Environmental risk factors in multiple sclerosis: bridging Mendelian randomization and observational studies.

Multiple sclerosis (MS) is a complex disease with both genetic variants and environmental factors involved in disease susceptibility. The main environmental risk factors associated with MS in observational studies include obesity, vitamin D deficiency, Epstein-Barr virus infection and smoking. As modifying these environmental and lifestyle factors may enable prevention, it is important to pinpoint causal links between these factors and MS. Leveraging genetics through the Mendelian randomization (MR) paradigm is an elegant way to inform prevention strategies in MS. In this review, we summarize MR studies regarding the impact of environmental factors on MS susceptibility, thereby paying attention to quality criteria which will aid readers in interpreting any MR studies. We draw parallels and differences with observational studies and randomized controlled trials and look forward to the challenges that such work presents going forward.

Urinary Sodium Profiling in Chronic Heart Failure to Detect Development of Acute Decompensated Heart Failure.

OBJECTIVES: This study sought to determine the relationship between urinary sodium (Una) concentration and the pathophysiologic interaction with the development of acute heart failure (AHF) hospitalization. BACKGROUND: No data are available on the longitudinal dynamics of Una concentration in patients with chronic heart failure (HF), including its temporal relationship with AHF hospitalization. METHODS: Stable, chronic HF patients with either reduced or preserved ejection fraction were prospectively included to undergo prospective collection of morning spot Una samples for 30 consecutive weeks. Linear mixed modeling was used to assess the longitudinal changes in Una concentration. Patients were followed for the development of the clinical endpoint of AHF. RESULTS: A total of 80 chronic HF patients (71 ± 11 years of age; an N-terminal pro-B-type natriuretic peptide [NT-proBNP] concentration of 771 [interquartile range: 221 to 1,906] ng/l; left ventricular ejection fraction [LVEF] 33 ± 7%) prospectively submitted weekly pre-diuretic first void morning Una samples for 30 weeks. A total of 1,970 Una samples were collected, with mean Una concentration of 81.6 ± 41 mmol/l. Sodium excretion remained stable over time on a population level (time effect p = 0.663). However, interindividual differences revealed the presence of high (88 mmol/l Una [n = 39]) and low (73 mmol/l Una [n = 41]) sodium excreters. Only younger age was an independent predictor of high sodium excretion (odds ratio [OR]: 0.91; 95% confidence interval [CI]: 0.83 to 1.00; p = 0.045 per year). During 587 ± 54 days of follow-up, 21 patients were admitted for AHF. Patients who developed AHF had significantly lower Una concentrations (F[1.80] = 24.063; p < 0.001). The discriminating capacity of Una concentration to detect AHF persisted after inclusion of NT-proBNP and estimated glomerular filtration rate (eGFR) measurements as random effects (p = 0.041). Furthermore, Una concentration dropped (Una = 46 ± 16 mmol/l vs. 70 ± 32 mmol/l, respectively; p = 0.003) in the week preceding the hospitalization and returned to the individual's baseline (Una = 71 ± 22 mmol/l; p = 0.002) following recompensation, while such early longitudinal changes in weight and dyspnea scores were not apparent in the week preceding decompensation. CONCLUSIONS: Overall, Una concentration remained relatively stable over time, but large interindividual differences existed in stable, chronic HF patients. Patients who developed AHF exhibited a chronically lower Una concentration and exhibited a further drop in Una concentration during the week preceding hospitalization. Ambulatory Una sample collection is feasible and may offer additional prognostic and therapeutic information.