SQOR and neuroblastoma: The levels of residual SQOR protein and the availability of catabolites seem to regulate the pathway downstream, since in patients and 4-NB treated fibroblasts, and in COQ8A depleted HeLa cells, SQOR protein levels are partially reduced, and the other enzymes of the pathway are increased; on the contrary, severe SQOR depletion in Hela cells shuts down the pathway (Ziosi et al., 2017).