Expanded molecular detection of MPL codon p.W515 and p.S505N mutations in myeloproliferative neoplasms

Background: Patients negative for the JAK2 p.V617F somatic variant are frequently reflexed to testing for MPL exon 10 variants. Detection of these variants via multiplexed allele-specific PCR followed by fragment analysis has been previously published. The present study builds on this concept by improving the detection of the p.W515A variant, adding a second allele-specific primer to detect the p.W515R variant, and incorporating an improved primer for p.S505N detection.Methods: The W515 amplification employs 5'-labeled allele-specific forward primers to detect p.W515K, p.W515L, p.W515R, and p.W515A. The p.S505N amplification includes an allele-specific reverse primer with a tail extension. Fragments were subject to capillary electrophoresis on an ABI 3500 Genetic Analyzer and analyzed using GeneMapper 6.0 (Thermo Fisher Scientific).Results: Thirty MPL-negative and 13 MPL-positive samples previously tested by a reference laboratory were tested with the MPL LDT. Results were 100% concordant. The MPL LDT has a limit of detection of at least 5% VAF for the p.W515 variants and 10% VAF for the p.S505N variant.Conclusion: Current MPL assays are predominantly focused on p.W515L/K and p.S505N mutations. We have engineered an MPL test for detecting p.W515A/L/K/R and p.S505N variants, thereby increasing the diagnostic yield with little additional expense or technician time.