Analysis of the MYD88 L265P mutation in IgM monoclonal gammopathy by semi-nested polymerase chain reaction-based restriction fragment length polymorphism method

MYD88 L265P mutation causes constitutive activation of NF-κB and possible driver mutation in B-cell lymphoid malignancies. It is frequently detected in Waldenstrom’s macroglobulinemia (WM) (50%-100%), and its detection is important in diagnostic and therapeutic targets of this syndrome. Standard detection method of MYD88 L265P mutation in clinical practice has yet to be established. We developed semi-nested PCR-based restriction fragment length polymorphism (snPCR-RFLP) to detect the mutation. The snPCR-RFLP method is a modification of the PCR-RFLP method, which uses the restriction enzyme BsiEI that recognizes CGACT / CG, intending to increase detection sensitivity by amplification of mutated allele in the DNA sample using semi-nested PCR before enzyme digestion. The detection sensitivity of snPCR-RFLP was estimated as 0.1%, by detecting mutated allele in wild-type allele in the cloned plasmid DNA, which is comparable with allele-specific (AS) PCR method widely used as sensitive detection method. By analyzing 40 cases with IgM monoclonal gammopathy, snPCR-RFLP detected 29/40 (70%) of all cases, 22 / 31 (70.9%) of WM, and 6/9 (66.6%) of IgM-type monoclonal gammopathy with undetermined significance (IgMMGUS), including five cases (three cases of WM and two cases of IgMMGUS) in which the mutation was detected only by snPCR-RFLP but not by Sanger sequencing method. Regarding DNA sample status, particularly five cases, a case was extracted from formalin-fixed paraffin-embedded tissue and four cases were extracted from cells by Ficoll-Hypaque density gradient. In correlation with clinical features, the MYD88 mutation detected by snPCR-RFLP method was associated with the adverse prognostic index (WMIPSS) of WM using patient age, hemoglobin (Hb) level, platelet count, β2MG level, and serum IgM level (p=0.055). The snPCR-RFLP method is a clinically useful MYD88 mutation detection method that can be performed in general laboratories.