Role of maternal immunoglobulins blocking TSH-induced thyroid growth in sporadic forms of congenital hypothyroidism.

Among 34 mothers of infants with sporadic congenital hypothyroidism detected in the Quebec screening programme, 15 had immunoglobulins blocking thyroid growth induced by thyroid-stimulating hormone (TSH) when tested in the sensitive Feulgen cytochemical bioassay. At the time of delivery all the mothers were clinically and biochemically euthyroid, and in general the growth-blocking immunoglobulins were found in the absence of thyroid antimicrosomal antibodies. 2 mothers, however, had significant titres of antimicrosomal antibodies. They became hypothyroid 1 and 3 years after delivery. 8 of 16 post-partum infant blood samples were positive for immunoglobulins blocking TSH-induced thyroid growth. 4 of 7 positive mothers tested up to 3 years after delivery had become negative, thus indicating a trend for these immunoglobulins to disappear from the maternal circulation. Thus, transplacental passage of maternal immunoglobulins influencing TSH-induced processes of thyroid growth may play a part in the pathogenesis of sporadic congenital hypothyroidism.