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J A Dennis

Publications and source records attributed to J A Dennis.

At least 19 recordsLinked to original sources
PubMed2001

A nonsense mutation in the alpha1 subunit of the inhibitory glycine receptor associated with bovine myoclonus.

Inherited congenital myoclonus of Poll Hereford calves is an autosomal recessive disease characterized by hyperesthesia and myoclonic jerks of the skeletal musculature that occur both spontaneously and in response to sensory stimuli. Binding studies have previously shown that myoclonus is associated with specific loss of [(3)H]strychnine-binding sites from spinal cord and brain stem in affected calves. In order to identify the mutation responsible for myoclonus, we examined the candidate genes, glycine receptor alpha1 (Glra1) and beta (Glrb) subunits, in affected and normal cattle. A nonsense mutation was found at amino acid 24, located in exon 2 of the Glra1 gene in both cDNA and genomic sequences from affected but not control animals. Immunohistochemistry, with a monoclonal antibody to alpha and beta subunits of the glycine receptor, revealed a loss of cell surface immunoreactivity in myoclonic animals, suggesting a failure in the assembly of the receptor that could explain the characteristic phenotype of the disease.

Alleles↗
PubMed2000

The bovine alpha-glucosidase gene: coding region, genomic structure, and mutations that cause bovine generalized glycogenosis.

We report here cDNA and genomic sequence of the bovine acidic alpha-glucosidase gene, from the initiation codon to the most 3' polyadenylation signal. The 2814-bp coding sequence predicts a 937-amino acid protein, which is highly conserved compared with the human alpha-glucosidase gene (86% and 83% identity respectively). The intron/exon boundaries are also conserved between the two species. Two mutations have been identified in Brahmans, and one in Shorthorns, that lead to generalized glycogenosis. All three mutations result in premature termination of translation. Evidence is also presented for a missense mutation segregating with the Brahman population, which is responsible for a 70-80% reduction in alpha-glucosidase activity.

Amino Acid Substitution↗
PubMed1999

Hepatocyte gene therapy in a large animal: a neonatal bovine model of citrullinemia.

The development of gene-replacement therapy for inborn errors of metabolism has been hindered by the limited number of suitable large-animal models of these diseases and by inadequate methods of assessing the efficacy of treatment. Such methods should provide sensitive detection of expression in vivo and should be unaffected by concurrent pharmacologic and dietary regimens. We present the results of studies in a neonatal bovine model of citrullinemia, an inborn error of urea-cycle metabolism characterized by deficiency of argininosuccinate synthetase and consequent life-threatening hyperammonemia. Measurements of the flux of nitrogen from orally administered 15NH4 to [15N]urea were used to determine urea-cycle activity in vivo. In control animals, these isotopic measurements proved to be unaffected by pharmacologic treatments. Systemic administration of a first-generation E1-deleted adenoviral vector expressing human argininosuccinate synthetase resulted in transduction of hepatocytes and partial correction of the enzyme defect. The isotopic method showed significant restoration of urea synthesis. Moreover, the calves showed clinical improvement and normalization of plasma glutamine levels after treatment. The results show the clinical efficacy of treating a large-animal model of an inborn error of hepatocyte metabolism in conjunction with a method for sensitively measuring correction in vivo. These studies will be applicable to human trials of the treatment of this disorder and other related urea-cycle disorders.

Adenoviridae↗
PubMed1999

Definition of the mutation responsible for maple syrup urine disease in Poll Shorthorns and genotyping Poll Shorthorns and Poll Herefords for maple syrup urine disease alleles.

The organisation of the E1alpha subunit of bovine branched-chain alpha-keto acid dehydrogenase gene was established. c DNA was cloned from Poll Shorthorn x Poll Hereford calves affected with Maple Syrup Urine Disease to identify the mutation responsible for the disease in Poll Shorthorns. Clones containing the c DNA sequences inherited from the Poll Shorthorn sire of the affected calves were identified. Paternal clones were sequenced and a cytidine to thymidine transition was found at nucleotide 1380. The mutation is predicted to substitute leucine in place of a highly conserved proline at codon 372. A polymerase chain reaction procedure was developed for detection of the 1380C-->T mutation in genomic DNA. Three Poll Shorthorn parents of affected calves and three affected Poll Shorthorn x Poll Hereford calves were heterozygous and an affected Poll Shorthorn calf was homozygous for this mutation. An improved polymerase chain reaction procedure was also devised to genotype Poll Herefords for the 248C-->T mutation. The procedures will facilitate disease prevention programs and assist in differential diagnosis of conditions in new-born calves that present with a rapid onset of progressive neurological disease and are characterised histologically by 'status spongiosus'. Maple Syrup Urine Disease (MSUD) is an autosomal recessive defect reported in humans (Danner and Elsas 1989), and in Poll Hereford (PH) and Poll Shorthorn (PS) calves (Harper et al 1986, Healy et al 1992). The clinical, biochemical and pathological manifestations of the disease are identical in the two breeds of cattle, and are characterised by the rapid onset of progressive neurological disease, leading to death within a few days of birth. The disease is caused by a deficiency of activity of the mitochondrial enzyme branched-chain alpha-keto acid dehydrogenase (BCKADH). This deficiency leads to elevated concentrations, in blood and tissues, of branched chain alpha-keto acids and their precursors, the branched chain amino acids, valine, leucine and isoleucine. BCKADH consists of four subunits E1alpha, E1beta, E2 and E3 that are encoded by separate genes, and MSUD may result from deficiency of any of the subunits. In PH s, the disease in caused by premature termination of translation, of the E1alpha subunit, that is induced by a cytidine to thymidine transition exon 2 (248C-->T), that converts the glutamine codon -6 to a stop codon (Q-6ST; Zhang et al 1990). We have shown that MSUD -affected PSxPH calves are heterozygous at the PH locus, illustrating molecular heterogeneity exists for bovine MSUD (Healy and Dennis 1994a). The fact that these crossbred calves are affected, indicates the PS, like the PH mutation, resides in the E1alpha subunit.

