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Studies Show Thyroid Disorders are Inherited and Often Hidden in Some Populations
Millions Found to Be Undiagnosed
 Related Information
• Research Reveals Millions of Thyroid Patients Undiagnosed
• Survey of TSH, T4, and Antibody Levels in the U.S.
• Guarding our Nation’s Thyroid Health

SOURCE: The Endocrine Society

February 11, 2002 -- Three new studies published in the February issue of the Journal of Clinical Endocrinology and Metabolism demonstrate the widespread prevalence and importance of thyroid disease in the United States. One study examined the existence of undiagnosed thyroid disease in different U.S. populations between 1988 and 1994; while the other two studies examined the role of genetics in congenital hypothyroidism (CH).

In the first study, researchers at the Centers for Disease Control and Prevention (CDC) evaluated the status of thyroid function by examining thyroid function tests including TSH and T4 (thyroxine) and thyroid antibodies in more than 17,000 subjects of the National Health and Nutritional Survey of the U.S. population from 1988 to 1994. The subjects were over the age of 12 and represented the geographic and ethnic distribution of the U.S. population.

Through their analysis of the study data, researchers discovered that nearly five percent of Americans suffer from often undiagnosed thyroid disease, with more than four percent experiencing hypothyroidism (an underactive thyroid). In addition, the study showed that hypothyroidism is more prevalent in white and Mexican Americans than in blacks. Researchers also found a higher rate of hypothyroidism among women and older Americans. Untreated thyroid disease may be associated with osteoporosis, cardiovascular disease, hyperlipidemia and neurological disease. Therefore, these findings have broad implications for the health of Americans.

"Our research shows that there is a large population of Americans who suffer from hidden thyroid disorders," said Dr. Joseph Hollowell, a researcher at the CDC and the lead investigator on the study. "More screening for at risk populations especially older women could help detect thyroid disorders earlier and possibly prevent complications."

An editorial written by Dr. John Dunn, titled "Guarding our Nation's Thyroid Health," accompanies Dr. Hollowell's study in the February issue of JCEM.

Two other studies from the February issue of JCEM considered the relationship between CH and congenital malformations (CM) as well as the prevalence of thyroid abnormalities in relatives of children with CH. In Italy, researchers examined the occurrence of congenital malformations (CM) in infants who suffered from CH, which is the absence or reduction of thyroid function in newborn babies. Dr. Antonella Olivieri and a group of researchers studied nearly 1,500 CH children in Italy between 1991 and 1998. The researchers found that children born with CH experienced additional CM four times more often than the rest of the Italian population.

"Cardiac anomalies were the most frequent malformation that we found to be associated with congenital hypothyroidism," said Dr. Olivieri. "However, we also observed a significant association between CH and anomalies of nervous system, eyes, heart (representing precocious structures in the developing embryo) and multiple congenital malformations. These findings strongly suggest a very early impairment in the first stages of embryo development with a consequent involvement of different organs and structures. This research suggests that there may be a genetic predisposition linking the development of congenital hypothyroidism with the occurrence of other congenital malformations."

Additionally, the authors of the Italian study are confident that elucidation of genetic-environmental networks and mechanisms underlying the development of thyroid and other organs provides hope that at least some types of thyroid dysgenesis may be prevented by modulating these cofactors.

In the second CH study, doctors at Robert Debre Hospital and Inserm unit U457 (National Institute of Health) in Paris, France investigated the development of thyroid abnormalities in first degree family members of children with CH. Researchers evaluated 241 relatives of 84 CH children and compared the results with 217 controls.

"We discovered that a significantly high number -- nearly eight percent -- of the first degree relatives suffered from asymptomatic thyroid developmental anomalies, although thyroid function was normal," said Dr. Juliane Leger, the lead investigator on the study. "This is nearly nine times higher than the control group. These numbers demonstrate that this type of congenital disorders of the thyroid gland have a genetic component and appear to be inherited."

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