Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To begin to study the importance of dopamine for executive function abilities dependent on prefrontal cortex during early childhood, the present investigation studied children in whom we predicted reduced dopamine in prefrontal cortex but otherwise normal brains. These are children treated early and continuously for the metabolic disorder phenylketonuria (PKU). Untreated PKU is the most common biochemical cause of mental retardation. The root problem is an inability to convert one amino acid, phenylalanine (Phe), into another, tyrosine (Tyr), the precursor of dopamine. Phe levels in the bloodstream soar; Tyr levels fall. Treatment with a diet low in Phe reduces the Phe:Tyr imbalance but cannot eliminate it. We hypothesized that the resultant modest elevation in the ratio of Phe to Tyr in the blood, which results in slightly less Tyr reaching the brain, uniquely affects the cognitive functions dependent on prefrontal cortex because of the special sensitivity of prefrontally projecting dopamine neurons to small decreases in Tyr. In a 4-year longitudinal study, we found that PKU children whose plasma Phe levels were three to five times normal (6-10 mg/dl) performed worse than other PKU children with lower Phe levels, matched controls, their own siblings, and children from the general population on tasks that required the working memory and inhibitory control abilities dependent on dorsolateral prefrontal cortex. The impairment was as evident in our oldest age range (3 1/2-7 years) as it was in the youngest (6-12 months). The higher a child's Phe level, the worse that child's performance. Girls were more adversely affected than boys. The deficit appears to be selective, affecting principally one neural system, since even PKU children with Phe levels three to five times normal performed well on the 13 control tasks. Clinical implications for the treatment of PKU and other neurodevelopmental disorders are discussed.
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PMID:Prefrontal cortex cognitive deficits in children treated early and continuously for PKU. 942 21

Phenylalanine hydroxylase (PheOH) catalyzes the conversion of L-phenylalanine to L-tyrosine, the rate-limiting step in the oxidative degradation of phenylalanine. Mutations in the human PheOH gene cause phenylketonuria, a common autosomal recessive metabolic disorder that in untreated patients often results in varying degrees of mental retardation. We have determined the crystal structure of human PheOH (residues 118-452). The enzyme crystallizes as a tetramer with each monomer consisting of a catalytic and a tetramerization domain. The tetramerization domain is characterized by the presence of a domain swapping arm that interacts with the other monomers forming an antiparallel coiled-coil. The structure is the first report of a tetrameric PheOH and displays an overall architecture similar to that of the functionally related tyrosine hydroxylase. In contrast to the tyrosine hydroxylase tetramer structure, a very pronounced asymmetry is observed in the phenylalanine hydroxylase, caused by the occurrence of two alternate conformations in the hinge region that leads to the coiled-coil helix. Examination of the mutations causing PKU shows that some of the most frequent mutations are located at the interface of the catalytic and tetramerization domains. Their effects on the structural and cellular stability of the enzyme are discussed.
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PMID:Structure of tetrameric human phenylalanine hydroxylase and its implications for phenylketonuria. 964 59

A case of severe photosensitivity in a girl with the Smith-Lemli-Opitz syndrome is reported. Children with this recessively inherited metabolic disorder of cholesterol metabolism present with a variety of congenital abnormalities of the nervous system and internal organs in association with varying degrees of mental retardation. Photosensitivity is a feature which has previously only briefly been mentioned in the literature in association with this syndrome. However, more recently, it has become apparent that photosensitivity is not uncommon among children with the Smith-Lemli-Opitz syndrome, although the nature of the photosensitivity in these patients has remained undefined. Our patient has suffered from sunlight intolerance since early infancy, with redness and pruritus of sun-exposed skin developing within minutes of sun exposure. Monochromator ultraviolet (UV) radiation and visible light testing revealed an immediate and persistent reaction to low-dose UVA at 350 nm, and an abnormal erythemal response to visible light at 400 nm.
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PMID:Photosensitivity associated with the Smith-Lemli-Opitz syndrome. 966 40

Late infantile GM1 gangliosidosis is an extremely rare metabolic disorder with clinical features of seizure and progressive motor and mental retardation without facial dysmorphism or visceral organomegaly. We report the CT and MR imaging findings in one infant, which included abnormalities of the cerebral cortex, white matter, and deep nuclei.
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PMID:Neuroimaging findings in late infantile GM1 gangliosidosis. 980 82

