Volume 16, Number 4
A Strep - Tourette Connection?
In the last decade, some neurologists have been building a case for a medically-intriguing subset of children who show classic signs of a tic disorder-repeatedly blinking eyes, for example, or head-jerking. But while their symptoms are casebook, the onset-abrupt and powerful-is not. Seemingly overnight, a full crescendo of jerks and grimaces appear to take control of some children's bodies.
How to explain such
a dramatic change?According to one hypothesis, children may be showing repercussions of a streptococcus infection-strep throat, for example-that provokes an autoimmune reaction. That, in turn, could trigger tics or other neurological symptoms akin to Tourette syndrome. Or it could exacerbate already existing tic or obsessive-compulsive disorders. Known as PANDAS-for pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections-the hypothesis has attracted public attention and raised hopes that curing tics might simply hinge on a course of penicillin.
Two studies, however, now challenge PANDAS. Researchers led by pediatric neurologist Harvey Singer, M.D., report that they cannot find the antibodies the model predicts should exist. "We're not at all sure it's valid," says Singer.
The PANDAS model grew out of observations by NIH researchers that a subgroup of children with obsessive-compulsive behaviors or with tics either showed their first symptoms or had symptom flare-ups after an infection with group A beta-hemolytic streptococcus. The scientists hypothesized that in predisposed children infected by strep, antibodies against the bacterium could attack neurons in the brain, bringing on symptoms.
If the hypothesis were correct, then anti-neuronal antibodies should appear in children with PANDAS. So in the first of two studies, Singer, internationally recognized as an expert on Tourette syndrome, worked with colleagues to examine blood samples from 15 children with PANDAS and a like number of healthy children. Overall, they found no major differences in antibodies between the two groups.
In a second study, Singer's group asked whether antibodies from PANDAS patients could induce tic-like behaviors in animals. They infused rat brains with either sera from PANDAS patients, Tourette syndrome patients or healthy volunteers and recorded the rats' activities for the next 10 days. No behavior differences appeared in any of the groups. "So we're unable to confirm that anti-neuronal antibodies play a role here," Singer concludes. Missing such a hallmark of autoimmunity, he adds, raises real doubts about the clinical signposts PANDAS advocates have laid down.
As for the strep-tic link, that may be coincidental. "In any population of children, both tics and strep infections are common. Some will have them both. Are the two related?" asks Singer. "Perhaps. Did one cause the other? We don't know.
"People are drawn to simple explanations for complex neuropsychiatric problems," he says. "In Tourette syndrome, most parents would rather you say that their child's disease is due to infection than to inheritance."
Now new NIH-sponsored studies with a Hopkins arm may clear up the enigma. Following PANDAS patients for two years, the researchers will test them for strep and tally anti-neuronal antibodies while monitoring health and behavior to see what, if anything, is tied to an upswing in symptoms. "Only a carefully controlled study," Singer remarks, "will reveal whether there is a true strep-tic connection."
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