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Genetic factors are more important than environmental factors in determining pituitary–thyroid function in normal subjects
The background of the study. Serum
thyroid hormone and thyrotropin (TSH) concentrations vary less in
an individual normal subject than among groups of subjects, suggesting
that each subject has a unique setting for TSH and, therefore, thyroid
secretion. In this study pituitary–thyroid function was assessed
in monozygotic and dizygotic twin pairs in an attempt to determine
the genetic influence on this setting.
How the study was done. Serum TSH, free thyroxine (T4), and triiodothyronine (T3) were measured in 690 Danish twin pairs (692 women and 688 men), including 284 monozygotic twin pairs, 286 same-sex dizygotic twin pairs, and 120 opposite-sex twin pairs. The mean age of all three types of twin pairs was 37 years.
The results of the study. The mean serum TSH concentrations were 1.8 mU/L in the women and 1.6 mU/L in the men. Serum TSH and free T4 or free T3 concentrations were not linearly related to each other in any of the three groups.
Among the monozygotic twin pairs, the serum TSH, free T4, and free
T3 concentrations in twins 1 and 2 were correlated. For the same-sex
dizygotic twin pairs, the values were less closely correlated. Based
on quantitative genetic modeling, genetic components were estimated
to account for 64 to 65 percent of the variation in serum TSH, free
T4, and free T3 concentrations and environmental effects for 35
to 36 percent.
The conclusions of the study. Serum
TSH and thyroid hormone concentrations are more closely correlated
with each other in monozygotic than dizygotic twins, indicating
that genetic factors are important determinants of variations in
pituitary–thyroid function in normal subjects.
The original article. Hansen PS, Brix TH, Sorensen TI, Kyvik KO, Hegedus L. Major genetic influence on the regulation of the pituitary-thyroid axis: a study of healthy Danish twins. J Clin Endocrinol Metab 2004;89:1181-7.
Next Article: The number
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