Month-of-birth and risk of multiple sclerosis in Kuwait: A population-based registry study
METHODS: We compared the months of birth of MS patients diagnosed and registered in Kuwait National MS Registry between January 1, 1950 and April 30, 2013 with births in general population during comparable period. We used the multivariable log-linear Poisson regression model to analyze the data.
RESULTS: A total of 1035 MS patients were diagnosed during the study period. Of these MS patients, 675 (65.2%) were female and 798 (77.1%) were Kuwaiti. Overall risk of MS births (per 105 births in general population) was 28.5; 95% CI: 26.8 -30.3). Multivariable log-linear Poisson regression model showed that based on the observed seasonal pattern in the data, the significant peak in the number of MS births was observed during December (θo = 340o; p = 0.004). During the peak month, the risk of MS birth was 1.3 times the risk of MS birth in the trough month after adjusting for the effects of gender and nationality (adjusted relative risk = 1.3; 95% CI: 1.1-1.6). The amplitude (∞ ± SD: 0.13 ± 0.014) of sinusoidal curve showed a significant difference of 13% from the mean to maximum MS births during peak the month.
CONCLUSIONS: This study showed a statistically significant month of birth effect on MS risk with 13% excess MS births during December in Kuwait. These results are comparable to a larger extent to those reported from other countries, but in contrast few recent claims of negligible month of birth effect on MS risk in areas with high sunlight exposure. Future studies may contemplate to ascertain the seasonal factors eliciting the observed association. The insight into such factors may help curtail MS risk in this and other similar settings in the region.