Smirnova et al. [133] administered neurotoxicants (MPP+ and rotenone) to dopaminergic neurons in 3D neuronal models derived from PD-iPSCs, and reported that dopaminergic neurons responded to toxicant exposure by upregulating one-carbon metabolism, transsulfuration pathways (ASS1, CTH and SHTM2) and α-synuclein associated microRNAs. Here, SNCA is linked to Parkinson disease.