The interleukin-7 receptor alpha-chain gene (IL7R) codes for the receptor for IL-7, which is an important T-cell growth factor in T- and B-cell expansion. There is an association between the IL7R T244I polymorphism and multiple sclerosis. The T244I variation is located in an important transmembrane domain of IL7R.
The “T” variant is the non-reference genotype and leads to the T244I amino acid variant. The “C” variant is reported to cause increased risk of MS — this is the reference genotype at this location and corresponds to the reference amino acid “244T”. Thus, T244I is slightly protective.
Because MS is quite rare with the high-end incidence estimate of .15%, the 1.3 odds ratio translates to less than .05% absolute increased risk for homozygous carriers of this variant.