What is KIT D816V mutation in the KIT (KIT proto-oncogene, receptor tyrosine kinase) gene?

What is KIT D816V?

KIT D816V is a specific point mutation at position 816 of the KIT gene where aspartic acid (Asp) is replaced by valine (Val), representing the most common activating mutation found in over 80% of adult patients with systemic mastocytosis. 1

Molecular Structure and Location

The KIT gene, located on chromosome 4q12, encodes a transmembrane receptor tyrosine kinase of 145 kDa consisting of 976 amino acids. 1 The mutation occurs at codon 816 within the phosphotransferase domain (PTD) of the kinase region, specifically in the C-lobe of the kinase domain. 1

• The D816V mutation causes constitutive tyrosine kinase activity, meaning the receptor is continuously activated without requiring its normal ligand (stem cell factor/SCF). 1
• This autonomous activation leads to uncontrolled mast cell proliferation and accumulation in tissues. 1

Clinical Significance and Prevalence

The KIT D816V mutation is found in more than 80% of all adult systemic mastocytosis patients, making it the hallmark genetic abnormality of this disease. 1

Age-Related Differences:

• In adults: D816V is present in >80% of systemic mastocytosis cases 1
• In children: D816V is found in approximately 30% of pediatric mastocytosis patients, with extracellular domain mutations being more common (40%) 1

Disease Association:

• The mutation is detectable in most categories of systemic mastocytosis, including indolent SM (ISM), aggressive SM (ASM), and mast cell leukemia (MCL). 2
• When KIT D816V is found in acute myeloid leukemia (AML) patients, it is highly associated with co-existing systemic mastocytosis (SM-AML), occurring in approximately 7% of AML cases. 3

Diagnostic Utility

KIT D816V detection is included as a minor diagnostic criterion for systemic mastocytosis according to WHO classification. 1

Detection Methods:

• Allele-specific quantitative PCR (ASO-qPCR) is the recommended highly sensitive method, with detection sensitivity of 0.01-0.1%. 2, 4
• The mutation can be detected in peripheral blood in most patients with advanced SM and in 46% of patients with indolent SM. 2
• Bone marrow testing is preferred for initial diagnosis, but peripheral blood screening with ASO-qPCR combined with serum tryptase measurement is recommended for initial screening. 1

Testing Algorithm:

• If peripheral blood ASO-qPCR is positive, proceed to bone marrow examination for confirmation. 1
• If peripheral blood is negative but clinical suspicion remains high (elevated tryptase >15 ng/mL or clinical symptoms), bone marrow testing should be performed. 1
• In 5-10% of patients where D816V is not detected, other codon 816 mutations (D816H, D816Y, D816F, D816I) or mutations in other KIT regions should be sought through sequencing. 1

Prognostic and Monitoring Value

The KIT D816V expressed allele burden (EAB) correlates strongly with disease activity, disease subtype, and survival. 2

• Higher allele burden is associated with more advanced disease categories (aggressive SM vs. indolent SM). 2
• Quantitative monitoring of KIT D816V allele burden is recommended before and during cytoreductive therapy in aggressive SM, and for patients enrolled in clinical trials. 1
• In patients with low mast cell burden ISM and stable clinical course, repeated allele burden testing is not necessary unless disease progression occurs. 1

Therapeutic Implications

The D816V mutation confers resistance to imatinib, as this tyrosine kinase inhibitor fails to block the kinase activity of mutated KIT D816V. 5

• Patients who are KIT D816V negative and have eosinophilia should be tested for FIP1L1-PDGFRA fusion, as these patients have excellent prognosis with imatinib therapy. 1, 6
• Newer targeted agents like PKC412 (midostaurin) and AMN107 can effectively inhibit D816V-mutated KIT activity. 5
• The presence of additional mutations beyond KIT D816V (in genes like SRSF2, ASXL1, RUNX1) is associated with worse overall survival in advanced SM. 1

Important Clinical Pitfalls

• False-negative results can occur in patients with low mast cell burden if assay sensitivity is insufficient or tissue sampling is suboptimal. 1
• Myeloid mutation panels using next-generation sequencing have relatively low sensitivity (~5%) for detecting KIT mutations and are not recommended as the primary detection method. 1
• In SM-AML cases, the D816V mutation may be present only in mast cells and not in leukemic blasts, which has implications for targeted therapy selection. 3