Little data is available on the endogenous function of TPMT; its role in metabolizing immunosuppressants and our PheWAS findings linking SNPs near TPMT to immune-related disorders like post-dysenteric arthropathy and Guillain-Barre syndrome suggest it may enhance immune activity, while our GO analysis suggested that it may be involved in metabolism, mitochondrial function, and cellular response to oxidative stress. This evidence concerns the gene TPMT and Guillain-Barre syndrome.