Major role of genes in the etiology of simple goiter in females: A population-based twin study

The etiology of simple goiter, affecting up to 5% of a population in nonend emic areas, is incompletely understood. It is generally believed to be mult ifactorial in origin, but the relative contributions of genetic and environ mental factors remain to be clarified. Therefore, we investigated a well de fined population of Danish twins. We performed a historical cohort study of 5.479 same sex twin pairs born between 1953 and 1972. Information on goite r was obtained from a nationwide questionnaire survey in 1994. Information from hospitals, out-patient clinics, and the subjects' general practitioner s was sought to verify the diagnoses. Concordance rates, tetrachoric correl ations, and heritability were determined. The crude probandwise concordance rates were 0.42 [95% confidence interval (CI), 0.26-0.59] and 0.13 (95% CI, 0.06-0.24) for female monozygotic and fe male dizygotic pairs, respectively. The age-adjusted cumulative probandwise risk for simple goiter from birth to age 43 yr was 0.53 (95% CI, 0.23-0.83 ) for female monozygotic twins and 0.18 (95% CI, 0.05-0.35) for female dizy gotic twins (P = 0.003). The tetrachoric correlations were substantially hi gher in monozygotic (0.82; se, 0.07) than in dizygotic twins (0.47; SE, 0.1 2). Model-fitting analysis suggested that the heritability of the liability to the development of simple goiter in women is approximately 82%. Individ ual-specific environmental factors not shared by cotwins seemed to explain the remaining 18%. We conclude that the etiology of clinically overt simple goiter is multifactorial. Genetic factors play a major role in the etiolog y of simple goiter in females, but environmental factors are also of import ance.