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)

Autism is a neuro-developmental syndrome that affects 0.1-0.5% of the population. It has been proposed that alterations in neuronal circuitry and/or neuronal signaling are responsible for the behavioral and cognitive aberrations in autism patients. However, the cellular basis of such alterations is unknown. Recently, point mutations in a family of neuronal cell adhesion molecules called neuroligins have been linked to autism-spectrum disorders and mental retardation. We investigated the consequences of these disease-associated mutations on neuroligin function. We demonstrate that the point mutation at arginine 451 and a nonsense mutation at aspartate 396 of neuroligin-3 and -4 (NL3 and NL4), respectively, result in intracellular retention of the mutant proteins. Over-expression of wild-type NL3 and NL4 proteins in hippocampal neurons stimulates the formation of presynaptic terminals, whereas the disease-associated mutations result in a loss of this synaptic function. Our findings suggest that the previously identified mutations in neuroligin genes are likely to be relevant for the neuro-developmental defects in autism-spectrum disorders and mental retardation since they impair the function of a synaptic cell adhesion molecule.
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PMID:Disorder-associated mutations lead to functional inactivation of neuroligins. 1515 Jan 61

Guanidinoacetate methyltransferase deficiency (GAMT-deficiency) is an inherited neurometabolic disorder clinically characterized by epilepsy and mental retardation and biochemically by accumulation of guanidinoacetate (GAA) and depletion of creatine. Although the neurological symptoms are predominant, the pathogenesis of the brain dysfunction in this disorder is not yet established. In the present study we investigated the in vitro effect of GAA on Na+, K+-ATPase and Mg2+-ATPase activities in synaptic plasma membrane from hippocampus of young rats. Results showed that GAA significantly inhibited Na+, K+-ATPase activity without affecting Mg2+-ATPase activity. We also evaluated the effect of glutathione (GSH), trolox, Nomega-nitro-L-arginine methyl ester (L-NAME) and taurine (Tau) on the inhibition elicited by GAA on Na+, K+-ATPase activity. GSH, trolox, L-NAME and Tau per se did not alter Na+, K+-ATPase activity. However, L-NAME and taurine prevented the inhibitory effect of GAA on this enzyme activity. Our findings suggest that the inhibition of Na+, K+-ATPase activity caused by GAA is possibly mediated by nitric oxide (NO) formation and/or synaptic membrane alteration. The present data may contribute to the understanding of the neurological dysfunction characteristic of GAMT-deficient patients.
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PMID:Evaluation of the mechanism underlying the inhibitory effect of guanidinoacetate on brain Na+, K+-ATPase activity. 1524 54

Nitric oxide (NO) is a short-life key bioregulatory active molecule in the cardiovascular, immune and nervous systems. NO is synthesized by converting L-arginine to L-citrulline by enzymes called NO synthase (NOS). The growing body of evidence strongly supports the theory that this molecule appears to be one of the key targets for the disruption of normal brain homeostasis, which causes the development of brain lesions and pathology such as in Alzheimer's disease (AD) or other related dementia. The vascular content of NO activity appears especially to be a main contributor to this pathology before the over-expression of other NOS isoforms activity in a different brain cellular compartment. We speculate that pharmacological intervention using NO donors and/or NO suppressors will be able to delay or minimize the development of brain pathology and further progression of mental retardation.
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PMID:Is nitric oxide a key target in the pathogenesis of brain lesions during the development of Alzheimer's disease? 1526 72

