Measurement of TSH receptor blocking immunoglobulins using 3H-adenine incorporation into FRTL-5 and JPO9 cells: use in a child with neonatal hypothyroidism

OBJECTIVE The aim of this study was to develop an assay for the measurement of thyroid blocking antibodies (TBAb), based on the ability of patient serum to inhibit TSH stimulated ³H-cAMP production following incubation of FRTL-5 or JPOS cells with ³H-adenine. The assay was then used to evaluate a child born with neonatal hypothyroidism. DESIGN The levels of TBAb, TSAb (thyroid stimulating antibodies), TBII (TSH binding Inhibitory antibodies), and the thyroid antibodies anti-thyroid peroxidase and thymoglobulin antibodies were measured in both mother and child over a 6-month post-natal period. PATIENT The assay for TBAb was used to evaluate a child born with neonatal hypothyroidism whose mother had a history of hypothyroidism due to Haehimoto's thyrolditis. A ^99mTc pertechnetate scan showed no evidence of functioning thyroid tissue. At 20 months of age an ultrasound verified a normally positioned thyroid. RESULTS Initially, high levels of TBII and antithyroid antibodies were present in the serum of both mother and child. In both, the levels of TSAb were undetectable but there were significant levels of TBAb. The levels of TBAb decreased to control levels in the child within 2 months of birth but remained elevated in the mother's serum. CONCLUSIONS This case of neonatal hypothyroidism associated with the passage of thyroid blocking antibodies demonstrates the utility of this new assay in the differential diagnosis of neonatal hypothyroidism.