To determine the genetic and clinical features of resistance to thyroid hormone in a study from a single institution.

Prospective, controlled study.

National Institutes of Health.

104 patients with resistance to thyroid hormone from 42 kindreds and 114 unaffected relatives sharing the patients' environmental and genetic back-grounds.

Thyroid, cardiovascular, psychometric, hearing, speech, and growth testing; thyroid tests done at baseline and after TSH-releasing hormone stimulation; and DNA analysis for detection of mutations in the thyroid hormone receptor β (TR β) gene (exons 9 and 10). Assessment of tissue-specific compensation for resistance.

Inheritance was autosomal dominant in 22 families, sporadic in 14 families, and unknown in 6 families. We found mutations in 25 kindreds (64 patients); 16 mutations were in exon 9 and 9 were in exon 10 of the TR β gene. In persons with resistance to thyroid hormone, we measured the increased incidence of goiter (65%), attention-deficit hyperactivity disorder (60%), IQ less than 85 (38%), speech impediment (35%), and short stature (18%). We also described new clinical features, such as frequent ear, nose, and throat infections (56%); low weight-for-height in children (32%); hearing loss (21%); and cardiac abnormalities (18%). Genotype, age, whether the mother had resistance to thyroid hormone, and sex influenced the phenotype. Tissue resistance varied from kindred to kindred and involved, in decreasing order, the pituitary gland, the brain, the bone, the liver, and the heart.

This study underscores the incidence of classic features of resistance to thyroid hormone, describes new clinical characteristics of this condition for the first time, and stresses the heterogeneity of the phenotype.

Ann Inten Med. 1995; 123:572-583.