The presence of a mutation in one of the following eight genes, seen frequently in MDS and termed ‘secondary-type mutations’, is >95% specific for sAML: serine and arginine-rich splicing factor-2 (SRSF2), splicing factor-3B, subunit 1 (SF3B1), U2 small nuclear RNA auxiliary factor-1 (U2AF1), zinc finger CCCH-type, RNA binding motif and serine/arginine-rich-2 (ZRSR2), additional sex combs-like-1 (ASXL1), enhancer of Zeste-2 polycomb repressive complex subunit-2 (EZH2), B-cell lymphoma-6 (BCL-6) corepressor (BCOR), or stromal antigen-2 (STAG2). The gene discussed is STAG2; the disease is myelodysplastic syndrome.