Lower IQ & ADHD in Thyroid Hormone Resistance

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Anecdotal observations in our patients and others suggest that

thyroid hormone may be beneficial. Specifically, we have found that

T3 seems more efficacious than T4; this suggests the possibility of

acquired deiodinase deficiency in persons with resistance to thyroid

hormone (indeed, the T4:T3 ratio is higher in persons with

resistance to thyroid hormone). Furthermore, preliminary data in a

controlled study suggest that T3 therapy may be useful in persons

with resistance to thyroid hormone (DUHHHH, says Janie) and

attention-deficit hyperactivity disorder but not in persons without

resistance who have attention-deficit hyperactivity disorder. This

suggests that one mechanism of the disorder in persons with

resistance to thyroid hormone could be relative hypothyroidism, and

this further supports the link between attention-deficit

hyperactivity disorder and resistance to thyroid hormone. Further

study is necessary to define the exact role of T3 and T4 therapy in

persons with resistance.

Although IQ scores are lower in persons with resistance to thyroid

hormone than in persons without resistance, mental retardation is

rare; furthermore, there is no correlation between attention-deficit

hyperactivity disorder and IQ. Because intelligence is adversely

affected in congenital hypothyroidism, the lower IQ found in persons

with resistance to thyroid hormone may be related to relative

hypothyroidism during early brain development. However, brain

dysfunction has been anecdotally reported in congenital

hyperthyroidism, raising questions about the mechanism of lower IQ

in persons with resistance to thyroid hormone.