May 16, 2002
High Bone Density Due to an LRP5 Mutation
Osteoporosis can be caused by a loss-of-function mutation in the gene for low-density lipoprotein receptor–related protein 5 (LRP5). In this study, the authors, reasoning that a gain-of-function mutation in the same gene might be associated with high bone density, performed biochemical and genetic analyses of a kindred with high bone density, a prominent mandible, and torus palatinus. Genetic analysis revealed an LRP5 mutation, the substitution of valine for glycine at codon 171, that segregated with the clinical findings. In vitro studies demonstrated that the defect in LRP5 resulted in changes in signaling events with other molecules that normally interact with this receptor-related protein, resulting in increased bone density. The findings suggest that molecules that interact with LRP5 may provide targets for the treatment of osteoporosis.
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Tissue Plasminogen Activator in Cardiac Arrest
Coronary thrombosis and pulmonary embolism are common causes of cardiac arrest, providing a rationale for the use of thrombolytic therapy in cases of cardiac arrest. In this study, patients with cardiac arrest and pulseless electrical activity were randomly assigned to receive tissue plasminogen activator (t-PA) or placebo in a double-blind fashion. Treatment with t-PA did not increase either the rate of survival to hospital discharge or the rate of return of spontaneous circulation. The study was relatively small and therefore does not exclude the possibility of a small beneficial effect of t-PA or an effect in selected subgroups of patients. However, on the basis of the findings, there is little reason for optimism regarding this therapeutic approach in cases of cardiac arrest.
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Bacteremia Due to Tampering with Narcotic Infusions
An outbreak of Serratia marcescens bacteremia among patients in a surgical intensive care unit was extensively investigated. A total of 26 infected patients were identified. In a case–control study, the main risk factors were receipt of continuous fentanyl infusions and exposure to two specific respiratory therapists. Isolates from the patients were similar to isolates from the infused medication. This large nosocomial outbreak appears to be the result of the actions of a single health care worker, whom a nurse reported for tampering with a needle and a narcotic infusion. Analysis of the worker's hair documented fentanyl exposure. With his removal from the unit, the outbreak ended.
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Relation between the Availability of Neonatal Intensive Care and Neonatal Mortality
Despite marked regional variation in the availability of neonatal intensive care, it is not known whether the supply of neonatologists or neonatal intensive care beds is associated with neonatal mortality. This retrospective cohort study involved almost 3.9 million U.S. infants with a birth weight of 500 g or greater who were born in 1995. As compared with infants born in regions with a very low supply of neonatologists (2.7 per 10,000 births), those from regions with a low supply of neonatologists (4.3 per 10,000 births) were less likely to die in the first 27 days of life. However, further increases in the supply of neonatologists were not associated with greater reductions in risk. Although a few regions in the United States may have an inadequate supply of neonatologists, when judged on the basis of neonatal mortality, many other regions may have more than they need. Whether the availability of neonatologists affects other health outcomes is not known.
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Brief Report: Tetragametic Chimerism
Chimerism is the presence of two genetically distinct cell lines in an organism. This report describes a phenotypically normal woman who was found to have tetragametic chimerism after histocompatibility testing of family members suggested that she was not the biologic mother of two of her three children. She had only one cell line in peripheral blood but had more than one in other tissues. Her T lymphocytes showed full tolerance of cells from family members with any combination of four familial HLA haplotypes. Chimerism is rare but is likely to be underdiagnosed. Molecular studies to detect chimerism should be considered in cases in which the results of histocompatibility testing suggest unexpectedly that family members are not related.
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Current Concepts: Major Radiation Exposure
This article reviews possible sources of major exposure to radiation, summarizes the physical and biologic principles of radiation exposure, and describes the main syndromes. The authors explain the medical management of radiation exposure, as well as the components of preparation for crisis management. The acute clinical effects of large doses of radiation are well known and can be assessed with simple laboratory tests.
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Legislation is pending in the Congress that could affect research using embryonic stem cells. In a Legal Issues in Medicine article, Annas outlines the bill passed by the House of Representatives, the bills pending in the Senate, and the position of the current administration on these issues. In his opinion, the issue of reproductive cloning must be considered separately from issues related to therapeutic cloning if any real progress is to be made. The controversy surrounding the scientific and medical use of stem cells is further explored in two Sounding Board articles by Weissman and Evers. Weissman discusses the situation in the United States, and Evers presents the European perspective.
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