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by Larry Scahill, M.S.N., M.P.H. and Pieter J. Van Wattum, M.D., Child Study Center, Yale University
Questions concerning tics, asthma and allergies are frequently asked by parents of children with TS. Some observe that their child's tics worsen when they eat certain foods or food additives (e.g., colorings or preservatives). In other cases, families report that the child's tics are more severe when the asthma is more acute. These observations lead many parents to wonder whether there is a link between allergies, asthma and having TS. In this article we discuss the connection between TS and these conditions.
The first problem in trying to uncover a biological connection here is that asthma and allergies are common conditions in the general population. For example, asthma occurs in 8-11% of children and, as with TS, asthma occurs more often in boys. Although estimates vary, allergies are even more common and they affect about 30% of the general population. To complicate matters further, 85-95% of children with asthma also have allergies. In contrast, TS is a relatively uncommon disorder affecting roughly 1 in every 2000 school-aged children.
Secondly, these three conditions have also been linked to other disorders such as attention-deficit hyperactivity disorder (ADHD). Indeed, some studies suggest that food allergies may play a role in causing ADHD or in the severity of ADHD symptoms in some children. The frequency of ADHD is also relatively high, affecting 6-9% of school-aged children. Even if we put aside the ongoing controversy about whether or not ADHD and TS share a common underlying cause, most researchers and clinicians would still agree that ADHD is much more common in children with TS than in the general population.
Thirdly, as with TS, asthma is a stress-sensitive, chronic condition. Therefore, TS and asthma might both be made worse by stressful life events, and therefore give the impression that the worsening asthma aggravated tic symptoms.
Given the overlap of allergies and asthma, TS and ADHD, the possibility that two or more of these disorders could co-occur by chance cannot be ruled out. Furthermore, the co-occurrence of two or even three disorders does not prove a causative connection. Nonetheless, even if TS, asthma and allergies are not causally related, having one disorder can influence the symptom severity of the other.
To say the least, trying to unravel the relationship between TS, ADHD, asthma and allergies is complicated. Numerous case reports and small studies have shown that children with allergies have more severe tics when exposed to allergens such as molds, pollens, dust and certain foods. Also, many clinicians have suspected that medications used to treat asthma can aggravate tics or behavior problems. For example, several bronchodilators used in treating asthma have been reported to worsen tics in some children. But case reports alone do not provide sufficient evidence that the two conditions are related.
Although few in number, carefully designed studies examining the relationship of TS, ADHD, asthma and allergies have been done. A large study recently completed at Harvard University compared 140 youngsters with ADHD and 120 controls without ADHD. The investigators found that asthma was not more common in the ADHD group. However, compared to the control families, asthma was found to be more common in the families of children who had ADHD and asthma. Moreover, in the ADHD group without asthma, the frequency of asthma was similar to that observed in the control families. These findings suggest that asthma and ADHD are not genetically related.
We recently evaluated the impact of having asthma on TS symptoms in a group of children from our clinic. This small study was not designed to determine whether asthma is more common in children with TS. Nevertheless, the study allowed us to compare children with TS alone with a group of children with both TS and asthma. Preliminary results suggest that children with TS and asthma show a similar range of TS symptoms when compared to children with just TS. But, among the children that had TS and asthma, those with more severe asthma also tended to have more severe TS. What this means exactly is not yet clear, but it might be that the complex immunological and psychological processes that influence the severity of asthma also affect the severity of TS. Also, as noted above, the medications used in the treatment of one disorder may affect the severity of the other disorder.
Another approach to the study of food intolerance in TS and ADHD is to deliberately expose the child to a suspected allergen. Although many studies of this type have been done in recent years, we could find only a handful that were well-designed and carefully conducted. The results of these rigorously conducted studies are not consistent. A recent Cornell Medical Center study of 19 children with ADHD showed that several foods and food colorings were associated with increased behavior problems. Taken together with past studies, the results of this study suggest that food intolerance or specific allergies may play a role in the onset and severity of ADHD in some children. However, the impact of food allergies on tics awaits further study.
In summary, there is a possibility that biological mechanisms responsible for asthma and allergies influence the course and severity of TS and/or ADHD. In the case of asthma and TS, future studies will probably focus on immunological and neurochemical mechanisms. In the case of food intolerance, researchers are also interested in the digestive system itself. For example, differences in enzyme concentrations of microorganism populations in the gastrointestinal system may influence body chemistry in important, but as yet, poorly understood ways.
Obviously, a great deal more study is needed to understand the relationship of asthma, allergies and TS.
Larry Scahill
Pieter J. Van Wattum
©2007 Tourette Syndrome Association, Inc. 42-40 Bell Boulevard / Bayside NY 11361 / 718-224-2999