Abstract 483

Approximately 2% of cases of congenital hypothyroidism(CH) are due to the transplacental passage of maternal thyrotropin (TSH) receptor blocking antibodies (Abs), a syndrome that may be difficult to distinguish from thyroid dysgenesis, a much more common cause of CH. We report 4 babies born to 3 mothers all of whom initially denied signs or symptoms suggestive of thyroid dysfunction but in whom profound hypothyroidism due to 1° myxedema was made after the diagnosis of CH in their offspring. As predicted, all 4 babies had a transient course, and in the one mother with multiple offspring, the subsequent baby was also affected. Clinical and biochemical data of the mothers and of their infants is presented in the table. Whereas the 1st child born to Case 3 was born with severe hypothyroidism both clinically and biochemically and had significant developmental delay, the 2nd child born after maternal thyroid replacement was initiated had much less severe CH at birth and developmental milestone have been normal to date. Maternal TSH receptor blocking Ab potency, as measured by radioreceptor assay did not differ at the time of delivery of her 1st as compared with her 2nd child. We conclude that: 1) TSH receptor blocking Ab-induced CH can occur in mothers who are unaware that they are hypothyroid; 2) The developmental delay in Case 3 was due to the severe fetal hypothyroidism and not to the TSH receptor Abs themselves; 3) In view of the relatively low cost and importance of making the diagnosis, TSH receptor blocking Abs should be measured in all babies with CH whatever the maternal or family history of thyroid disease.

Table 1 No caption available.
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