Identical mutations in unrelated families with generalized resistance to thyroid hormone occur in cytosine-guanine-rich areas of the thyroid hormone receptor beta gene. Analysis of 15 families

Generalized resistance to thyroid hormone (GRTH) is a syndrome of variable reduction of tissue responsiveness to thyroid hormone. 28 different point mutations in the human thyroid hormone receptor beta (TRβ) gene have been associated with GRTH. These mutations are clustered in two regions of the T₃ binding domain of the TRβ (codons 310-347 and 417-453). We now report point mutations in the TRβ gene of six additional families with GRTH and show that three mutations occurred each in three families with GRTH, and that three other mutations were each present in two families. In 11 of these 15 families, lack of a common ancestor could be confirmed by genetic analysis. 28 of the 38 point mutations so far identified, including all those occurring in more than one family, are located in cytosine-guanine-rich areas of the TRβ gene. Differences in clinical and laboratory findings in unrelated families harboring the same TRβ mutation suggest that genetic variability of other factors modulate the expression of thyroid hormone action.