Resistance to thyroid hormone due to a novel mutation of thyroid hormone receptor beta gene

Resistance to thyroid hormone (RTH) is a rare inherited syndrome characterized by diminished response of the target tissue to thyroid hormone caused, in the majority of cases, by mutation of the thyroid hormone receptor beta (THRβ) gene. Despite elevated serum levels of free thyroid hormones and thyroid stimulating hormone (TSH), the paucity of symptoms and signs of thyroid dysfunction suggest RTH. We report the case of a 9-year-old girl with goiter. Her thyroid function tests showed increased serum levels of free thyroxine, triiodothyronine, and TSH. The genetic analysis of THRβ confirmed a novel mutation in exon 9; this was a heterozygous C-to-T change in the 327th codon, substituting threonine for isoleucine (T327I).