fWIW I feel there is definitely a genetic component and the NMSS is addressses this topic.

“What makes people susceptible to multiple sclerosis?” Most scientists and physicians who have studied this question are convinced that heredity—the genes we inherit from our ancestors—is one factor."

"The average person in the United States has about one chance in 750 of developing MS. But relatives
of people with MS, such as children, siblings or nonidentical twins, have a higher chance—ranging from one in
100 to one in 40. The identical twin of someone with MS, who shares all the same genes, has a one in four chance of developing the disease."

From:
http://www.nationalmssociety.org/download.aspx?id=28