The thyroid hormone resistance syndromes are disorders in which the body's 
tissues are resistant to the effects of thyroid hormone. Generalized resistance 
to thyroid hormone (GRTH) is characterized by resistance in the pituitary gland 
and in most or all of the peripheral tissues. Affected individuals have elevated 
serum thyroid hormone levels and inappropriately normal or elevated 
thyroid-stimulating hormone (TSH) but are usually clinically euthyroid and 
require no treatment. Selective pituitary resistance to thyroid hormone (PRTH) 
is characterized by resistance in the pituitary gland but not in peripheral 
tissues. Patients have elevated serum thyroid hormone levels and normal or 
elevated TSH levels and are clinically thyrotoxic. Therapy is usually necessary, 
but current choices are not completely satisfactory. Selective peripheral 
resistance to thyroid hormone (PerRTH) is characterized by resistance in 
peripheral tissues but not in the pituitary. The only patient thus far described 
had normal serum thyroid hormone and TSH levels but was clinically hypothyroid 
and improved with thyroid hormone administration. All of these disorders are 
probably more common than is generally recognized and are often misdiagnosed and 
inappropriately treated. GRTH, in most cases studied, results from a mutation in 
the thyroid hormone receptor beta gene causing an amino acid substitution in or 
a partial or complete deletion of the thyroid hormone-binding domain of the 
receptor. The causes of PRTH and PerRTH remain to be determined.