Highly sensitive molecular techniques for mutation detection in the diagnosis of systemic mastocytosis (SM) should be employed when possible, according to a recent review article in Preprints.
More than 90% of patients with SM are estimated to have a mutation in the c-KIT gene, which codes for a protein that is involved with several molecular pathways and plays a key role in regulating cell survival.
What is a KIT gene mutation?
SM is usually caused by a sporadic mutation in the KIT gene, which codes for a protein called CD117 transmembrane tyrosine kinase. The protein is involved in the growth, survival and migration of mast cells. The most common KIT mutation associated with SM is the D816V mutation, which results in the amino acid aspartic acid being replaced by the amino acid valine in the protein chain.
SM is usually caused by a sporadic mutation in the KIT gene, which codes for a protein called CD117 transmembrane tyrosine kinase. The protein is involved in the growth, survival and migration of mast cells. The most common KIT mutation associated with SM is the D816V mutation, which results in the amino acid aspartic acid being replaced by the amino acid valine in the protein chain.
Mutations in this gene can lead to proliferation of mast cells, causing a wide range of symptoms affecting several organ systems. The majority of patients have a mutation in which the 816th amino acid of c-KIT, aspartic acid, is replaced with valine. But much rarer mutations have also been observed.
“Although the presence of c-KIT mutations is a diagnostic criterion for systemic mastocytosis, there is currently no globally accepted standardized method for its detection,” the authors said. In their review, the authors discussed several methods of c-KIT mutation detection and offered recommendations for more accurate diagnosis.
Read more about SM testing and diagnosis
Because of the risk of false negative results, the authors advised that either allele-specific oligonucleotide polymerase chain reaction (ASO-PCR) or digital droplet PCR (ddPCR) be used in the diagnosis of SM. These molecular tests are highly effective at detecting the presence of a mutation even when there is a relatively low level of the mutated gene in a sample. The ratio of mutated to nonmutated versions of a particular gene is known as allele burden.
A patient’s allele burden may also serve as an important biomarker of their response to certain therapies. For example, some studies have shown that the frequency of the mutated allele may decrease after certain SM treatments, including midostaurin.
Most reliable tissue test
Bone marrow is generally the most reliable tissue for molecular testing in SM. While mast cells are not found in peripheral blood (the blood that circulates throughout the entire body), it does contain the precursors to mast cells. But testing of peripheral blood may lead to false negative results and should generally be used for screening; bone marrow is favored for a more definitive diagnosis.
Furthermore, the authors reported that either genomic DNA (gDNA) or messenger RNA (mRNA) can be used for genetic testing. The literature suggested the use of gDNA in peripheral blood analysis and the use of mRNA in bone marrow analysis.
“Patients affected by mastocytosis are often characterized by additional mutations beyond c-KIT,” the authors said. “These mutations are frequently associated with a worse prognosis.”
Next-generation sequencing, a relatively new sequencing technology, may also provide insight. Although additional mutations are not always associated with changes in prognosis, mutations in the genes SRSF2, ASXL1 and RUNX1 are associated with worse prognoses.
