In 2013, somatic CALR mutations were identified in most JAK2-unmutated patients with essential thrombocythaemia or primary myelofibrosis patients.5, 6 Multiple CALR mutations that generated a +1 bp frameshift and resulted in mutant proteins with a novel C-terminus were demonstrated in exon 9. The gene discussed is JAK2; the disease is primary myelofibrosis.