BACKGROUND: Thyroid hormones govern a wide range of metabolic processes in the 
body via thyroid hormone receptors (TR). We report a patient with mild 
resistance to thyroid hormone who was initially misdiagnosed and treated as 
having thyrotoxicosis.
METHODS: We used direct DNA sequencing of the THRB gene.
RESULTS: We identified a novel missense mutation, I276L, located in exon 8 of 
the gene. The mutation is located in cluster 3 of the ligand-binding domain, a 
protein domain associated with resistance to thyroid hormone.
CONCLUSION: DNA-based diagnosis of thyroid hormone resistance syndrome is 
simple, reliable, and economical compared to traditional biochemical tests. Once 
the mutation is identified, targeted screening for the whole family can be 
performed and the unnecessary use of anti-thyroid drugs or thyroidectomy can be 
avoided.