Author(s): Brix TH, Kyvik KO, Hegeds L
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Abstract Hashimoto's thyroiditis (HT), atrophic thyroiditis (AT), and Graves' disease are autoimmune thyroid diseases in which genetic factors are suspected to play an important role in disease susceptibility. In a recent population-based twin study we rendered it probable that a substantial part of the susceptibility to Graves' disease is attributable to genetic factors. At present there are no population-based twin studies supporting such a genetic influence in the etiology of HT/AT. To elucidate whether there is a genetic influence in the etiology of HT/AT, we studied the distribution of HT/AT in a population-based sample of 2945 Danish female-female twin pairs (5890 individuals) born between 1953 and 1972. Information on hypothyroidism was obtained from a nationwide questionnaire survey in 1994. Information from hospitals, out-patient clinics, general practitioners, and specialists was sought to verify the diagnosis. The overall prevalence of autoimmune hypothyroidism was 0.41\% (24 of 5890). The prevalence did not differ between monozygotic and dizygotic twins (0.42\% and 0.40\%, respectively). The crude proband-wise concordance rates were significantly higher for monozygotic compared to dizygotic twin pairs: 0.55 (95\% confidence interval, 0.23-0.83) vs. 0.0 (95\% confidence interval, 0.0-0.25; P = 0.01). All of the healthy cotwins (n = 15) of twins with clinically overt autoimmune hypothyroidism were biochemically euthyroid. Overall, regardless of zygosity 53\% (8 of 15) of the healthy cotwins were positive for antithyroid antibodies. The prevalence of autoantibodies among the monozygotic cotwins was 80\% (4 of 5) and 40\% (4 of 10) among dizygotic cotwins (P = 0.36). In conclusion, the higher concordance rate in monozygotic compared to dizygotic pairs indicates that genetic factors play a role in the etiology of HT/AT among Caucasian women living in areas with borderline iodine deficiency. However, the fact that the concordance rate among MZ twins was below 1 suggests that environmental factors also are of etiological importance.
This article was published in J Clin Endocrinol Metab
and referenced in Journal of Thyroid Disorders & Therapy