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Query: UMLS:C0917816 (mental retardation)
 15,867 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Systematic neonatal screening for congenital hypothyroidism (CH), which was progressively implemented in industrialized countries over the past 15 to 25 years, has been extremely successful in eradicating severe mental deficiency resulting from CH. However, in the first generation of children diagnosed by screening, the concept that CH has a threshold effect on intelligence was confirmed. In spite of earlier diagnosis through screening, children with severe CH (i.e., those with a marked retardation of bone age and/or a low circulating thyroxine [T4] before treatment) still had clinically significant intellectual sequelae, amounting to a loss of 6 to 19 IQ points. Recent studies suggest that this developmental gap may be closed by treating more rapidly after birth (2 weeks instead of 4-5 weeks in the early years of the screening era) and by using a higher initial dose of levothyroxine (10-15 instead of 5-8 microg/kg per day). This regimen induces transient hyperthyroxinemia, but no clinical signs or symptoms of hyperthyroidism. Longer term follow-up of larger numbers of patients remains necessary to confirm the normalization of intellectual development and the absence of untowards effects of the treatment regimen in children with severe CH.
Thyroid 1999 Jan
PMID:Neonatal hypothyroidism: treatment and outcome. 1003 81

Congenital hypothyroidism is a common preventable cause of mental retardation. The overall incidence is approximately 1:4000; females are affected about twice as often as males. Approximately 85% of cases are sporadic, while 15% are hereditary. The most common sporadic etiology is thyroid dysgenesis, with ectopic glands more common than aplasia or hypoplasia. While the pathogenesis of dysgenesis is largely unknown, some cases are now discovered to be the result of mutations in the transcription factors PAX-8 and TTF-2. Loss of function mutations in the thyrotropin (TSH) receptor have been demonstrated to cause some familial forms of athyreosis. The most common hereditary etiology is the inborn errors of thyroxine (T4) synthesis. Recent mutations have been described in the genes coding for the sodium/iodide symporter, thyroid peroxidase (TPO), and thyroglobulin. Transplacental passage of a maternal thyrotropin receptor blocking antibody (TRB-Ab) causes a transient form of familial congenital hypothyroidism. The vast majority of infants are now diagnosed after detection through newborn screening programs using a primary T4-backup TSH or primary TSH test. Screening test results must be confirmed by serum thyroid function tests. Thyroid scintigraphy, using 99mTc or 123I, is the most accurate diagnostic test to detect thyroid dysgenesis or one of the inborn errors of T4 synthesis. Thyroid sonography is nearly as accurate, but it may miss some cases of ectopic glands. If maternal antibody-mediated hypothyroidism is suspected, measurement of maternal and/or neonatal TRB-Ab will confirm the diagnosis. The goals of treatment are to raise the serum T4 as rapidly as possible into the normal range, adjust the levothyroxine dose with growth to keep the serum T4 (or free T4) in the upper half of the normal range and the TSH normal, and maintain normal growth and development while avoiding overtreatment. An initial starting dose of 10-15 microg/kg per day is recommended; this dose will decrease on a weight basis over time. Serum T4 (or free T4) and TSH should be monitored every 1-2 months in the first year of life and every 2-3 months in the second and third years.
Thyroid 1999 Jul
PMID:Congenital hypothyroidism: etiologies, diagnosis, and management. 1044 22

Although mental retardation associated with congenital hypothyroidism (CH) is prevented by newborn screening and early treatment, affected children still undergo a brief period of thyroid hormone deficiency reflecting etiology of thyroid disease, illness severity, and treatment factors. Because thyroid hormone is essential for normal brain development and because some processes require thyroid hormone in the period when thyroid hormone was lacking, children with CH treated early may still have subtle neurocognitive deficits. As the period when thyroid hormone is needed differs for different brain regions, there may be different types of deficits depending on when thyroid hormone levels were insufficient. Since 1980, we have been following a large cohort of Toronto-based children with congenital hypothyroidism identified by newborn screening from infancy to adolescence. Early findings revealed a 5-10-point decline in IQ, poorer visuomotor and visuospatial abilities, delayed speech and language development, selective neuromotor deficiencies, and poorer attention and memory skills, which were correlated with different disease and treatment factors. Now a comparison between 48 subjects at adolescence and matched controls indicates that deficits persist in visuospatial, memory, and attention domains and these are correlated with severity of early hypothyroidism. Negative relationships between attention indices and thyroxine (T4) elevations at time of testing also suggest a role for thyroid hormone in the regulation of attention.
Thyroid 1999 Jul
PMID:Congenital hypothyroidism: long-term outcome. 1044 23

