A case of suspected familial non-autoimmune hyperthyroidism

Abstract

We report the case of a 46-year-old man who had persistently high thyroid hormone and low TSH levels for approximately 3 years. Although his thyroid gland was enlarged, with an estimated weight of 52 g, TRAb, TSAb, TgAb, and TPOAb were all negative. The I-123 thyroidal uptake rate was high, and scintigraphy showed diffuse enlargement of the thyroid gland. A study of the TSHR (TSH receptor) gene identified a heterozygous variant in codon 523 of Exon 10. This variant resulted in an amino acid substitution from ATC (Ile) to TTC (Phe). His mother and older sister also had hyperthyroidism and were negative for TRAb, TSAb, and TPOAb. Although the TSHR genes of the mother and sister have not been identified due to lack of consent from the family, familial non-autoimmune hyperthyroidism was suspected in this case. The patient’s thyroid function is currently well controlled with thiamazole. However, we will continue to monitor the patient closely as antithyroid medication cannot induce remission in non- autoimmune hyperthyroidism.