Whereas the frequency of CALR mutations in MPNs is quite consistent in recent studies, it is unclear whether CALR mutations occur in up to 8.3% of patients with MDS (10 of 120 MDS patients) as reported by Nangalia et al. [2], or are infrequent in MDS (none of 73) and AML (none of 254) patients as reported by Klampfl et al. [1]. The gene discussed is CALR; the disease is myelodysplastic syndrome.