Evaluation of the Cobas TaqMan MTB test for direct detection of Mycobacterium tuberculosis complex in respiratory specimens

The Cobas TaqMan MTB test, based on real-time PCR technology, was evaluated for direct detection of Mycobacterium tuberculosis complex (MTBC) in respiratory specimens. A total of 1,093 samples from 446 patients, including 118 acid-fast smear-positive and 975 acid-fast smear-negative specimens, were investigated. Diagnostic cultures performed with 7H11 agar, Löwenstein-Jensen medium, and the Bactec MGIT 960 system were considered the reference methods. When discrepant results between the Cobas TaqMan MTB test and culture occurred, additional results from the BD MGIT TBc identification test and the GenoType Mycobacterium CM test performed on growth-positive and acid-fast-stain-positive MGIT tubes and review of the patient''s medical history were used for discrepancy analysis. The overall sensitivity, specificity, positive predictive value, and negative predictive value for the Cobas TaqMan MTB test were 91.5%, 98.7%, 91.5%, and 98.7%, respectively. In general, the performance of the new Cobas TaqMan MTB test was comparable to that of the replaced Cobas Amplicor MTB system. The most prominent feature of the new system was its extraordinarily high sensitivity (79.5%) for detecting MTBC in smear-negative specimens; out of 44 smear-negative but culture-positive specimens, 35 were positive by the new system. The Cobas TaqMan MTB assay, including DNA extraction, can be completed within 3 h.     

Lipoprotein lipase variants associated with an endophenotype of hypertension: hypertension combined with elevated triglycerides

Previously, we observed that young-onset hypertension was independently associated with elevated plasma triglyceride(s) (TG) levels to a greater extent than other metabolic risk factors. Thus, focusing on the endophenotype--hypertension combined with elevated TG--we designed a family-based haplotype association study to explore its genetic connection with novel genetic variants of lipoprotein lipase gene (LPL), which encodes a major lipid metabolizing enzyme. Young-onset hypertension probands and their families were recruited, numbering 1,002 individuals from 345 families. Single-nucleotide polymorphism discovery for LPL, linkage disequilibrium (LD) analysis, transmission disequilibrium tests (TDT), bin construction, haplotype TDT association and logistic regression analysis were performed. We found that the CC- haplotype (i) spanning from intron 2 to intron 4 and the ACATT haplotype (ii) spanning from intron 5 to intron 6 were significantly associated with hypertension-related phenotypes: hypertension (ii, P=0.05), elevated TG (i, P=0.01), and hypertension combined with elevated TG (i, P=0.001; ii, P<0.0001), according to TDT. The risk of this hypertension subtype increased with the number of risk haplotypes in the two loci, using logistic regression model after adjusting within-family correlation. The relationships between LPL variants and hypertension-related disorders were also confirmed by an independent association study. Finally, we showed a trend that individuals with homozygous risk haplotypes had decreased LPL expression after a fatty meal, as opposed to those with protective haplotypes. In conclusion, this study strongly suggests that two LPL intronic variants may be associated with development of the hypertension endophenotype with elevated TG.     

Population pharmacokinetics of valproic acid concentrations in elderly nursing home residents

The objective of this study was to identify factors that affect valproic acid (VPA) apparent clearance (CL/F) in elderly nursing home residents. Inclusion criteria included residency in a nursing home for at least 2 months, aged 65 years or older, a stable dosing regimen of VPA for at least 4 weeks, VPA concentration, and complete dosing information. CL/F was analyzed by a nonlinear mixed effects model. A one-compartment model with first-order absorption and elimination was used. Both volume and absorption rate constant were fixed (14 L and 1 hr, respectively). Covariates were tested by forward inclusion and backward elimination. Interindividual variability in clearance was estimated using an exponential error model and expressed as a coefficient of variation. Residual error was estimated using a combined additive and constant coefficient of variation error model. The study consisted of 405 observations from 146 (52 men, 94 women) elderly nursing home residents. CL/F was not affected by age or weight. The population CL/F was 0.843 L/hr. CL/F was 1) 27% lower in female residents; 2) 41% greater when the resident was on concomitant metabolic inducers carbamazepine or phenytoin cotherapy; and 3) 25% greater when the syrup formulation was used. Variability in CL/F was 32.9%. Coefficient of variation and standard deviation of the residual error were 18.2% and 10.6 mg/L, respectively. The increased CL/F in patients taking VPA syrup may be the result of a decreased bioavailability (F) rather than an increased CL that could be associated with pathology requiring use of the syrup rather than an inherent property of the drug formulation. The results from this study may be useful for individualizing dose regimens in the nursing home population based on patient-specific factors.     

Hemophagocytic syndrome associated with antiepileptic drug

An 8-year-3-month-old male with right porencephaly and epilepsy was found to have skin rash 2 weeks after the beginning of treatment with lamotrigine. One month later he suffered from impaired liver function and pancytopenia in the presence of hypocellular bone marrow with hemophagocytosis. No evidence of infection was evident. Intravenous immunoglobulin and steroid were administered with discontinuation of lamotrigine; the hemogram and liver function profile improved dramatically. Hemophagocytic syndrome should be considered a possible cause of pancytopenia in patients taking new antiepileptic drugs such as lamotrigine.     

Resistance of Australian Helicoverpa armigera to fenvalerate is due to the chimeric P450 enzyme CYP337B3

Worldwide, increasing numbers of insects have evolved resistance to a wide range of pesticides, which hampers their control in the field and, therefore, threatens agriculture. Members of the carboxylesterase and cytochrome P450 monooxygenase superfamilies are prominent candidates to confer metabolic resistance to pyrethroid insecticides. Both carboxylesterases and P450 enzymes have been shown to be involved in pyrethroid resistance in Australian Helicoverpa armigera, the noctuid species possessing by far the most reported resistance cases worldwide. However, specific enzymes responsible for pyrethroid resistance in field populations of this species have not yet been identified. Here, we show that the resistance toward fenvalerate in an Australian strain of H. armigera is due to a unique P450 enzyme, CYP337B3, which arose from unequal crossing-over between two parental P450 genes, resulting in a chimeric enzyme. CYP337B3 is capable of metabolizing fenvalerate into 4′-hydroxyfenvalerate, which exhibits no toxic effect on susceptible larvae; enzymes from the parental P450 genes showed no detectable fenvalerate metabolism. Furthermore, a polymorphic H. armigera strain could be bred into a susceptible line possessing the parental genes CYP337B1 and CYP337B2 and a resistant line possessing only CYP337B3. The exclusive presence of CYP337B3 in resistant insects of this strain confers a 42-fold resistance to fenvalerate. Thus, in addition to previously documented genetic mechanisms of resistance, recombination can also generate selectively advantageous variants, such as this chimeric P450 enzyme with an altered substrate specificity leading to a potent resistance mechanism.