Calreticulin Mutations Variants of ET and PMF Patients Studied in Almazov Medical Research Center Russian Federation
Authors: Butylin Pavel , Matyuhina Natalia , Lisina Ekaterina , Siordia Nadia , Senderova Olga , Lomaia Elza , Zaritskey Andrey 
Published: October 2019

We analyzed CALR mutations in cohort of patients with ET and PMF. Diagnoses were determined according to the WHO criteria. 33 PMF and 45 ET patients that were negative for JAK2V617F and MPL515L/K mutations have been studied for CALR mutations presence as described in original paper (Т.Klampfi , 2013). 29 ET and 25 PMF patients found mutated. In PMF group sex ratio was equal - 12 males/13 females, in ET group females prevailed - 21 males/69 females. Median age in PMF group was 64 (41-78) and in ET group 58 (22-80). Exon 9 was Sanger sequenced and mutation type identified. All the mutated CALR sequences were translated with verified +1 frameshift with alternative C-end. In PMF group we found type 1 52bp deletion p.L367fs*46 (n=11), type 2 TTGCT insertion p.K385fs*47 (n=5), type 3 p.L367fs*48 (n=3), type 7 p.K368fs*45 (n=2), type 19 p.E372fs*48 (n=2) and single cases of p.K368fs*51, p.K385fs*47 , p.Q365fs*50. In ET group we found type1 52bp deletion p.L367fs*46 (n=10), type 2 TTGCT insertion p.K385fs*47 (n=6), and single cases of p.L367fs*52, p.K368fs*51, p.E378fs*45, p.K374fs*49), p.E364fs*49. Also in ET group we identified two cases with alternative insertion c.1154_1155insGTGTC p.E386fs*46. In one ET case we found complex CALR mutation variant c. с.1126_1142delInsACCTTTGCATTTT (p.R376fs*53). In this case alternative C-end, different from what was described before will be formed. CALR mutations were grouped in Type1 like and Type2 like according to protein sequence similarity (A. Tefferi, 2014). In PMF group type1/2 like mutation ratio was 18/7 and in ET group it was 16/13, confirming higher CALR type2 like mutations rate in ET.

We analyzed CALR mutations in cohort of patients with ET and PMF. Diagnoses were determined according to the WHO criteria. 33 PMF and 45 ET patients that were negative for JAK2V617F and MPL515L/K mutations have been studied for CALR mutations presence as described in original paper (Т.Klampfi, 2013). 29 ET and 25 PMF patients found mutated. In PMF group sex ratio was equal - 12 males/13 females, in ET group females prevailed - 21 males/69 females. Median age in PMF group was 64 (41-78) and in ET group 58 (22-80). Exon 9 was Sanger sequenced and mutation type identified. All the mutated CALR sequences were translated with verified +1 frameshift with alternative C-end. In PMF group we found type 1 52bp deletion p.L367fs*46 (n=11), type 2 TTGCT insertion p.K385fs*47 (n=5), type 3 p.L367fs*48 (n=3), type 7 p.K368fs*45 (n=2), type 19 p.E372fs*48 (n=2) and single cases of p.K368fs*51, p.K385fs*47 , p.Q365fs*50. In ET group we found type1 52bp deletion p.L367fs*46 (n=10), type 2 TTGCT insertion p.K385fs*47 (n=6), and single cases of p.L367fs*52, p.K368fs*51, p.E378fs*45, p.K374fs*49), p.E364fs*49. Also in ET group we identified two cases with alternative insertion c.1154_1155insGTGTC p.E386fs*46. In one ET case we found complex CALR mutation variant c. с.1126_1142delInsACCTTTGCATTTT (p.R376fs*53). In this case alternative C-end, different from what was described before will be formed. CALR mutations were grouped in Type1 like and Type2 like according to protein sequence similarity (A. Tefferi, 2014). In PMF group type1/2 like mutation ratio was 18/7 and in ET group it was 16/13, confirming higher CALR type2 like mutations rate in ET.

Klampfl T. et al. Somatic mutations of calreticulin in myeloproliferative neoplasms. N Engl J Med. 2013 Dec 19;369(25):2379-90.

Tefferi A. et al. The prognostic advantage of calreticulin mutations in myelofibrosis might be confined to type 1 or type 1-like CALR variants. Blood. 2014 Oct 9;124(15):2465-6.

Disclosures

Zaritskey: Janssen: Consultancy; Novartis: Consultancy.