In this review, we report on the recent discovery of recessive mutations in sorbitol dehydrogenase as one of the most common and potentially treatable causes of axonal CMT (CMT2) [1] and how advances in genetic discovery have expanded the phenotypes attributable to individual genes, none more so than dominant mutations in SPTLC1 that are known to cause HSN1 but in which a new set of mutations now give rise to ALS [2, 3]. This evidence concerns the gene SPTLC1 and Charcot-Marie-Tooth disease type 2.