Children with attention deficit hyperactive disorder — and their mothers — are more likely to have shorter than normal telomere length, a sign of cellular aging, a new study finds.

The shorter the telomeres, the shorter the life expectancy, say scientists. Often described as similar to the hard plastic ends of a shoe string, telomeres "cap" the ends of chromosomes, protecting against the loss of DNA during cell division. Telomere length (at birth) appears to be genetic. Length is anywhere from 34 percent to 82 percent inherited, scientists estimate, yet this is a controversial topic.

Some researchers say a child’s telomere length is more strongly related to the mother than the father, yet past studies have shown the father’s age exerts some influence on a child’s telomere length. That said, a decrease in telomere length happens naturally as we age, though many researchers believe this decline may be accelerated by stress. Previous studies have linked shortened telomere length to conditions such as autism.

Could ADHD also be linked to telomere length... and if so, is that due to genetics or stress?

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To test this possibility, a team of researchers from Brazil’s D'Or Institute of Research and Education and Federal University of Minas Gerais designed a simple study. They measured telomere length for 61 ADHD children, ages 6 through 16, and their parents, in all cases controlling for the age of all participants. Analyzing the data, the researchers discovered no significant differences in telomere length linked to socioeconomic factors.

Among the children, though, the researchers found shorter telomere length than normal. While maternal telomeres were also shorter, no alteration existed in paternal telomere length. Interestingly, inattention symptoms appeared to have less impact on telomere length than other symptoms of ADHD.

“Higher levels of hyperactivity-impulsivity were associated with shorter relative telomere length in ADHD children and in their mothers,” the researchers noted. While stress may contribute to this, the researchers say inheritance is the true culprit.

“We found general heritability to be the major mechanism explaining interindividual telomere length variation in ADHD,” wrote the authors. “Our results also suggest a relationship between child hyperactive-impulsive symptoms and maternal telomere length.”

Shortened telomere length, a sign of cellular aging, is associated with increased risk for chronic diseases and conditions, including diabetes and cancer, say the researchers. They also suggest future studies investigating the speed of telomere attrition should delve into inherited telomere length. After all, abnormally short telomeres at age 11 may have little to do with the rate of attrition and everything to do with the original length at birth.

Source: de Souza Costa D, Freitas Rosa DV, Almeida Barros AG, et al. Telomere length is highly inherited and associated with hyperactivity-impulsivity in children with attention deficit/hyperactivity disorder. Frontiers of Molecular Neuroscience. 2015.