We describe a new creatine metabolism disorder in 2 young sisters who suffered from mental retardation and severe language delay. Blood examination, investigation of the most common neurometabolic disorders, and brain magnetic resonance imaging were normal. Diagnosis was established only by means of in vivo proton magnetic resonance spectroscopy, which disclosed generalized depletion of creatine in the brain. Creatine monohydrate oral administration led to almost complete brain creatine level restoration along with improvement of the patients' disabilities.
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PMID:Reversible brain creatine deficiency in two sisters with normal blood creatine level. 1076 63

Homocysteine is a sulphur-containing amino acid that is derived primarily from protein of animal origin. Classical homocystinuria is an inherited metabolic disorder that arises from defects in either the re-methylation or trans-sulphuration pathways of homocysteine metabolism and leads to skeletal abnormalities, mental retardation and a high risk of vascular disease. In contrast, moderate hyperhomocysteinaemia is associated with an increased risk of both arterial and venous thrombotic disease but no other abnormalities. This increased risk appears to be independent of other conventional risk factors. Many cases of hyperhomocysteineaemia have been attributed to defects in the enzyme cystathionine-beta-synthase (CBS) but this accounts for less than 1.5% of cases. A thermolabile variant of the enzyme methylenetetrahydrofolate reductase (MTHFR) arises from a C --> T transition at nucleotide 677 in the MTHFR gene resulting in an alanine-to-valine substitution. While the mutation does not appear to be associated with an increased risk of vascular disease, it results in excessively high homocysteine levels in response to a low or low-normal serum folate. Supplementation of the diet with folate, B6 and B12 can reduce homocysteine levels and this is the mainstay of treatment. Supplementation of grain with folate is undertaken in the USA to reduce the risk of neural tube defects in pregnant women. However, by reducing plasma homocysteine levels, it is estimated that this will save up to 50,000 lives per annum.
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PMID:Hyperhomocysteinaemia. 1085 81

Smith-Lemli-Opitz syndrome (SLOS, RSH/SLO syndrome, MIM 270400) is an autosomal recessive multiple malformation/mental retardation syndrome initially described by Smith et al. [1964] that is due to a defect in cholesterol biosynthesis. The behavioral phenotype of Smith-Lemli-Opitz syndrome demonstrates cognitive abilities from borderline intellectual functioning to profound mental retardation, sensory hyperreactivity, irritability, language impairment, sleep cycle disturbance, self-injurious behavior, and autism spectrum behaviors. In a recent study of 28 subjects, 14 subjects (50%) with SLOS also exhibited the behavior of throwing themselves backward in a characteristic upper body movement ("opisthokinesis") and 2 adolescents had a stretching motion of the upper body accompanied by hand flicking [Tierney et al., 1999]. In that same study, 6 of 13 subjects (46%) met the Autism Diagnostic Interview-Revised (ADI-R) algorithm criteria (Lord et al. [1993] Infant Mental Health 14:234-252; Lord et al. [1994] J Autism Dev Disord 24:659-685) and the Diagnostic and Statistical Manual (APA [1994] DSM-IV) diagnostic criteria for autistic disorder. Smith-Lemli-Opitz syndrome is a metabolic disorder that is associated with autism. MRDD Research Reviews 2000;6:131-134.
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PMID:Behavioral phenotype of RSH/Smith-Lemli-Opitz syndrome. 1089 6

The Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive metabolic disorder characterized by variable congenital malformations, facial dysmorphism, and mental retardation. Mutations in the DHCR7 gene have been identified in SLOS patients. This gene encodes for the enzyme Delta7-sterol reductase which catalyses the last step of cholesterol biosynthesis. Among the 73 different mutations observed so far, including 10 novel mutations reported in this review, the majority are missense mutations (65) which cluster in three domains of the protein: in the transmembrane domain (TM mutations), in the fourth cytoplasmic loop (4L mutations), and at the C-terminus (CT mutations). Two nonsense mutations, one splice site mutation, two single nucleotide insertions, and three deletions which likely all represent null mutations were also described. Expression studies have demonstrated a decreased protein stability for all analyzed missense mutations. By comparing clinical severity scores, biochemical data, and mutations in SLOS patients a genotype-phenotype correlation has been established. The null and 4L mutations are associated with a severe clinical phenotype, and TM and CT mutations are associated with a mild clinical phenotype. DHCR7 mutational spectra in SLOS patients of British, German, Italian, and Polish origin demonstrate significant geographic frequency differences of common DHCR7 mutations.
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PMID:Mutations in the human DHCR7 gene. 1124 39

