These segments, known as copy number variations (CNVs), play an important role, acting rather like a control valve over genes, which make the body's all-important proteins. If CNVs are missing or duplicated, they can alter the dosage of genes by 50 percent, up or down.
"We've known for many years that ADHD may well be genetic because it tends to run in families in many instances. What's really exciting is that we've found the first direct genetic link," said Anita Thapar, a professor of neuropsychiatric genetics at Cardiff University, Wales.
Even more intriguing is the discovery that these CNVs appear to cluster in key areas, notably in Chromosome 16, that overlap with regions implicated in autism and schizophrenia -- two other enigmatic, but now firmly acknowledged, brain disorders.
"ADHD can be stigmatizing because there's a lot of public misunderstanding about it," Thapar said in a press conference webcast from London.
"For example, some people say it's not a real disorder or it's the result of bad parenting, and parents and children can encounter much stigma because of this. So finding this direct genetic link to ADHD should help clear this misunderstanding and address this stigma."