HSP caused by mutations in ALDH18A1 (MIM#616586), encoding delta-1-pyrroline-5-carboxylate synthase (P5CS), has been reported as hereditary spastic paraplegia type 9 (SPG9), i.e., SPG9A and SPG9B, which are distinguished by autosomal dominant and autosomal recessive modes of inheritance, respectively (2, 3). The gene discussed is ALDH18A1; the disease is hereditary spastic paraplegia.