[Reflections on mental retardation and congenital hypothyroidism: effects of trace mineral deficiencies]

While deficiencies of trace minerals and vitamins are rare in humans eating a variety of food, they can occur in premature infants and those with disturbances in dietary behavior for physical or psychological reasons and during parenteral or enteral nutrition. Some deficiencies - such as iron and iodine - cause such serious specific disorders that they must be considered separately. Congenital hypothyroidism induced by iodine deficiency is a major problem. Its public health importance comes from the neurological complications that lead to the most severe forms of endemic congenital hypothyroidism (cretinism). In areas without iodine deficiency, the standard incidence of this disease in the West is 1/4,500 live births. In areas with iodine deficiency, however, its incidence varies from 1 to 5%! It is nonetheless underestimated, because the screening methods revolutionized 20 years ago are still not applied systematically. Additional factors include the thiocyanates in cassava, the selenium deficiency resulting in selenium-dependent glutathione peroxidase deficiency, and the natural goitrogens in some foods: milk, millet, walnuts, and bacterial and chemical water pollutants. Adolescents and adults need 100 microg/day, children aged 1-10 years 60-100 microg, and babies under one year, 35-40 microg, but these daily requirements are not necessarily met. This threat weighs on a billion people, 50-100 million in Europe, especially pregnant women, fetuses, newborns, and young children whose cerebral development may be negatively affected in the womb and in early life. According to some authors, subjects with cretinism syndrome should be found in places where goiter prevalence exceeds 20%. Evaluation of diffuse intellectual impairment in the population would require tools too specific for most studies. Generations of children are the victims throughout wide swaths of the African ecosystem in which it is endemic and associated with poor adaptation to the environment. But studies of isolated places cannot be transposed to entire populations. Because pregnancy in women with hypothyroidism is often thought to have a very negative prognosis, the two cases we report merit attention. In one case, despite certainly insufficient thyroid hormone replacement treatment, the child was born alive and healthy. In the second case, where hypothyroidism followed a thyroidectomy in a woman with Graves disease, a hydrocephalic child was liveborn, without any replacement treatment. In her next pregnancy, she received optimal hormonal treatment and delivered a healthy liveborn child. The disorders due to severe iodine deficiency did not affect our two patients. In a series of 166 cases of congenital hypothyroidism in newborns, only two cases had maternal antithyroid antibodies. Elsewhere, 9 women with hypothyroidism had 11 pregnancies, 9 normal children, 1 premature child (mother had eclampsia), and 1 with Down syndrome and an Ostium primum defect (mother aged 41 years). Ontogenesis of the hypothalamo-pituitary-thyroid axis of the fetus still appears today to develop independently of the mother in cases of hypothyroidism. An important role is played by type III deiodinase, which is especially active in the placenta during pregnancy, probably involving the T3 activity on nuclear and also mitochondrial receptors. The maturation of these receptors is not well understood.