IDH1 and myelodysplastic syndrome: IDH1 and IDH2 have been reported to be frequently mutated in AML, Myelodysplastic Syndromes (MDS) and chronic Myeloproliferative Neoplasms (MPNs), the most frequent mutations being single-nucleotide variants involving the exon 4 at the arginine hotspot R140 or R172.