Cretinism during development

Experimental Models of Iodine Deficiency and Cretinism during Development The Role of the Mother... 

The demonstration of the prevention of cretinism with iodized oil in a double-blind controlled trial in Papua New Guinea established the causal role of iodine deficiency in cretinism by an effect on the developing fetal brain (Pharoah et al, 1971). Cretinism could not be prevented unless the iodized oil was given before pregnancy, as injection during pregnancy was ineffective (Table 62.2). 

The neurological abnormalities observed in neurological cretinism seem to be caused by maternal hypothyroxinemia during the first period of brain development, early in pregnancy. In iodine deficiency the maternal plasma T4 is low, even if plasma T3 and TSH are normal. 

The importance of the transfer of thyroid hormones from the mother to the fetus during the second half of pregnancy in humans has received increasing attention (Burrow et ai, 1994). Recently, it has become evident that maternal hypothyroxinemia results not only in the birth of children with neurological cretinism, but also in decreased mental and psychomotor development of the rest of the population without cretinism (Beichrodt and Born, 1994). 

The method of detecting iodine supply levels and the evaluation of the effect of the lack or oversupply (Boyages, 1993) of iodine on the condition of the thyroid gland (its size, function and the impact on the autoimmunity process) and the resulting evaluation of the overall condition of health of an entire population (from the occurrence of endemic cretinism due to significant lack of iodine to mild occurrence of brain dysfunction due to lack of iodine during intrauterine development) problems in the development of the somatic. 

Cretinism, the Irreversible clinical entity characterized by defective physical and mental development, appears when thyroid hormone Is not available during early childhood for normal bone formation and normal brain growth and differentiation. 

Up until the 1970 s there was dispute as to whether cretinism was truly related to iodine deficiency. The spontaneous decline during the 19th century, without formal iodisation programs, raised this possibility. It is now recognised that this spontaneous decline was probably due to increase in iodine intake associated with social and economic development. 

Although cretinism was already described by the turn of the century, the involvement of thyroid deficiency in this malady was not reported until the 1930 s (Kerley, 1936). Soon thereafter, animal studies were carried out which made clear the necessity of thyroid hormones for general somatic and neural development during the neonatal and early postnatal period in the rat, which is roughly equivalent to the first year of life in the human (Salmon, 1936 Scow and Simpson, 1945 Eayrs and Taylor, 1951 Eayrs and Horn, 1955 Hamburg and Vicari, 1957 Eayrs, 1961). 

The data suggesting the direct role of elemental iodine on brain development is the observation that correction of iodine deficiency in mothers prevents the emergence of neurological cretinism only if correction takes place before or during early gestation, thus before the onset of fetal thyroid function (83). What we would like to know in greater detail is which parameter is corrected in the human fetus when maternal iodine deficiency is corrected before the onset of fetal thyroid function Is it the fetal deficiency in iodine, in thyroid hormones or in both ... 

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