A Case of Thyroid Hormone Resistance Syndrome Beta (RTH<i>β</i>) Diagnosed in a 3-Year-Old Girl

Thyroid hormone resistance syndrome (RTH) is a rare disorder characterized by elevated thyroid hormone and non-suppressed thyroid stimulating hormone levels.In most cases, it is caused by mutations in the thyroid hormone receptor beta (THRB) gene, a condition referred to as thyroid hormone resistance syndrome beta (RTH).Patients with RTH can exhibit with features of hyperthyroidism or hypothyroidism or simple goiter, and the condition is often misdiagnosed clinically.Differential diagnoses for elevated TH levels with non-suppressed thyroid stimulating hormone (TSH) include pituitary TSH-secreting adenomas, familial dysalbuminemic hyperthyroxinemia, and assay interference.Genetic testing plays a critical role in establishing an accurate diagnosis and preventing unnecessary or inappropriate treatment.We report a case of a 3-year-old girl with language developmental delay, poor weight gain, and short stature who was diagnosed with RTH due to a heterozygous likely pathogenic variant (c.803CA; p.Ala268Asp) in the THRB gene, which has been previously identified in RTH patients.To our knowledge, this is one of the few reported cases in Korea.