Mutations in the acid ceramidase (ASAH1) gene (an enzyme of lysosomal ceramide hydrolysis) determine a whole range of motor neuron diseases: from Farber’s disease, a fatal disease of early childhood characterized by a decrease in ASAH1 activity by more than 90%, to atypical forms of SMA with a decrease in ASAH1 activity by 70% [89]. This evidence concerns the gene ASAH1 and proximal spinal muscular atrophy.