Although multiple sclerosis is not believed to be hereditary, meaning it is not passed from parents to children, if it runs in the family, the chance of developing it increases. This is especially true with siblings, and between parents and children. If one parent is affected, a child will have only a 2 percent chance of developing MS. Chances are that when one identical twin has MS, the other will not, even though they have the same genetic information. In fact, when one twin is affected, the chance the other will be is only around 20-30 percent. Families with more than one case of MS share genetic factors. Scientists theorize that some people have a genetic predisposition toward the disease, making it easier to trigger. Scientists have found that dozens of genes may be involved in MS risk. Most of them influence components of the immune system through a possible association with environmental factors, such as exposure to the Epstein-Barr virus, low levels of vitamin D and smoking. The HLA-DRB1 gene plays a key role in building a protein vital to the immune system, the human leukocyte antigen (HLA) complex. It helps the immune system differentiate the body’s own proteins from proteins produced by viruses and bacteria. The MS genetic factor with the strongest link to MS is HLA-DRB1*15:01. Another MS-related gene is IL7R. It contains information for the production of part of two immune system receptor proteins: the interleukin 7 receptor and thymic stromal lymphopoietin (TSLP). These receptors identify ways for immune cells to grow and divide. A genetic variation found in people with MS leads to the production of an IL-7 receptor that instead of being in the cell membrane is in the interior of the cell. These variations in the HLA-DRB1 and IL-7R genes affect the immune system. That impact may be related to the autoimmune response that damages the myelin sheath and nerve cells of people with MS. Note: Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.