Endemic cretinism in Thailand: a multidisciplinary survey

The Thyroid Condition and Residual Clinical Signs in 31 Existing Endemic Neurological Cretins After 42 Years of Iodine Supplementation in China

BACKGROUD

Endemic cretinism is the most severe manifestation among the iodine deficiency-related disorders. The clinical status of the cretins may be modified subsequently by the duration and severity of the disease. We aimed to reassess the clinical status and thyroid function of 31 surviving "neurological cretins" after 42 years of iodine supplementation in a historically severely iodine deficiency area of China.

METHODS

It was a cross-sectional study in design and we investigated all 31 surviving neurological cretins and 85 controls. A detailed neurological examination was conducted on each patients. All the participants were given a questionnaire and underwent B-mode ultrasonography of the thyroid. The serum levels of thyroid hormones, thyroid antibodies, serum iodine concentration (SIC) and urine iodine concentration (UIC) were measured.

RESULTS

The neurological cretins had shorter stature than that of the control. Neurological damage is still present in patients with cretinism. The prevalence of subclinical hypothyroidism and thyroid nodule in the cretins was significantly higher (χ² =4.766, P=0.029 and χ² =17.077, P<0.0001, respectively) compared with the control. After adjusting for confounding factors, endemic neurocretinism was found to be an independent risk factor for subclinical hypothyroidism (OR=4.412; 95% CI: 1.358-14.334; P=0.014) and thyroid nodule (OR=6.433; 95% CI: 2.323-17.816; P<0.0001).

CONCLUSIONS

Iodine supplementation after birth does not reverse the neurological damage that results from maternal/foetal hypothyroidism in utero and is subsequently manifested as neurological cretinism. There is a cross-sectional association between endemic neurocretinism and subclinical hypothyroidism and thyroid nodule.

Making sense with thyroid hormone--the role of T(3) in auditory development

The senses are our window to the world, our interface with the habitat in which we live in and the basis for our communication with each other. Although sensory systems are not generally viewed as major targets of endocrine regulation, sensory development is profoundly influenced by thyroid hormone (T(3)) signalling. In this article, we discuss this developmental role of T(3) and highlight the auditory system as the best-studied example of the interplay between systemic and local tissue mechanisms by which T(3) stimulates the onset of sensory function. Several genes that mediate the action of T(3) are known to promote sensory development in mice, including genes that encode T(3) receptors and deiodinase enzymes that amplify or deplete levels of T(3). We also discuss the current knowledge of sensory defects in human genetic disorders in which T(3) signalling is impaired. As sensory input provides the only means of acquiring information from the environment, the stimulation of sensory development is one of the most fundamental functions of T(3) signalling.

Iodine deficiency in pregnancy: the effect on neurodevelopment in the child

Iodine is an integral part of the thyroid hormones, thyroxine (T₄) and tri-iodothyronine (T₃), necessary for normal growth and development. An adequate supply of cerebral T₃, generated in the fetal brain from maternal free T₄ (fT₄), is needed by the fetus for thyroid hormone dependent neurodevelopment, which begins in the second half of the first trimester of pregnancy. Around the beginning of the second trimester the fetal thyroid also begins to produce hormones but the reserves of the fetal gland are low, thus maternal thyroid hormones contribute to total fetal thyroid hormone concentrations until birth. In order for pregnant women to produce enough thyroid hormones to meet both her own and her baby’s requirements, a 50% increase in iodine intake is recommended. A lack of iodine in the diet may result in the mother becoming iodine deficient, and subsequently the fetus. In iodine deficiency, hypothyroxinemia (i.e., low maternal fT₄) results in damage to the developing brain, which is further aggravated by hypothyroidism in the fetus. The most serious consequence of iodine deficiency is cretinism, characterised by profound mental retardation. There is unequivocal evidence that severe iodine deficiency in pregnancy impairs brain development in the child. However, only two intervention trials have assessed neurodevelopment in children of moderately iodine deficient mothers finding improved neurodevelopment in children of mothers supplemented earlier rather than later in pregnancy; both studies were not randomised and were uncontrolled. Thus, there is a need for well-designed trials to determine the effect of iodine supplementation in moderate to mildly iodine deficient pregnant women on neurodevelopment in the child.

