It is well-established that DNA demethylation caused by DNMT deficiency induces aneuploidies: in Dnmt1 hypomorphic cells in vivo80,81, in peripheral T cell lymphomas arising from haematopoietic stem/precursor cells conditionally disrupted for Dnmt3a82,83 and in Dnmt3b deficiency mimicking ICF syndrome (immunodeficiency, centromere instability and facial abnormalities) in vivo84. The gene discussed is DNMT1; the disease is peripheral T-cell lymphoma, not otherwise specified.