Thyrotrophin Blocking Antibodies in the Sera of Mothers With Congenitally Hypothyroid Infants

We examined IgG from 15 mothers of infants with congenital hypothyroidism for their ability to block TSH-stimulated iodine organification in vitro. Only one out of 15 of these IgGs exhibited TSH-blocking activity. This IgG could inhibit TSH action by 30-50%. It could not block radiolabelled TSH from binding to its receptor but did inhibit dibutyryl cyclic AMP stimulation of iodine organification implying a unique effect on post-receptor processes via a membrane binding site distant from the TSH binding site. Interestingly there was no evidence of autoimmune thyroid disease in the mother. These results suggest that the transplacental passage of TSH-blocking antibodies plays little, if any, role in the development of congenital hypothyroidism.