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

Hypothyroidism causes mental retardation secondary to changes in the organization of the CNS. These changes affect higher brain functions for which interhemispheric transfer of information is crucial. In present study, the anterior commissure (AC) and corpus callosum (CC) of normal (C) and hypothyroid (H) rats has been examined using quantitative electron microscopy. H rats received an antithyroid treatment with methimazole from embryonic day 14 (E14) and surgical thyroidectomy at postnatal day 6 (P6). In the AC, the number of axons (unmyelinated and myelinated) increased from 0.17 x 10(6) axons at E18 to 1.08 x 10(6) axons at P4 and it was almost the same at P180 (1.01 x 10(6) axons). In H rats the number of axons between P14 and P180 was similar to that of C rats. In contrast, there were only 0.11 x 10(6) myelinated axons at P180 resulting in a 66% reduction with respect to C rats (0.36 x 10(6) axons). In the CC of C rats, the number of myelinated axons increased from 1.76 x 10(3) axons at P12 to 3.34 x 10(6) axons at P184. In H rats, there were only 0.84 x 10(6) axons at P184 resulting in a 76% reduction with respect to C rats. This reduction was more important in the posterior sector of the CC (95%) than in the rest (on average 63%). Therefore these results show that thyroid hormones play an important role in the processes involved in the maturation of commissural axons.
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PMID:Role of thyroid hormones in the maturation of interhemispheric connections in rats. 784 Aug 96

The Schinzel-Giedion is an autosomal recessive syndrome characterized by midface retraction, hypertrichosis, multiple skeletal anomalies, cardiac and renal malformations and mental retardation. We describe a female child with this syndrome and a clinical status complicated by hypernatremic dehydration, hypothyroidism and diabetes insipidus at the age of 10 months.
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PMID:Schinzel-Giedion syndrome. A patient with hypothyroidism and diabetes insipidus. 791 31

This paper reviews present knowledge on the etiology, pathophysiology, complications, prevention, and therapy of the disorders induced by iodine deficiency. The recommended dietary allowances of iodine are 100 micrograms/day for adults and adolescents, 60-100 micrograms/day for children aged 1 to 10 years, and 35-40 micrograms/day in infants aged less than 1 year. When the physiological requirements of iodine are not met in a given population, a series of functional and developmental abnormalities occur including thyroid function abnormalities and, when iodine deficiency is severe, endemic goiter and cretinism, endemic mental retardation, decreased fertility rate, increased perinatal death, and infant mortality. These complications, which constitute a hindrance to the development of the affected populations, are grouped under the general heading of iodine deficiency disorders (IDD). At least one billion people are at risk of IDD. Iodine deficiency, therefore, constitutes one of the most common preventable causes of mental deficiency in the world today. Most of the affected populations live in mountainous areas in preindustrialized countries, but 50 to 100 million people are still at risk in Europe. The most important target groups to the effects of iodine deficiency from a public health point of view are pregnant mothers, fetuses, neonates, and young infants because the main complication of IDD, i.e., brain damage resulting in irreversible mental retardation, is the consequence of thyroid failure occurring during pregnancy, fetal, and early postnatal life. The main cause of endemic goiter and cretinism is an insufficient dietary supply of iodine. The additional role of naturally occurring goitrogens has been documented in the case of certain foods (milk, cassava, millet, nuts) and bacterial and chemical water pollutants. The mechanism by which the thyroid gland adapts to an insufficient iodine supply is to increase the trapping of iodide as well as the subsequent steps of the intrathyroidal metabolism of iodine leading to preferential synthesis and secretion of triiodotyronine (T3). They are triggered and maintained by increased secretion of TSH, which is ultimately responsible for the development of goiter. The acceleration of the main steps of iodine kinetics and the degree of hyperstimulation by TSH are much more marked in the pediatric age groups, including neonates, than in adults, and the development of goiter appears as an unfavorable side effect in the process of adaptation to iodine deficiency during growth. The most serious complication of iodine deficiency is endemic cretinism, a syndrome characterized by irreversible mental retardation together with either a predominant neurological syndrome or predominant hypothyroidism, or a combination of both syndromes.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The disorders induced by iodine deficiency. 805 57

