Molecular diagnosis of mast cell disorders: a paper from the 2005 William Beaumont Hospital Symposium on Molecular Pathology

Abstract

Mastocytosis is a disease characterized by pathological mast cell accumulation and activation in tissues. Most patients with mastocytosis exhibit the D816V point mutation in the tyrosine kinase domain of the transmembrane receptor protein Kit, leading to its constitutive activation in bone marrow or lesional skin tissue. Detection of a codon 816 c-kit mutation is included as a minor diagnostic criterion in the World Health Organization's diagnostic criteria for systemic mastocytosis. Determining mutational status of the c-kit gene also has pharmacogenomic implications in patients considered for investigational mast cell cytoreductive therapies. This article reviews diagnostic and therapeutic implications of c-kit mutations as well as other less common molecular abnormalities observed in mast cell disease.

Figure 1

Multifocal clusters of mast cells in a bone marrow biopsy visualized by immunohistochemical staining for tryptase satisfy the World Health Organization major diagnostic criterion in this patient with indolent systemic mastocytosis.

Figure 2

Mast cells in bone marrow aspirate smears show aberrant morphological features such as spindling and hypogranulation (A), as compared to normal mast cells with a round and centrally located nucleus and dense cytoplasmic granulation (B).

Figure 3

C-kitmutations in mastocytosis. EC, extracellular (ligand binding); TM, transmembrane; JM, juxtamembrane; TK, tyrosine kinase domain. The most common mutation, D816V, is shown boxed.

Figure 4

Demonstration of D816V c-kitmutation by RFLP (A) and capillary sequencing (B). A:HinfI digestion of the RT-PCR product from HMC1.2 cell line (lane 1, positive control) and patient samples in lanes 4 and 6 show the presence of an additional band (arrow) as a result of creating a new restriction site by A>T nucleotide change in c-kitcodon 816. Lanes 2, 3, and 5 show wild-type pattern codon 816. B: Demonstration of the heterozygous A>T nucleotide change in cDNA position 2468 (corresponding to amino acid change D816V) by direct capillary sequencing (right), and its comparison to the wild-type sequence (left).