Most published pharmacogenetic studies on fluoropyrimidine toxicity and its relationship to the DPYD gene focus on a few variants [9], such as DPYD*2A and DPYD*13, which are associated with near-complete protein deficiency in homozygotes [10], and c.2846A>T (rs67376798) and HapB3 (c.1129-5923C>G + c.1236G>A), which are associated with a moderate loss of protein function [11]. The gene discussed is DPYD; the disease is hereditary thrombophilia due to congenital protein S deficiency.