Mendelian randomization in the multivariate general linear model framework.

Mendelian randomization (MR) is an application of instrumental variable (IV) methods to observational data in which the IV is a genetic variant. MR methods applicable to the general exponential family of distributions are currently not well characterized. We adapt a general linear model framework to the IV setting and propose a general MR method applicable to any full-rank distribution from the exponential family. Empirical bias and coverage are estimated via simulations. The proposed method is compared to several existing MR methods. Real data analyses are performed using data from the REGARDS study to estimate the potential causal effect of smoking frequency on stroke risk in African Americans. In simulations with binary variates and very weak instruments the proposed method had the lowest median [Q1 , Q3 ] bias (0.10 [-3.68 to 3.62]); compared with 2SPS (0.27 [-3.74 to 4.26]) and the Wald method (-0.69 [-1.72 to 0.35]). Low bias was observed throughout other simulation scenarios; as well as more than 90% coverage for the proposed method. In simulations with count variates, the proposed method performed comparably to 2SPS; the Wald method maintained the most consistent low bias; and 2SRI was biased towards the null. Real data analyses find no evidence for a causal effect of smoking frequency on stroke risk. The proposed MR method has low bias and acceptable coverage across a wide range of distributional scenarios and instrument strengths; and provides a more parsimonious framework for asymptotic hypothesis testing compared to existing two-stage procedures.

Cross-sectional analysis of the Myasthenia Gravis Patient Registry: Disability and treatment.

INTRODUCTION: The Myasthenia Gravis Patient Registry (MGR) is a voluntary, patient-submitted database dedicated to improve understanding of care/burden of myasthenia gravis (MG). METHODS: In this study we present analyses of baseline records through July 2017 (n = 1140) containing data on the MG-Activities of Daily Living (MG-ADL) and the MG 15-item Quality of Life (MG-QOL15) instruments, two validated scales assessing quality of life in MG patients at sign-up into the MGR. RESULTS: Most registrants reported moderate to severe impairment of health-related quality of life, with a median MG-ADL score of 6 and a median MG-QOL15 score of 21. Seventy-one percent of the patients had received pyridostigmine. Corticosteroids, mycophenolate mofetil, and azathioprine were the most common immunomodulators/immunosuppressants, with 85% of participants having ever using one of these agents. Forty-seven registrants reported receiving intravenous immunoglobulin, and 30% received plasma exchange. Twelve percent reported other treatments, and 40% were unsure whether they received less common therapies. Forty percent had undergone thymectomy. DISCUSSION: The MGR data correlate well with other MG cohorts. Many MG patients remain negatively impacted despite treatment.

Outcomes of shared institutional review board compared with multiple individual site institutional review board models in a multisite clinical trial.

BACKGROUND: Institutional review boards play a crucial role in initiating clinical trials. Although many multicenter clinical trials use an individual institutional review board model, where each institution uses their local institutional review board, it is unknown if a shared (single institutional review board) model would reduce the time required to approve a standard institutional review board protocol. OBJECTIVE: This study aimed to compare processing times and other processing characteristics between sites using a single institutional review board model and those using their individual site institutional review board model in a multicenter clinical trial. STUDY DESIGN: This was a retrospective study of sites in an open-label, multicenter randomized control trial from 2014 to 2021. Participating sites in the multicenter Chronic Hypertension and Pregnancy trial were asked to complete a survey collecting data describing their institutional review board approval process. RESULTS: A total of 45 sites participated in the survey (7 used a shared institutional review board model and 38 used their individual institutional review board model). Most sites (86%) using the shared institutional review board model did not require a full-board institutional review board meeting before protocol approval, compared with 1 site (3%) using the individual institutional review board model (P<.001). Median total approval times (41 vs 56 days; P=.42), numbers of submission rounds (1 vs 2; P=.09), and numbers of institutional review board stipulations (1 vs 4; P=.12) were lower for the group using the shared institutional review board model than those using the individual site institutional review board model; however, these differences were not statistically significant. CONCLUSION: The findings supported the hypothesis that the shared institutional review board model for multicenter studies may be more efficient in terms of cumulative time and effort required to obtain approval of an institutional review board protocol than the individual institutional review board model. Given that these data have important implications for multicenter clinical trials, future research should evaluate these findings using larger or multiple multicenter trials.

Longitudinal Analysis of Disease Burden in Refractory and Nonrefractory Generalized Myasthenia Gravis in the United States.

OBJECTIVE: To compare temporal trends in clinical and health care resource utilization (HRU) outcomes in people with refractory and nonrefractory generalized myasthenia gravis (gMG). METHODS: A retrospective analysis of data from adults with gMG in the Myasthenia Gravis Foundation of America Patient Registry. gMG status (ever-refractory or always nonrefractory) and clinical (Myasthenia Gravis-Activities of Daily Living [MG-ADL] scores, exacerbations) and HRU outcomes were determined from questionnaires self-completed 6-monthly for up to 4 years. The probability of each outcome was compared for the 2 groups over time. RESULTS: The mean MG-ADL score and the probability of experiencing each outcome were significantly greater in the ever-refractory versus nonrefractory groups during each year of follow-up. Between-group differences in time trends were statistically significant for intensive care and feeding-tube use. CONCLUSIONS: People who have ever had refractory gMG may have worse functional status, more exacerbations, and higher HRU than people with consistently nonrefractory disease.

An introduction to Mendelian randomization with applications in neurology.

Mendelian randomization studies have become increasingly common due to the maturation of genome-wide association studies and its potential to ascertain causal relationships. With the increasing use of this method comes the need for medical practitioners and clinicians to develop an understanding of its rationale, limitations, and interpretation. Mendelian randomization attempts to ascertain a causal relationship between some risk factor of interest and some outcome or disease of interest. It exploits Mendel's law on the random assortment of genetic variants. This random assortment of genetic variants mimics the main principle of randomization used in clinical trials; with the genetic variant replacing the randomly allocated treatment. In this paper we provide a readable introduction to the rationale behind Mendelian randomization and its limitations. We also discuss and interpret several examples of Mendelian randomization analyses which pertain to neurological diseases.