A Novel Thyroid Hormone Receptor Beta Gene Mutation (G251V) in a Thai Patient with Resistance to Thyroid Hormone Coexisting with Pituitary Incidentaloma.

A patient is reported with resistance to thyroid hormone beta caused by a novel THRB gene mutation and coexisting pituitary microadenoma. A 41-year-old Thai woman presented with elevated serum thyroid hormone levels and non-suppressed thyrotropin (TSH). Magnetic resonance imaging showed a 4 mm × 2 mm pituitary adenoma. Five of her relatives had similar thyroid tests abnormalities, but a sister had Graves' disease. Thyroperoxidase and thyroglobulin antibodies were positive in all affected family members, except for the proband's 4.5-year-old niece. Lack of thyrotoxic symptoms and TSH suppression by triiodothyronine indicated incidentaloma rather than a TSH-secreting pituitary adenoma. Genetic analysis revealed a THRB gene mutation (c.1037G>T), resulting in p.G251V.