Hyperactivity, Thyroid Abnormalities May Be Linked, Study Finds
Attention-deficit-hyperactivi-ty disorder, a condition affecting an estimated 3 percent to 10 percent of all schoolchildren, may be linked in some individuals to thyroid abnormalities, according to a new study.
Researchers at the National Institutes of Health studied 18 families with a history of generalized resistance to thyroid hormone. That condition occurs when the hormone fails to bind securely to "receptors'' inside the nucleus of most cells. To compensate, the body produces more of the hormone.
The study team found that family members with the thyroid abnormality were 2.5 times more likely than their unaffected relatives to also meet the diagnostic criteria for attention-deficit-hyperactivity disorder, or A.D.H.D.
"I think it's evidence that this is something that is physiologically based and there's a genetic cause for it,'' said Dr. Peter Hauser, a psychiatrist and the lead author of the study, which was published April 8 in the New England Journal of Medicine.
"It takes the onus off of parents that they caused this particular disease in the way they're raising their children,'' he said.
Disability-rights advocates and parents have long fought against the common misperceptions that children with A.D.H.D. are simply "bad'' or overly rambunctious.
Children with the disorder tend to be impulsive, inattentive, and easily distracted. Often, such symptoms are accompanied by hyperactivity.
Dr. Hauser said the findings suggest that children at risk of having the disorder could be identified at birth through a simple, inexpensive test that detects high levels of thyroid hormone in the blood.
The research also raises the hope that new and better ways of treating the disorder can be found. Currently, many children with A.D.H.D. are treated through a combination of behavior modification and stimulant drugs.
The drug of choice for most of the children is methylphenidate, better known by its trade name Ritalin. While Ritalin mutes most of the behaviors associated with A.D.H.D., its use has been controversial.
Some parents and religious groups campaigned against the drug in the 1980's, claiming schools were promoting it as a way of "controlling'' children. In a small number of users, Ritalin also causes stunted growth, muscle tics, and other side effects.
Dr. Hauser said the treatment for generalized resistance to thyroid hormone may also help in treating A.D.H.D.
"First, there are studies that have to be done,'' he said, "but in our patients we have treated with thyroid hormone we feel it ameliorates the behavior problem.''
18 Families Studied
The 18 families in the study included 104 children and adults, about half of whom have generalized resistance to thyroid hormone.
Through psychiatric interviews, the researchers determined that half of the 22 affected adults had symptoms of A.D.H.D. either as children, adults, or both. In contrast, only two of the 30 unaffected adults met the criteria for the disorder.
Among the affected children, 70 percent--or 19 out of 27--had A.D.H.D. It was diagnosed in only five of the 25 unaffected children.
As is the case generally, the attention disorder was more common in male family members than in females.
Wade Horn, the executive director of Children and Adults with Attention Deficit Disorder, an advocacy group, said the new findings, while hopeful, do not "mean everybody with A.D.H.D. should be tested'' for generalized resistance to thyroid hormone.
That condition "is a very rare disorder, and A.D.H.D. is much more common,'' he said.
The N.I.H. team has begun a pilot study in New York State to determine whether screening for the thyroid condition is feasible.
Newborn babies are already routinely screened for a deficiency in
thyroid hormones that can lead to mental retardation. Researchers hope
to use materials from the same test to screen for generalized
resistance to thyroid hormone.