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Biomedical subjects

M J Bennett

Publications and source records attributed to M J Bennett.

At least 73 records · Page 4Linked to original sources
PubMed1999

Tissue expression and subcellular localization of CLN3, the Batten disease protein.

Juvenile neuronal ceroid lipofuscinosis (Batten disease) is a progressive neurologic disorder which results from mutations in the CLN3 gene, which normally produces a 48-kDa polypeptide of unknown function. To help characterize the CLN3 protein, we have studied its tissue distribution and subcellular localization in human tissues using three epitope-specific polyclonal antibodies to human CLN3 by immunoblot, immunocytochemical, and immunoelectron microscopic analysis. The most abundant CLN3 protein expression was in the gray matter of the brain, where it was localized to astrocytes, capillary endothelium, and neurons. CLN3 was also evident in peripheral nerve, in pancreatic islet cells, and within the seminiferous tubules in the testis. Staining was generally diffuse within the cytoplasm with some nuclear reactivity. Subcellular localization identified the CLN3 protein within the nucleus and along cell membranes. These results were contrasted with the cellular distribution of palmitoyl-protein thioesterase (PPT), the enzyme whose deficiency is responsible for infantile neuronal ceroid lipofuscinosis (CLN1). PPT was most abundant in brain and visceral macrophages where it displayed a coarse granular staining pattern typical of lysosomal distribution. Immunoelectron microscopy confirmed that PPT immunoreactivity was limited to lysosomes.

Brain↗
PubMed1999

N-acetylaspartylglutamate in Canavan disease: an adverse effector?

UNLABELLED: We measured N-acetylaspartate and its precursor/product N-acetylaspartylglutamate (NAAG) in urine of patients with Canavan disease using capillary zone electrophoresis. Abnormal levels of NAAG were found in 32 of 43 patients examined. Elevated NAAG was also present in the CSF of one patient. Given that NAAG may interfere with N-methyl-D-aspartate receptor function, the occurrence of high levels of NAAG in patients' urine conceivably represents a participating factor in the pathogenesis of Canavan disease. CONCLUSION: The biochemical role of N-acetylaspartylglutamate and its relationship to glutamatergic function may be relevant to the pathogenesis of Canavan disease.

Adolescent↗
PubMed1999

Inherited long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency and a fetal-maternal interaction cause maternal liver disease and other pregnancy complications.

Fetal-maternal interactions are critical determinants of maternal health during pregnancy and perinatal outcome. This review explores the causative relationship of a fetal disorder of mitochondrial fatty acid oxidation, long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, and the serious maternal liver diseases of pregnancy-preeclampsia, the HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet counts), and acute fatty liver of pregnancy. Features of the metabolic adaptation necessitated during the fetal-neonatal transition; common phenotypes of pediatric fatty acid oxidation disorders, including neonatal hypoketotic, hypoglycemia and hepatic crisis; and clinical abnormalities of HELLP and acute fatty liver of pregnancy are presented. Evidence that a common mutation in the alpha-subunit (LCHAD) of trifunctional protein, E474Q, is always one of the mutant alleles in fetal isolated LCHAD deficiency associated with these disorders of pregnancy that cause high maternal, fetal, and newborn morbidity and mortality is reviewed. Recommendations for molecular testing for LCHAD deficiency in families with life-threatening maternal liver disease are given.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1999

Hypoketotic hypoglycemic coma in a 21-month-old child.

We present the case of a 21-month-old child with hypoketotic hypoglycemic coma. The differential diagnosis initially included metabolic causes versus a toxicologic emergency (unripe ackee fruit poisoning). Using information obtained from the emergency department, the diagnosis was confirmed as the late-onset form of glutaric acidemia type II. This case illustrates the importance of emergency physicians in the diagnosis and management of children with inborn errors of metabolism.

Acidosis↗
PubMed1999

The neuronal ceroid-lipofuscinoses (Batten disease): a new class of lysosomal storage diseases.

The neuronal ceroid-lipofuscinoses (Batten disease) are a group of severe neurodegenerative disorders characterized clinically by visual loss, seizures and psychomotor degeneration, and pathologically by loss of neurons and lysosomal accumulation of autofluorescent storage material resembling ageing pigment. To date, eight genetic loci have been identified (CLN1-8). Four CLN genes have been isolated (CLN1, CLN2, CLN3 and CLN5) and their gene products have been characterized. CLN1 is a lysosomal palmitoyl-protein thioesterase (PPT) and CLN2 is a lysosomal pepstatin-insensitive peptidase. CLN3 and CLN5 are proteins with multiple membrane-spanning regions and have no homologies to other proteins that would suggest their function. The CLN3 protein is associated with lysosomal membranes and the intracellular location of the CLN5 protein is unknown. Therefore, there is ample evidence that the neuronal ceroid-lipofuscinoses represent a new class of lysosomal storage disorders.

Animals↗
PubMed1999

PTEN mutation spectrum and genotype-phenotype correlations in Bannayan-Riley-Ruvalcaba syndrome suggest a single entity with Cowden syndrome.

