Heterozygous GBA1 variants account for the most significant genetic risk factor for Parkinson disease (PD), the second most common neurodegenerative disease following Alzheimer’s disease with a reported prevalence rate of 315 per 100,000 persons worldwide (Sidransky et al. 2009; Pringsheim et al. 2014). The gene discussed is GBA1; the disease is Parkinson disease.