Tobacco use as a risk factor for reoperation in patients with stress urinary incontinence: a multi-institutional electronic medical record database analysis.

INTRODUCTION AND HYPOTHESIS: Recurrence rates of stress urinary incontinence after surgery are reported to be between 8 to 15%. Both surgical technique and non-surgical risk factors have been shown to affect post-operative outcomes. Tobacco use is a possible risk factor that may increase the surgical failure rate, however, there are currently conflicting reports in the literature regarding the affect of tobacco use on surgical outcomes. Our objective is to evaluate the effect of tobacco use on the risk of repeat surgery for stress urinary incontinence (SUI). METHODS: We performed a retrospective cohort analysis using a de-identified clinical database from a large multi-institution electronic health records data web application EPM:ExploreTM (Explorys Inc, Cleveland, Ohio) to identify women with and without a history of tobacco use who underwent reoperation for stress urinary incontinence within 2 years of the first surgery. We then evaluated previously described risk factors for reoperation: diabetes mellitus (DM), pelvic organ prolapse (POP), anti-muscarinic (AM) use at initial surgery, obesity, and advanced age on rate of reoperation and the impact of tobacco use on these risk factors. RESULTS: Tobacco use was associated with an increased rate of a second surgery for SUI (OR=1.43, p <0.001), as was anti-muscarinic use (OR = 1.68, p<0.001), DM (OR = 1.21, p = 0.005), age >50 years (OR= 1.16, p = 0.040), and BMI > 30 kg/m2 (OR = 2.97 p<0.001). The odds of a second surgery for SUI in patients who used tobacco and anti-muscarinic medications or had pelvic organ prolapse were lower when compared to non-users. The odds of a second surgery for SUI were higher in patients who used tobacco and had asthma when compared to non-users who had asthma. CONCLUSIONS: Tobacco increases the overall risk of second surgery for SUI, however, in patients with specific risk factors, tobacco use is associated with a decrease risk of reoperation.

How meaningful are heritability estimates of liability?

It is commonly acknowledged that estimates of heritability from classical twin studies have many potential shortcomings. Despite this, in the post-GWAS era, these heritability estimates have come to be a continual source of interest and controversy. While the heritability estimates of a quantitative trait are subject to a number of biases, in this article we will argue that the standard statistical approach to estimating the heritability of a binary trait relies on some additional untestable assumptions which, if violated, can lead to badly biased estimates. The ACE liability threshold model assumes at its heart that each individual has an underlying liability or propensity to acquire the binary trait (e.g., disease), and that this unobservable liability is multivariate normally distributed. We investigated a number of different scenarios violating this assumption such as the existence of a single causal diallelic gene and the existence of a dichotomous exposure. For each scenario, we found that substantial asymptotic biases can occur, which no increase in sample size can remove. Asymptotic biases as much as four times larger than the true value were observed, and numerous cases also showed large negative biases. Additionally, regions of low bias occurred for specific parameter combinations. Using simulations, we also investigated the situation where all of the assumptions of the ACE liability model are met. We found that commonly used sample sizes can lead to biased heritability estimates. Thus, even if we are willing to accept the meaningfulness of the liability construct, heritability estimates under the ACE liability threshold model may not accurately reflect the heritability of this construct. The points made in this paper should be kept in mind when considering the meaningfulness of a reported heritability estimate for any specific disease.