Germline mutations in the tumour suppressor gene PTEN have been implicated in two hamartoma syndromes that exhibit some clinical overlap, Cowden syndrome (CS) and Bannayan-Riley-Ruvalcaba syndrome (BRR). PTEN maps to 10q23 and encodes a dual specificity phosphatase, a substrate of which is phosphatidylinositol 3,4,5-triphosphate, a phospholipid in the phosphatidylinositol 3-kinase pathway. CS is characterized by multiple hamartomas and an increased risk of benign and malignant disease of the breast, thyroid and central nervous system, whilst the presence of cancer has not been formally documented in BRR. The partial clinical overlap in these two syndromes is exemplified by the hallmark features of BRR: macrocephaly and multiple lipomas, the latter of which occur in a minority of individuals with CS. Additional features observed in BRR, which may also occur in a minority of CS patients, include Hashimoto's thyroiditis, vascular malformations and mental retardation. Pigmented macules of the glans penis, delayed motor development and neonatal or infant onset are noted only in BRR. In this study, constitutive DNA samples from 43 BRR individuals comprising 16 sporadic and 27 familial cases, 11 of which were families with both CS and BRR, were screened for PTEN mutations. Mutations were identified in 26 of 43 (60%) BRR cases. Genotype-phenotype analyses within the BRR group suggested a number of correlations, including the association of PTEN mutation and cancer or breast fibroadenoma in any given CS, BRR or BRR/CS overlap family ( P = 0.014), and, in particular, truncating mutations were associated with the presence of cancer and breast fibroadenoma in a given family ( P = 0.024). Additionally, the presence of lipomas was correlated with the presence of PTEN mutation in BRR patients ( P = 0.028). In contrast to a prior report, no significant difference in mutation status was found in familial versus sporadic cases of BRR ( P = 0.113). Comparisons between BRR and a previously studied group of 37 CS families suggested an increased likelihood of identifying a germline PTEN mutation in families with either CS alone or both CS and BRR when compared with BRR alone ( P = 0.002). Among CS, BRR and BRR/CS overlap families that are PTEN mutation positive, the mutation spectra appear similar. Thus, PTEN mutation-positive CS and BRR may be different presentations of a single syndrome and, hence, both should receive equal attention with respect to cancer surveillance.

Abnormalities, Multiple↗
PubMed1999

Cloning and mutational analysis of human malonyl-coenzyme A decarboxylase.

Malonyl coenzyme A (CoA) decarboxylase (E.C.4. 1.1.9) catalyzes the conversion of malonyl CoA to acetyl CoA. The metabolic role of malonyl CoA decarboxylase has not been fully defined, but deficiency of the enzyme has been associated with mild mental retardation, seizures, hypotonia, cardiomyopathy, vomiting, hypoglycemia, metabolic acidosis, and malonic aciduria. Here we report the isolation and sequencing of the human gene encoding malonyl CoA decarboxylase, and the identification of a mutation causing malonyl CoA decarboxylase deficiency. Human malonyl CoA decarboxylase cDNA sequences were identified by homology to the goose gene, and the intron/exon boundaries were determined by direct sequencing of a PAC clone containing the entire human gene. The 1479 basepair human cDNA is 70 percent identical to the goose sequence, and the intron/exon boundaries are completely conserved between the two species. The genetic mutation underlying malonyl CoA decarboxylase deficiency was determined in a patient with clinical features of this defect, malonic aciduria, and markedly reduced malonyl CoA decarboxylase activity.

Amino Acid Sequence↗
PubMed1998

Going the distance with auxin: unravelling the molecular basis of auxin transport.

Auxin represents one of the most important classes of signalling molecules described in plants. Auxins regulate several fundamental cellular processes including division, elongation and differentiation. Indole-3-acetic acid (IAA), the principal form of auxin in higher plants, is first synthesized within young apical tissues, then conveyed to its basal target tissues by a specialized delivery system termed polar auxin transport. The polarity of IAA movement represents one of the most novel aspect of auxin signalling. IAA transport has been demonstrated to involve auxin influx and efflux carrier activities. The adoption of a mutational approach in the model plant Arabidopsis thaliana has led to the identification of a number of genes which encode components for, or regulate the activity of, the auxin transport machinery. This paper will review the advances being made in identifying and characterizing these auxin transport-related gene products and discuss their importance within the context of Arabidopsis development.

Arabidopsis↗
PubMed1998

Mild trifunctional protein deficiency is associated with progressive neuropathy and myopathy and suggests a novel genotype-phenotype correlation.

