SuperRCA assay of KIT p.D816V mutation load reveals novel correlation to clinical phenotype

Background The KIT p.D816V mutation is seen in more than 90% of patients with systemic mastocytosis (SM). A high variant allele fraction (VAF) is associated with adverse outcome; however, no correlations betwen mutation burden and clinical symptoms have hitherto been established.Objective Our aim was to quantify KIT p.D816V VAF in blood and bone marrow (BM) by using the ultrasensitive superRCA method and correlate the VAF with clinical symptoms.Method A total of 107 blood and BM samples from patients with SM were analyzed.Results In 78 of the 107 samples, a DNA input concentration of 660 ng was used to obtain a sensitivity for KIT p.D816V mutation of 0.0016% VAF. In paired analysis, level of KIT p.D816V VAF was significantly higher in BM than in blood, and it correlated with SM disease burden (ie, serum tryptase level and percentage of BM mast cell infiltration). No correlations were found between VAF and anaphylaxis, osteoporosis, or gastrointestinal symptoms. Among the patients with indolent SM (ISM), those with skin involvement had a higher blood VAF despite a similar percentage of BM mast cell infiltration.Conclusion By using SuperRCA KIT p.D816V detection, we demonstrated that in the blood of patients with ISM, VAF is higher in patients with mastocytosis in the skin than in the patients without skin involvement, leading us to hypothesize that circulating KIT p.D816V-mutated progenitors with mast cell potential may drive the cutaneous phenotype. In addition, our findings in paired blood and BM samples support the findings of previous studies and provide further evidence supporting higher VAFs in BM than in blood as well as a correlation of VAF with disease burden.