If it’s in the family, will I get Multiple Sclerosis?
The short answer is probably not. There is no doubt that genetic factors play a part in the development of MS by conferring varying degrees of individual susceptibility. MS has a familial recurrence rate of about 15% overall. The Canadian study of familial MS took a baseline risk of 0.2% and showed a risk of 3% in first degree relatives, and 1% in second degree relatives. More specifically, in the UK the risk is increased as follows: sister, 4.4%; brother, 3.2%; parent, 2.1%; child, 1.8%; all first and second degree relatives, 2.8 and 1% respectively. 5 Where both parents have MS, the risk to offspring is significantly higher, with an age-adjusted rate about ten times that of children with only one affected parent, so approaching 20%.
Twin studies are a valuable tool for exploring the genetic component of risk for any disease with multifactorial causation: if there is observed difference between pairs of identical and non-identical twins, then, assuming the environment of both types to be the same at the relevant stage of life, the difference must be due to genetic factors. There are practical problems with twins studies, such as ascertainment, and a tendency to over-representation of females and identical twin pairs, but assuming these problems are identified and controlled for, the outcome can provide highly valuable information.
In MS, all studies except one from France show similar results. For identical twins the concordance rate is 25-30%, whereas for non-identical twins it is approximately the same as ordinary siblings at 3% genetic mechanisms (probably several in any one person), and possibly time-dependent factors such as current immune status and other infection. One thing is certain. We do not know the cause of MS, and so far no one has come close.
