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

After dealing with the biochemistry of tryptophan metabolism the most important results obtained in humans are presented. Special emphasis is given to the hereditary defects of tryptophan metabolism associated with mental retardation and convulsions due to lack of pyridoxine. The author's findings demonstrate the existence of a hereditary disturbance of the tryptophan metabolism via kynurenine in a certain part of oligophrenic patients. This metabolic defect can be controlled by high doses of vitamin B6. Furthermore investigations conducted with a view to interpreting these results are discussed, especially the determination of kynureninase activity, serotonin blood levels and pyridine nucleotide synthesis.
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PMID:[Tryptophan metabolism and oligophrenia (author's transl)]. 14 46

Glutaric aciduria is a disorcer of lysine, tryptophan, and hydroxylysine metabolism characterized by intermittent metabolic acidemia, dystonia, athetosis and mental retardation. It is due to a recessively inherited deficiency of glutaryl-CoA dehydrogeanse, the enzyme(s) which catalyze the dehydrogenation of glutaryl-CoA to glutaconyl-CoA and decarboxylation of the latter to crotonyl-CoA. Abnormal quantities of glutaric, beta-hydroxyglutaric, and glutaconic acids are found in the urine of these patients. The nature of the movement disorder prompted study of the effects of the abnormally excreted metabolites on brain glutamate decarboxylase, an enzyme implicated in the pathogenesis of Huntington's chorea. Glutamate decarboxylase activity was examined in rat and rabbit brain acetone powders, stabilized with pyridoxal phosphate and glutathione. Glutarate, beta-hydroxyglutarate, and glutaconate were competitive inhibitors of this emzyme, Ki values being 1.3 X 10(-3) mol/l, 2.5 X 10(-4) mol/l, respectively. This inhibition may explain the neurological accompaniments of this syndrome.
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PMID:Inhibition of brain glutamate decarboxylase by glutarate, glutaconate, and beta-hydroxyglutarate: explanation of the symptoms in glutaric aciduria? 124 44

The hyperphenylalaninemias are caused by the defect of either phenylalanine hydroxylase (PAH) or tetrahydrobiopterin (BH4) cofactor. The former is diagnosed as phenylketonuria (PKU) or benign hyperphenylalaninemia, based on the serum phenylalanine values. The latter, so called malignant hyperphenylalaninemia, includes three enzyme defects, dihydropteridine reductase (DHPR), 6-pyruvoyl tetrahydropterin synthase (PT PS) and guanosine triphosphate cyclohydrolase (GTP-CH). Excess phenylalanine and its metabolites cause brain damage before 6 years of age. Deficiency of BH4 impairs two other hydroxylases (tyrosine and tryptophan), and severe neurological symptoms develop because of the lack of neurotransmitters. Tyrosinemia I, II, and III are different enzyme defects, fumarylacetoacetate hydrolyase (FAH), hepatic tyrosine aminotransferase (TAT), and 4-hydroxyphenylpyruvate acid oxidase, respectively. Tyrosinemia I is associated with severe involvement of the liver, kidney and central nervous system. Tyrosinemia II has mental retardation, palmar hyperkeratosis and corneal ulcers. Tyrosinemia III has mild mental retardation but no eye or skin manifestations.
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PMID:[The metabolic basis of the hyperphenylalaninemias and tyrosinemia]. 135 1

In a male infant with macrocephaly and dystonic cerebral palsy glutaric aciduria type I was detected by analysis of urine for organic acids. Glutaric aciduria type I is an inherited metabolic disorder of organic acids due to a defect of glutaryl-CoA-dehydrogenase in the intermediate metabolic step of lysine and tryptophan degradation. In the urine glutaric acid is usually accompanied by 3-hydroxy-glutaric acid in abnormal quantities. The enzyme defect in our patient was proved in cultured fibroblasts. In the cerebral computer tomography marked atrophy of bilateral frontotemporal regions could be demonstrated. The amount of urinary glutarat excretion decreased after protein but especially after lysine and tryptophan restriction in the diet. The administration of carnitine improved carnitine levels in blood and urine. Although the progression of neurological impairment could be stopped, dystonia and dyskinesis remained nearly unaltered. In spite of severe motor retardation, recognition and vocalisation were established. In the two year old patient mental retardation is relatively mild comparing with motor retardation. The administration of 100 or 200 mg Riboflavin/day was stopped, as it did not alter clinical symptoms or excretion of glutarat. Baclofen, an analogue of gamma-amino-butyric acid, was orally given (2 mg/kg/day) and improved dystonia, but did not influence organic aciduria. The neurological manifestations may be due in part to inhibition of neuronal glutamat decarboxylase by glutaric acid with decreased gamma-amino-butyric acid biosynthesis. The characteristic clinical symptoms with macrocephaly and dystonia and the very typical pattern of organic acids in urine are a challenge for rapid diagnosis and therapy.
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PMID:[Macrocephaly and dystonic cerebral palsy in a child with type I glutaric aciduria]. 194 71

