Learning Disabilities in Patients with Autoimmune Thyroid Disease and Their Families

Lawrence C. Wood, MD, FACP
Massachusetts General Hospital, Boston
President, Thyroid Foundation of America, Inc.

Address to the Kingston Area Chapter of the Thyroid Foundation of Canada

Hyperthyroidism and hypothyroidism are common disorders. Studies done in the United Kingdom and in the United States have given us a good idea of the prevalence of thyroid dysfunction in the population at large, and suggest that there are about eleven million people in the United States and Canada who have an overactive or underactive thyroid, two million of whom do not realize that they are sick. The actual prevalence of the "tendency" toward thyroid trouble is likely to be even greater as suggested by research showing an elevated serum Thyroid Stimulating Hormone (TSH) in ten to fifteen per cent of women over the age of fifty.

Disorders Associated with Autoimmune Thyroid Disease
I have long been interested in this 10-15% of the population who have the "tendency" toward autoimmune thyroid disease. I have wondered what else they might have problems with - what other sorts of disorders might show up in them and in their families because of this tendency.

The research that has been done suggests that the patients and their families will likely show tendencies not only to hyperthyroidism and hypothyroidism, but also to certain other conditions, more commonly than those in other families who lack this evidence for thyroid problems. Thus we will see an increased risk among those family members for insulin-dependent diabetes, pernicious anemia (anemia due to lack of vitamin B-12), prematurely gray hair, the white spots on the skin known as vitiligo, certain forms of arthritis, and probably certain allergic conditions including asthma, hives, and hay fever.

My most recent interest in the field of thyroid-related problems has to do with an apparent increased tendency for the men in these families to have various types of perceptual learning problems. I say men because males are far more commonly affected than females with these learning problems, though women occasionally may have such problems as well.

I suspect that the reason this relationship has not been noted until recently is that the women of the family tend to get thyroid problems while the men in the family (not seen by the physician as a rule) have the learning problems. In fact it took a chance event to make me aware of this relationship. I have known for some time that prematurely gray hair tends to occur more commonly in patients with autoimmune thyroid disease and in their family members in comparison with the general population. Once, while a discussing this with a colleague who was a pediatrician and who ran a school for dyslectic children, he commented to me that it was his impression that there was an increased tendency toward prematurely gray hair in the parents of children who attended his special school. To prove that such a relationship existed has been difficult and the exact frequency of association is still under investigation.

Developmental Dyslexia
Before proceeding further, however, I would like to define the type of learning disability (also known as developmental dyslexia) that I am talking about. The World Foundation of Neurology in 1968 defined developmental dyslexia as "a disorder in children who, despite conventional classroom experience, fail to attain the language skills of reading, writing, and spelling commensurate with their intellectual abilities". A subsequent committee expanded that definition in 1981 by including difficulties in the acquisition and use of listening, speaking, reading, writing, reasoning, or mathematical abilities-these difficulties not being due to any sort of handicap or environmental effect.

Children with dyslexia tend to be intelligent, their average IQ being about 130, and therefore are often able to cover up their difficulties if they are embarrassed by them. Nevertheless, an alert parent or teacher may note word omissions in reading, pauses during reading, a marked greater ability in verbal skill as opposed to reading and writing, errors in spelling, poor handwriting, or hyperactivity with a short attention span. There is a tendency for the problem to run in families, and some traits persist in adulthood.

Quite frankly, I knew very little about dyslexia when I began my studies of this problem, but I was aware that Doctors Norman Geschwind and Peter Behan had shown that both learning disabilities and some forms of autoimmunity were more common in lefthanders than in a control righthanded population. Therefore we began by looking at the incidence of lefthandedness among patients with various types of thyroid problems. In a normal population, approximately 10% of individuals will be either lefthanded or ambidextrous, and that is the frequency of these traits I found among patients with thyroid cancer, nodular goiters, overactive thyroid nodules, and in control patients who had no thyroid trouble. Among such patients and their families the overall incidence of these traits was 11%. In contrast, there was a 17% incidence of lefthandedness and ambidexterity in patients with Graves' disease, Hashimoto's disease, primary hypothyroidism, and their family members.

To gain further confirmation for the hypothesis that learning disabilities were more common in the males in thyroid families, I studied a group of men with thyroid problems. Sixteen out of 22 men with Graves' disease (73%) were lefthanded or ambidextrous, in comparison with three out of 18 control patients (17%). In addition, when these adult men were questioned about traits which might suggest the learning disabilities were present, the incidence of reversals of letters or numbers, stuttering, reading and writing difficulty, poor spelling, grade failure in school, and developmental delays in childhood, were 2.5 times as common among the men with hyper- and hypothyroidism in comparison with the control population.

Better Screening Techniques Needed
The fact that learning disabilities of this sort seem to be more common in the men and a few women in these thyroid families is not a cause for alarm in my judgement. The high intelligence, good verbal skills, high mathematical skills, as well as the artistic and athletic ability which such individuals often show, make them fascinating people to know and may give them certain advantages in careers such as architecture, engineering, politics, and sales. Indeed, among those known to be "afflicted" with dyslexia are Leonardo da Vinci, Nelson Rockefeller, Gustave Flaubert, Thomas Edison, Agatha Christie, General George Patton, and the Olympic athlete Bruce Jenner.

Copyright © Thyroid Foundation of Canada/La Fondation canadienne de la Thyroïde.
Reprinted from Thyrobulletin, Vol. 7, No. 1.
To order a reprint ($2 P&H) contact the National Office or your local chapter.

Reviewed 2000