Brain cretinism

A deficiency of iodine results iu insufficient synthesis of thyroxine and a low plasma level, so that secretion of TSH is increased in an attempt to stimulate synthesis but this results in enlargement of the thyroid gland (goitre). Iodine deficiency in pregnancy impairs brain development in the foetus, causing mental retardation (known as cretinism). Indeed iodine deficiency is one of the major public health issues worldwide an estimated 200 million people are affected. 

Nonmetallic elements predominating in the ash are phosphorus (700 g in the human body), sulfur (175 g), and chlorine (105 g). Not only are these three elements essential to all living cells but also selenium, fluorine, silicon (Box 4-B), iodine, and boron are needed by higher animals and boron by plants (Fig. 1-17). Iodine deficiency may affect one billion human beings and may cause 20 million cases per year of cretinism, or less severe brain damage.158... 

Or, to put it more positively, by adding small amounts of iodide to common salt we can prevent the medical condition known technically as cretinism, a life-long affliction of innately low intelligence caused by iodine deficiency, and which causes permanent brain damage. Nor does this simple dietary requirement cost very much. To provide all 6.5 billion people on the planet with the 70 micrograms of iodine they need every day would require only 166 tonnes of iodine per year, which represent a mere 2% of the iodine the world produces annually. This is an amount that chemists could easily extract from seaweed, making it a sustainable resource, and indeed this was once the way they obtained this remarkable element. 

It has long been known that thyroid hormone deficiency, when established prior to the critical period of brain development, produces severe and permanent mental retardation both in humans ( cretinism ) and in experimental animals (see Refs. 6 and 101). Most of the early studies aimed at describing the behavioural, physiolog-... 

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). 

Further studies in sheep of the effect of correction of iodine deficiency by iodized oil injection at 100 days gestation (end of second trimester) revealed only partial correction of the effect on brain strucmre by the end of gestation (Potter et al.y 1984). This requires follow-up with observations of behavior and neurological stams into the postnatal period. Such studies could also be carried out in marmosets (primate model) with greater relevance to humans. However, the finding in sheep is consistent with observations in humans that the injection of iodized oil in the latter half of pregnancy may not prevent cretinism in the infant (Pharoah et al., 1971). Similar observations have been made by Cao et al. (1994) in China. 

The major features of the IDD effects on brain function arise from fetal damage (neurological cretinism) or hypothyroidism at various stages of life - fetus, neonate, juvenile and adult (Table 62.3). 

The WHO (1990) has estimated that 20 million worldwide from an at-risk population of 1 billion are suffering from varying degrees of preventable brain damage, based on a ratio of three to one for the estimates of the numbers of subcretins and cretins. ... 

To understand the brain damage observed in neurological cretinism it is important to keep in mind the main findings related to the presence and protective role of maternal... 

With respect to experimental studies in rats born from mothers with severe iodine deficiency, several neurological abnormalities have been demonstrated. The progeny has susceptibihty to audiogenic seizures, associated with irreversible hearing defects, similar to those found in neurological cretinism. Several areas of the brain, such as the cerebral cortex, hippocampus and cerebellum, present morphological abnormalities (Martinez-Galan et al, 1997). 

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. 

These studies reveal a broad spectrum of effects on fetal development, ranging from mortality to cretinism, and psychomotor defects due to retarded brain development in apparently normal children. All such consequences may be prevented by supplementing iodine in mothers prior to pregnancy. 

In 1966, iodized oil was injected in residents of Papua New Guinea, where the severity of endemic goiter and cretinism was high. A follow-up study showed that cretinism disappeared almost completely from the offspring of mothers who received iodized oil. The effect of iodine supplementation on the survival of the fetus and on their brain development was established. 

Iodine deficiency is the most preventable cause of mental retardation. The food produced in iodine-deficient areas fails to provide sufficient iodine intake, resulting in reduced production of the thyroid hormone thyroxin, which is critical for brain development (Bernal et ai, 2003). Depending on its severity, iodine deficiency affects mental and physical development up to the most severe form of hypothyroidism and cretinism. 

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. 

At the most severe end of the spectrum this manifests as endemic cretinism, but even mild iodine deficiency can affect cognitive development and subsequent intellectual abifi-ties, as well as, causing deficits in hearing and reproduction (Bleichrodt and Born, 1994 Dunn, 1996 Hetzel, 2004). Detailed consideration of the effects of iodine deficiency on brain function can be found in the chapter in the handbook entitled Iodine Deficiency and the Brain by Basil Hetzel. 

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