Has one in ten adults developed ADHD? - hyperactivity disorder, or ADHD. More than 5 per cent of adults might develop the condition later in life, a new study suggests. About 7% of children are diagnosed with ADHD, which is associated with symptoms of restlessness, poor concentration and impulsive behaviour. Fortunately, although some individuals diagnosed with ADHD do experience persistent symptoms as adults, the majority of children "grow out of" the problem, suggesting that it might reflect a delay in brain maturation. In recent years though, cases of ADHD in adulthood have begun to crop up but without any obvious history of prior ADHD in childhood, suggesting that there may be adult-onset manifestations of the condition. How commonly this occurs though wasn't known. Now Jessica Agnew-Blais, a researcher at Kings College London, has followed up more than 2000 twins from England and Wales. These individuals were recruited at birth in 1994-1995 and assessed on a range of measures, including for ADHD, at ages 5, 7, 10 and 12, and then again at age 18. Of 2040 twins who were included in the analysis, 247 fitted the definition of having ADHD in childhood. By age 18, 80% of them were no longer showing signs of the condition. But, by age 18, 112 individuals with no past history of ADHD as a child were now displaying symptoms of the condition. Unlike their younger-afflicted counterparts, these adult-onset ADHD cases tended to report fewer externalising symptoms, such as disruptive behaviour, and were more prone to anxiety and depression. "What we don't know yet is whether this is the same condition that these adults are developing, or something different to classical childhood ADHD," Agnew-Blais explains. "It may be the same and the environment is playing a role in determining when and how the condition manifests itself." Perhaps during childhood, she speculates, the supportive influence of family life or being buffered from life's stresses helps to stop the condition from manifesting. But in adulthood, the loss of that support, different life pressures and also drug use might cause the condition to disclose itself. The findings have important implications for how we manage adults with a range of neuropsychiatric disorders. "The absence of a childhood diagnosis of ADHD should no preclude adults with ADHD from receiving clinical attention," Agnew-Blais cautions in her paper, published this week in JAMA Psychiatry. "How best to treat individuals with adult-onset ADHD is an open question that we need to look into..."