For example, having a homozygous rare allele of the −511 ​C ​> ​T SNP of interleukin-1 beta (IL-1β) was associated with higher depression risk,59 while having that of the rs1800795 and rs2069840 of interleukin 6 (IL-6) could confer higher depression severity.40 Here, IL1B is linked to major depressive disorder.