N-acyl sphingosine amidohydrolase 1 (ASAH1) encodes the lysosomal acid ceramidase that hydrolyses the bioactive sphingolipid Cer into sphingosine and free fatty acids under acidic pH conditions, and loss-of-function mutations in this gene cause two different disorders, Farber disease (FD) and a rare form of spinal muscular atrophy combined with progressive myoclonic epilepsy (SMA-PME) [48, 49]. The gene discussed is ASAH1; the disease is proximal spinal muscular atrophy.