Studies of family members of MS patients has shown that the more closely related you are to an MS patient the higher your risk of the disease. For example, if you are a sibling or child of an MS patient your risk is about 3%. This shows that genes play a role in MS.
Studies over the last 30 years has shown that a region of DNA on chromosome 6 is the main genetic locus in MS. The main gene involved is called HLA-DRB1 and this gene has an immune function. HLA-DRB1 comes in over 400 different forms (or alleles). A common form in Europe, named 15, increases the risk of MS by 3-fold. Other alleles of this gene also play a role in the disease. For example, 14 protects individuals from getting the disease. As each person has two copies of all genes (one from your mother and one from your father), it is important as to which two copies of HLA-DRB1 you have. For example, 14 completely cancels the risk increasing effect of 15 when they are inherited together. This may explain, in part, why MS is rare in Asia; there, the 14 allele is common.
More recently, large scale studies have identified a number of other genes involved in MS, including the interleukin 7 receptor alpha (IL7RA), interleukin 2 receptor alpha (IL2RA), the c type lectin 16 a gene (CLEC16A) and interferon response factor 8 (IRF8) genes. These genes increase disease risk by a substantially smaller amount compared to HLA-DRB1, but due to their role in the immune response highlight that the key mechanism of the disease appears to be immune dysfunction.
Dr Sreeram Ramagopalan, post-doctoral scientist