Evidence for a protective role of the Gardos channel against hemolysis in murine spherocytosis

It has been shown that mice with complete deficiency of all 4.1R protein isoforms (4.1-/-) exhibit moderate hemolytic anemia, with abnormal erythrocyte morphology (spherocytosis) and decreased membrane stability. Here, we characterized the Gardos channel function in vitro and in vivo in erythrocytes of 4.1-/- mice. Compared with wild-type, the Gardos channel of 4.1-/- erythrocytes showed an increase in Vmax (9.75 +/- 1.06 vs 6.08 +/- 0.09 mM cell x minute; P < .04) and a decrease in Km (1.01 +/- 0.06 vs 1.47 +/- 1.02 microM; P < .03), indicating an increased sensitivity to activation by intracellular calcium. In vivo function of the Gardos channel was assessed by the oral administration of clotrimazole, a well-characterized Gardos channel blocker. Clotrimazole treatment resulted in worsening of anemia and hemolysis, with decreased red cell survival and increased numbers of circulating hyperchromic spherocytes and microspherocytes. Clotrimazole induced similar changes in 4.2-/- and band 3+/- mice, indicating that these effects of the Gardos channel are shared in different models of murine spherocytosis. Thus, potassium and water loss through the Gardos channel may play an important protective role in compensating for the reduced surface-membrane area of hereditary spherocytosis (HS) erythrocytes and reducing hemolysis in erythrocytes with cytoskeletal impairments.     

Critical function for the Ras-GTPase activating protein RASA3 in vertebrate erythropoiesis and megakaryopoiesis

Phenotype-driven approaches to gene discovery using inbred mice have been instrumental in identifying genetic determinants of inherited blood dyscrasias. The recessive mutant scat (severe combined anemia and thrombocytopenia) alternates between crisis and remission episodes, indicating an aberrant regulatory feedback mechanism common to erythrocyte and platelet formation. Here, we identify a missense mutation (G125V) in the scat Rasa3 gene, encoding a Ras GTPase activating protein (RasGAP), and elucidate the mechanism producing crisis episodes. The mutation causes mislocalization of RASA3 to the cytosol in scat red cells where it is inactive, leading to increased GTP-bound Ras. Erythropoiesis is severely blocked in scat crisis mice, and ~94% succumb during the second crisis (~30 d of age) from catastrophic hematopoietic failure in the spleen and bone marrow. Megakaryopoiesis is also defective during crisis. Notably, the scat phenotype is recapitulated in zebrafish when rasa3 is silenced. These results highlight a critical, conserved, and nonredundant role for RASA3 in vertebrate hematopoiesis.     

Role of biofilms in neurosurgical device-related infections

Bacterial biofilms have recently been shown to be important in neurosurgical device-related infections. Because the concept of biofilms is novel to most practitioners, it is important to understand that both traditional pharmaceutical therapies and host defense mechanisms that are aimed at treating or overcoming free-swimming bacteria are largely ineffective against the sessile bacteria in a biofilm. Bacterial biofilms are complex surface-attached structures that are composed of an extruded extracellular matrix in which the individual bacteria are embedded. Superimposed on this physical architecture is a complex system of intercellular signaling, termed quorum sensing. These complex organizational features endow biofilms with numerous microenvironments and a concomitant number of distinct bacterial phenotypes. Each of the bacterial phenotypes within the biofilm displays a unique gene expression pattern tied to nutrient availability and waste transport. Such diversity provides the biofilm as a whole with an enormous survival advantage when compared to the individual component bacterial cells. Thus, it is appropriate to view the biofilm as a multicellular organism, akin to metazoan eukaryotic life. Bacterial biofilms are much hardier than free floating or planktonic bacteria and are primarily responsible for device-related infections. Now that basic research has demonstrated that the vast majority of bacteria exist in biofilms, the paradigm of biofilm-associated chronic infections is spreading to the clinical world. Understanding how these biofilm infections affect patients with neurosurgical devices is a prerequisite to developing strategies for their treatment and prevention.     

