Congenital hypothyroidism and hyperthyroidism in monozygotic twin girls.

This report describes monozygous twin girls with different forms of thyroid dysfunction. Twin A was found to have athyreotic hypothyroidism during the first week of life; twin B developed acute hyperthyroidism at 16 years of age. While concordance and discordance for congenital hypothyroidism has been reported in several sets of twins (Table I) there have been no prior reports of congenital hypothyroidism and hyperthyroidism in a single twin pair. Two different forms of thyroid disorder have been reported (Jayson et al, 1967) in only one set of twins: one twin developed hypothyroidism with a Hashimoto's thyroiditis at 29 years of age and her co-twin developed hyperthyroidism at 31 years of age. Although the thyroid disorders in the latter twins occurred in adulthood, the authors suggested a possible biological unity underlying the two forms of thyroid disorder. The present report provides further evidence in support of this possibility.