Summary
Resistance to thyroid hormone (RTH) is a syndrome of reduced tissue sensitivity to thyroid hormone. In the majority of subjects, RTH is caused by mutant thyroid hormone receptors (TR) ß molecules that interfere with the function of the normal TRß, thus resulting in a dominant mode of inheritance. RTH caused by TRβ gene deletion, on the other hand, is inherited as a recessive trait. In as many as 15% of families, RTH manifests in the absence of a TR gene abnormality. The clinical manifestations and laboratory abnormalities in such subjects are not significantly different than those found in individuals with TRß defects. We propose that the molecular defect causing RTH without TR gene mutations must be elsewhere in the pathway of thyroid hormone action.