Activating mutations of the thyroid-stimulating hormone receptor (TSHr) have been identified as a cause of toxic adenomas. Germline-inactivating TSHr mutations have beendescribedas a cause of congenital hypothyroidism. The effects of combining activating and inactivating mutations within a single receptor was studied. The double mutant T477I/P639S contained an activating TSHr mutation (P639S) togetherwithan inactivatingone (T477I). Theother one (I486M/P639S) contained two activating mutations.
