page_title: Multiple sclerosis
section_title: Genetics
hierarchical_section_title: Multiple sclerosis / Causes / Genetics
context_page_description: Multiple sclerosis is a demyelinating disease in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This damage disrupts the ability of parts of the nervous system to transmit signals, resulting in a range of signs and symptoms, including physical, mental, and sometimes psychiatric problems. Specific symptoms can include double vision, blindness in one eye, muscle weakness and trouble with sensation or coordination. MS takes several forms, with new symptoms either occurring in isolated attacks or building up over time. Between attacks, symptoms may disappear completely; however, permanent neurological problems often remain, especially as the disease advances.
  While the cause is unclear, the underlying mechanism is thought to be either destruction by the immune system or failure of the myelin-producing cells. Proposed causes for this include genetics and environmental factors being triggered by a viral infection. MS is usually diagnosed based on the presenting signs and symptoms and the results of supporting medical tests.
  There is no known cure for multiple sclerosis. Treatments attempt to improve function after an attack and prevent new attacks.
context_section_description: MS is not considered a hereditary disease; however, a number of genetic variations have been shown to increase the risk. Some of these genes appear to have higher levels of expression in microglial cells than expected by chance. The probability of developing the disease is higher in relatives of an affected person, with a greater risk among those more closely related. In identical twins both are affected about 30% of the time, while around 5% for non-identical twins and 2.5% of siblings are affected with a lower percentage of half-siblings. If both parents are affected the risk in their children is 10 times that of the general population. MS is also more common in some ethnic groups than others.
  Specific genes that have been linked with MS include differences in the human leukocyte antigen (HLA) system—a group of genes on chromosome 6 that serves as the major histocompatibility complex (MHC). That differences in the HLA region are related to susceptibility has been known since the 1980s, and this same region has also been implicated in the development of other autoimmune diseases such as diabetes type I and systemic lupus erythematosus. The most consistent finding is the association between multiple sclerosis and alleles of the MHC defined as DR15 and DQ6. Other loci have shown a protective effect, such as HLA-C554 and HLA-DRB1*11. Overall, it has been estimated that HLA differences account for between 20% and 60% of the genetic predisposition. Modern genetic methods (genome-wide association studies) have revealed at least twelve other genes outside the HLA locus that modestly increase the probability of MS.
caption: HLA region of Chromosome 6. Changes in this area increase the probability of getting MS.