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.