SPTLC1 and amyotrophic lateral sclerosis: In the SPTLC1-ALS–expressing cells and patient-derived fibroblasts, the relative increase was the highest for SLs conjugated to C18:0, C20:0, and C22:0 acyl chains, which are usually minor species and barely detected in control cells (Figure 4, Supplemental Figure 4, A–C, and Supplemental Figure 5).