In 471 adult mentally retarded adult patients (mean age 46 years; 92.6% males) living in an institution for the mentally retarded, a clinical examination, cytogenetic and molecular studies were done. 306 patients were screened for metabolic disorders. In 7 additional patients a metabolic disorder (phenylketonuria (n = 5), mucopolysaccharidosis type III (Sanfilippo syndrome, type A) (n = 1) and mucopolysaccharidosis type VII (Sly syndrome) (n = 1)) was diagnosed in the past. The abnormal metabolic findings in this group of 313 patients were classified in three categories and the clinical findings are reported: 1. metabolic disorders as the cause of mental retardation (MR), 2. metabolic disorders not explaining the MR, and 3. metabolic abnormalities of unknown significance. The first two groups included 16 patients, i.e. 26.2% of the group of monogenic disorders and 3.4% of the total population: phenylketonuria (PKU) (n = 5), S-sulfocysteinuria (n = 3), mucopolysaccharidosis type III (Sanfilippo syndrome, type A) (n = 1) and Gm1-gangliosidosis type 3 (n = 1) (first group), and mucopolysaccharidosis type VII (Sly syndrome) (n = 1), Niemann-Pick syndrome, type B (n = 1), cystinuria (n = 1) and hyperprolinemia type 1 (n = 3) (second group). The third group included patients with citrullinemia (n = 2), methionine sulphoxide reductase deficiency (n = 1), ornithinemia (n = 1), glycinuria (n = 20), neuraminaciduria (n = 8), uraciluria (n = 6) and diabetes mellitus (n = 2). Screening for Congenital Disorders of Glycosylation (CDG) in 144 patients and for Smith-Lemli-Opitz syndrome (SLO) in a selected group of 6 patients was normal. Of the total group of 306 patients screened for inborn errors of metabolism, only 5 (1.6%) were found with a true metabolic disorder. These 5 patients presented clinical symptoms, neurodegenerative or behavioural problems, indicating further metabolic screening. The present study illustrates that a selected group of patients with mental retardation of unknown origin are candidates for metabolic screening, especially if aberrant behaviour, neurodegenerative problems or dysmorphic features are present.
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PMID:Metabolic studies in older mentally retarded patients: significance of metabolic testing and correlation with the clinical phenotype. 1133 72

Maple syrup urine disease (MSUD) is a metabolic disorder associated with often-fatal ketoacidosis, neurological derangement, and mental retardation. In this study, we identify and characterize two novel type IB MSUD mutations in Israeli patients, which affect the E1beta subunit in the decarboxylase (E1) component of the branched-chain alpha-ketoacid dehydrogenase complex. The recombinant mutant E1 carrying the prevalent S289L-beta (TCG --> TTG) mutation in the Druze kindred exists as a stable inactive alphabeta heterodimer. Based on the human E1 structure, the S289L-beta mutation disrupts the interactions between Ser-289-beta and Glu-290-beta', and between Arg-309-beta and Glu-290-beta', which are essential for native alpha(2)beta(2) heterotetrameric assembly. The R133P-beta (CGG --> CCG) mutation, on the other hand, is inefficiently expressed in Escherichia coli as heterotetramers in a temperature-dependent manner. The R133P-beta mutant E1 exhibits significant residual activity but is markedly less stable than the wild-type, as measured by thermal inactivation and free energy change of denaturation. The R133P-beta substitution abrogates the coordination of Arg-133-beta to Ala-95-beta, Glu-96-beta, and Ile-97-beta, which is important for strand-strand interactions and K(+) ion binding in the beta subunit. These findings provide new insights into folding and assembly of human E1 and will facilitate DNA-based diagnosis for MSUD in the Israeli population.
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PMID:Biochemical basis of type IB (E1beta ) mutations in maple syrup urine disease. A prevalent allele in patients from the Druze kindred in Israel. 1144 70


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