Subclinical hyperthyroidism due to a thyrotropin receptor (TSHR) gene mutation (S505R)

AIM: To identify the molecular defect by which non-autoimmune subclinical hyperthyroidism was caused in a 6-mo-old infant who presented with weight loss. METHODS: Congenital non-autoimmune hyperthyroidism is caused by activating germline mutations in the thyrotropin receptor (TSHR) gene. Therefore, the TSHR gene was sequenced directly from the patient's genomic DNA. RESULTS: Molecular analysis revealed a heterozygous point mutation (S505R) in the TSHR gene as the underlying defect. CONCLUSION: A constitutively activating mutation in the TSHR gene has to be considered not only in patients with severe congenital non-autoimmune hyperthyroidism, but also in children with subclinical non-autoimmune hyperthyroidism.