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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A 9-year-old boy, the product of a consanguineous marriage, had visual acuity of 6/60, pendular nystagmus, and a bull's-eye type of macular atrophy. A sensorineural deafness was present. The photopic electroretinogram was extinguished; the electro-oculogram was normal. There was associated mental retardation and failure of inhibition of the pituitary gland by high levels of circulating thyroid hormone. Two older siblings although not examined, had similar endocrine abnormalities. Non-involvement of three half-siblings suggested autosomal recessive inheritance.
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PMID:[Typical monochromacy, congenital deafness, and resistance to intracellular action of thyroid hormone (author's transl)]. 30 3

The basal ganglia are presently implicated in learning, and thyroid deficiency induced neonatally is known to affect mentation. The effects of such a deficiency on the developing causate nucleus might be used to provide insight into structure and function of the normal subcortical brain, as well as possible influences of these extrapyramidal structures on mental retardation. Propylthiouracil was added to the diet of lactating rat dams and observations of the developing caudate nuclei of normal hypothyroid rats were made at 8, 14, 20, 30 and 42 days by using various tissue stains and Golgi-Cox preparations. Seven different types of neurons were distinguished in the caudate nucleus. Differences in the size of cell somata and the varying morphology of axons and dendrites were criteria used to make distinctions. Normally, the nucleus acquires cytoarchitectural complexity during the first three postnatal weeks. Within this period, neuron incidence increases in the caudate neuropil with age while the germinal matrix density decreases. Neuron accumulation reaches a plateau after the third week and cell migration is essentially complete at the end of the first postnatal month as shown by computer analysis of Nissl stained cell counts. Branching of cellular processes, attainment of receptor spines and complexity of the fiber network also appeared during this period. Retardation of structural development with thyroid hormone deficiency was shown by decreased numbers of neurons, inhibition of dendritic arborization, decreased numbers of dendritic spines and a reduced complexity of axonal plexuses. Thyroid deficiency delays cell migration during the first three weeks when compared to age-matched normal controls. The lack of thyroid hormone does not appear to influence the size of neuron somata, and the extent of related dendritic fields, nor does hypothyroidism affect a specific cell type population. Generalized disturbances of caudate nuclear morphological maturation are caused by the deficiency. An apparent compensatory process, including a spurt of neural growth and differentiation, takes place in the period between days 14 and 30 in the deficient animals and a seemingly "normal" caudate cytoarchitecture is seen after the third postnatal week. Quantitative data, however, show that this rapid "catch up" process is inadequate. The developmental imperfection of the caudate nucleus which persists might be a part of the underlying substrate for the mental retardation, disturbed motor performance and perceptual handicaps which are found in the human patient.
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PMID:The developing caudate nucleus in the euthyroid and hypothyroid rat. 83 51

A woman in her 24th week of gestation was referred for treatment of hypothyroidism, after she underwent radioablation of the thyroid during the 13th week of gestation. Because of the high risk of hypothyroidism in the fetus, prenatal administration of intramuscular T-4 to the fetus was begun at 32 weeks. The last dose of T-4 was given 2 weeks before delivery; cord blood levels of T-4 and T-3 were undetectable and the TSH concentration was markedly elevated. The case illustrates several important physiological concepts regarding thyroid hormone and TSH metabolism in the fetal-placental unit, including the minimal placental permeability to iodothyronines and TSH, independent function (including feedback control) of the fetal hypothalamic-pituitary-thyroid axis, and the TSH response at parturition. In addition we suggest that administration of T-4 to the hypothyroid fetus in utero is an acceptable modality of treatment and may help to minimize irreversible mental retardation in known high risk infants. However, further studies are necessary to assess the effectiveness and safety of this approach.
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PMID:Intra-uterine treatment of a hypothyroid fetus. 111 55

