THYROTROPHIN BLOCKING ANTIBODIES IN THE SERA OF MOTHERS WITH CONGENITALLY HYPOTHYROID INFANTS

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Abstract
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 hypothyrodism.