Regional variation of multiple sclerosis prevalence in Canada

OBJECTIVE: To describe the regional distribution of multiple sclerosis (MS) prevalence in Canada, controlling for age and sex. METHODS: This study used data from the Canadian Community Health Survey, a large general health survey (n = 131,535) conducted in 2000/2001. Subjects aged 18 and over were included in the current analysis (n = 116,109). The presence of MS was determined by self-report. Prevalence was computed in five regions (Atlantic, Quebec, Ontario, Prairies and British Columbia). Logistic regression was used to compare regions and examine for confounding/interaction by age and sex. RESULTS: The overall Canadian MS prevalence was 240 per 100000 (95%CI: 210 280). Prevalence ranged from 180 (95%CI: 90-260) in Quebec to 350 (95%CI: 230-470) in Atlantic Canada. Logistic regression revealed no statistical difference between the odds of MS in Quebec, Ontario and British Columbia adjusted for age and sex. The adjusted odds of MS in the Prairies and Atlantic regions were significantly higher than in the other regions combined, with odds ratios of 1.7 (95%CI: 1.1-2.4, P <0.01) and 1.6 (95%CI: 1.1-2.4, P <0.05) respectively. Sensitivity analysis demonstrated similar prevalence in the nonaboriginal/nonimmigrant group (n = 96219). CONCLUSION: Results suggest that Canadian MS prevalence differs by region. If validated, these regional differences may facilitate investigation of environmental influences.     

Foreign accent syndrome in a patient with multiple sclerosis

BACKGROUND: Foreign accent syndrome is a speech disorder which leads listeners to perceive the patient as having a foreign accent. It has been recognized previously after stroke, brain injury or unknown causes. CASE REPORT: A 52-year-old woman with clinically definite relapsing remitting multiple sclerosis (MS) presented with episodes of what was perceived as a Dutch accent along with other neurologic symptoms that would resolve simultaneously. She was assessed by a speech therapist both during an episode and after complete recovery. Speech and MRI changes (showing deep white matter lesions in the corpus callosum, left pariental lobe and left frontal lobe) were consistent with previous reports of foreign accent syndrome. CONCLUSIONS: This patient's episodes of foreign accent are thought to be due to her MS.     

Analysis of an improved survival rate for congenital diaphragmatic hernia

Background/Purpose: Congenital diaphragmatic hernia (CDH) is a condition associated with significant mortality. This study examines the survival rate of neonates with CDH treated by a multidisciplinary team in a single pediatric hospital. Actual survival rate is compared with predicted outcome based on severity of illness. Methods: A consecutive series of neonates with CDH was evaluated beginning January 1, 2000. There were no excluded patients. A treatment protocol emphasizing minimal barotrauma and control of pulmonary hypertension was used. Predicted survival rate was estimated using birth weight and Apgar score at 5 minutes per the logistic regression equation published by the CDH Study Group. Actual survival rates were calculated and compared with predicted values using a one sample binomial test with significance deemed to be present at P less than .05. Results: Thirty-six of 39 (93%) neonates with CDH survived, whereas the predicted survival rate for this cohort was 68% (P [lt ] .001). Twelve of 14 (86%) neonates requiring extracorporeal membrane oxygenation (ECMO) survived, despite a predicted survival rate of 52% for this subset (P [lt ] .01). Twenty-five percent of survivors required supplemental oxygen at home. Conclusions: Using a simple analysis, centers may now objectively compare their CDH survival rates with predicted outcomes adjusted for disease severity. This technique confirmed that a consecutive series of neonates with CDH, treated in one hospital, had a significantly higher than predicted survival rate. Thus, it may be possible to identify other centers with higher than expected survival rates and to define common therapeutic strategies associated with decreased mortality. J Pediatr Surg 38:729-732. [copy ] 2003 Elsevier Inc. All rights reserved.