Thinness and Thyroid Hormone Resistance (and ADHD)

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Among the newly recognized features of resistance to thyroid hormone

is low body weight; this is particularly characteristic of children.

One third of children with resistance are too thin for their age,

and one third are too thin for their height. The percentile for

weight correlates with free T4 levels, age, and basal metabolic

rate in persons with resistance to thyroid hormone, and it may be a

sign of relative hyperthyroidism.

However, the percentile for weight tends to correlate with attention-

deficit hyperactivity disorder, raising the possibility that

hyperactivity in children results in both lower caloric intake and

higher caloric expenditure. This correlation is not found in

adults, in whom attention-deficit hyperactivity disorder,

particularly its hyperactivity component, is much less frequent.

Another contributing factor could be a specific impairment of genes

involved in fat regulation or metabolism.