Search PubMed⌕ Search

Biomedical subjects

D A Morrison

Publications and source records attributed to D A Morrison.

At least 55 records · Page 3Linked to original sources
PubMed1997

Sellar and suprasellar hemangiopericytoma mimicking pituitary adenoma.

Hemangiopericytoma is a vascular neoplasm of variable and unpredictable malignancy, composed of proliferating capillary pericytes surrounding endothelial-lined tubes or sprouts. The histological appearance is diagnostic. The treatment of primary intracranial hemangiopericytoma is surgical excision, supplemented by radiotherapy. Local tumor recurrence after many years is common, and late and widespread metastasis can occur. Long-term follow-up is mandatory.

Adenoma↗
PubMed1997

Angioplasty and stenting of an unprotected left main bifurcation lesion.

A case of unprotected bifurcation left main disease treated on 2 occasions by angioplasty and stenting is presented. This case demonstrates the 2 main features of salvage angioplasty, namely medically refractory rest angina and refused bypass surgery. In addition, it presents short inflation time angioplasty for sole or main conduits and treating the left main as a bifurcation lesion.

Aged↗
PubMed1997

Evolution of the genus Leishmania revealed by comparison of DNA and RNA polymerase gene sequences.

Previous hypotheses of Leishmania evolution are undermined by limitations in the phylogenetic reconstruction method employed or due to the omission of key parasites. In this experiment, sequences of the gene encoding the DNA polymerase alpha catalytic polypeptide (POLA) were analysed phylogenetically in combination with those encoding the RNA polymerase II largest subunit gene (RPOIILS) to infer a comprehensive phylogeny of Leishmania. Nineteen species of parasites were studied, comprising representatives of each Leishmania species-complex (Leishmania Leishmania tropica, Leishmania Leishmania donovani, Leishmania Leishmania mexicana, Leishmania Leishmania hertigi and Leishmania Viannia braziliensis), as well as parasites of questionable taxonomy (Leishmania herreri, Sauroleishmania adleri, Sauroleishmania deanei, Sauroleishmania gymnodactyli and Sauroleishmania tarentolae). The analyses presented here provide strong support for the hypothesis that the Leishmania that infect reptiles (also known as Sauroleishmania) evolved from mammalian Leishmania. One implication of this finding is that the taxonomic definition of Leishmania should be broadened to encompass characteristics of the reptilian parasites. However, this taxonomic revision is complicated in that Leishmania (L.) hertigi, Leishmania (L.) deanei and Leishmania herreri, which exhibit some biological properties of Leishmania, are more closely related to Endotrypanum on the basis of these sequence comparisons. Consequently, the taxonomic discrimination between Leishmania that infect mammals, Leishmania that infect reptiles and Endotrypanum may be more problematic than has been previously thought. Since our resulting phylogenetic hypothesis is supported by the analyses of two different genes, we speculate on the origin and evolutionary expansion of this lineage of kinetoplastid protozoa.

Animals↗
PubMed1997

Coronary angioplasty for elderly patients with "high risk" unstable angina: short-term outcomes and long-term survival.

OBJECTIVES: We sought to compare the short- and long-term mortality rates in patients > or = 70 years old with unstable angina undergoing percutaneous transluminal coronary angioplasty (PTCA) with predicted coronary artery bypass graft surgery (CABG) short-term and U.S. census long-term mortality rates. BACKGROUND: Coronary angioplasty is an alternative revascularization strategy for patients with medically refractory rest angina and a high risk of adverse outcomes with CABG. Patients > or = 70 years old are a specific high risk subset. METHODS: A total of 131 consecutive patients aged > or = 70 years with unstable angina underwent PTCA; 82 (62%) of 131 had been refused CABG. Mortality over time was obtained from the Veterans Affairs Beneficiary Index Records Locator Subsystem. Predicted 30-day CABG-associated mortality was obtained from the Veterans Affairs Cardiac Risk Assessment Model. Mortality over time was expressed with Kaplan-Meier curves. RESULTS: The observed 30-day angioplasty survival rate was 87% compared with the predicted surgical 30-day survival rate of 85.5%. In those patients who survived 6 months after angioplasty (84%), their subsequent 1-, 2-, 3-, 4- and 5-year survival rates were comparable to age-matched subjects in the U.S. census. Mortality in certain subsets known to be at very high risk for CABG-for example, patients who had a previous CABG-was not high in this cohort of elderly subjects. The extremely high risk subsets identified in this PTCA cohort (shock, heart failure, pressors required, balloon pump required) were relatively infrequent subsets. CONCLUSIONS: For selected elderly patients with unstable angina deemed to be at "high risk" or even "prohibitive risk" for CABG, PTCA is an alternative revascularization strategy. The long-term mortality of successfully treated elderly patients is comparable to age-matched subjects. A prospective, multicenter, randomized trial of CABG versus PTCA, which includes patients > or = 70 years old, is being conducted (Veterans Affairs Cooperative Study 385: AWESOME).