Cognitive disorders affect thinking and perceptual processes and the acquisition of knowledge and new information. They have an enormous societal impact because special educational resources are required, and independent living often cannot be achieved. Learning problems may lead to behavioral disorders in the home and community. The pathogenesis of most mild and moderate cognitive disorders is poorly understood. Severe cognitive impairment is usually accompanied by somatic abnormalities, and an etiology can be identified in many cases. Specific treatments are available for disorders such as cogenital hypothyroidism, some metabolic acidurias, and congenital toxoplasmosis. Other disorders affecting cognition such as fetal alcohol syndrome, maternal cocaine and heroin exposure, HIV encephalopathy, and prematurity require aggressive prevention and education to reduce their occurrence. The recent advances in molecular genetics offer a faster and better method of diagnosing fragile X syndrome, now recognized as the most common inheritable cause of mental retardation. In the future, DNA analysis may elucidate the basis of many other cognitive disorders.
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PMID:Cognitive disorders in children. 812 19

Generalized resistance to thyroid hormone (GRTH) is an inherited syndrome characterized by hyposensitivity of target tissues to thyroid hormone. The clinical presentation is variable. The syndrome is usually suspected when elevated serum thyroid hormone levels are associated with a non-suppressed thyroid-stimulating hormone (TSH). While goiter and thyroid test abnormalities have more often led to the suspicion of thyroid gland dysfunction, short stature, hyperactivity, learning disability and goiter in children or adolescents and recalcitrant goiter in adults, should raise the suspicion of GRTH. Hypothyroidism has been considered when growth or mental retardation was the presenting symptom and thyrotoxicosis when confronted with attention deficit, hyperactivity or tachycardia. Failure to recognize the inappropriate persistence of TSH secretion in spite of elevated thyroid hormone levels has commonly resulted in erroneous diagnosis leading to antithyroid treatment. More than 300 subjects with this syndrome have been identified. The mode of inheritance in the majority of families is autosomal dominant. Recessive transmission has been found in only one family. It has long been speculated that this defect is likely to be caused by an abnormal thyroid hormone receptor (TR), but this hypothesis could not be directly tested until the isolation of two TR genes, TR alpha and TR beta. Mutations in the TR beta gene have been identified in 42 families with GRTH. All are located in the T3-binding domain straddling the putative dimerization region and exhibit various degrees of hormone-binding impairment. This finding, and the fact that heterozygous subjects with complete TR deletion are not affected while those with point mutations are, indicates that interactions of a mutant TR with normal TR and with other factors are responsible for the dominant inheritance of GRTH and its heterogeneity. Elucidation of the etiology of GRTH has not only added a new means for the early diagnosis of the syndrome but provided new insights in the understanding of the mechanism of hormone action.
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PMID:Resistance to thyroid hormone and its molecular basis. 816 97

Macro-orchidism (MO) is the increase of the testicular volume, up to 25 ml in the adult male. It is frequently associated with mental retardation (MR) with fragile X-chromosome (FXC) (Martin-Bell syndrome). Sometimes it is of unknown origin and is called "benign idiopathic macro-orchidism" (BIMO). MO has also been described in association with bilateral testicular tumors, idiopathic precocious puberty, juvenile hypothyroidism and, more rarely, with congenital testicular cysts (cystic testicular dysplasia) and testicular microlithiasis in a patient treated with GH. The most common presentation is MR associated with MO, with positive or negative FXC. Among MO with MR and FXC-marfanoid habitus patients have been described and in the Atkin-Flaitz syndrome patients. Management of MO must be conservative in all cases and testicular biopsy must only be performed to diagnose leukemic infiltration or carcinoma in situ (CIS), or as the last fertility diagnostic test in BIMO. A wide range of primary testicular lesions may histopathologically be found: preserved spermatogenesis tubes, only Sertoli cell pattern and complete tubular sclerosis. Interstitial edema, frequently implicated in the MO pathogeny, does not explain by itself the important increase in testicular volume. In our laboratory, we have demonstrated that the increment of the testicular volume in MO is associated with a significant increase in the length of the seminiferous tubules. MO may pathogenically be intimately related to some hormonal regulation mechanism or to a higher seminiferous tubule sensitivity to FSH.
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PMID:[Macro-orchidism: new pathogenetic and histopathologic aspects]. 819

