title: A population-based study of chronic autoimmune hypothyroidism in Danish twins.
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.
authors.affiliation: Department of Endocrinology M, Odense University Hospital, Denmark. tBRIX@HEALTH.SDU.OK
authors.forename: T H
authors.initials: TH
authors.lastname: Brix
authors.forename: K O
authors.initials: KO
authors.lastname: Kyvik
authors.forename: L
authors.initials: L
authors.lastname: Hegedüs
mesh_terms: D000328:Adult; D001323:Autoantibodies / Q000032:analysis; D001327:Autoimmune Diseases / Q000150:complications*; D002908:Chronic Disease; D003718:Denmark; D004200:Diseases in Twins; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000453:epidemiology / Q000209:etiology* / Q000235:genetics / Q000276:immunology; D015995:Prevalence; D012016:Reference Values; D013961:Thyroid Gland / Q000276:immunology; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics
chemical_list: D001323:Autoantibodies