In the first estimate of its kind, US health officials report that three of every 1 000 children, mostly boys, are diagnosed with Tourette Syndrome.
Tourette Syndrome is a neurological disorder that usually begins in early childhood, with symptoms typically becoming more severe between the ages of 10 and 12. The key features of the condition are recurring motor tics plus at least one vocal tic, according the US Centres for Disease Control and Prevention.
"These are diagnosed cases, not necessarily all the cases that are out there," noted study author Lawrence D. Scahill, an associate professor of nursing and child psychiatry at Yale University School of Medicine. "There is good reason to believe it's an underestimate of the likely prevalence."
More common than thought
People used to think that Tourette Syndrome was rare and uniformly severe, Scahill said. In 1980, the definition of the condition was broadened to include milder cases, he added. "As soon as that happened, the prevalence went up."
Earlier studies had put the prevalence of Tourette Syndrome at six probable cases per 1 000 children, Scahill said.
"The difference of the three per 1 000 of diagnosed cases and the six per 1 000 probable cases is the difference between identified cases and cases that are out there, but haven't been diagnosed," he said. "This tells us we are not doing so badly in terms of identifying cases. Half of the cases are being identified and monitored, but half are not."
Other developmental problems
Even though most cases are mild, with barely notable tics, these children can suffer from other developmental problems, he added. "The frequency of attention-deficit/hyperactivity disorder (ADHD) is over 60% in this population, the frequency of behavioural problems is over 40%, anxiety [is] 40%," Scahill said.
Scahill noted there are effective treatments for ADHD and medication and behavioural therapy can help control severe tics. "It's a minority of individuals who have significant problems with cursing or inappropriate outbursts of one sort or another," he said.
The report is published in the CDC's Morbidity and Mortality Weekly Report.
First study of its kind
For the study, researchers collected data on almost 92 000 households who participated in the National Survey of Children's Health. Telephone interviews were conducted from April 2007 through July 2008.
"This is the first-ever estimate of Tourette Syndrome from a nationally representative sample of US children," said report co-author Rebecca Bitsko, a CDC health scientist. "It's a baseline estimate for us to work with, and it's going to allow us to begin to understand the impact of Tourette Syndrome and also to look at trends in Tourette Syndrome over time."
In their study, the researchers found that the condition is three times more common in boys than in girls, and twice as common in children between 12 and 17 compared with children aged 6 to 12.
About 27% of children with Tourette Syndrome have moderate or severe disease. In addition, 79% of children with the condition have at least one other neuro-developmental problem, the researchers found.
More common in white population
White children are more than twice as likely as black children or Hispanic children to have been diagnosed with Tourette Syndrome.
This could mean that minority populations may have some protection against the condition, Scahill said. "But quite honestly, I sort of doubt that. The other explanation is that these children are less likely to come to treatment attention. It looks like we are missing more children in minority populations."
Dr Robert King, medical director of the Tourette's Clinic at the Yale Child Study Centre, said this is an important study that adds to the understanding of how widespread the condition is.
"As Tourette Syndrome was once, and sometimes still is, mistakenly believed to be inevitably a very rare, severe chronic disorder, these findings confirm an updated view of Tourette Syndrome as relatively common, usually mild, and likely to improve spontaneously by young adulthood," King said.
The prevalence may be even higher than the survey shows, since diagnosis was based on whether a health-care provider ever told the parent that the child had Tourette Syndrome, King said.
"Hence, the study may not have picked up on milder cases that had not been brought to clinical attention or those in populations with less access to clinicians knowledgeable about Tourette Syndrome and hence able or inclined to make the diagnosis," he said.
"The study also confirms the high rates of co-morbidity with other disorders, such as ADHD, anxiety, learning problems, underlining the importance of diagnosis even if the tics themselves are not a source of distress or disability," he said. - (Steven Reinberg/HealthDay News, June 2009)
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