Differences in DPYD Population Frequencies Observed in Galicians Compared to Europeans and Spanish from PhotoDPYD Study

<b>Background/Objectives</b>: Fluoropyrimidine derivatives, 5-fluorouracil (5-FU) and its prodrugs (capecitabine and tegafur), are widely used in patients suffering from colorectal cancer. The enzyme responsible for their metabolization, dihydropyrimidine dehydrogenase (DPD), is encoded by the <i>DPYD</i> gene, which is highly polymorphic and may contain polymorphisms which could severely compromise its function. This article aims to describe the prevalence of the four main <i>DPYD</i> polymorphisms in the Galician population (Spain) and to compare these frequencies with data obtained from European cohorts in genetic databases and a Spanish study. <b>Methods</b>: Galician data frequencies for the four main <i>DPYD</i> polymorphisms recommended by the European Medicine Agency (EMA) and the Spanish Agency for Medicines and Health Products (AEMPS) (rs3918290 (c.1905+1G>A), rs55886062 (c.1679T>G), rs56038477 (c.1236G>A) and rs67376798 (c.2846A>T)) were collected, as well as data from the genomic databases 1000 Genomes and gnomAD. Additionally, the results from a Spanish <i>DPYD</i> study were included. <b>Results</b>: Significant differences in <i>DPYD</i> variant allele frequencies were observed in the Galician population compared to the frequencies reported in the European population, as well as in the Spanish PhotoDPYD study. Specifically, the rs56038477-T variant (most prevalent) along with the rs3918290-T variant, exhibited significantly lower frequencies than anticipated in the Galician cohort, with a high degree of statistical significance. <b>Conclusions</b>: Observed allele frequencies for the four <i>DPYD</i> variants suggest that Europeans and Spanish frequencies may not be fully applicable to the Galician population. These results emphasize the emerging need for incorporating the genetic information of populations that might be underrepresented into populational databases available worldwide.