Identification of a novel THRB mutation causing thyroid hormone resistance syndrome.

Resistance to thyroid hormone syndrome (RTHS) is a rare disorder caused by mutations in the thyroid hormone receptor beta (THRB) gene, resulting in impaired action of thyroid hormones on target tissues and organs. We report a case of a 57-year-old Chinese male who presented with palpitations and hand tremors. Laboratory tests revealed elevated serum thyroid hormone levels, while serum thyroid-stimulating hormone (TSH) levels remained within the normal range. Enhanced magnetic resonance imaging of the pituitary gland showed no abnormalities. Through genetic testing, we identified a rare heterozygous point mutation in the THRB gene, specifically c.938T>C: p.M313T. To the best of our knowledge, this mutation site has not been previously reported in the literature. Clinically, RTHS is often misdiagnosed as hyperthyroidism, leading to inappropriate treatment and potential exacerbation of thyroid hormone resistance. Therefore, accurate diagnosis of this condition is crucial. Given the rarity of RTHS, we hope that this case report will enhance the understanding of its clinical manifestations and management, particularly in patients with THRB gene mutations.