Phenylketonuria (PKU) has become a paradigm of a disease that can be identified by screening in the newborn period and treated to prevent serious complications. After many years of experience treating PKU, new challenges have emerged. It has become apparent that defective activity of phenylalanine hydroxylase leads to a spectrum of clinical presentations that has led to subclassifications of PKU. Blood phenylalanine greater than 1200 mumol/L usually indicates severe deficiency of phenylalanine hydroxylase and is often called "classical PKU." Blood phenylalanine levels between 600 and 1200 mumol/L lead to "atypical PKU." Cases where blood phenylalanine remains between 120 and 480 mumol/L on a normal diet are termed "benign hyperphenylalaninemia." A deficiency of the cofactor tetrahydrobiopterin (BH4), which is required for phenylalanine hydroxylase activity, leads to hyperphenylalaninemia. This cofactor is also required for the enzymatic hydroxylation of tyrosine and tryptophan. Cofactor defects account for only 1-3% of hyperphenylalaninemia, which has been termed "malignant PKU", but they must be identified so that appropriate treatment can be established. Long-term treatment of PKU is currently advised because loss of IQ, poor school performance, and behavior problems occur when blood phenylalanine levels increase. Therefore, there is reason to continue the diet as patients become older. When blood phenylalanine levels are elevated during pregnancy a "maternal PKU syndrome" may result. Babies born to untreated mothers with PKU are at risk for being small for gestational age with microcephaly, mental retardation and congenital heart defects. A national collaborative study for the treatment of maternal PKU is underway. The characterization of the gene for phenylalanine hydroxylase has added a new exciting chapter to the study of PKU.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Phenylketonuria: screening, treatment and maternal PKU. 195 25

Harthnup disease clinical picture without aminoaciduria or other identified metabolic disturb (New entity?). The authors present a patient with clinical picture superposed to the Hartnup disease's, a rare, autosomic and recessive metabolic disturbance, characterized by typical aminoaciduria consequent to tryptophan and other neutral aminoacids defective transport by jejunal mucous membrane and renal tubules, clinically expressed by photosensitive pellagra-like dermatitis, mental retardation and intermittent cerebellar ataxia. The laboratorial results did not confirm Hartnup aminoaciduria nor other identified metabolic change that justify his clinical manifestations.
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PMID:[Clinical picture of Hartnup disease. Without urine amino acids or any other identified metabolic disorder (a new entity)]. 207 8

The transport of the eight amino acids (phenylalanine, tyrosine, tryptophan, valine, leucine, isoleucine, histidine and methionine) using the large neutral amino acid transporter of the blood-brain barrier (BBB) has been calculated using published kinetic data. The fate of the amino acids has been followed from blood to interstitial space, to cell and through metabolism which included, for tyrosine and tryptophan, the hydroxylases. The system was analysed in terms of flux control coefficients. Since the summation theorem did not hold, the system clearly behaved as a non-homogeneous system. At physiological levels of these eight amino acids, the largest contribution to the control of the flux of tyrosine is given by the hydroxylase step, followed by the diffusional component of the transport across the BBB. For tryptophan it is the hydroxylase step, followed by the carrier-mediated transport across the BBB. For the other amino acids it is the metabolism, followed by the diffusional component of the BBB transport. These parameters for tyrosine and tryptophan were determined at increased levels of blood phenylalanine, tyrosine or histidine. The flux through tryptophan hydroxylase can be affected by high blood levels of tyrosine and histidine to values also observed in hyperphenylalaninaemia. Since hypertyrosinaemia (type II) and hyperhistidinaemia are not associated with mental retardation, it is concluded that interference with transport across the BBB of tyrosine and tryptophan, as well as the flux through tryptophan hydroxylase leading to the synthesis of 5-hydroxytryptamine, do not contribute to the cause of permanent brain dysfunction in hyperphenylalaninaemia. It can be calculated that addition of tyrosine to the diet to raise the blood tyrosine level in phenylketonuria patients may have a beneficial effect for the synthesis of neurotransmitters derived from tyrosine.
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PMID:The control of 5-hydroxytryptamine and dopamine synthesis in the brain: a theoretical approach. 210 47

