ATP13A3 and neuroblastoma: However, stable overexpression of the L675V and M850I missense variant proteins did significantly decrease basal SPD and SPM levels in neuroblastoma SH-SY5Y cells (see Supplementary material online, Figure S8D–F), suggesting a cell-type-specific phenotype for these variants.To analyse the intracellular localization of the protein variants, we transiently overexpressed GFP-tagged WT, D498N, and the five PAH-associated ATP13A3 protein variants in HMEC-1 cells.