Aged↗
PubMed1997

Streptococcal competence for genetic transformation: regulation by peptide pheromones.

Although the capacity for genetic transformation is perhaps the most famous attribute of pneumococcus, use of this genetic phenomenon as a tool for study of the biology of the organism and of its pathogenicity has been largely restricted to a few favored unencapsulated strains, both by the delicacy of the conditions required for development of competence, and by experience that encapsulated strains transformed poorly. We discuss here the recent discovery of a small stable inexpensive peptide pheromone that acts as a quorum-sensing signal and that induces competence under a wide variety of conditions and in encapsulated strains. Its use circumvents some if not all limitations to the expression of transformability in pneumococcus and therefore expands opportunities for application of tools molecular genetics to many strains of pneumococcus without prior genetic manipulation.

Peptides↗
PubMed1997

Ubiquitous distribution of the competence related genes comA and comC among isolates of Streptococcus pneumoniae.

DNA probes specific for the pneumococcal competence regulatory genes comA and comC were used to test the presence of these genes in 214 pneumococcal isolates selected to represent a wide variety of clonal types and genetic backgrounds (as defined by chromosomal macrorestriction patterns and multilocus enzyme analysis), a variety of serotypes, isolation dates (between 1916 and 1996), geographic origins (on four continents), as well as different clinical origins (including both infection sites and colonization sites). Each isolate gave positive signal with both DNA probes. The comA and comC genes were never on the same SmaI restriction fragment and the comA gene showed a considerable degree of polymorphism from one strain to another. While DNA sequencing of 50 of the isolates have identified three distinct alleles of the comC gene, the number of mutations within the leader peptide were minimal. The results suggest that the mechanism to undergo genetic transformation is widespread within the species of Streptococcus pneumoniae.

Alleles↗
PubMed1997

Effects of nucleotide sequence alignment on phylogeny estimation: a case study of 18S rDNAs of apicomplexa.

The reconstruction of phylogenetic history is predicated on being able to accurately establish hypotheses of character homology, which involves sequence alignment for studies based on molecular sequence data. In an empirical study investigating nucleotide sequence alignment, we inferred phylogenetic trees for 43 species of the Apicomplexa and 3 of Dinozoa based on complete small-subunit rDNA sequences, using six different multiple-alignment procedures: manual alignment based on the secondary structure of the 18S rRNA molecule, and automated similarity-based alignment algorithms using the PileUp, ClustalW, TreeAlign, MALIGN, and SAM computer programs. Trees were constructed using neighboring-joining, weighted-parsimony, and maximum-likelihood methods. All of the multiple sequence alignment procedures yielded the same basic structure for the estimate of the phylogenetic relationship among the taxa, which presumably represents the underlying phylogenetic signal. However, the placement of many of the taxa was sensitive to the alignment procedure used; and the different alignments produced trees that were on average more dissimilar from each other than did the different tree-building methods used. The multiple alignments from the different procedures varied greatly in length, but aligned sequence length was not a good predictor of the similarity of the resulting phylogenetic trees. We also systematically varied the gap weights (the relative cost of inserting a new gap into a sequence or extending an already-existing gap) for the ClustalW program, and this produced alignments that were at least as different from each other as those produced by the different alignment algorithms. Furthermore, there was no combination of gap weights that produced the same tree as that from the structure alignment, in spite of the fact that many of the alignments were similar in length to the structure alignment. We also investigated the phylogenetic information content of the helical and nonhelical regions of the rDNA, and conclude that the helical regions are the most informative. We therefore conclude that many of the literature disagreements concerning the phylogeny of the Apicomplexa are probably based on differences in sequence alignment strategies rather than differences in data or tree-building methods.

Algorithms↗
PubMed1997

The "harlequin" sign and congenital Horner's syndrome.

When trying to establish the likely anatomical site (preganglionic or postganglionic) of a lesion causing congenital Horner's syndrome, the distribution of facial flushing (the "harlequin" sign), may be seen. In babies and young children, facial flushing is a relatively simple clinical sign to demonstrate, compared with facial sweating. In unilateral facial flushing the areas that do not flush are almost always identical to the anhidrotic areas. However, neither facial flushing nor testing the pupil reactions with pholedrine or hydroxyamphetamine can be relied on to predict the probable site of any lesion causing congenital Horner's syndrome. Two patients with congenital Horner's syndrome are presented which demonstrated the "harlequin" sign and in whom clinical examination and pharmacological testing gave conflicting evidence for localisation of the site of the causative lesion. The presentation of congenital Horner's syndrome should be investigated and include MRI or CT to exclude a serious underlying cause.

