Improved detection of the KIT D816V mutation in patients with systemic mastocytosis using a quantitative and highly sensitive real-time qPCR assay.

The vast majority of patients with systemic mastocytosis (SM) carry the somatic D816V mutation in the KIT gene. The KIT D816V mutation is one of the minor criteria for a diagnosis of SM according to the 2008 World Health Organization classification of myeloproliferative neoplasms. In the present study, we present a real-time qPCR assay that allows quantification of as little as 0.003% KIT D816V mutation-positive cells. A total of 61 samples from 31 cases of SM were included in the study. We detected the mutation in skin or bone marrow in 95% of the cases of SM. We demonstrate the clinical relevance of the assay by identifying as little as 0.03% mutation-positive cells in bone marrow aspirates from SM patients and calculate the analytical sensitivity of negative samples to determine the reliability of the result. We further demonstrate that this method also detects the KIT D816V mutation in peripheral blood in 81% of the mutation-positive cases with SM. The method also allows comparison of mutation-positive and mast cell fractions to determine whether the mutation is present in non-mast cells, a parameter that has recently been reported to be of prognostic importance in patients with indolent SM. Finally, the assay is suitable for use in prospective studies of the KIT D816V allele burden as a treatment endpoint in SM.