OLIG2 and neoplasm: Each of these models differs in important respects, including the germline Nf1 gene mutation (OPG-2; c.2041C>T; p.R681X as seen in several patients with NF1-OPG [12]), the presence of additional genetic mutations (OPG-3; additionally harboring heterozygous Pten loss [11]), and the tumor cell of origin (OPG-4; Nf1flox/mut; Olig2-Cre in which tumors arise from Olig2+ cells).