Epidemiology of familial multiple sclerosis: A population-based study in Tehran during 1999-2018

Familial multiple sclerosis (FMS) studies are valuable as they reveal the effects of environment and genes on the etiology of the disease.

The present study was carried out to examine the significant variables related to the risk of FMS and its epidemiological characteristics.

This cross-sectional population-based study was conducted on 21,580 MS patients registered in the Iranian MS Society (IMSS) registry system of Tehran from 1999 to 2018. P-values < 0.05 were considered significant.

Familial MS was found among 13.04% of patients. The age-standardized prevalence of FMS increased from 9.3 to 18.3 per 100,000 people during the study period. The FMS recurrence was found to be significantly higher among women as compared with men (P-value = 0.001). Most of FMS patients were 18-29 years of age at disease onset, and the mean age of onset was 28.49 years. The occurrence rate of pediatric MS was higher in patients with FMS as compared with those without a history of MS (8.1% vs. 6.6%, respectively). The majority of FMS cases were observed among first-degree relatives, with the highest rate in male siblings (35.38%). The results indicated that the probability of MS occurrence among the offspring of mothers with MS (7.99%) was higher than its probability among the offspring of fathers with MS (2.34%).

The increasing prevalence of FMS in Tehran over time emphasizes the importance of conducting more investigations on the substantial role of genetic and environmental factors in FMS pathogenesis and inheritance.