Because studies of aberrant gene expression in terminally differentiated cells of different genetic backgrounds often fail to clarify mechanisms that operate in less differentiated developing systems such as those of the developing mammalian CNS, we elected first to identify gene expression aberrations in HPRT-knockdown human fibroblasts, then to validate them in HPRT-deficient human DA cells such as the SH-SY5Y neuroblastoma and then finally to validate candidate gene defects in cells derived from LND patients. Here, HPRT1 is linked to neuroblastoma.