Comparison of lesional skin c-KIT mutations with clinical phenotype in patients with mastocytosis

Summary

Background

Activating c-KIT mutations cause abnormal mast cell growth and appear to play a role in mastocytosis. However, the correlation of c-KIT mutations with disease phenotypes is poorly characterized.

Aim

To evaluate the correlation of c-KIT mutations with clinical presentations and laboratory findings.

Methods

Total cellular RNA was isolated from the skin lesions of 43 adults and 7 children with mastocytosis, and PCR amplicons of cDNA were sequenced for c-KIT mutations.

Results

The most common activating mutation, KIT-D816V, was identified in 72% of adults and 57% of children. Additional activating mutations, namely, V560G and the internal tandem duplications (ITDs) 502-503dupAY, were detected in 12% of adults and 8% of children. V560G occurred more commonly in our patients than previously reported, and it appeared to be associated with more advanced disease. Otherwise, the presence or absence of activating mutations did not correlate with skin lesion morphology, disease extent or total serum tryptase levels. Four adults had expression only of wild-type KIT, while two others had expression of a truncated KIT lacking tyrosine kinase activity; yet these patients were clinically indistinguishable from those patients with activating c-KIT mutations.

Conclusions

Activating c-KIT mutations exist in a significant portion of patients with mastocytosis, but not all patients showed expression of these mutations. Except for V560G, the presence or absence of activating c-KIT mutations did not predict the extent of disease. These observations suggest that although activating c-KIT mutations are associated with mast cell growth, other genes probably play a role in the cause of mastocytosis.