Subtle abnormalities in chromosomal structure are significantly more frequent among people with attention-deficit/hyperactivity disorder than in controls, according to a Lancet study.

Researchers performed genome-wide analyses in 350 British children with ADHD and 1000 controls. Abnormalities (called copy-number variants) larger than 500 kilobases occurred with twice the frequency in ADHD. Among subjects with ADHD and intellectual disability, the frequency was almost six times as great. The abnormalities were centered on a location in chromosome 16 that is also linked to autism and schizophrenia. The findings were confirmed in a separate cohort of Icelanders.

The authors say their findings refute the idea that ADHD “is purely a social construct.”

Asked to comment, Dr. Barbara Geller of Journal Watch Psychiatry said: “These findings, and recent work on both structural and functional imaging differences between ADHD and neurodevelopmentally healthy controls will, hopefully, soon lead to specific biological tests for clinical use.”