Presence of JAK2 V617F Mutation in Peripheral Blood of Blood Donors with Upper-Limit Hematocrit and Platelet Values.

The somatic mutation V617F of JAK2 gene has been identified as a pathogenic factor in typical chronic myeloproliferative diseases (MPDs), in particular polycythemia vera, essential thrombocythemia, and myelofibrosis with myeloid metaplasia. Recently, two studies showed the presence of this mutation also in 37/3935 subjects with non haematological diseases (Xu et al, 2006) and 5/52 healthy donors (Sidon et al, 2006), suggesting that V617F mutation may occur in the absence of MPD phenotype and that probably is not sufficient per se to induce MPDs. The aim of this study was to search for the presence of JAK2 V617F mutation in healthy blood donors with confirmed upper-limit Hct and/or Plts values. Actually, previous studies indicated that some subjects with upper-limit Hct levels have early stages of polycythemia vera (Zanella et al, 1987). We studied 177 consecutive repeat blood donors (92 M, 85 F; median age 45 years, range 19–66) displaying Hct and/or Plts values higher than the 75° percentile of the normal reference distribution (Hct > 0.47 for M and > 0.42 for F; Plts > 300×10⁹/L), confirmed on at least two different occasions in the last 12 months. All subjects had been accepted for blood donation on the basis of negative clinical history and normal results on both physical examination and routine laboratory testing. 83 of them (55 M and 28 F) had upper-limit Hct levels (median 0.48, range 0.47-0.51 for M; 0.43, range 0.42-0.47 for F); 85 had Plts > 300×10⁹/L (median 338×10⁹/L, range 300–454), and 9 donors had both upper-limit Hct and Plts. DNA was extracted from whole blood; all samples were analyzed by allele-specific polymerase chain reaction (PCR) according to Baxter et al (2005), and by fluorescent allele specific PCR (McClure et al, 2006) on ABI PRISM 310 Genetic Analyzer. Ten subjects were found to be positive for V617F mutation by fluorescent PCR, showing a positive signal when compared to a positive control corresponding to 2% of V617F mutated allele. Six of them showed a positive band also on agarose gel when analyzed with allele specific PCR. The presence of mutation was confirmed by enzymatic digestion with BsaXI. Hematological data of mutated subject are reported in the table. No statistically significant differences of hematological parameters were present between V617F positive and negative subjects. In conclusion, the presence of a V617F positive clone (albeit in a small amount), was found in 4% (3 F and 1 M) donors with upper-limit Hct and in 6% (2 F, 4 M) donors with Plts > 300×10⁹/L. The follow up of these subjects will ascertain whether V617F mutation is a prelude to a myeloproliferative disease.