Transient thyrotoxicosis in an infant delivered to a long-acting thyroid stimulator (LATS)- and LATS protector-negative, thyroid-stimulating antibody-positive woman with Hashimoto's thyroiditis.

A thyrotoxic infant was delivered to a woman with a long-standing history of Hashimoto's thyroiditis, but with no evidence of Graves' disease. Long-acting thyroid stimulator (LATS) and LATS protector were absent, but thyroid-stimulating antibody was transiently present in the infant and markedly and persistently elevated in the mother. It is concluded that the maternal level of thyroid-stimulating immunoglobulins determines the presence and duration of transient neonatal thyrotoxicosis, and that thyroid-stimulating antibody is distinct from LATS and LATS protector.