Endemic cretinism is the most severe manifestation of dietary iodine deficiency. Two forms of the syndrome are traditionally described: neurological and myxoedematous. Although this classification highlights the important neurological sequelae of the disorder it implies that myxoedematous cretins have an alternative mechanism. Further, the nature of the neurological deficit associated with both types of endemic cretinism has received scant attention in recent times considering that it remains a common disorder in many parts of the world. The nature and extent of the neurological deficit found in endemic cretinism was investigated in 104 cretins from a predominantly myxoedematous endemia in western China and in 35 cretins from central Java, Indonesia, a predominantly neurological endemia. We found a similar pattern of neurological involvement in nearly all cretins from both endemias, regardless of type (myxoedematous or neurological), and of current thyroid function. Hallmarks of the neurological features included mental retardation, pyramidal signs in a proximal distribution and extrapyramidal signs. Many patients exhibited a characteristic gait. This probably reflected pyramidal and extrapyramidal dysfunction, although joint laxity and deformity were important contributing factors. Other frequently encountered clinical features were squint, deafness, and primitive reflexes. Cerebral computerized tomography (CT) revealed basal ganglia calcification in 15 of 50 subjects. The presence of basal ganglia calcification was confined to cretins with severe hypothyroidism. Otherwise, cerebral CT scanning demonstrated only minor abnormalities which did not contribute to the localization of the clinical deficits. We conclude that the same neurological disorder is present in both types of endemic cretinism reflecting a diffuse insult to the developing fetal nervous system. These clinical findings support the concept of maternal and fetal hypothyroxinaemia, arising from severe iodine deficiency, as the primary pathophysiological event in endemic cretinism. Differences between the two types of cretinism may be explained by continuing postnatal thyroid hormone deficiency in the myxoedematous type, which results in impaired growth, skeletal retardation and sexual immaturity.
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PMID:The neurology of endemic cretinism. A study of two endemias. 204 52

Fetal alcohol syndrome (FAS) is noted for poor growth, developmental delays, and mental retardation. In animals, prenatal alcohol exposure alters anatomical, physiological, and neurochemical maturation and produces behavioral changes similar to those in children. Since thyroid hormones are critical trophic factors for normal somatic and neural maturation, and since fetal thyroid hormones are profoundly affected by acute maternal ethanol administration, we hypothesized that postnatal effects of prenatal alcohol exposure may be related to abnormal thyroid hormone development. We report here that young rats exposed to alcohol in utero have significantly lower serum total thyroxine (T4) concentrations than normal and pair-fed control rats. The results suggest prenatal ethanol exposure may compromise thyroid development in ways not attributable to undernutrition or developmental delays alone. Lowered total T4 levels may be a teratogenic outcome of prenatal alcohol exposure, which could contribute to impaired growth, altered neural organization, and behavioral dysfunction.
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PMID:Lower serum thyroxine levels in rats following prenatal exposure to ethanol. 237 31

In the Finnish programme of screening for congenital hypothyroidism (CHT), thyroid replacement therapy is started very early (at a median age of 6 days). Our experience with the first 50 patients detected by this programme confirms that clinically relevant mental retardation is avoided by early therapy. But some intrauterine damage is inevitable and its degree correlates with the severity of the CHT. Age at the start of therapy, in our narrow range, did not appear to influence the outcome, as we found only a paradoxical positive correlation between the two. Our results suggest that thyroid hormone is transferred from the mother to her hypothyroid child during delivery.
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PMID:Multivariate analysis of psychomotor development in congenital hypothyroidism. 274 82

It is well known that insufficient production of thyroid hormones during the fetal and neonatal period of development may result in permanent brain damage unless treatment with thyroid hormone is instituted very soon after birth. But congenital hypothyroidism is not the only situation in which brain damage may be related to insufficient thyroid function. Cretinism is the most severe manifestation of iodine deficiency disorders found in areas where iodine intake is greatly reduced. Some of the manifestations of cretinism suggest that the insult to the developing brain starts earlier than in the case of congenital hypothyroidism. Hypothyroxinemia of mothers with adequate iodine intake may also leave permanent, though less severe, mental retardation. For these reasons the possible role of maternal transfer of thyroid hormones during early fetal development have been reinvestigated, using the rat to obtain various experimental models. It has been shown that thyroid hormones are found in embryonic tissues before onset of fetal thyroid function and that thyroidectomy of the mother results in delayed development of the concepta. The concentrations of T4 and T3 in embryonic tissues from thyroidectomized dams were undetectable before the onset of fetal thyroid function, and still reduced in some tissues near term, despite the onset of fetal thyroid function. Treatment of control and thyroidectomized dams with methyl-mercaptoimidazole to block fetal thyroid function reduced thyroid hormone concentrations in fetal tissues near term, but this decrease could be partially avoided by infusion of physiological doses of thyroxine to the mothers. Iodine deficiency of the mothers resulted in thyroid hormone deficiency of the developing embryo, which was very marked until term in all tissues including the brain. The results strongly support a role of maternal thyroid hormones in fetal thyroid hormone economy both before and after the onset of the fetal thyroid function, at least in the rat. They also support a role of the hypothyroxinemia of iodine-deficient mothers in initiating the brain damage of the endemic cretin, a damage which would not be corrected once the fetal thyroid becomes active, as iodine-deficiency of the fetus would impair adequate production of hormones by its own thyroid, and maternal transfer would continue to be low.
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PMID:Fetal and maternal thyroid hormones. 329 61