Congenital hypothyroidism is one of the most common diseases in paediatric endocrinology. Thyroid hormones are essential in brain development, which takes place during foetal life and early postnatal life up to the 2nd year of age. The main etiologic factors of congenital hypothyroidism are anomalies of development, function and regulation of the thyroid gland. Clinical signs of thyroid hormone deficiency in infants are non-specific. Early diagnosis is based on newborn screening for congenital hypothyroidism, which was started in Poland in 1977. Treatment within the first days of life with appropriate dosage of thyroxine prevents mental retardation. This paper summarises current knowledge on congenital hypothyroidism in children.
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PMID:[Congenital hypothyroidism]. 1122 3

Iodine deficiency is the leading cause of preventable mental retardation. Universal salt iodization (USI), calling for all salt used in agriculture, food processing, catering and household to be iodized, is the agreed strategy for achieving iodine sufficiency. This article reviews published information on programs for the sustainable elimination of the iodine deficiency disorders and reports new data on monitoring and impact of salt iodization programs at the population level. Currently, 68% of households from areas of the world with previous iodine deficiency have access to iodized salt, compared to less than 10% a decade ago. This great achievement, a public health success unprecedented in the field of noncommunicable diseases, must be better recognized by the health sector, including thyroidologists. On the other hand, the managers and sponsors of programs of iodized salt must appreciate the continuing need for greatly improved monitoring and quality control. For example, partnership evaluation of iodine nutrition using the ThyroMobil model in 35,223 schoolchildren at 378 sites of 28 countries has shown that many previously iodine deficient parts of the world now have median urinary iodine concentrations well above 300 microg/L, which is excessive and carries the risk of adverse health consequences. The elimination of iodine deficiency is within reach but major additional efforts are required to cover the whole population at risk and to ensure quality control and sustainability.
Thyroid 2001 May
PMID:Iodine deficiency in the world: where do we stand at the turn of the century? 1139 2

Thyroid hormone (3,5,3'-triiodo-l-thyronine or T3) exerts a pleiotropic activity during central nervous system development. Hypothyroidism during the fetal and postnatal life results in an irreversible mental retardation syndrome. At the cellular level, T3 is known to act on neuronal and glial lineages and to control cell proliferation, apoptosis, migration, and differentiation. Oligodendrocyte precursor cells (OPC) found at birth in the optic nerves are self-renewing cells that normally differentiate during the first 3 weeks of rodent postnatal life into postmitotic myelinating oligodendrocytes. In vitro, the addition of T3 to OPC is sufficient to trigger their terminal differentiation. The present analysis of T3 receptor knockout mice reveals that the absence of all T3 receptor results in the persistence of OPC proliferation in adult optic nerves, in a default in myelination, and sometimes in the degeneration of the retinal ganglion neurons. Thus, T3 signaling is necessary in vivo to promote the complete differentiation of OPC.
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PMID:Persistence of oligodendrocyte precursor cells and altered myelination in optic nerve associated to retina degeneration in mice devoid of all thyroid hormone receptors. 1186 29

Iodine deficiency is the most common cause of hypothyroidism worldwide. In persons living in iodine-replete areas, causes are congenital, spontaneous because of chronic autoimmune disease (atrophic autoimmune thyroiditis or goitrous autoimmune thyroiditis [Hashimoto's thyroiditis]), or iatrogenic because of goitrogens, drugs, or destructive treatment for thyrotoxicosis. Screening for congenital hypothyroidism exists and its use prevents mental retardation. The prevalence of spontaneous hypothyroidism is between 1% and 2% and is more common in older women and 10 times more common in women than in men. A significant proportion of subjects have asymptomatic chronic autoimmune thyroiditis and 8% of women (10% of women over 55 years of age) and 3% of men have subclinical hypothyroidism. Approximately one third of patients with newly diagnosed overt hypothyroidism have received destructive therapy for hyperthyroidism and indefinite surveillance is required. There is not much that can be done to prevent the occurrence of spontaneous autoimmune hypothyroidism, but if identified early, something can be done to prevent progression to overt disease. Controversy exists as to whether healthy adults would benefit from screening for autoimmune thyroid disease because a significant proportion of subjects tested will have evidence of mild thyroid failure. Case finding in women at menopause or visiting a primary care physician with nonspecific symptoms appears justified.
Thyroid 2002 Oct
PMID:Epidemiology and prevention of clinical and subclinical hypothyroidism. 1248 65

