ICOSLG and Dravet syndrome: At least four genes mapping to chromosome 21 are involved in immune functions and have been postulated to account for some of the biological and clinical findings related to immunity in DS: interferon alpha receptor 1 (IFNAR1); interferon gamma receptor chain 2 (IFNGR2); ICOS ligand (ICOSLG), which encodes CD275; and integrin beta chain 2 (ITGB2), which encodes CD18.