Decreased necrotizing fasciitis capacity caused by a single nucleotide mutation that alters a multiple gene virulence axis.

Single-nucleotide changes are the most common cause of natural genetic variation among members of the same species, but there is remarkably little information bearing on how they alter bacterial virulence. We recently discovered a single-nucleotide mutation in the group A Streptococcus genome that is epidemiologically associated with decreased human necrotizing fasciitis ("flesh-eating disease"). Working from this clinical observation, we find that wild-type mtsR function is required for group A Streptococcus to cause necrotizing fasciitis in mice and nonhuman primates. Expression microarray analysis revealed that mtsR inactivation results in overexpression of PrsA, a chaperonin involved in posttranslational maturation of SpeB, an extracellular cysteine protease. Isogenic mutant strains that overexpress prsA or lack speB had decreased secreted protease activity in vivo and recapitulated the necrotizing fasciitis-negative phenotype of the DeltamtsR mutant strain in mice and monkeys. mtsR inactivation results in increased PrsA expression, which in turn causes decreased SpeB secreted protease activity and reduced necrotizing fasciitis capacity. Thus, a naturally occurring single-nucleotide mutation dramatically alters virulence by dysregulating a multiple gene virulence axis. Our discovery has broad implications for the confluence of population genomics and molecular pathogenesis research.

Silicone thorax due to a ruptured breast implant.

A woman with a history of bilateral mastectomy and silicone implants for fibrocystic disease and a history of atrial septal defect repair presented with pleural nodules on a chest radiograph. A thorascopic biopsy performed for possible mesothelioma demonstrated chronic inflammation and focal pleural fibrosis due to a foreign-body reaction secondary to silicone. This was confirmed using scanning electron microscopy and energy-dispersive radiograph elemental analysis. As the population ages, the increasing frequency of ruptured silicone implants and the need for heart surgery may result in a corresponding increase in the risk for fibrothorax secondary to inadvertent silicone introduction during surgery.

Light chain crystal deposition as a manifestation of plasma cell dyscrasias: the role of immunoelectron microscopy.

Light chain crystal deposition disease is a rare and poorly characterized entity that can be confused with a number of different conditions, depending on where the disease process is manifested. The present study explored the role of ultrastructural immunogold labeling in the diagnosis of this condition. Seven cases of light chain crystal deposition (kappa light chain-related) are reported. Immunohistochemistry and immunofluorescence techniques play a rather limited role in the evaluation of these cases, as a result of the inability to detect monoclonal kappa light chains in association with the crystalline structures or high background staining. Ultrastructural labeling is the method of choice to fully characterize these cases. However, surgical pathologists must learn to recognize the findings associated with this condition to avoid misdiagnosis. If the diagnosis is at least suspected, then a complete hematologic workup may identify the underlying plasma cell dyscrasia. It must be emphasized that in some patients the plasma cell dyscrasia does not become clinically manifested until years after the diagnosis of light chain crystal deposition.

Are gadolinium-based contrast media nephrotoxic? A renal biopsy study.

Gadolinium-based contrast media were originally introduced as alternatives to iodinated media for magnetic resonance imaging. Although originally thought to be nonnephrotoxic, gadolinium-based contrast media have recently been reported to be associated with acute renal failure; the mechanism and the underlying renal injury are not completely understood. We report what is, to our knowledge, the first renal biopsy in this context. A 56-year-old patient underwent 2 consecutive vascular imaging procedures in conjunction with gadolinium-based contrast medium administration. A few days later, the patient developed acute renal failure. A renal biopsy showed acute tubular cell injury including patchy tubular cell necrosis, tubular cell degeneration, and marked proliferation of tubular cells, together with mild interstitial edema and interstitial inflammation, but without significant glomerular or vascular changes. During supportive therapy, renal function was partially regained. This case emphasizes the potential nephrotoxicity of gadolinium-based contrast media and suggests that the nephrotoxicity is related to potentially reversible acute tubular cell injury.

Reelin promotes peripheral synapse elimination and maturation.

Reelin is an extracellular protein that is crucial for layer formation in the embryonic brain. Here, we demonstrate that Reelin functions postnatally to regulate the development of the neuromuscular junction. Reelin is required for motor end-plate maturation and proper nerve-muscle connectivity, and it directly promotes synapse elimination. Unlike layer formation, neuromuscular junction development requires a function of Reelin that is not mediated by Disabled1 or very-low-density lipoprotein receptors and apolipoprotein E receptor 2 receptors but by a distinct mechanism involving its protease activity.