Child↗
PubMed1996

Percutaneous transluminal angioplasty of internal mammary arteries in patients with rest angina.

Angioplasty of the internal mammary artery (IMA) bypass graft has been shown to be a safe and effective revascularization procedure. However, angiographic and long term clinical outcomes in the high-risk group of patients presenting with rest angina has not been well documented. We report the results of IMA angioplasty in 20 patients with rest angina out of 614 (3.2%) who received a left IMA graft at our institution between April 1987 and September 1994. All patients were admitted with rest angina, 12 patients demonstrated persistent ischemia despite medical therapy, two patients were in heart failure, and one patient was in cardiogenic shock. Balloon angioplasty was successful in 15 of 20 patients (75%). Failed angioplasty was associated with either severe IMA tortuousity (three patients) or inability to cross the anastomotic stenosis with the guide wire (two patients). Each of these five patients required angioplasty of either the native left anterior descending artery or other saphenous vein grafts for clinical stabilization. No patient suffered a major complication (myocardial infarction, emergent coronary bypass surgery, death). Clinical follow-up was obtained in all 20 patients (6 months, 7 years, mean 27 months). Twelve patients (60%) were asymptomatic or had stable angina at follow-up, and 8 returned with anginal symptoms. Four patients required repeat angioplasty for disease in other vessels, two were treated medically for angina, one underwent repeat CABG, and cardiac transplantation was performed in one patient for refractory heart failure. Angiographic follow up was obtained in 10/15 (66%) successful angioplasty patients, and only one patient demonstrated restenosis at the treated site (10%). During follow up one patient developed an IMA stenosis at a previous dissection site in the body of the graft that was treated with angioplasty. These results suggest that IMA angioplasty in patients with rest angina is associated with excellent long term patency and clinical efficacy, as well as low procedural risk.

Adult↗
PubMed1996

Phylogenetic tree-building.

Cladistic analysis is an approach to phylogeny reconstruction that groups taxa in such a way that those with historically more-recent ancestors form groups nested within groups of taxa with more-distant ancestors. This nested set of taxa can be represented as a branching diagram or tree (a cladogram), which is an hypothesis of the evolutionary history of the taxa. The analysis is performed by searching for nested groups of shared derived character states. These shared derived character states define monophyletic groups of taxa (clades), which include all of the descendants of the most recent common ancestor. If all of the characters for a set of taxa are congruent, then reconstructing the phylogenetic tree is unproblematic. However, most real data sets contain incongruent characters, and consequently a wide range of tree-building methods has been developed. These methods differ in a variety of characteristics, and they may produce topologically distinct trees for a single data set. None of the currently-available methods are simultaneously efficient, powerful, consistent and robust, and thus there is no single ideal method. However, many of them appear to perform well under a wide range of conditions, with the exception of the UPGMA method and the Invariants method.

Algorithms↗
PubMed1996

Regulation of competence for genetic transformation in Streptococcus pneumoniae by an auto-induced peptide pheromone and a two-component regulatory system.

The regulation of competence for genetic transformation in Streptococcus pneumoniae depends on a quorum-sensing system, but the only molecular elements of the system whose specific role have been identified are an extracellular peptide signal and an ABC-transporter required for its export. Here we show that transcription of comC, the gene encoding a predicted 41-residue precursor peptide that is thought to be processed and secreted as the 17-residue mature competence activator, increased approximately 40-fold above its basal level of expression in response to exogenous synthetic activator, consistent with earlier experiments indicating that the activator acts autocatalytically. We also describe two new genes, comD and comE, that encode members of histidine protein kinase and response-regulator families and are linked to comC. Disruption of comE abolished both response to synthetic activator peptide and endogenous competence induction.

Amino Acid Sequence↗
PubMed1996

Identification of the streptococcal competence-pheromone receptor.

