Down's syndrome and thyroid dysfunction.

A child with Down's syndrome (DS) and associated hyperthyroidism is described and studies pertinent to DS and thyroid function are discussed. A majority of data supports a hypothesis of immunological abnormalities in DS, with resultant thyroid dysfunction. It is puzzling that overt disease is not more common in DS, since the incidence of thyroid autoantibodies is high and autoimmunity and Hashimoto's thyroiditis are often associated with clinical thyroid disease. A physician who cares for children should consider thyroid disease in any child with DS who manifests a single compatible symptom. Palpation of the thyroid gland is essential during each physical examination.