Allgrove syndrome is a rare autosomal recessive disorder characterized by the triad of adrenal insufficiency, achalasia and alacrima. This syndrome, also known as triple A syndrome, is now known to be caused by mutations in the AAAS gene. In the present study, we report two new patients of Allgrove syndrome with mutations in the AAAS gene. Patient 1 was a 22-year-old Japanese woman, born to consanguineous parents. She was confirmed to have adrenal insufficiency at the age of 3 years and 6 months. She developed alacrima and bilateral optic nerve atrophy at the age of 8 years. She had been noticed to have dysphagia. Based on these findings, she was diagnosed as having Allgrove syndrome. Mutation analysis revealed a novel homozygous point mutation in exon 7 of her AAAS gene, changing codon 194 encoding Arg (CGA) to a stop codon (TGA) (R194X). Patient 2 was a 7-year-old Japanese boy, born to consanguineous parents. At the age of 1 year, he was noticed to be unable to produce tears. He was confirmed to have adrenal insufficiency, mental retardation and spastic diplegia at the age of 5 years and 4 months. He was tentatively diagnosed as having Allgrove syndrome, although he has never complained of dysphasia. Mutation analysis revealed a homozygous point mutation in exon 4 of his AAAS gene, changing codon 119 encoding Arg (CGA) to a stop codon (TGA) (R119X). Both of the R119X and R194X mutations are predicted to result in truncated and non-functioning ALADIN proteins, and thus the diagnosis of Allgrove syndrome was confirmed by the mutation analyses. These findings indicate that there exist significant clinical variability and mutational heterogeneities in Japanese patients with this syndrome.
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PMID:Two cases of Allgrove syndrome with mutations in the AAAS gene. 1551 81

Creatine deficiency syndromes are a newly described group of inborn errors of creatine synthesis (arginine:glycine amidinotransferase (AGAT) deficiency and guanidinoacetate methyltransferase (GAMT) deficiency) and of creatine transport (creatine transporter (CRTR) deficiency). The common clinical feature of creatine deficiency syndromes is mental retardation and epilepsy suggesting main involvement of cerebral gray matter. The typical biochemical abnormality of creatine deficiency syndromes is cerebral creatine deficiency, which is demonstrated by in vivo proton magnetic resonance spectroscopy. Measurement of guanidinoacetate in body fluids may discriminate between the GAMT (high concentration), AGAT (low concentration) and CRTR (normal concentration) deficiencies. Further biochemical characteristics include changes in creatine and creatinine concentrations in body fluids. GAMT and AGAT deficiency are treatable by oral creatine supplementation, while patients with CRTR deficiency do not respond to this type of treatment. The creatine deficiency syndromes are underdiagnosed, so their possibility should be considered in all children affected by unexplained mental retardation, seizures and speech delay.
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PMID:Biochemical and clinical characteristics of creatine deficiency syndromes. 1562 59

Autosomal recessive primary microcephaly (MCPH) is a rare neurodevelopmental disorder characterized by mental retardation and congenital microcephaly with a head circumference at least 4 SD below age and sex means, in the absence of other significant malformations or neurological deficits. Truncating alterations in the MCPH1 gene have previously been shown to exhibit a distinct cellular phenotype, with a high proportion of prophase-like cells (>10%) due to premature chromosome condensation in early G2- and delayed decondensation in early G1-phase of the cell cycle. We report here the first patient with a homozygous substitution of a highly conserved threonine residue by an arginine (c.80C>G, Thr27Arg) localized in the N-terminal BRCT domain of MCPH1. The cellular and clinical phenotype of this patient is much less pronounced than that of previously described patients with truncating alterations in the MCPH1 gene. Firstly, the fraction of prophase-like cells accounts for just 3-4% of the cell population. Secondly, clinically, he has only a very mild mental retardation with predominantly delayed motor skills but normal verbal IQ attainment. Additionally, head circumference was less severely affected, being -2.4 SD at birth and -3 SD at the age of six years. This justifies reconsideration and widening of the clinical phenotype definition of MCPH1.
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PMID:The first missense alteration in the MCPH1 gene causes autosomal recessive microcephaly with an extremely mild cellular and clinical phenotype. 1621 57