Alleles↗
PubMed1998

Evaluation of gene therapy for citrullinaemia using murine and bovine models.

Citrullinaemia is an autosomal recessive disorder caused by the deficiency of argininosuccinate synthase. The deficiency of this enzyme results in an interruption in the urea cycle and the inability to dispose of excess ammonia derived from the metabolism of protein. The only treatment for this disorder has been dietary restriction of protein and supplementation with medications allowing for alternative excretion of excess nitrogen. Gene therapy offers the possibility of a long-term cure for disorders like citrullinaemia by expressing the deficient gene in the target organ. We have explored the use of adenoviral vectors as a treatment modality for citrullinaemia in two animal models, a naturally occurring bovine model and a murine model created by molecular mutagenesis. Mice treated with adenoviral vectors expressing argininosuccinate synthase lived significantly longer than untreated animals (11 days vs 1 day; however, the animals did not exhibit normal weight gain during the experiment, indicating that the therapeutic effectiveness of the transducing virus was suboptimal. It is speculated that part of the failure to observe better clinical outcome might be due to the deficiency of arginine. In the bovine model, the use of adenoviral vectors did not result in any change in the clinical condition of the animals or in the level of plasma ammonia. However, the use of 15N isotopic ammonia allowed us to assess the flux of nitrogen through the urea cycle during the experiment. These studies revealed a significant increase in the flux through the urea cycle following administration of adenoviral vectors expressing argininosuccinate synthase. We conclude that the use of adenoviral vectors in the treatment of citrullinaemia is a viable approach to therapy but that it will be necessary to increase the level of transduction and to increase the level of enzyme produced from the recombinant viral vector. Future experiments will be designed to address these issues.

Adenoviruses, Human↗
PubMed1995

Heterozygote detection for maple syrup urine disease in cattle.

The clinical, pathological and biochemical manifestations of maple syrup urine disease (MSUD) are similar in Poll Hereford and Poll Shorthorn x Poll Hereford calves. No significant differences were observed in branched-chain amino acid concentrations in plasma, or of branched-chain keto acid dehydrogenase activity in fibroblasts, between Poll Herefords homozygous normal and heterozygous for the mutation responsible for MSUD. Haemopoietic chimerism resulted in incorrect diagnosis of the MSUD genotype in 30% of non-identical twins when blood DNA was analysed using allele-specific amplification. Hair roots are shown to be a suitable source of target DNA for genotyping Poll Hereford cattle for the MSUD mutation. Twelve of 203 (5.8%) aged Poll Hereford bulls, sampled at saleyards during the last 4 months of 1993, were found to be heterozygous for the mutation. In contrast, the mutant sequence was detected in only 1 of 150 (0.7%) 2- and 3-year-old Poll Hereford bulls offered for sale at 2 stud sales held during 1993, suggesting that the prevalence of the disease may decline over the next few years.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1994

Molecular heterogeneity for bovine maple syrup urine disease.

In Poll Herefords, it is known that maple syrup urine disease results from a nonsense mutation in codon -6 of the gene for the E1 alpha subunit of branched-chain alpha-keto acid dehydrogenase. The disease also occurs in Poll Shorthorns, but its molecular basis in this breed has not yet been determined. Allele-specific hybridization and allele-specific amplification, both based on the Poll Hereford mutation, failed to detect the mutant allele in Poll Shorthorn heterozygotes, and detected the normal allele in affected Poll Hereford-cross-Poll Shorthorn calves. These results demonstrate between breed molecular heterogeneity for bovine maple syrup urine disease.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1994

Haemopoietic chimaerism: a complication in heterozygote detection tests for inherited defects in cattle.

Several observations are documented which illustrate that haemopoietic chimaerism is a potential source of error when using assays of cellular components of blood to determine genotype for inherited defects in cattle. Acidic alpha-glucosidase activity in peripheral mononuclear cells of a twin Brahman bull that had sired calves affected with generalized glycogenosis was similar to that in cells from homozygous normal animals. Activity in fibroblasts from this bull was similar to that in heterozygotes. alpha-mannosidase activity in fibroblasts of a twin Murray Grey bull with low activity in peripheral granulocytes but high activity in plasma was similar to that in animals homozygous normal for alpha-mannosidosis. Normal argininosuccinate synthetase nucleotide sequence was detected in leucocytes from two calves affected with citrullinemia and mutant sequence detected in leucocytes from their homozygous normal co-twins.

