whether girls with ADHD experience similar patterns in motor skill development as boys with the disorder.

"These findings suggest that sex-related differences in children with ADHD extend beyond symptom presentation to development of motor control," said E. Mark Mahone, Ph.D., ABPP, lead study author and a research scientist at the Kennedy Krieger Institute. "By elementary school, girls with ADHD may be relatively free from motor skills deficits because the female brain matures earlier than the male brain."

Previous studies have shown that brain regions considered vital for motor control reach their maximum size one year earlier in girls than boys. Girls may "outgrow" ADHD-related motor skill deficits before age 7, the minimum age of girls enrolled in this study. It is also possible that the motor tests used in this study are more sensitive to the hyperactivity symptoms of ADHD. Boys with ADHD tend to have more hyperactivity, while girls generally have more inattentive and emotional control symptoms.

Two hundred sixty-eight children between the ages of 7 and 15 were studied, including 136 typically developing children and 132 children with ADHD. All of the children were tested on their speed, ability to keep rhythm and number of extraneous movements while completing simple motor tasks, such as finger-tapping and walking on their toes. Two hundred twenty-five of the children were also tested for inhibitory control, or the ability to over-ride automatic responses. The scores were then examined using linear regression analyses.

"Studying motor function is critical to understanding the causes and effects of developmental disorders such as ADHD," said Dr. Mahone. "Assessment of motor skills gives researchers a window into brain development, and allows us to more precisely understand the nature of cognitive difficulties in developmental disorders such as ADHD."

Given these study findings, future research examining the developmental patterns of executive and motor control in children with ADHD should look at boys and girls separately, and at younger ages, for a fuller understanding of female-specific patterns. Researchers involved in this study also recommend that future studies examine the association between motor skills performance and the neuroanatomic differences in children with ADHD revealed by MRI scans, while considering the different patterns in boys and girls.

Source: Kennedy Krieger Institute