Maternal iodine status and neonatal thyroid-stimulating hormone concentration: a community survey in Songkhla, southern Thailand

OBJECTIVE

To determine iodine intake and urinary iodine excretion (UIE) in a group of pregnant Thai women and the concentration of thyroid-stimulating hormone (TSH) in their neonates.

DESIGN

A prospective cohort study.

SETTING

Three districts of Songkhla, southern Thailand.

SUBJECTS

Two hundred and thirty-six pregnant women.

RESULTS

A quarter of the participants lacked knowledge of iodine and the prevention of iodine deficiency, although 70 % used iodized salt. Those who did not use iodized salt stated that they had no knowledge about iodine (57 %) and no iodized salt was sold in their village (36 %). The median iodine intake in the three districts was 205-240 microg/d, with 53-74 % of pregnant women having iodine intake <250 microg/d. The median UIE in the three districts was 51-106 microg/l, with 24-35 % having UIE < 50 microg/l. The mean neonatal TSH was 2.40 (sd 1.56) mU/l, with 8.9 % of neonates having TSH > 5 mU/l.

CONCLUSIONS

The studied women and their fetuses were at risk of mild iodine deficiency. About a quarter of the participants lacked knowledge of the importance of iodine. Education regarding the importance of iodine supplements and the promotion of iodized salt should be added to national health-care policies in order to prevent iodine-deficiency disorders, diseases that are subclinical but have long-term sequelae.

Chronic iodine deprivation attenuates stress-induced and diurnal variation in corticosterone secretion in female Wistar rats

Many millions of people throughout the world are at risk of developing iodine deficiency-associated disorders. The underlying effects of iodine deficiency on neuroendocrine function are poorly defined. We have studied stress-induced and diurnal variation in corticosterone secretion in female rats rendered chronically hypothyroid by feeding them an iodine-free diet for 6 months. Corticosterone secretory responses in iodine deficient animals were compared to those seen in animals rendered hypothyroid with propylthiouracil and untreated controls. By using a well-validated, automated blood sampling system to collect small samples of blood over the complete daily cycle in unrestrained animals, we have demonstrated for the first time that the normal diurnal rhythm of corticosterone secretion is lost in chronic iodine deficiency and that the corticosterone secretory response to the psychological stress of 10 min exposure to white noise is attenuated. Despite restoration of circulating triiodothyronine and thyrotropin releasing hormone- and thyroid stimulating hormone beta-transcript prevalence in the hypothalamus and pituitary, respectively, 1 month after restoration of normal iodine-containing diet both the diurnal variation in corticosterone levels and the corticosterone secretory response to the noise stress remained reduced in amplitude compared to control animals. Thus, chronic hypothyroidism induced by iodine deficiency significantly attenuates hypothalamo-pituitary-adrenal axis activity, an effect that persists after functional recovery of the thyroid axis.

The role of iodine in brain development

I is required for the synthesis of thyroid hormones. These hormones, in turn, are required for brain development, which occurs during fetal and early postnatal life. The present paper reviews the impact of I deficiency (1) on thyroid function during pregnancy and in the neonate, and (2) on the intellectual development of infants and children. All extents of I deficiency (based on I intake (microgram/d); mild 50-99, moderate 20-49, severe > 20) affect the thyroid function of the mother and neonate, and the mental development of the child. The damage increases with the extent of the deficiency, with overt endemic cretinism as the severest consequence. This syndrome combines irreversible mental retardation, neurological damage and thyroid failure. Maternal hypothyroxinaemia during early pregnancy is a key factor in the development of the neurological damage in the cretin. Se deficiency superimposed on I deficiency partly prevents the neurological damage, but precipitates severe hypothyroidism in cretins. I deficiency results in a global loss of 10-15 intellectual quotient points at a population level, and constitutes the world's greatest single cause of preventable brain damage and mental retardation.