A Generalized Concordance Correlation Coefficient Based on the Variance Components Generalized Linear Mixed Models for Overdispersed Count Data

Summary The classical concordance correlation coefficient (CCC) to measure agreement among a set of observers assumes data to be distributed as normal and a linear relationship between the mean and the subject and observer effects. Here, the CCC is generalized to afford any distribution from the exponential family by means of the generalized linear mixed models (GLMMs) theory and applied to the case of overdispersed count data. An example of CD34+ cell count data is provided to show the applicability of the procedure. In the latter case, different CCCs are defined and applied to the data by changing the GLMM that fits the data. A simulation study is carried out to explore the behavior of the procedure with a small and moderate sample size.     

Association of Parathyroidectomy With 5-Year Clinically Significant Kidney Stone Events in Patients With Primary Hyperparathyroidism

ObjectivePatients with primary hyperparathyroidism (PHPT) are at increased risk of kidney stones. Guidelines recommend parathyroidectomy in patients with PHPT with a history of stone disease. This study aimed to compare the 5-year incidence of clinically significant kidney stone events in patients with PHPT treated with parathyroidectomy versus nonoperative management.MethodsWe performed a longitudinal cohort study of patients with PHPT in a national commercial insurance claims database (2006-2019). Propensity score inverse probability weighting-adjusted multivariable regression models were calculated.ResultsWe identified 7623 patients aged ≥35 years old with continuous enrollment >1 year before and >5 years after PHPT diagnosis. A total of 2933 patients (38.5%) were treated with parathyroidectomy. The cohort had a mean age of 66.5 years, 5953 (78.1%) were female, and 5520 (72.4%) were White. Over 5 years, the unadjusted incidence of ≥1 kidney stone event was higher in patients who were managed with parathyroidectomy compared with those who were managed nonoperatively overall (5.4% vs 4.1%, respectively) and among those with a history of kidney stones at PHPT diagnosis (17.9% vs 16.4%, respectively). On multivariable analysis, parathyroidectomy was associated with no statistically significant difference in the odds of a 5-year kidney stone event among patients with a history of kidney stones (odds ratio, 1.03; 95% CI, 0.71-1.50) or those without a history of kidney stones (odds ratio, 1.16; 95% CI, 0.84-1.60).ConclusionBased on this claim analysis, there was no difference in the odds of 5-year kidney stone events in patients with PHPT who were treated with parathyroidectomy versus nonoperative management. Time horizon for benefit should be considered when making treatment decisions for PHPT based on the risk of kidney stone events.     

Insights into the oligomeric structure of the HIV-1 Vpu protein

The HIV-1-encoded protein Vpu forms an oligomeric ion channel/pore in membranes and interacts with host proteins to support the virus lifecycle. However, Vpu molecular mechanisms are currently not well understood. Here, we report on the Vpu oligomeric organization under membrane and aqueous conditions and provide insights into how the Vpu environment affects the oligomer formation. For these studies, we designed a maltose-binding protein (MBP)-Vpu chimera protein and produced it in E. coli in soluble form. We analyzed this protein using analytical size-exclusion chromatography (SEC), negative staining electron microscopy (nsEM), and electron paramagnetic resonance (EPR) spectroscopy. Surprisingly, we found that MBP-Vpu formed stable oligomers in solution, seemingly driven by Vpu transmembrane domain self-association. A coarse modeling of nsEM data as well as SEC and EPR data suggests that these oligomers most likely are pentamers, similar to what was reported regarding membrane-bound Vpu. We also noticed reduced MBP-Vpu oligomer stability upon reconstitution of the protein in β-DDM detergent and mixtures of lyso-PC/PG or DHPC/DHPG. In these cases, we observed greater oligomer heterogeneity, with MBP-Vpu oligomeric order generally lower than in solution; however, larger oligomers were also present. Notably, we found that in lyso-PC/PG, above a certain protein concentration, MBP-Vpu assembles into extended structures, which had not been reported for Vpu. Therefore, we captured various Vpu oligomeric forms, which can shed light on Vpu quaternary organization. Our findings could be useful in understanding Vpu organization and function in cellular membranes and could provide information regarding the biophysical properties of single-pass transmembrane proteins.     

The PurR binding site in the glyA prometer region of Escherichia coli

Site-directed mutagenesis was used to change the PurR binding site in the control region of a glyA-lac gene fusion. Mutations that changed the PurR binding sequence away from the consensus sequence reduced PurR binding, which correlated with reduced purine-mediated repression. Mutations that changed the binding sequence toward the consensus sequence had no significant effect on either PurR binding or purine-mediated repression. Hypoxanthine and guanine, co-repressors for PurR-mediated regulation of the pur regulon, increased binding of PurR to glyA operator DNA.     

Quantile regression for nonignorable missing data with its application of analyzing electronic medical records

Over the past decade, there has been growing enthusiasm for using electronic medical records (EMRs) for biomedical research. Quantile regression estimates distributional associations, providing unique insights into the intricacies and heterogeneity of the EMR data. However, the widespread nonignorable missing observations in EMR often obscure the true associations and challenge its potential for robust biomedical discoveries. We propose a novel method to estimate the covariate effects in the presence of nonignorable missing responses under quantile regression. This method imposes no parametric specifications on response distributions, which subtly uses implicit distributions induced by the corresponding quantile regression models. We show that the proposed estimator is consistent and asymptotically normal. We also provide an efficient algorithm to obtain the proposed estimate and a randomly weighted bootstrap approach for statistical inferences. Numerical studies, including an empirical analysis of real-world EMR data, are used to assess the proposed method's finite-sample performance compared to existing literature.     

The Almost-one Parameter Hypothesis Applied to Pharmacokinetics of Ethanol Infusion

They say that the pharmacokinetics of constant-rate intravenous infusion of ethanol obeys the Henri-Michaelis-Menten (H-M-M) model. In analysing the original data from the viewpoint of the almost-one parameter hypothesis (see box 1), we found that the whole process should be divided into four phases and the H-M-M model was valid only in the last phase.     

A theoretical approach to G-protein modulation of cellular responsiveness

 Structure and function of cells often depend critically on molecular signals arriving at their surface. There are universal mechanisms of signal transduction and signal processing across cell membranes. In this paper the mechanisms involving guanine-nucleotide regulatory proteins (“G-proteins”) and certain receptor-kinases are considered. On the basis of recent findings in molecular biology a mathematical model is developed taking into account all essential components in the biochemical network between first and second messenger. There are two coupled feedback loops inherent in this process. The model finally consists of three nonlinear equations, which are obtained from a system of originally ten equations by using conservation laws and quasi-steady state conditions. The second part of the paper contains a mathematical analysis of the model. Solutions describing the temporal development of the involved biochemical species are shown to be bounded, more specifically to remain, independent of the size of the input signal, in a bounded domain of the state space. For the situation of stationary input signals existence, uniqueness and asymptotic stability of steady states are derived. We also demonstrate biologically relevant stimulus-response properties like monotonicity and saturation effects. For temporally non-constant input signals we show numerically that the model is able to produce phenomena of hypersensitivity and desensitization which are important characteristics of cellular responsiveness. Received 18 March 1996; received in revised form 15 April 1996