SLC22A1 and type 2 diabetes mellitus: In a study of 1,915 completely metformin-tolerant and 251 intolerant T2D patients, allelic variants of OCT1 rs12208357/R61C, rs72552763/M420del, rs34130495/G401S, rs55918055/C88R, and rs34059508/G465R were found to be related to metformin intolerance due to increased metformin accumulation in enterocytes 54.