Department G.F. Ingrassia Section of Neurosciences, University of Catania, Catania, Italy

Objective: To study the blood levels of selected trace elements (TE) in Multiple Sclerosis (MS) patients living in high-incidence cluster areas in the Etna volcano region. Methods: MS patients living in the province of Catania have been retrospectively enrolled among those followed by the Neurologic Clinic of the AOU Policlinico “G. Rodolico-San Marco” who had the disease onset between 2005 and 2020.Aserumsample was used for the determination of TE levels (As,Cd, Cr, Cu, Fe, Mg, Mn, Ni, Se, Zn). All the analyses have been conducted with an ICPMS with the standard addition technique, previous digestion of the samples with nitric acid. MS patients living the high incidence clusters were frequency matched with MS patients living outside the clusters. Comparisons of TE across the groups were conducted using the Mann-Whitney test. Results: A total of 86 (48 women; 55.8%) MS patients was recruited, with a mean age of 41.6±13.1 years, a mean disease duration of 2.0±2.6 years and a mean Expanded Disability Status Scale of 2.3±1.7. Of these patients, 40 belonged to high incidence clusters and 46 were outside the clusters. No differences were found in demographic characteristics between the groups. Concerning TE, we found a significant higher concentration of Mn in incluster patients (6.7±16.6 μg/L vs 2.5±5.9 μg/L). Discussion: Several environmental factors may modulate the pathogenesis of the disease, and among them TE play an important role. Our findings suggest that Manganese, which has several toxic effects, might contribute to the higher incidence of MS previously observed in a cluster of communalities in the south-eastern flank of the Etna volcano, where volcanic ashes rich in TE usually fall due to the prevailing winds. Conclusions: Exposition to high levels of Mn could be a cofactor in the pathogenesis of MS.

Background: Trace elements have been hypothesised to be involved in the pathogenesis of Multiple Sclerosis and volcanic degassing is the major natural sources of trace elements. Both incidence of Multiple Sclerosis in Catania and volcanic activity of Mount Etna have been significantly increased during the last 30 years. Due to prevailing trade winds direction, volcanic gases from Etna summit craters are mostly blown towards the eastern and southern sectors of the volcano. Objective: To evaluate the possible association between Multiple Sclerosis and exposure to volcanogenic trace elements. Methods: We evaluated prevalence and incidence of Multiple Sclerosis in four communities (47,234 inhabitants) located in the eastern flank and in two communities (52,210 inhabitants) located in the western flank of Mount Etna, respectively the most and least exposed area to crater gas emissions. Results: A higher prevalence was found in the population of the eastern flank compared to the population of the western one (137.6/100,000 versus 94.3/100,000; p-value 0.04). We found a borderline significantly higher incidence risk during the incidence study period (1980–2009) in the population of the eastern flank 4.6/100,000 (95% CI 3.1–5.9), compared with the western population 3.2/100,000 (95% CI 2.4–4.2) with a RR of 1.41 (95% CI 0.97–2.05; p-value 0.06). Incidence risks have increased over the time in both populations reaching a peak of 6.4/100,000 in the eastern flank and of 4.4/100.000 in the western flank during 2000–2009. Conclusion: We found a higher prevalence and incidence of Multiple Sclerosis among populations living in the eastern flank of Mount Etna. According to our data a possible role of TE cannot be ruled out as possible co-factor in the MS pathogenesis. However larger epidemiological study are needed to confirm this hypothesis.

Previously, we described a significantly higher risk of amyotrophic lateral sclerosis (ALS) among the population living on the eastern flank of Mount Etna with respect to the western flank [relative risk 2.75; 95% confidence interval (CI) 1.64– 4.89] [1]. Since winds usually blow Etna ash from west to northwest [2], the eastern flank is the most exposed area and volcanogenic metals were proposed as a possible explanation. Here, we further investigated the spatial distribution of ALS cases in the Mount Etna region during 2005–2015, performing a geostatistical cluster analysis. The study was conducted in the province of Catania. ALS patients were diagnosed according to the El Escorial revised criteria [3]. Standardized incidence ratios (SIRs) of each communality were calculated using the annual population of the entire province as a reference through an age- and sex-adjusted indirect standardization. Cluster analysis was performed using both a local Moran index (also termed Local Indicators of Spatial Association, LISA) [4] and Kulldorff’s spatial scan statistics [5]. The Monte Carlo simulation was used to assess the statistical significance of the results (P value was set at 0.05%). The Kulldorff spatial scan statistic was implemented using SatScan software, version 9.4.4 [6]. A total of 202 residents were diagnosed with ALS during 2005–2015 giving a mean annual crude incidence rate of 1.70/100 000 person-years (95% CI 1.47– 1.94) (Table S1). Two communalities, both located on the southeastern flank of the volcano, showed an SIR higher than 1 (SIR 1.80, 95% CI 1.07–2.84, and SIR 2.28, 95% CI 1.18–3.99) (Fig. 1a). LISA analysis showed the presence of an aggregative spatial structure on the southeastern flank of Mount Etna and Kulldorff’s statistic confirmed the above indication by revealing a higher incidence spatio-temporal cluster that includes 13 communalities in the same area. During the 2006–2010 period, 13.24 cases were expected whereas 33 were observed, therefore resulting in an SIR of 2.49 (95% CI 1.72–3.50, P value 0.007) (Fig. 1b). Purely spatial analysis revealed a smaller cluster including four communalities, with an SIR of 2.2 (95% CI 1.39–3.3) (Fig. 1b). Several genetic and environmental factors have been proposed to play a role in the ALS pathogenesis. Among environmental factors, metals seem to play a relevant role [7]. Volcanoes are a major source of metals [8] and Mount Etna is the largest active volcano in Europe. We found a higher incidence spatio-temporal cluster (2006–2010) on the southeastern flank of the volcano, the area most exposed to volcanic ash. In fact, during 2001–2003 an intense and long-lasting explosive activity ofMount Etna was recorded from eruptive fissures located on the southern and the eastern flanks of the volcano and during this period about 2.1 kg/m2 of ash was deposited in 3 days [9]. This finding could further suggest the possible role of volcanogenic metals in ALS pathogenesis. Nonetheless, we cannot exclude that other factors, both genetic and environmental, may have contributed to the higher incidence of ALS on the southeastern flank of Mount Etna. Further studies are needed in order to explore possible alternative hypotheses.