Human mitochondrial trifunctional protein (TFP) is a heterooctamer of four alpha- and four beta-subunits that catalyzes three steps in the beta-oxidation spiral of long-chain fatty acids. TFP deficiency causes a Reye-like syndrome, cardiomyopathy, or sudden, unexpected death. We delineated the molecular basis for TFP deficiency in two patients with a unique phenotype characterized by chronic progressive polyneuropathy and myopathy without hepatic or cardiac involvement. Single-stranded conformation variance and nucleotide sequencing identified all patient mutations in exon 9 of the alpha-subunit. One patient is homozygous for the T845A mutation that substitutes aspartic acid for valine at residue 246. The second patient is a compound heterozygote for the T914A that substitutes asparagine for isoleucine at residue 269 and a C871T that creates a premature termination at residue 255. Allele-specific oligonucleotide hybridization studies revealed undetectable levels of the mRNA corresponding to the mutant allele carrying the termination codon. This study suggests a novel genotype-phenotype correlation in TFP deficiency; that is, mutations in exon 9 of the alpha-subunit, which encodes a linker domain between the NH2-terminal hydratase and the COOH-terminal 3-hydroxyacyl-CoA dehydrogenase, result in a unique neuromuscular phenotype.

Adolescent↗
PubMed1998

Calnexin association is not sufficient to protect T cell receptor alpha proteins from rapid degradation in CD4+CD8+ thymocytes.

During T cell development, assembly of the mutisubunit T cell receptor (TCR) complex is regulated by the differential stability of newly synthesized TCRalpha molecules, having a half-life of approximately 20 min in immature CD4+CD8+ thymocytes compared with >75 min in mature T cells. The molecular basis for TCRalpha instability in CD4+CD8+ thymocytes is unknown but has been postulated to involve abnormalities in N-glycan processing and calnexin assembly as perturbation of these pathways markedly destabilizes TCRalpha proteins in all other T cell types examined. Here, we compared the processing of TCRalpha glycoproteins and their assembly with calnexin and calreticulin chaperones in CD4+CD8+ thymocytes and splenic T cells. These studies show that TCRalpha glycoproteins synthesized in CD4+CD8+ thymocytes were processed in a similar manner as those made in splenic T cells and that TCRalpha proteins stably associated with calnexin in both cell types. Interestingly, however, TCRalpha association with the calnexin-related molecule calreticulin was decreased in CD4+CD8+ thymocytes compared with splenic T cells. Finally, TCRalpha degradation in CD4+CD8+ thymocytes was impaired by inhibitors of proteasome activity, which was correlated with stabilization of calnexin.TCRalpha complexes. These data demonstrate that calnexin association is not sufficient to protect TCRalpha proteins from rapid degradation in CD4+CD8+ thymocytes, suggesting that additional components of the quality control system of the endoplasmic reticulum operate to ensure the proper folding of nascent TCRalpha glycoproteins.

Acetylcysteine↗
PubMed1998

Crystal structure of the hemochromatosis protein HFE and characterization of its interaction with transferrin receptor.

HFE is an MHC-related protein that is mutated in the iron-overload disease hereditary hemochromatosis. HFE binds to transferrin receptor (TfR) and reduces its affinity for iron-loaded transferrin, implicating HFE in iron metabolism. The 2.6 A crystal structure of HFE reveals the locations of hemochromatosis mutations and a patch of histidines that could be involved in pH-dependent interactions. We also demonstrate that soluble TfR and HFE bind tightly at the basic pH of the cell surface, but not at the acidic pH of intracellular vesicles. TfR:HFE stoichiometry (2:1) differs from TfR:transferrin stoichiometry (2:2), implying a different mode of binding for HFE and transferrin to TfR, consistent with our demonstration that HFE, transferrin, and TfR form a ternary complex.

Amino Acid Sequence↗
PubMed1998

3-Methylcrotonyl-coenzyme A carboxylase deficiency in Amish/Mennonite adults identified by detection of increased acylcarnitines in blood spots of their children.

Isolated 3-methylcrotonyl coenzyme A carboxylase (MCC) deficiency was documented in four adult women from the Amish/Mennonite population of Lancaster County, Pennsylvania. Metabolic and enzymatic investigations in these individuals were instituted after the detection of abnormal acylcarnitine profiles in blood spots obtained from their newborn children, in whom MCC activity was normal.

Adult↗
PubMed1998

The Arabidopsis AUX1 gene: a model system to study mRNA processing in plants.

It is advantageous for an organism to be able to remove aberrant mRNAs that have either been incorrectly transcribed or processed in order to prevent the accumulation of potentially harmful proteins. The selective degradation of nonsense containing transcripts has been described in yeast. Caenorhabditis elegans and plants. The ease of identification of new mutant alleles in the AUX1 gene of Arabidopsis thaliana has provided a useful system to study novel mutations affecting mRNA stability and pre-mRNA splicing. To date 50 alleles of AUX1 have been identified of which 14 have been characterised at the sequence level. Eight of the characterised alleles encode missense mutations while the others cause nonsense mutations or splicing defects. The 2 splicing mutants identified affect the 5' or 3' splice sites and lead to cryptic splicing events resulting in premature stop codons. The AUX1 mRNA levels of the nonsense containing mutants are reduced compared to the wild-type or missense mutants whereas those of a control transcript (SecY) are unaltered. This provides further evidence for a nonsense-mediated mRNA degradation mechanism in plants and provides a system to study the phenomenon further in Arabidopsis.

Alleles↗