Familial Nonautoimmune Hyperthyroidism Research Articles

The First Activating TSH Receptor Mutation in Transmembrane Domain 1 Identified in a Family with Nonautoimmune Hyperthyroidism

Sporadic and familial nonautoimmune hyperthyroidism are very rarely occurring diseases. Within the last years constitutively activating TSH receptor mutations were identified as one possible pathomechanism. Except for S281N in the extracellular N-terminal domain, all other germline mutations are located in the transmembrane domains 2, 3, 5, 6, and 7 of the TSH receptor, whereas no mutation was reported in transmembrane domains 1 and 4 to date. Here we report the first family with a constitutively active TSHR mutation in transmembrane domain 1 resulting in a substitution of the conserved Gly431 for Ser. This mutation was found in the investigated patient, his father, and the paternal grandmother. As known from other familial cases of nonautoimmune hyperthyroidism, the age of onset of the disease was variable, ranging from early childhood in the patient and his father to adolescence in the grandmother. Functional characterization of this mutation showed a constitutive activation of the Gs/adenylyl cyclase system. Moreover, this germline mutation also activates the Gq/11/phospholipase C pathway. The importance of Gly431 for receptor quiescence is supported further by introduction of other mutations at this position, all leading to constitutive receptor activity. Our data show now that constitutively activating mutations can be found in the entire transmembrane domain region of the TSH receptor, indicating the important role of all parts of the transmembrane domain region for maintaining the inactive receptor conformation.

Constitutively activating TSH-receptor mutations as a molecular cause of non-autoimmune hyperthyroidism in childhood.

The glycoprotein hormone TSH (thyroid-stimulating hormone) and its receptor, the TSH-receptor (TSHR), play a crucial role in thyroid growth and function. Constitutively activating germline mutations within the TSHR gene were identified in patients with sporadic or familial non-autoimmune hyperthyroidism. Inheritance of these mutations is autosomal dominant. We investigated two patients with neonatal onset of non-autoimmune hyperthyroidism and two families in whom the child and one parent are affected. Hyperthyroidism was difficult to treat in all of these patients and was complicated by premature craniosynostosis. Sequencing of all exons of the TSHR gene in one family with hyperthyroidism revealed a mutation in exon 10 (T6321), which was first identified in toxic adenomas and found to constitutively activate the TSHR. In the other family, we identified a new mutation in the first membrane spanning segment (G431S). In both patients with sporadic hyperthyroidism, a heterozygous mutation in exon 9 (S281N) was detected. The functional characterization of S281N and G431S demonstrated that both mutants were constitutively active. Therefore, these mutations are the molecular cause of non-autoimmune hyperthyroidism in the patients. For patients suffering from non-autoimmune hyperthyroidism, screening for mutations and their functional characterization is recommended. In case of an ineffective hyperthyroidism treatment, thyroidectomy should be performed to prevent lengthy anti-thyroid drug treatment and complications like premature craniosynostosis.