Amplification of ribosomal RNA genes in acute myeloid leukemia

Gene amplification is a relatively rare event in acute myeloid leukemia (AML). Double minutes (dmin) and homogeneously staining regions are well established phenomena as cytogenetic correlates of gene amplification. Recently, however, two additional mechanisms leading to gene amplification, i.e., segmental jumping translocations and formation of ring chromosomes, have been described. We report four patients with AML, in whom bone marrow cells exhibited amplifications of ribosomal RNA (rRNA) genes in the form of ring chromosomes or a hsr. In two patients, the MLL gene, and in one patient the CBFA2 gene were shown to be co-amplified with rRNA genes. In two of the four patients, multiple copies of alpha-satellite sequences of the centromeres 13 and 21, respectively, were also demonstrated. In three of the four patients, the clinical course was very aggressive, leading to death within 2-8 months. In these three patients, complex karyotype abnormalities were found, whereas the karyotype of Patient 4 was characterized only by supernumerary ring 21 chromosomes of different sizes and a trisomy 8 in half of the metaphases. Modes of origin and clinical significance of the amplification of rRNA genes are discussed.