We report a novel germline PAX5 alteration, a deletion including exon 6, in a boy who developed t(1;19)(q23;p13) (TCF3::PBX1) rearrangement-positive BCP-ALL at the age of 5. Somatic PAX5 aberrations are detected in ~20% of the cases with TCF3::PBX1 BCP-ALL [10]. The gene discussed is PBX1; the disease is acute lymphoblastic leukemia.