In patients with ASXL1 mutations, the mutations are typically heterozygous and occur near the 5′ end of exon 12, thus producing C-terminally truncated forms of ASXL1 probably escaping from nonsense-mediated decay (NMD) of mRNA, and indeed truncated ASXL1 proteins are expressed in MDS cells20. Here, ASXL1 is linked to myelodysplastic syndrome.