Non-parametric analysis of seasonality in birth and multiple sclerosis risk in second generation of migrants in Kuwait

BACKGROUND There are inconsistent reports about multiple sclerosis (MS) risk among migrants from low to high MS risk geographical regions. This study assessed the overall MS incidence and evaluated seasonality in birth and subsequent MS risk later in the life in second generation of migrants born and lived in Kuwait. METHODS We assessed the overall and gender-specific MS risk in second generation of migrants born and lived in Kuwait between January 1, 1950 and April 30, 2013. Data on migrants' MS patients diagnosed and registered in Kuwait National MS Registry were used. Hewitt's non-parametric test was carried out to evaluate the seasonality in migrants' MS births in comparison with the second generation migrants' births in general population. RESULTS During the study period, an overall risk of migrants' MS births (per 100,000 non-Kuwaiti births in general population) was 23.8 (95% CI: 20.8 - 27.0). Gender-specific MS risk showed that non-Kuwaiti female had statistically significant (p = 0.003) higher risk (28.6; 95% CI: 24.2 - 33.7) than non-Kuwaiti males (18.7; 95% CI: 15.1-23.0). The month-specific distribution of migrants' MS births compared with migrants' births in general population did not differ significantly (χ2 goodness-of-fit test statistic = 9.51, p = 0.575). Hewitt's non-parametric test revealed an evidence of slight but statistically non-significant (p = 0.090) increased tendency of migrants' MS births during September through February. CONCLUSIONS The proportion of migrants' MS births (per 100,000 migrants' births in general population) over the study period was 23.8 (95% CI: 20.8 - 27.0), which was statistically significantly higher than the previously reported Kuwaiti national MS births (16.2; 95% CI: 15.1-17.4) in Kuwait. Non-parametric analysis showed slight but statistically non-significant increased tendency of migrants' MS births from September through February. Knowledge of MS risk factors and how and when they act among genetically vulnerable individuals from gestation to early adulthood will help design prevention strategies.