Some studies suggest thyroid hormones may regulate the human immune system. In order to evaluate the effect of thyroid hormone deficiency on antibody production, we evaluated serum IgA and IgM concentrations in 83 children with congenital hypothyroidism (CH), diagnosed by neonatal screening. Patients were compared to two healthy, age-matched control groups. Patients with permanent CH had a significantly higher frequency of undetectable IgA concentrations (thyroid agenesis, P < 10 À5 ; thyroid ectopy, P = 0.013) and lower concentrations of IgA (thyroid agenesis, P < 10 À6 ; thyroid ectopy, P < 10 À5 ; dyshormonogenesis, P = 0.0002) and IgM (thyroid agenesis, P = 0.0002; thyroid ectopy, P < 10 À6 ; dyshormonogenesis, P = 0.0017) compared to control group. No difference was observed between patients with transient hypothyroidism and controls. A significant correlation was observed between serum IgA and IgM concentrations and fT 4 levels. IgA and IgM deficiency is correlated with the severity of congenital hypothyroidism and may help to evaluate the duration and severity of thyroid hormone deficiency during prenatal life. D

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