The genetics of t-MDS. Panel A shows the spectrum of recurrent gene mutations in a cohort of 311 t-MDS cases. Each column represents one patient, and colored bars are mutations. TP53 and PPM1D mutations are found in one-half of cases, and they frequently cooccur in individual patients. Panel B represents key components of the DNA damage response. Red circles with “P” represent phosphates that are regulated by PPM1D phosphatase activity.