Competence for genetic transformation in certain species of streptococci has been known for many years to be induced by a secreted protease-sensitive pheromone, referred to as the competence factor or activator, which acts as a quorum-sensing signal to co-ordinate expression of late competence genes. We recently reported identification of the pheromone of Streptococcus pneumoniae strain Rx as a small unmodified peptide, which was termed competence-stimulating peptide (CSP). By identifying the gene (comC) encoding the Rx CSP we were able to show that it is synthesized as a precursor peptide containing an N-terminal double-glycine type leader. In the present work, we describe two alleles of the corresponding gene from Streptococcus gordonii strains Challis and NCTC 7865, which are strains with distinct competence pheromones and corresponding specific pheromone reactivities. In addition, the nucleic acid sequences of two genes located downstream of comC were determined; interestingly, these genes encode a two-component signal transduction system. We therefore speculated that their products, a histidine kinase (ComD) and its cognate response regulator (ComE), act downstream of the CSP in competence regulation. By tracing the CSP specificity of the competence response in these strains to strain-specific alleles of comD, we obtained evidence demonstrating that the histidine kinase ComD is the competence-pheromone receptor.

Alleles↗
PubMed1996

DNA polymorphisms and variant penicillin-binding proteins as evidence that relatively penicillin-resistant pneumococci in western Canada are clonally related.

Previous studies have suggested that relatively penicillin-resistant (RPR) capsular group 9L strains in western Canada may be clonally related. To test this hypothesis, restriction fragment length polymorphisms (RFLPs) were examined using DNA probes for pspA and a newly recognized pneumococcal genetic element, IS1167. Penicillin-binding proteins (PBPs) and PBP genes from representative strains were also studied. All RPR type 9L strains demonstrated an identical RFLP when probed with IS1167, and 12 of 14 RPR strains had the same RFLP when examined with pspA. Amplification of pspA by polymerase chain reaction and restriction endonuclease digestion showed that the 9L strains had common DNA fragments not identified in any of the penicillin-susceptible strains. The 9L strains apparently have a low-affinity PBP 2B distinct from those of other capsular types. These data derived from new genetic markers and PBP analysis strongly support a clonal origin of RPR type 9L pneumococci of western Canada.

Bacterial Proteins↗
PubMed1996

Competence pheromone, oligopeptide permease, and induction of competence in Streptococcus pneumoniae.

An unmodified heptadecapeptide pheromone capable of eliciting competence for genetic transformation in Streptococcus pneumoniae has recently been identified and characterized. In considering possible signal-transduction mechanisms for the peptide, the previously characterized Ami oligopeptide permease and the three highly homologous oligopeptide-binding lipo-proteins. AmiA, AliA, and AliB, appeared to be good candidates for receptors. We therefore compared the spontaneous transformability of Ami, AliA and AliB mutants to that of an isogenic wild-type strain and we investigated the response of the various mutants to treatment with synthetic competence-stimulating peptide (CSP). Our results clearly demonstrate that neither Ami nor any of the three highly homologous oligopeptide-binding lipoproteins identified so far in S. pneumoniae are required for competence induction following treatment with synthetic CSP. Although the existence of a fourth unidentified oligopeptide-binding lipoprotein and/or a second oligopeptide permease operon could not be completely ruled out, we favour the hypothesis that CSP signal transmission rather involves a two-component regulatory system. Although none of the single or double Ami and All mutants tested appeared severely affected for competence, an exceptional aliB plasmid-insertion mutation abolished competence completely. In addition, the triple AmiA-AliA-AliB mutant differed from wild type in showing no sharp peak of competence but exhibiting transformability throughout the exponential phase of growth. These and previous observations are discussed and a general hypothesis is proposed to account for the modulation of competence by peptide permease mutants in S. pneumoniae.

Bacterial Proteins↗
PubMed1996

The capsule polysaccharide synthesis locus of streptococcus pneumoniae serotype 14: Identification of the glycosyl transferase gene cps14E.

To identify a chromosomal region of Streptococcus pneumoniae serotype 14 involved in capsule polysaccharide synthesis, two strategies were used: (i) Tn916 mutagenesis, followed by the characterization of four unencapsulated mutants, and (ii) cross-hybridization with a capsule polysaccharide synthesis gene (cps) probe from S. agalactiae, which has a structurally similar capsule. The two approaches detected the same chromosomal region consisting of two adjacent EcoRI fragments. One of these EcoRI fragments was cloned and hybridized with a cosmid library. This resulted in clone cMKO2. A similar cosmid clone was obtained from an unencapsulated Tn916 mutant, Spnl4.H. Sequence analysis of the two cosmid clones revealed that in the Tn916 mutant, a gene, cps14E, which is homologous to other bacterial genes encoding glycosyl transferases, had been inactivated. An open reading frame immediately downstream of cps14E, designated cps14F, shows no significant homology with any known genes or proteins. A functional assay showed that cps14E encodes a glycosyl transferase and that a gene-specific knockout mutant lacks this enzyme activity, whereas inactivation of cps14F does not have this effect.

Bacterial Capsules↗