A novel type of +2‐base pair frameshift CALR mutation in a patient with myeloproliferative neoplasm
Somatic CALR mutations have been identified in the majority of JAK2 mutation‐negative essential thrombocythaemia (ET) and primary myelofibrosis. Almost all CALR mutations have been reported to typically generate a +1‐base pair (bp) frameshift in the open reading frame. Here, we describe an ET patient with a +2‐bp frameshift CALR mutation. A 41‐year‐old man was admitted because of headache, and diagnosed as JAK2‐negative ET. After 4 years, his disease progressed to post‐ET myelofibrosis, and CALR mutation analysis demonstrated a +2‐bp frameshift CALR mutation caused by two different CALR mutations, c.1139_1151del and c.1211_1215delinsTTGA, on the same allele. The resultant mutant protein sequence shared 19 amino acids with those from type 1 and type 2 CALR mutations, but the downstream C‐terminal sequences were different. To our knowledge, CALR double mutations causing +2‐bp frameshift are extremely rare. Identification of this novel type of CALR mutation has potential implications for better understanding of CALR oncogenesis.
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