To investigate the clinical significance of PBSC-MRD, we first determined the levels of each NB-mRNA (CRMP1, DBH, DDC, GAP43, ISL1, PHOX2B, and TH mRNA) and 7NB-mRNAs by ddPCR in 20 PBSC grafts collected from 20 high-risk NB patients. The gene discussed is DDC; the disease is neuroblastoma.