Mutations in eight nuclear genes have been identified as causes of infantile MDS (TK2, DGUOK, POLG, MPV17, RRM2B, SUCLA2, SUCLG1, and C10orf2) (Mandel et al, 2001; Saada et al, 2003; Naviaux & Nguyen, 2004; Elpeleg et al, 2005; Spinazzola et al, 2006; Bourdon et al, 2007; Ostergaard et al, 2007; Sarzi et al, 2007); 7 of the genes encode proteins involved in mtDNA replication or in the metabolism of deoxynucleotide triphosphate pools utilized as precursors for DNA replication (Copeland, 2012). The gene discussed is TK2; the disease is myelodysplastic syndrome.