My understanding is that susceptibility to MS may have an inherited genetic component. Someone with a parent with MS is something like 4 or 8 times more likely to also have it. That's not the same as being hereditary, though -- it seems that some kind of additional environmental or trigger mechanism may be necessary to result in MS.

There is a 2 - 4% increase chance of offspring developing MS when a parent has MS.

oopoopoop is corrent that there could be an environmental trigger...(which could turn an inactive MS gene on but not always the case.)

Also believed to be a virus that some people are genetically susceptible to So in a way yes it is hereditary they do have a slight greater risk, but not only one gene determines the susceptability of MS. People who have no genetic disposition to MS can still develop it