Severe congenital non-autoimmune hyperthyroidism associated to a mutation in the extracellular domain of thyrotropin receptor gene.

Activating mutations in the TSH Receptor (TSHR) gene have been identified as the molecular basis for congenital non-autoimmune hyperthyroidism. We describe the clinical findings and molecular characterization in a girl who presented severe non-autoimmune hyperthyroidism since birth, born to a mother with autoimmune thyroid disease. She was treated with methylmercaptoimidazol and β-blockers, but remained hyperthyroid and required total thyroidectomy. To characterize the presence of an activating mutation, the whole coding sequence and intron-exon boundaries of TSHR gene were analyzed. The patient was heterozygous for p.Ser281Asn mutation and p.Asp727Glu polymorphism. This recurrent mutation, p.Ser281Asn, characterized in vitro by increased basal production of cAMP, is the unique germline activating gene variant described so far in the extracellular domain of TSH receptor. Interestingly, the patient's mother presented hyperthyroidism but without any TSHR gene activating mutation. Although congenital non-autoimmune hyperthyroidism is a rare condition, it should be investigated when severe disease persists, even in a newborn from an autoimmune hyperthyroid mother, in order to differentiate it from the more common congenital autoimmune disease.