Detection of a Mutation in the Thyroid Hormone Receptor Beta Gene as a Cause of Pathological Laboratory Test Results in an Euthyreotic Toddler

Introduction ▼ Resistance to thyroid hormone (RTH) is a rare and in the majority of cases autosomal-dominant inherited disorder which leads to reduced responsiveness of target tissue to thyroid hormone. Frequently, this is due to mutations in the thyroid hormone receptor beta gene. Most patients are reported to be in an euthyroid or in a hyperthyroid state, depending on the compartments affected by RTH [2] . Although there may be an overlap usually 3 clinical conditions are distin guished: a) generalized resistance aff ecting all tissues including the pituitary gland. These pa tients are expected to be clinically euthyroid because the thyrotropic axis adjusts to a new equilibrium with higher thyroid hormone concentrations needed for normal function of peripheral tissues. b) Pituitary RTH with a hyperthyroid state because of normal peripheral response to circulating thyroid hormones. c) Isolated peripheral tissue RTH resulting in clinical hypothy roidism. This has been reported in very few pa tients only.