Recessive mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene are responsible for neuropathic (Type A) and non-neuropathic (Type B) Niemann-Pick disease (NPD) [195, 299], while heterozygous mutations are associated with an increased risk of developing PD [106]. The gene discussed is SMPD1; the disease is Niemann-Pick disease.