NOS1 and Parkinson disease: Several single nucleotide polymorphisms (SNPs) in the NOS1 and NOS2A genes have previously been linked to PD risk, but few reports have implicated the same SNPs (Hague et al. 2004; Hancock et al. 2008; Huerta et al. 2007; Levecque et al. 2003; Schulte et al. 2006).