Another autosomal recessive lysosomal storage disorder, Niemann-Pick (NP) type A and B, which results from mutations in the sphingomyelin phosphodiesterase 1 (SMPD1) gene is also reported as a risk-factor for PD [41], while heterozygous carriers of the autosomal recessive lysosomal storage disorder NP type C1 (NPC1), with mutations in the NPC1 gene, have also been reported to present with PD [42]. Here, SMPD1 is linked to Parkinson disease.