Here we report the case of a 14-month-old male infant affected by EBV-positive DLBCL in whom homozygosity for the same RAG1 Slavic founder variant was identified postmortem after targeted Sanger sequencing of 24 available DNA samples out of 71 patients who developed lymphoma aged <3 years from the Belarusian cancer registry between 1986 and 2023. This evidence concerns the gene RAG1 and diffuse large B-cell lymphoma.