Trichothiodystrophy is characterized by sparse, short, sulfur-deficient hair. Numerous symptom complexes have been described in which the hair abnormality represents a constant feature. We report a boy with trichothiodystrophy, ichthyotic skin changes, onychodystrophy, chronic neutropenia, osteosclerosis, hypothyroidism, nystagmus, growth and mental retardation, and microcephaly, who developed a progressive encephalopathy with ataxia and optic atrophy at 2.5 years of age. In addition to a deficient cystine level identified on a hair sample, a disturbance in the composition of other amino acids was present. Although features were reminiscent of osteosclerosis, ichthyosis, brittle hair due to trichothiodystrophy, impaired intelligence, decreased fertility, and short stature (SIBIDS) and could represent a variant of this disorder, findings in our patient may reflect a new trichothiodystrophy symptom complex that carries a poor prognosis for survival beyond childhood.
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PMID:Trichothiodystrophy and associated anomalies: a variant of SIBIDS or new symptom complex? 834

We examined a German family with five members affected by Albright hereditary osteodystrophy (AHO). The only patient with pseudohypoparathyroidism type Ia (PHP-Ia) presented clinically with latent tetany, mental retardation, round face, short stature, brachymetacarpia and calcifications of subcutaneous tissue, heart and brain, whereas all other four members with pseudopseudohypoparathyroidism (pseudo-PHP) showed only subcutaneous calcifications and brachymetaphalangia. The PHP-Ia patient exhibited hypocalcaemia, hyperphosphataemia, elevated immunoreactive parathyroid hormone (PTH), and a blunted response of cyclic adenosine monophosphate (cAMP) in plasma and urine to synthetic 1-38 hPTH. In addition, latent primary hypothyroidism was found. In contrast, all tested healthy family members as well as the patients with pseudo-PHP exhibited normal calcium metabolism including cAMP response to exogenous PTH. In Northern blot experiments all patients with AHO, regardless whether affected by PHP-Ia or pseudo-PHP, revealed significantly reduced mRNA levels coding for the alpha subunit of the G protein that stimulates adenylyl cyclase (Gs alpha), when compared with healthy family members. In contrast, there was no significant difference between healthy and affected subjects with regard to the levels of the mRNA coding for the alpha subunit of Gi alpha-2, the main inhibitory G protein of adenylyl cyclase. The results indicate that reduced expression of Gs alpha is a useful genetic marker in some families with AHO, regardless whether patients are affected by PHP-Ia or by pseudo-PHP.
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PMID:Endocrine and molecular biological studies in a German family with Albright hereditary osteodystrophy. 844 41

Down syndrome remains one of the most common causes of mental retardation. Although knowledge of pathogenesis remains incomplete, recent molecular biologic techniques have identified regions of the 21st chromosome critical for expression of the Down syndrome phenotype, and animal models have helped elucidate the origins of the neurochemical and neuropathologic abnormalities. There also has been an improved understanding of the spectrum of medical complications of this disorder and the need for anticipatory management, including the search for atlantoaxial subluxation and hypothyroidism. With its increased risk of Alzheimer disease, Down syndrome is proving to be a useful model for studying aging. Accompanying greater knowledge has been improved functional outcome. Better medical care has made individuals with Down syndrome healthier; remaining at home through childhood has increased their cognitive function; and availability of increased numbers of group homes and supported employment opportunities has permitted the young adult with Down syndrome to live a more independent and full life. In this climate, the role of the pediatrician in early intervention and anticipatory guidance cannot be overemphasized.
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PMID:Down syndrome. 849 63

Normal development of the CNS requires adequate thyroid hormone exposure. Since iodine is an essential component of the thyroid hormone molecule, its deficiency during fetal development can cause hypothyroidism and irreversible mental retardation. The full-blown syndrome, called cretinism, includes deaf-mutism, short stature, spasticity, and profound mental retardation. The clinical spectrum can vary in degree and combination of these features. Screening programs in iodine-deficient countries show that up to 10% of neonates have elevated serum TSH levels, putting them at theoretical risk for permanent brain damage. About one billion people worldwide risk the consequences of iodine deficiency, all of which can be prevented by adequate maternal and infant iodine nutrition. Iodized salt is usually the preferred prophylactic vehicle, but iodized vegetable oil, iodized water, and iodine tablets are also occasionally used. The United Nations and the heads of state of most countries have pledged the virtual elimination of iodine deficiency by the year 2000. This goal is technically feasible if pursued with sufficient vigor and resources.
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PMID:Iodine supplementation and the prevention of cretinism. 849 59


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