Thyroid dysfunctions can produce reproductive problems. Untreated maternal hypothyroidism has serious consequences on development of offspring, resulting in stunted growth and mental retardation. The effects of propylthiouracyl-induced hypothyroidism (0.1 g l(-1) in drinking water starting 8 days before mating, or given to virgin rats for 30 or 50 days) on the serum profiles of hormones related to reproduction and mammary function (prolactin, growth hormone (GH), progesterone, corticosterone, oestradiol, insulin-like growth factor I (IGF-I), thyroid-stimulating hormone (TSH), triiodothyronine and tetraiodothyronine), and on mammary function in virgin, pregnant and lactating rats, were investigated. Propylthiouracyl treatment severely decreased circulating triiodothyronine and tetraiodothyronine concentrations, and increased serum TSH concentrations. Virgin rats showed prolonged periods of vaginal dioestrus, increased circulating progesterone concentrations and afternoon peaks of prolactin concentration, which are indicative of prolactin-induced pseudopregnancy. Propylthiouracyl-treated virgin rats had mammary development comparable to that of midpregnancy, and half of these rats had increased mammary casein and lactose concentrations. Serum prolactin concentrations were decreased on the afternoon of day 5 of pregnancy, increased during late pregnancy (days 15-21) and were normal during lactation. Circulating GH concentrations decreased on days 15-21 of pregnancy, whereas progesterone concentrations increased during late pregnancy and early lactation. Circulating oestradiol (measured in late pregnancy and in virgin rats), IGF-I and corticosterone concentrations were decreased. Although assessment of mammary histology showed no differences in extent of development, casein content was increased in propylthiouracyl-treated rats on day 21 of pregnancy; litter growth was severely reduced and at day 20 of age the pups were hypothyroid, with decreased GH serum concentrations. An acute suckling experiment was performed on days 10-12 of lactation to determine whether some impairment in mammary function or the suckling reflex might account for these differences. After an 8 h separation of mothers from their litters and 30 min of suckling, circulating prolactin values were not affected by propylthiouracyl treatment, but serum oxytocin concentration and milk excretion were reduced. In conclusion, hypothyroidism induces various alterations in the hormone profiles of virgin and pregnant rats, and induces pseudopregnancies and mammary development in virgin rats. These alterations do not appear to have an overt impact on the outcome of pregnancy and on mammary function during lactation, with the exception of the milk ejection reflex, which may account at least partially for the reduced litter growth.
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PMID:Effect of hypothyroidism on hormone profiles in virgin, pregnant and lactating rats, and on lactation. 1296 45

Neonatal screening programs for congenital hypothyroidism (CH) were initiated in the 1970s to ensure early treatment in order to prevent mental retardation. With screening, developmental prognosis is considerably improved, but follow-up studies still report developmental delay compared to controls. To explain the delay, most studies have focused on effects of CH severity, supposedly caused by prenatal hypothyroidism. Nonoptimal treatment could also be an explanatory factor. Treatment guidelines have changed; now, a higher levothyroxine starting dose is recommended. In this review, we first summarize outcome studies in CH versus controls and in mild versus severe CH. Second, we report results on the association between levothyroxine treatment variables and developmental outcome. Six research groups have reported results on the association between levothyroxine starting dose and intelligence, and eight groups on the association between circulating thyroid hormones and intelligence. Most studies found a positive association between a high level of treatment, primarily treatment during the first year and later intelligence. However, negative associations between high-dose treatment and outcome have been reported, and the question of optimal treatment in relation to developmental outcome has not been answered. Effects of high levothyroxine dosage should be documented in samples that have been treated according to recent recommendations.
Thyroid 2003 Nov
PMID:Congenital hypothyroidism: developmental outcome in relation to levothyroxine treatment variables. 1465 87

Unrecognized congenital hypothyroidism leads to mental retardation. Newborn screening and thyroid therapy started within 2 weeks of age can normalize cognitive development. The primary thyroid-stimulating hormone screening has become standard in many parts of the world. However, newborn thyroid screening is not yet universal in some countries. Initial dosage of 10 to 15 microg/kg levothyroxine is recommended. The goals of thyroid hormone therapy should be to maintain frequent evaluations of total thyroxine or free thyroxine in the upper half of the reference range during the first 3 years of life and to normalize the serum thyroid-stimulating hormone concentration to ensure optimal thyroid hormone dosage and compliance. Improvements in screening and therapy have led to improved developmental outcomes in adults with congenital hypothyroidism who are now in their 20s and 30s. Thyroid hormone regimens used today are more aggressive in targeting early correction of thyroid-stimulating hormone than were those used 20 or even 10 years ago. Thus, newborn infants with congenital hypothyroidism today may have an even better intellectual and neurologic prognosis. Efforts are ongoing to establish the optimal therapy that leads to maximum potential for normal development for infants with congenital hypothyroidism. Remaining controversy centers on infants whose abnormality in neonatal thyroid function is transient or mild and on optimal care of very low birth weight or preterm infants. Of note, thyroid-stimulating hormone is not elevated in central hypothyroidism. An algorithm is proposed for diagnosis and management. Physicians must not relinquish their clinical judgment and experience in the face of normal newborn thyroid test results. Hypothyroidism can be acquired after the newborn screening. When clinical symptoms and signs suggest hypothyroidism, regardless of newborn screening results, serum free thyroxine and thyroid-stimulating hormone determinations should be performed.
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PMID:Update of newborn screening and therapy for congenital hypothyroidism. 1674 Aug 80


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