POLG and myelodysplastic syndrome: MDS can be caused by mutations in nuclear genes involved either in nucleotide biosynthesis (TK2, SUCLA2, SUCLG1, RRM2B, DGUOK, and TYMP), in nucleotide transport (MPV17 and SLC25A4/ANT1) or mtDNA replication (POLG, POLG2, SSBP1, TWNK, TFAM, LIG3 and MGME1) [4].