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A recent large study on the genetics of Tourette’s syndrome has added clout to what many experts suspect: that underlying biology—common genes, most likely—can tie together Tourette’s, obsessive compulsive disorder (OCD) and ADHD.
That doesn’t mean all patients with Tourette’s also have OCD and ADHD, says pediatric psychiatrist Marco Grados, who leads Hopkins’ part of an international consortium. “But likely a third of children with Tourette’s belong to a subset with all three disorders.” And being aware of that, Grados says, makes therapy more precise. It also supports what’s known of the pathology.
“We see child after child at our clinic primarily with the motor or vocal tics of Tourette’s. But after a workup, you often find anxiety-based obsessive thinking and inattention with hyperactivity. Or perhaps they come with OCD and you see the other two.” Children may be prescribed conflicting therapies. And parents are frustrated, says Grados. They’ve often shuttled kids from a hometown pediatrician who diagnoses one disorder, to a psychologist who says it’s another, to a neurologist who finds yet a third.
It can be a confused family that comes to Hopkins.
The new NIH-sponsored work looked at more than 950 patients, siblings and parents from 220 families with Tourette’s, as collected by the Tourette Syndrome Association International Consortium on Genetics. From his background in mathematics and genetic epidemiology, Grados saw the sense of using “latent class analysis” on the large population. That’s a statistical technique that cherry-picks groups of people from a mass of motley data. A result? Patients with all three disorders newly stood out.
A second analysis—calculate the odds of having family members with the triple problems—confirmed that if you have all three disorders, it’s more than likely that relatives do too. Such “breeding true” cries out, a culprit gene!
“Perhaps”—and it’s a big perhaps, Grados says—“we should think of this triple disorder as a single new one.”
The study makes ideas about a common pathology more plausible. OCD, ADHD and Tourette’s, it’s believed, likely live in the large circuit that connects various parts of the brain’s basal ganglia with the cerebral cortex. If, because of an errant gene, the loop is overactive or otherwise out of control, it makes sense that all three disorders would surface.
All three developmental disorders are marked by a lack of inhibition, whether it’s not being able to control OCD’s intrusive thoughts or Tourette’s motor tics. It’s also intriguing, Grados adds, that the three illnesses tend to fade after adolescence. “Sometimes one or another will just melt away,” he says. Is it coincidental that Mother Nature’s so-called maturity pathways—those descending from the reasoning cortex to lower regions like the basal ganglia—get stronger then?
More immediate, though, is the clinical value of seeing the disorders as a set. “Because treatments for all three diverge,” says Grados, “prescribing becomes a careful balancing act.” Tourette’s for example, calls for medications that turn down dopamine. ADHD requires just the opposite with stimulants like Ritalin. “You can’t just say, the ADHD’s the worst. I’m going to treat that and let the others ride. That could aggravate the Tourette’s.
“You put the pieces together,” he says, “and things start to make sense.”
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