Fragile X syndrome is the most common form of inherited mental retardation and is caused by the absence of expression of the FMR1 gene. The protein encoded by this gene, Fmrp, is an RNA-binding protein that binds a subset of mRNAs and regulates their translation, leading to normal cognitive function. Although the association with RNAs is well established, it is still unknown how Fmrp finds and assembles with its RNA cargoes and how these activities are regulated. We show here that Fmrp is post-translationally methylated, primarily on its arginine-glycine-glycine box. We identify the four arginines that are methylated and show that cellular Fmrp is monomethylated and asymmetrically dimethylated. We also show that the autosomal paralog Fxr1 and the Drosophila ortholog dFmr1 are methylated post-translationally. Recombinant protein arginine methyl transferase 1 (PRMT1) methylates Fmrp on the same arginines in vitro as in cells. In vitro methylation of Fmrp results in reduced binding to the minimal RNA sequence sc1, which encodes a stem loop G-quartet structure. Our data identify an additional mechanism, arginine methylation, for modifying Fmrp function and suggest that methylation occurs to limit or modulate RNA binding by Fmrp.
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PMID:Identification and characterization of the methyl arginines in the fragile X mental retardation protein Fmrp. 1631 29

X-linked mental retardation (XLMR) is an extremely heterogeneous condition that account for 15-25% of all mentally retarded patients. The number of genes newly reported in relation with this condition has been rapidly increased in the past years. One of the latest is called Jumonji AT-rich interactive domain 1C (JARID1C). This gene encodes for a member of a recently discovered protein family that harbours DNA-binding motifs, suggesting a possible role in transcriptional regulation and in the modification of chromatin structure. In this work we describe the results obtained by screening JARID1C gene in 24 mentally retarded males with history of at least two affected males. Remarkably, we have found a novel missense mutation in exon 10 of the gene that results in a Serine-to-arginine change at amino-acid 451 (S451R). This nucleotide change appears to be restricted to mentally retarded patients, since it has not been detected in control samples. Familial analysis has confirmed the segregation of this mutation with mental retardation. Furthermore, sequence alignment analysis with the different members of the human JARID1 family and with homologous proteins of mouse and fruit fly has revealed that the affected amino acid is conserved. Our data highlights the importance of reporting mutations in this gene since it might support the recent findings that implicates JARID1C with XLMR.
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PMID:A novel mutation in JARID1C gene associated with mental retardation. 1653 22

Arginine:glycine amidinotransferase deficiency is a treatable inborn error of creatine synthesis, characterized by mental retardation, language impairment, and behavioral disorders. We describe a patient in whom arginine:glycine amidinotransferase was diagnosed at birth and treated at 4 months with creatine supplementation. In contrast with his 2 older sisters, he had normal psychomotor development at 18 months.
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PMID:Arginine:glycine amidinotransferase (AGAT) deficiency in a newborn: early treatment can prevent phenotypic expression of the disease. 1676 97

Genetic mutations of the X-linked gene MECP2, encoding methyl-CpG-binding protein 2, cause Rett syndrome (RTT) and other neurological disorders. It is increasingly recognized that MECP2 is a multifunctional protein, with at least four different functional domains: (1) a methyl-CpG-binding domain; (2) an arginine-glycine repeat RNA-binding domain; (3) a transcriptional repression domain; and (4) an RNA splicing factor binding region (WW group II binding domain). There is evidence that MECP2 is important for large-scale reorganization of pericentromeric heterochromatin during differentiation. Studies in MECP2-deficient mouse brain have identified a diverse set of genes with altered levels of mRNA expression or splicing. It is still unclear how altered MECP2 function ultimately results in neuronal disease after a period of grossly normal development. However, mounting evidence suggests that neuronal health and development depend on precise regulation of MECP2 expression. In genetically engineered mice, both increased and decreased levels of MECP2 result in a neurological phenotype. Furthermore, it was recently discovered that MECP2 gene duplications underlie a small number of atypical Rett cases and mental retardation syndromes. The finding that MECP2 levels are tightly regulated in neurons has important implications for the design of gene replacement or reactivation strategies for treatment of RTT, because affected individuals typically are somatic mosaics with one set of cells expressing a mutated MECP2 from the affected X, and another set expressing normal MECP2 from the unaffected X. Further studies are necessary to elucidate the molecular pathology of both loss-of-function and gain-of-function mutations in MECP2.
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PMID:The molecular pathology of Rett syndrome: synopsis and update. 1702 71


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