Patients with other myeloid disorders (acute myeloid leukemia, chronic myeloid leukemia, myelodysplastic syndrome (MDS), chronic myelomonocytic leukemia, refractory anemia with ring sideroblasts associated with marked thrombocytosis (RARS-T)) were screened for mutations in CALR exon 9. The gene discussed is CALR; the disease is myelodysplastic syndrome with ring sideroblasts.