Editing Multiple sclerosis (section)

=== Genetics ===
[[File:HLA.svg|thumb|HLA region of chromosome&nbsp;6: Changes in this area increase the probability of getting MS.]]

MS is not considered a [[hereditary disease]], but several [[genetics|genetic variations]] have been shown to increase its risk.<ref name="pmid14747002">{{cite journal | vauthors = Dyment DA, Ebers GC, Sadovnick AD | title = Genetics of multiple sclerosis | journal = The Lancet. Neurology | volume = 3 | issue = 2 | pages = 104–10 | date = February 2004 | pmid = 14747002 | doi = 10.1016/S1474-4422(03)00663-X | s2cid = 16707321 | citeseerx = 10.1.1.334.1312 }}</ref> Some of these genes appear to have higher expression levels in [[microglia|microglial cells]] than expected by chance.<ref name="SkeneGrant2016">{{cite journal | vauthors = Skene NG, Grant SG | title = Identification of Vulnerable Cell Types in Major Brain Disorders Using Single Cell Transcriptomes and Expression Weighted Cell Type Enrichment | journal = Frontiers in Neuroscience | volume = 10 | pages = 16 | year = 2016 | pmid = 26858593 | doi = 10.3389/fnins.2016.00016 | pmc = 4730103 | doi-access = free }}</ref> The probability of developing MS is higher in relatives of an affected person, with a greater risk among those more closely related.<ref name="pmid119555563"/> An [[identical twin]] of an affected individual has a 30% chance of developing MS, 5% for a nonidentical twin, 2.5% for a sibling, and an even lower chance for a half-sibling.<ref name="pmid1897097722"/><ref name="pmid119555563"/><ref>{{cite journal | vauthors = Hassan-Smith G, Douglas MR | title = Epidemiology and diagnosis of multiple sclerosis | journal = British Journal of Hospital Medicine | volume = 72 | issue = 10 | pages = M146-51 | date = October 2011 | pmid = 22041658 | doi = 10.12968/hmed.2011.72.Sup10.M146 }}</ref> MS is also more common in some ethnic groups than others.<ref name="pmid11603614">{{cite journal | vauthors = Rosati G | title = The prevalence of multiple sclerosis in the world: an update | journal = Neurological Sciences | volume = 22 | issue = 2 | pages = 117–39 | date = April 2001 | pmid = 11603614 | doi = 10.1007/s100720170011 | s2cid = 207051545 }}</ref>

Specific [[gene]]s linked with MS include differences in the [[human leukocyte antigen]] (HLA) system—a group of genes on [[chromosome 6 (human)|chromosome 6]] that serves as the [[major histocompatibility complex]] (MHC).<ref name="pmid1897097722"/> The contribution of HLA variants to MS susceptibility has been known since the 1980s,<ref name="pmid21247752">{{cite journal | vauthors = Baranzini SE | title = Revealing the genetic basis of multiple sclerosis: are we there yet? | journal = Current Opinion in Genetics & Development | volume = 21 | issue = 3 | pages = 317–24 | date = June 2011 | pmid = 21247752 | pmc = 3105160 | doi = 10.1016/j.gde.2010.12.006 }}</ref> and it has also been implicated in the development of other autoimmune diseases, such as [[diabetes type I|type 1 diabetes]] and [[systemic lupus erythematosus]].<ref name="pmid21247752" /> The most consistent finding is the association between higher risk MS development and the MHC [[allele]] ''[[HLA-DR15|DR15]]'', which is present in 30% of the U.S. and Northern European population.<ref name="Ward 988–1005"/><ref name="pmid1897097722"/> Other [[Locus (genetics)|loci]] exhibit a protective effect, such as ''[[HLA-C554]] ''and ''[[HLA-DRB1]]*11''.<ref name="pmid1897097722"/> HLA differences account for an estimated 20 to 60% of the [[genetic predisposition]].<ref name="pmid21247752" /> [[Genome-wide association study|Genome-wide association studies]] have revealed at least 200 MS-associated variants outside the HLA locus.<ref name="pmid31604244">{{cite journal| author=International Multiple Sclerosis Genetics Consortium| title=Multiple sclerosis genomic map implicates peripheral immune cells and microglia in susceptibility. | journal=Science | year= 2019 | volume= 365 | issue= 6460 | pmid=31604244 | doi=10.1126/science.aav7188 | pmc=7241648 }}</ref>