It is interesting to observe that while the prevalence of each gene variant is largely dependent on the ethnicity of the patients, in our study, mainly represented by Caucasian kidney transplant recipients, there was a small but significant proportion of CYP3A5 expressers and CYP3A4*22 allele carriers, which led to a representative number of patients with a distinct global TAC-metabolizing capacity. The gene discussed is CYP3A4; the disease is kidney transplant.