Congenital Hypothyroidism due to a Low Level of Maternal Thyrotropin Receptor-Blocking Antibodies

Introduction: Maternal TSH receptor antibodies (TRAbs) can cross the placenta and affect fetal and neonatal thyroid function. Maternal TSH receptor-blocking antibodies (TBAbs) are a rare cause of congenital hypothyroidism. Case Report: Following the discovery of a highly elevated TSH on her neonatal screening test, a 10-day-old girl with no familial history of thyroid disorder was referred to the pediatric endocrinology unit. Hypothyroidism was confirmed with a highly elevated TSH (817 mIU/L, reference range 0.4–3.1) and very low levels of FT4 (1.8 pmol/L, reference range 12–22). Anti-TPO antibodies were at 81 IU/mL (reference range Conclusion: We report herein a case of transient congenital hypothyroidism with a normal neonatal TRAbs level. In case of maternal TBAbs, similar activity of maternal TBAbs must be expected in the neonate, independently of the neonatal level of TRAbs.