Severe congenital hyperthyroidism caused by a germ-line neo mutation in the extracellular portion of the thyrotropin receptor.

Gain of function mutations in the TSH receptor (TSHR) have been identified as the molecular basis for congenital and acquired forms of autonomous thyroid function. Herein, we report the molecular characterization of a case of severe congenital hyperthyroidism with a history of hyperthyroidism in the paternal aunt and the paternal grandmother, who were both found to be heterozygous for a mutation (R528H) located in exon 10 of the TSHR gene. Functional expression of the mutant TSHR-R528H in COS-7 cells, however, did not result in constitutive activity of the TSHR. Subsequent analysis of exons 1–9 led to the detection of an additional heterozygous mutation (S281N) in the patient, but not in other family members. Interestingly, the latter mutation is located in the extracellular domain of the TSHR, and functional studies revealed a marked increase in basal cAMP levels when the mutant receptor was expressed in COS-7 cells. To address the question of whether both mutations were present on the same allele, a dou...