All the Y640F mutations were found in T-LGLL patients (seven cases with CD8+CD57+, one in CD4+ and 1 in CD8−CD4−), whereas D661Y was present in five patients with CD8+CD57+ T-LGLL and in two patients with CLPD-NK. Here, B3GAT1 is linked to T-cell large granular lymphocyte leukemia.