GBA1 and Parkinson disease: Furthermore, PD patients with severe heterozygous GBA1 mutations and PD patients with homozygous or compound heterozygous GBA1 mutations have been found to have higher unified Parkinson's disease rating scale (UPDRS) scores compared to patients with mild heterozygous GBA1 mutations, as well as higher incidence of rapid eye movement (REM) sleep behavior disorder (RBD) and hallucinations (Thaler et al., 2018).