Calculations on the rate of entry of the neutral amino acids into the brain via the blood-brain barrier show that a considerable decrease in this rate, particularly for tryptophan and tyrosine, takes place in histidinaemia and tyrosinaemia, type II. These conditions are, however, not associated with mental retardation. It is therefore concluded that effects at the blood-brain barrier alone do not provide an adequate explanation for the aetiology of permanent brain dysfunction in hyperphenylalaninaemia.
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PMID:The role of the blood-brain barrier in the aetiology of permanent brain dysfunction in hyperphenylalaninaemia. 250 82

Forty patients with the Prader-Willi syndrome have been examined. The typical features begin in gestational life with poor fetal vigor and difficulties with birth and post-partum feeding. The classical features of hypotonia, small hands and feet, cryptorchidism can be identified at this time. The delayed milestones, mental retardation and obesity become more prominent later. The average height of the patients in this series who were admitted to the Clinical Study Center was 149 cm and their weight was 114 kg. The weight and height curves show that Prader-Willi individuals are consistently shorter and heavier than normal children. Tests of endocrine function showed normal glucose tolerance. Insulin secretion was increased in relation to obesity. The rise in growth hormone (hGH) after injecting insulin to induce hypoglycemia and after the infusion of arginine was comparable to other obese individuals but was low in comparison to normal weight subjects. There was no rise in growth hormone with L-dopa administration, but there was a rise in hGH with the administration of 2-deoxy-D-glucose. The hypoglycemia produced by insulin was greater in the Prader-Willi patient than in obese controls. The rise in TRH (thyrotropin-releasing hormone) following the injection of TSH (thyrotropin stimulating hormone) was greater in the Prader-Willi patients than in the obese controls. Hypogonadism was routine in this series, and the response to LRH (luteinizing releasing hormone) was absent in all tested subjects. Treatment with clomiphene for 30 to 90 days significantly increased the response to LRH in three adult individuals who had not been treated with gonadal steroids previously and who were hypogonadal. Rectal temperature declined in three of the five Prader-Willi patients during exposure to an ambient temperature of 4 degrees C, but none of the three obese controls showed a decline. Food intake averaged 5167 kcal/d when six patients were given trays containing more food than they could eat. Food intake was not reduced when tryptophan was added to the diet. Salivary secretion was reduced in the Prader-Willi patients. A number of pulmonary function tests were significantly reduced in the study patients compared to obese or normal weight controls. The anatomic findings in four autopsied patients with the Prader-Willi syndrome showed no significant differences from those of obese subjects without this syndrome. The chromosomal pattern showed a deletion or translocation at chromosome 15 in 3 of 12 patients in whom this test was performed. These findings in 40 patients with the Prader-Willi syndrome have been compared with the information contained in 159 reports published in the medical literature.
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PMID:The Prader-Willi syndrome: a study of 40 patients and a review of the literature. 633 43

Recent work has shown that in phenylketonuria, PKU, in which phenylalanine accumulates in the blood, the damage to the brain, which so often leads to mental retardation, is not solely due to the large quantities of phenylalanine that enter the brain. The raised levels of phenylalanine in the blood lead to a partial exclusion of various other amino acids from the brain and this exclusion in itself damages the brain. Based on this evidence, that in PKU some amino acids are partially excluded from entering the brain, proposals are made for a modified dietary treatment of this disease. In this diet the phenylalainine is not so greatly reduced as in the standard diet for PKU, whilst supplements of other amino acids are added. The rationale for this new diet is that the partial exclusion from the brain of various amino acids (methionine, tryptophan, histidine, tryosine, isoleucine, leucine and valine) by the raised level of phenylalanine in the blood, acting as a competitive inhibitor, can be largely prevented by increasing the blood levels of these excluded amino acids. Raising slightly their blood levels overcomes the excluding effect of moderately raised levels of phenylalanine in the blood. The advantages of the new diet are that not only is it more palatable than a diet very low in phenylalanine, so that it is more likely to continue to prove acceptable to older children and adolescents, as well as to PKU women who expect to become pregnant, but also that its margin of safety is greater if the patient does take unsuitable food.
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PMID:A new approach to the treatment of phenylketonuria. 719 42


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