Estimation of Residual Valve Gradient from Incomplete Data with Outliers

An important indicator for the long-term recovery after valve replacement surgery is postoperative valve gradient. This information is available only for patients received catheterization or echocardiogram postoperatively. It is plausible that sicker patients are more inclined to undergo these postoperative procedures and their valve gradients tend to be higher. Under this situation, ignoring the missing values and using sample mean based on the available information as an estimate of the whole study population leads to overestimation. Regression estimator is a reasonable choice to eliminate this bias if independent (explanatory) variables closely associated with both residual valve gradient and non-response mechanism can be identified. Using a series of patients receiving St. Jude Medical prosthetic valves, we found that valve area index can be used as an independent variable in the regression estimator. Two digressions from the standard assumptions used in linear regression, heteroscedastic trend of the error term and outliers were found in the data set. Iteratively reweighted least square (IRLS) was adopted to handle heteroscedasticity. Influence function approach was used to evaluate the sensitivity of outliers in regression estimator. Under an equal response rate mechanism, IRLS not only solves the problem of heteroscedasticity, but is also less sensitive to outliers.     

Computational phenotyping of brain-behavior dynamics underlying approach-avoidance conflict in major depressive disorder

Adaptive behavior requires balancing approach and avoidance based on the rewarding and aversive consequences of actions. Imbalances in this evaluation are thought to characterize mood disorders such as major depressive disorder (MDD). We present a novel application of the drift diffusion model (DDM) suited to quantify how offers of reward and aversiveness, and neural correlates thereof, are dynamically integrated to form decisions, and how such processes are altered in MDD. Hierarchical parameter estimation from the DDM demonstrated that the MDD group differed in three distinct reward-related parameters driving approach-based decision making. First, MDD was associated with reduced reward sensitivity, measured as the impact of offered reward on evidence accumulation. Notably, this effect was replicated in a follow-up study. Second, the MDD group showed lower starting point bias towards approaching offers. Third, this starting point was influenced in opposite directions by Pavlovian effects and by nucleus accumbens activity across the groups: greater accumbens activity was related to approach bias in controls but avoid bias in MDD. Cross-validation revealed that the combination of these computational biomarkers were diagnostic of patient status, with accumbens influences being particularly diagnostic. Finally, within the MDD group, reward sensitivity and nucleus accumbens parameters were differentially related to symptoms of perceived stress and depression. Collectively, these findings establish the promise of computational psychiatry approaches to dissecting approach-avoidance decision dynamics relevant for affective disorders.     

Processing of the L1 52/55k Protein by the Adenovirus Protease: a New Substrate and New Insights into Virion Maturation

Late in adenovirus assembly, the viral protease (AVP) becomes activated and cleaves multiple copies of three capsid and three core proteins. Proteolytic maturation is an absolute requirement to render the viral particle infectious. We show here that the L1 52/55k protein, which is present in empty capsids but not in mature virions and is required for genome packaging, is the seventh substrate for AVP. A new estimate on its copy number indicates that there are about 50 molecules of the L1 52/55k protein in the immature virus particle. Using a quasi-in vivo situation, i.e., the addition of recombinant AVP to mildly disrupted immature virus particles, we show that cleavage of L1 52/55k is DNA dependent, as is the cleavage of the other viral precursor proteins, and occurs at multiple sites, many not conforming to AVP consensus cleavage sites. Proteolytic processing of L1 52/55k disrupts its interactions with other capsid and core proteins, providing a mechanism for its removal during viral maturation. Our results support a model in which the role of L1 52/55k protein during assembly consists in tethering the viral core to the icosahedral shell and in which maturation proceeds simultaneously with packaging, before the viral particle is sealed.