Thyroid dysfunction in Down's syndrome.

One hundred and sixteen children with Down's syndrome, living in the community, were examined for clinical or laboratory evidence of thyroid dysfunction. Three were hypothyroid and one was hyperthyroid. Twenty eight (29%) had thyroid autoantibodies. Autoimmune conditions were present in first or second degree relatives of 35 (30%) of the children, and in 17 (15%) this was a thyroid disorder. The families of normal control children also showed a 30% incidence of overt autoimmune conditions, and 19 (16%) families showed overt thyroid disease.