A large prospective study investigated prenatal and perinatal antecedents of chronic motor dysfunction (cerebral palsy [CP]), evaluating approximately 400 characteristics of the mothers, pregnancies, or deliveries. In addition to confirming some, but not all, of the classic risk factors for CP, this study observed relatively large increases in the CP rate in association with maternal mental retardation, seizure disorders, hyperthyroidism, or with the administration of thyroid hormone and estrogen in pregnancy. Some risk factors were predictive of CP only insofar as they were associated with low birth weight or low Apgar scores. Among factors not significantly related to CP rate were maternal age, parity, socioeconomic status, smoking history, maternal diabetes, first trimester vaginal bleeding, kidney or bladder infection, moderate hypertension, long cord, use of anesthetic agents, or use of oxytoxics for initiation or augmentation of labor. Duration of labor, whether precipitate or prolonged, was not a risk factor for CP.
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PMID:Antecedents of cerebral palsy. I. Univariate analysis of risks. 403 90

Resistance to the action of thyroid hormone can involve both peripheral tissues and the pituitary (global resistance), the pituitary only or peripheral tissues alone. Global resistance is of variable severity and has been observed in more than 60 individuals, the majority occurring in 17 families. Affected subjects are commonly eumetabolic and have goiters, elevated plasma levels of total and free thyroxine and triiodothyronine, normal thyroid hormone metabolism, and normal serum TSH levels (albeit high for the corresponding levels of thyroid hormone). A variable degree of delayed bone maturation, mental retardation, learning disabilities, and hearing defects have been reported; and a variety of treatment regimens, most of which are aimed at reducing the level of plasma hormones and/or goiter, have been attempted before the correct diagnosis has been reached. The clinical disorder is equally common in males and females and appears to be due to one or more autosomal gene mutations. The causes for the hormone resistance may be heterogeneous, either influencing the receptor for thyroid hormones or some unidentified steps in hormone action. At present, the diagnosis is one of exclusion; no effective therapy is available, and all measures designed to lower serum thyroid hormone levels should be avoided.
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PMID:Syndromes of thyroid hormone resistance. 628 48

The management of cervicofacial teratomas in neonates is often complicated and may result in significant morbidity and death. A Childrens Cancer Group (CCG) retrospective study was conducted to evaluate a multiinstitutional experience with the treatment of these extremely rare neoplasms. Twenty neonates with cervicofacial teratomas, presenting from 1971 to 1994, were identified from nine CCG institutions. Fourteen neonates had cervical teratomas, and six had orofacial teratomas. There were 12 males and eight females. A diagnostic prenatal ultrasound examination was performed in six cases. Life-threatening airway obstruction occurred in seven infants (35%) in the early postnatal period. Two neonates died in the delivery room without ever having their airway secured. Two other infants with a prenatal diagnosis survived only because tracheostomies were performed by pediatric surgeons who were in the delivery room. Three other patients were orally intubated, one after sustaining hypoxic cardiac arrest. Eighteen infants had their primary tumor excised. Three patients required tracheostomy. After resection, two patients had evidence of unilateral recurrent laryngeal nerve injury, and two required prolonged thyroid hormone replacement. Histological examination showed eight mature and seven immature teratomas. Four infants (20%) clearly had malignant lesions. Pulmonary metastases occurred in two patients and contributed to one late death at 6 months of age. The overall survival rate was 85%, and the mean follow-up period was 5 years (range, 2 months to 16 years). Twelve of 17 surviving patients (70%) have had an excellent functional and cosmetic outcome. Four children have varying degrees of developmental delay and mental retardation. Hypoxia at birth was believed to have contributed to these problems in two cases.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Diagnosis, management, and outcome of cervicofacial teratomas in neonates: a Childrens Cancer Group study. 753 9


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