Mutation analysis for systemic mastocytosis

Mast cells from over 80% of adult systemic mastocytosis (SM) patients carry an activating mutation at codon 816 of the KIT gene. In fact, a KIT mutation constitutes one of the minor WHO 2008 classification criteria for SM. The most common is the c.2447A>T: p.Arg816Val (D816V) mutation. The KIT gene encodes a type III transmembrane receptor tyrosine kinase whose ligand is stem cell factor. Activation of KIT mediates proliferation and maturation signalling. D816 V causes constitutive activation of the KIT tyrosine kinase activity, which also results in resistance to the tyrosine kinase inhibitor imatinib mesylate. Therefore knowing the mutational status of KIT codon 816 is important for diagnosis and treatment strategy. The population of mutant mast cells is often low in relation to normal cells and so a sensitive molecular detection technique is required. Several have been reported in the literature, the most sensitive include RT-PCR + RFLP, PNA-mediated PCR and allele-specific PCR. Within the diagnostic setting the Peter MacCallum uses the rapid and highly sensitive allele-specific competitive blocker PCR (ACB-PCR) assay with a sensitivity level of between 1 and 0.1%. Between Jan 2008 and Oct 2010, 338 samples were tested, of which 58% were positive.