IDH1 and astrocytoma (excluding glioblastoma): Of the remaining 33 mutations (Table S2), including an in-frame deletion in ATRX, which is often mutated in IDH-mutant astrocytomas [37], 18 were validated by Sanger sequencing and deep sequencing of PCR amplicons spanning each mutation (amp-seq; Table S3), five were validated only by amp-seq, and ten (mostly indels) could not be validated (Table S2).