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The majority of patients appeared to be eumetabolic and maintained a near normal serum TSH concentration. They were classified as having generalized resistance to TH (GRTH). In such individuals, the defect seemed to be compensated by the high levels of TH. In contrast, patients with equally high levels of TH and nonsuppressed TSH that appeared to be hypermetabolic, because they were restless or had sinus tachycardia, were classified as having selective pituitary resistance to TH (PRTH). Finally, the occurrence of isolated peripheral tissue resistance to TH (PTRTH) was reported in a single patient (42). No mutation in the THRB gene of this patient was found (43) and no similar cases have been reported. More common in clinical practice is the apparent tolerance of some individuals to the ingestion of supraphysiological doses of TH.