Mutations in the sphingomyelin phosphodiesterase (SMPD1) gene, which cleaves the phosphocholine head group of sphingomyelin to produce ceramide (Schuchman et al., 1992), have been identified as a risk factor for PD (Foo et al., 2013; Mao et al., 2017). The gene discussed is SMPD1; the disease is Parkinson disease.