An Adult Female With Resistance to Thyroid Hormone Mediated by Defective Thyroid Hormone Receptor α

Context: The firsthumancases (female, age 6 y; father and daughter, ages 47 and 11 y, respectively) with growth retardation/short stature, skeletal dysplasia, constipation, and defective thyroid receptor alpha (TR alpha) have been recently described. Objective: A 45-year-old, short, overweight female with cognitive impairment, epilepsy, and constipation was investigated. Design and Intervention: Clinical, biochemical, and radiological assessment and THRA sequencing were undertaken. The patient's thyroid status and her biochemical and physiological parameters were evaluated at baseline and after T4 therapy. Results: The patient exhibits disproportionate short stature, macrocephaly, low free T4/free T3 ratio and rT3 levels, together with subnormal heart and basal metabolic rate. She is heterozygous for a novel frameshift/premature stop (Ala382ProfsX7) THRA mutation, generating a mutant TR alpha with constitutive corepressor binding and negligible coactivator recruitment, which inhibits its wildtype counterpart in a dominant-negative manner-both in vitro and in mutation-containing patient blood mononuclear cells studied ex vivo. Her alertness and constipation responded to T4 therapy, which readily suppressed TSH levels, raised basal metabolic rate, and normalized elevated muscle creatine kinase, but cardiac parameters (heart rate, contractility) remained relatively refractory. Thepatientanda previous childhood caseshowedreduced red cell mass with macrocytosis unresponsive to T4 therapy. Conclusions: Clinical (short stature, macrocephaly, constipation) and biochemical (low free T4/free T3 ratio, subnormal rT3) findings that are congruent with previous cases and newly recognized features (epilepsy) in this adult female with defective TR alpha define a shared phenotype in TR alpha mediated resistance to thyroid hormone, with differential tissue responses to T-4 treatment.