Cytogenetic and Molecular Genetic Abnormalities in Agnogenic Myeloid Metaplasia

Agnogenic myeloid metaplasia (AMM), a clonal hematopoietic stem cell disorder also known as chronic idiopathic myelofibrosis, is characterized by a polyclonal, or reactive, stromal proliferation, resulting from the inappropriate release of megakaryocyte/monocyte-derived growth factors. Cytogenetic studies indicate that 30% of cases possess a clonal cytogenetic abnormality at diagnosis, a figure that increases to approximately 90% following leukemic transformation. Patients with specific abnormal karyotypes have a poor prognosis and may fail to respond to androgen therapy. The incidence of chromosomal abnormalities is significantly less in younger patients, a fact that may explain their more favorable prognosis. Common findings include 13q−, 20q−, trisomy 8, and abnormalities of chromosomes 1, 7, and 9. However, detailed cytogenetic analysis has not yet led to the identification of pathogenetically relevant genes and, as a result, the molecular mechanisms responsible for the clonal proliferation remain unknown. Targeted gene screening has revealed only rare oncogenic point mutations in N-RAS, p53, and c-KIT.