SPTLC1 and amyotrophic lateral sclerosis: A comparison of the plasma SL profile between the ALS patients carrying the Y23F, L39del, and F40S41del variants and unrelated HSAN1 patients carrying the C133W variant revealed similar changes in SL profiles, with increased SL levels in ALS patient plasma and higher 1-deoxyceramide levels in the HSAN1 patients (Supplemental Figure 3, A–D).