WASHINGTON - TOURETTE'S syndrome affects an estimated 148,000 US children, many of whom have other disabilities such as attention deficit hyperactivity disorder, US researchers reported on Thursday.

Their survey suggests that about a third of a per cent - three in every 1,000 children - have the disorder, characterized by sometimes debilitating tics such as repetitive, stereotypic movements or inappropriate vocalisations.

'Having an estimate of the number of US children who are diagnosed with Tourette's syndrome is a first step toward understanding the overall impact of this condition in the population,' said Dr Rebecca Bitsko of the Centers for Disease Control and Prevention, who worked on the study.

'Tourette's syndrome and tic disorders have been linked to higher rates of attention deficit hyperactivity disorder, obsessive-compulsive disorder, and impairments associated with these conditions, such as learning disabilities and problems with peer relations,' Dr Bitsko added.

For their study, the researchers looked at data from the 2007 National Survey of Children's Health, which included questions about Tourette's for the first time. 'Complete data on Tourette's syndrome were available for 64,034 persons aged 6 to 17 years,' they wrote.

'The estimated prevalence for ever receiving a Tourette's syndrome diagnosis, by parent report, was 3 per 1,000, representing approximately 148,000 children,' they added.

Boys were far more likely than girls to be diagnosed, the researchers reported in the CDC's weekly report on death and disease. 'The reason boys are more likely than girls to express symptoms of TS is unclear and is likely the result of a combination of genetic, hormonal, and environmental factors,' they wrote. -- REUTERS