Animals↗
PubMed1993

Inherited enzyme deficiencies in livestock.

The biochemical basis of over 300 inherited diseases has been defined in humans, and the majority involve abnormalities in enzymes. The rate of discovery of new defects is accelerating as biochemical and molecular technologies improve. The majority of inherited defects are expressed before puberty and approximately 25% are apparent at birth. Genomes of other mammals are similar and have been subjected to similar mutation pressures; therefore, it is probable that a range of inherited defects exists in livestock similar to that in humans. Because modern livestock populations have emerged from small population bases, the range of genetic aberrations, within breeds, will be less than in the general human population. Even if there is a 10-fold difference, however, there will be a bewildering array of defects possible in each breed. Because the level of inbreeding within livestock populations is greater than in the general human population, on the other hand, the prevalence of specific defects will be higher. It is probable that a high prevalence of a lethal recessive defect could occur within a particular livestock population and escape recognition. First, livestock producers accept a relatively high neonatal mortality rate without seeking a diagnosis. Second, few if any veterinary diagnostic facilities possess either the instrumentation or the analytic skills essential for investigating the vast range of potential inborn errors of metabolism. Third, national selection programs--e.g., those employed within the dairy industry--tend to use production data from adult progeny in selection. Consequently, the programs would not detect differences in fetal or neonatal mortality rates among descendants of specific sires until a deleterious defect had been widely disseminated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Glutamate and gamma-aminobutyric acid neurotransmitter systems in the acute phase of maple syrup urine disease and citrullinemia encephalopathies in newborn calves.

Cerebral cortex tissue was obtained at autopsy from neonatal Poll Hereford calves with clinically confirmed maple syrup urine disease (MSUD), neonatal Holstein-Friesian calves with clinically confirmed citrullinemia, and matched controls. From this, synaptosomes were prepared for studies of neurotransmitter amino acid uptake and stimulus-induced release, and synaptic plasma membranes were obtained for studies of associated postsynaptic receptor binding sites. As well as having abnormal brain tissue concentrations of the pathognomic plasma amino acids (markedly increased levels of the branched-chain compounds valine, isoleucine, and leucine in MSUD; marked elevation of citrulline levels in citrullinemia), both groups of diseased animals showed reduced brain tissue concentrations of each of the transmitter amino acids glutamate, aspartate, and gamma-aminobutyric acid (GABA). Nontransmitter amino acids were generally unaffected in either disease. Citrullinemic calves showed a marked increase in brain glutamine concentration; in calves with MSUD, the glutamine concentration was raised, but to a much lesser extent. The Na(+)-dependent synaptosomal uptake of both glutamate and GABA was markedly reduced (to less than 50% of control values in both cases) in citrullinemic calves but was unaltered in calves with MSUD. Whereas synaptosomes from normal calves showed the expected stimulus-coupled release of transmitter amino acids, especially glutamate and aspartate, and no response to stimulus of nontransmitter amino acids, there was no increased release of transmitter amino acids in response to depolarization in synaptosomes from citrullinemic calves.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute-Phase Reaction↗
PubMed1990

Dosimetric aspects of exposure of the population to ionizing radiation.

Radiation carcinogenesis is generally considered to be the most important detrimental effect of exposure to ionizing radiation. The collective effective dose-equivalent values due to medical procedures amount to values between 10 and 20 per cent of the doses received from natural radiation. Risk factors have been derived up to the present from three large epidemiological studies, notably atomic bomb survivors, spondylitis patients and female patients treated for cancer of the cervix. The assessment of the absorbed doses received by the inhabitants of Hiroshima and Nagasaki has received continuous attention and the latest estimates are summarized. On the basis of original radiotherapy records the absorbed doses in organs adjacent to the primary treatment field can be derived from computerized dosimetry and this source of information should be further exploited. European co-operation has been established to investigate dosimetric problems for medical applications and radiation protection. The risk factors obtained up to the present are derived at relatively high dose levels (in excess of 0.3 Gy). The uncertainties in the extrapolation of these values to the area of low doses administered at low dose rates are discussed.

Europe↗
PubMed1990

Bovine citrullinaemia: a clinical, pathological, biochemical and genetic study.

Calves affected with citrullinaemia are clinically normal immediately after birth. In the majority of calves the clinical course of the disease was similar. Within 24 hours of birth they become depressed; then within 3 to 4 days were observed to wander aimlessly or stand with their head pressed against a wall or fence. By day 4 to 5 they become recumbent, developed convulsions, followed by collapse and death. Oedema of the cerebral cortex is a consistent histological lesion. Citrulline concentration in blood, cerebrospinal fluid, eye fluid and cerebral tissue is greatly elevated. Information gathered from pedigrees of affected calves indicate that the defect is widely disseminated throughout the Australian Friesian population.

Animals↗