The mannose-6-phosphate receptor (M6PR), Tsg101, Rab4, Rab5, Rab9 and flotillin 1 were not present in the CSF at detectable levels using this method; however, all proteins were detectable in human SH-SY5Y neuroblastoma cell lysates, confirming the ability of the antibodies to recognize the epitopes (data not shown). Here, M6PR is linked to neuroblastoma.