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West Nile Virus in the New York City Area
In August 1999, the New York City Department of Health learned of a cluster of cases of meningoencephalitis with muscle weakness. Active surveillance identified 59 patients hospitalized with West Nile virus infection during August and September of that year. The attack rate increased sharply with age, and seven patients died. There was muscle weakness in 27 percent of the patients, and six patients had flaccid paralysis.
This outbreak represents the first detection of this arbovirus in the Western Hemisphere. It has since been identified in birds and mosquitoes along the East Coast of the United States. A diagnosis of West Nile virus infection should be considered in patients with viral meningitis or encephalitis, especially in older patients with muscle weakness.
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Hematopoietic Engraftment and Survival in Adult Recipients of Umbilical-Cord Blood
In this study, adults with life-threatening hematologic diseases received intensive chemotherapy or total-body irradiation, followed by hematopoietic rescue with cord-blood cells from unrelated donors. In many recipients, there were two or more HLA mismatches. Nevertheless, the cells engrafted in most patients, and the incidence of graft-versus-host disease was not excessive.
Umbilical-cord blood has been used successfully for hematopoietic rescue in children. The applicability of this approach to adults has been in doubt because the number of hematopoietic progenitor cells in a unit of cord blood is small. This study demonstrates that cord blood is a feasible source of stem cells for patients who have no alternative donor. Cord blood, which is routinely discarded, has therapeutic applications in children and adults.
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Identification of a Gene Responsible for Familial Wolff-Parkinson-White Syndrome
The Wolff-Parkinson-White syndrome, a common cause of supraventricular tachycardia, is due to the presence of accessory conduction pathways linking the atrial and ventricular myocardium, which results in ventricular preexcitation. The cause is unknown. In this study of two families affected by the Wolff-Parkinson-White syndrome, a probable causative mutation was identified in a protein kinase gene (PRKAG2) on chromosome 7.
The authors hypothesize that the defective gene may result in the persistence of accessory conduction pathways that normally regress during cardiogenesis and may also be involved in triggering supraventricular arrhythmias. These important findings provide insight into the pathogenesis of this puzzling syndrome and may eventually lead to new therapies.
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The Urea Cycle and Nitric Oxide in Newborns
Nitric oxide, a potent pulmonary vasodilator, probably has a role in the regulation of pulmonary arterial pressure. Among newborns with respiratory distress, those with persistent pulmonary hypertension were found to have lower plasma concentrations of arginine (an essential precursor of nitric oxide) than those without pulmonary hypertension. Among the newborns with pulmonary hypertension, the investigators suggest, a genetic variant of an enzyme of the urea cycle may limit the production of arginine.
Pulmonary hypertension in newborns, though uncommon, is fatal in more than 10 percent of cases. Since inhaled nitric oxide is an effective treatment for the condition, it is possible that a lack of endogenous nitric oxide causes elevated pulmonary vascular resistance in neonates. This study found evidence that a genetic variant of an enzyme of the urea cycle limits the production of arginine, the amino acid that endothelial cells use to produce nitric oxide.
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Clinical Practice: Noninvasive Tests for Stable Coronary Artery Disease
A 58-year-old woman presents with exertional chest discomfort. How should she be evaluated? This Clinical Practice article discusses the advantages and disadvantages of various noninvasive testing strategies in patients with coronary artery disease and provides testing recommendations based on clinical presentation. The authors discuss the relative merits of exercise electrocardiography, radionuclide imaging, and stress echocardiography in the evaluation of stable coronary disease.
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Current Concepts: The Irritable Bowel Syndrome
Irritable bowel syndrome is the most common diagnosis made by gastroenterologists in the United States. Annually it accounts for about $8 billion in direct medical costs and about $25 billion in indirect costs. This review summarizes current information about the pathophysiology of this common disorder. Symptom-guided therapy can help alleviate the pain and suffering of patients with the syndrome. Repeated testing should be avoided.
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