Although KITD816V occurs universally in adult systemic mastocytosis (SM), the clinical heterogeneity of SM suggests presence of additional phenotype-patterning mutations. Because up to 25% of SM patients have KITD816V-positive eosinophilia, we undertook whole-exome sequencing in a patient with aggressive SM with eosinophilia to identify novel genetic alterations. We conducted sequencing of purified eosinophils (clone/tumor sample), with T-lymphocytes as the matched control/non-tumor sample. In addition to KITD816V, we identified a somatic missense mutation in ethanolamine kinase 1 (ETNK1N244S) that was not present in 50 healthy controls. Targeted resequencing of 290 patients showed ETNK1 mutations to be distributed as follows: (i) SM (n = 82; 6% mutated); (ii) chronic myelomonocytic leukemia (CMML; n = 29; 14% mutated); (iii) idiopathic hypereosinophilia (n = 137; o1% mutated); (iv) primary myelofibrosis (n = 32; 0% mutated); and (v) others (n = 10; 0% mutated). Of the 82 SM cases, 25 had significant eosinophilia; of these 20% carried ETNK1 mutations. The ten mutations (N244S = 6, N244T = 1, N244K = 1, G245A = 2) targeted two contiguous amino acids in the ETNK1 kinase domain, and are predicted to be functionally disruptive. In summary, we identified novel somatic missense ETNK1 mutations that were most frequent in SM with eosinophilia and CMML; this suggests a potential pathogenetic role for dysregulated cytidine diphosphate-ethanolamine pathway metabolites in these diseases.
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