MEASUREMENT OF TSH RECEPTOR BLOCKING IMMUNOGLOBULINS USING H-3 ADENINE INCORPORATION INTO FRTL-5 AND JP09 CELLS - USE IN A CHILD WITH NEONATAL-HYPOTHYROIDISM

OBJECTIVE The aim of this study was to develop an assay for the measur ement of thyroid blacking antibodies (TBAb), based on the ability of p atient serum to inhibit TSH stimulated H-3-cAMP production following i ncubation of FRTL-5 or JPO9 cells with H-3-adenine. The assay was then used to evaluate a child born with neonatal hypothyroidism. DESIGN Th e levels of TBAb, TSAb (thyroid stimulating antibodies), TBII (TSH bin ding inhibitory antibodies), and the thyroid antibodies anti-thyroid p eroxidase and thyroglobulin antibodies were measured in both mother an d child over a 6-month post-natal period. PATIENT The assay for TBAb w as used to evaluate a child born with neonatal hypothyroidism whose mo ther had a history of hypothyroidism due to Hashimoto's thyroiditis. A Tc-99m pertechnetate scan showed no evidence of functioning thyroid t issue. At 20 months of age an ultrasound verified a normally positione d thyroid. RESULTS Initially, high levels of TBII and antithyroid anti bodies were present in the serum of both mother and child. In both, th e levels of TSAb were undetectable but there were significant levels o f TBAb. The levels of TBAb decreased to control levels in the child wi thin 2 months of birth but remained elevated in the mother's serum. CO NCLUSIONS This case of neonatal hypothyroidism associated with the pas sage of thyroid blocking antibodies demonstrates the utility of this n ew assay in the differential diagnosis of neonatal hypothyroidism.