The ASM-1 patient cells used in this manuscript have 5% left of acid sphingomyelinase activity, and present the expected signs of lysosomal impairment, specifically (a) decreased autophagic capacity with accumulation of autophagic substrates (p62 also known as Sequestosome 1, Sqstm1) and autophagosomes, as assessed by the autophagosomal marker LC3B-II. Blots are representative of biological triplicates and adjacent plots are depicted as average ± s.e.m., n = 3. T-test p-value **p<0.01 (b) decreased lysosomal proteolytic capacity, as assessed by the rate of DQ-BSA degradation by the lysosomal proteases in whole cells normalized to protein content. Quantification represents mean ± s.e.m., n = 3 (c–e) transfection of all patient lines with the corresponding wildtype protein rescues mitochondrial respiration as assessed by increased OCRs in ASM deficient lines with cherry ASM overexpression and in NPC1 deficient line with NPC1wt overexpression. Quantifications are presented underneath each seahorse profile in panel d) as average ± s.e.m., n = 2 with eight technical replicates per condition. T.test p-value **p<0.01 and ***p<0.001. (e) Mitochondrial gene expression, as assessed by qPCR, is increased in all patient lines following overexpression of corresponding wiltype proteins. The data is presented in a heatmap for n = 3, in which red denotes increased expression in wiltype protein-overexpressing patient lines compared to white, which represents no change relative to the control values.