A new study shows that about one in five children with Tourette syndrome also meet criteria for autism. But the researchers believe this prevalence may be due to a similarity in symptoms rather than actual autism.
Researchers at the University of California San Francisco (UCSF) tested 294 children and 241 adults with Tourette’s for autism, using a self-reporting test called the Social Responsiveness Scale. The findings show that 22.8 percent of the children reached the cutoff for autism, versus 8.7 percent of the adults. In the general population, autism is estimated to affect only 0.3 to 2.9 percent, according to studies cited in the paper.
The findings are published in the Journal of the American Academy of Child and Adolescent Psychiatry.
The Social Responsiveness Scale Second Edition is a 65-item quantitative measure of autism symptoms that assesses the ability to engage in “emotionally appropriate reciprocal social interactions.” It evaluates levels of social awareness, social cognition, social communication, social motivation, and restrictive interests and repetitive behavior.
The researchers wanted to examine autism symptoms in patients with Tourette’s, including those who also have obsessive-compulsive disorder (OCD) or attention deficit hyperactivity disorder (ADHD), conditions that frequently co-occur and are known to share common symptoms and genetic relationships.
“Assessing autism symptom patterns in a large Tourette’s sample may be helpful in determining whether some of this overlap is due to symptoms found in both disorders, rather than an overlapping etiology,” said first author Sabrina Darrow, Ph.D., assistant professor in the department of psychiatry at UCSF.
“Our results suggest that although autism diagnoses were higher in individuals with Tourette’s, some of the increase may be due to autism-like symptoms, especially repetitive behaviors that are more strongly related to obsessive-compulsive disorder.”
The findings show that the highest scores on the Social Responsiveness Scale (which met autism criteria) were found in participants with Tourette’s and either OCD or ADHD. In addition, among those with Tourette’s who met the cutoff for autism, 83 percent also met criteria for OCD. The researchers note that the high scores were especially prominent in the part of the autism test that measures restrictive interests and repetitive behavior.
An important finding was the wide discrepancy between children and adults with Tourette’s who met the diagnostic criteria for autism. Tourette’s is usually diagnosed between the ages of 3 and 9; symptoms most often peak in the early teens and start to abate in the early 20s, with continued improvement in early adulthood.
“Children were more than twice as likely to meet the cutoff than adults, indicating that as tics recede, so do symptoms of autism. In contrast, autism is usually lifelong,” said Darrow.
“Previous studies have shown that children with mood and anxiety disorders also have higher rates of autism symptoms, based on the Social Responsiveness Scale,” said senior author Carol Mathews, M.D., who did the research while a professor of psychiatry at UCSF. She currently is adjunct professor of psychiatry at UCSF and professor of psychiatry at the University of Florida in Gainesville.
“This suggests that some of the increase may reflect underlying psychiatric impairment rather than being specific for autism. Some of the children in the study probably have autism, others have symptoms that mimic autism, but are not really due to autism. These symptoms are called phenocopies.”