PSEN1 and neuroblastoma: Particularly, the levels of methylation of CpG islands in the promoters of the APP and the PSEN1 (Presenilin 1, the core of the (γ-secretase activity that cleaves APP) genes were analyzed on human neuroblastoma SK-N-SH or SK-N-BE cell lines, and it was observed that under conditions of folate and vitamin B12 deprivation from the media, the status of methylation of the promoter of the PSEN1 gene underwent a variation, with a subsequent deregulation of the production of presenilin1, BACE1 and APP proteins [134].