Familial MS Most Common in Children, Women, Warmer Climates

Inherited or familial multiple sclerosis (MS) occurs most frequently in children, women, and people living in warmer climates, a new study suggests.

Prevalence rates also differ according to geographical areas, with Canada exhibiting the highest rates and Hungary the lowest.

The study, “The global prevalence of familial multiple sclerosis: an updated systematic review and meta-analysis,” was published in the journal BMC Neurology.

MS is the most common cause of non-traumatic neurological disability, affecting more than 2.5 million people worldwide. The exact cause of MS is unknown, but it is thought to be triggered by environmental and genetic factors.

Environmental factors linked to MS include Epstein-Barr virus infection, vitamin D deficiency, lack of sunlight, smoking, obesity, and latitude (distance from the equator).

Although many genes are implicated in MS, changes in the HLA-DRB1*15:01 gene are associated with the highest risk of developing MS. People who inherit the mutation from one parent have a 3.5-fold increased risk of developing MS, rising to eightfold if inherited from both parents.

Previous studies have tried to determine the frequency of MS inheritance within families (familial MS). However, these studies have focused only on inheritance rates in first-degree relatives and ignored second- and third-degree relatives.

In the current study, researchers in Iran attempted to expand the current knowledge of familial MS prevalence by investigating global rates in children and adults, and in both men and women. They also examined familial MS rates based on geographical area and latitude.

The team looked for peer-review research articles investigating familial MS rates that were published from 1984 to 2020. After excluding articles that did not meet their criteria, a total of 49 studies from 46 articles with a sample size of 16,179 familial MS cases were included in the final analysis.

The total prevalence rate of familial MS in the group analyzed was 11.8%, with the highest prevalence found in Saskatchewan, Canada (32.7%), and the lowest in Hungary (2.2%).

Familial MS occurred more frequently in children (15.5%) than in adults (10.8%), and its onset in adults was at a mean age of 28.7 years — indicating an earlier age of onset in comparison to sporadic (not inherited) MS cases.

Familial MS also affected women more frequently than men — 15.4% vs. 13.7%, respectively.

Interestingly, subgroup analysis revealed that familial MS occurred significantly less frequently in higher latitudes and in regions with high MS prevalence.

The researchers suggested that increased public awareness of MS in regions with high disease rates and genetic counseling may have reduced marriages between affected families, leading to lower rates of familial MS in these regions.

Overall, “the findings of this study demonstrated that the prevalence of FMS [familial MS] is higher in pediatric-onset MS cases than that of adult-onset MS, is different between geographical areas, and reduces with the higher MS prevalence and latitude,” the researchers concluded. “Also, the symptoms initiate relatively at younger ages in the FMS cases.”

The team noted, however, that long-term studies are needed to confirm the findings and “to provide time for the development of new cases in relatives,” they wrote.