Thyroid hormone resistance due to a novel mutation in thyroid hormone receptor presenting as attention deficit hyperactivity disorder.

Resistance to thyroid hormone (RTH) is rare and is characterized by high circulating levels of thyroid hormones in the presence of either normal or elevated thyroid stimulating hormone (TSH) levels. Decreased responsiveness of the peripheral tissues to thyroid hormones owing to defective thyroid receptor function is the underlying cause. RTH is variable in its presentation. We report a 21-year-old man with long-standing attention deficit hyperactivity disorder (ADHD) and learning disabilities. His thyroid function tests showed an increased free T3 and T4 in the presence of a non-suppressed TSH. Other pituitary hormones were normal. Subsequently, a genetic analysis revealed a heterozygous mutation (Pro452Thr) in THRβ gene, establishing the diagnosis of RTH. Thus, this was a RTH presenting as ADHD due to a novel mutation in the thyroid hormone receptor gene.