Detection of Monosomy 7 in Bone Marrow by Fluorescence In Situ Hybridization: A Study of Fanconi Anemia Patients and Review of the Literature

Monosomy 7 is frequently found in the bone marrow of patients with Fanconi anemia (FA), marrow myelodysplasia, or acute myelogenous leukemia and is associated with poor prognosis. In our laboratory, cytogenetic analysis of bone marrow from an FA patient found 2 of 30 cells with monosomy 7, but the results of fluorescence in situ hybridization (FISH) indicated that 83 of 207 cells (40%) had monosomy 7. FISH was then used to analyze two earlier samples from the index case, neither of which had monosomy 7 as determined by standard cytogenetics. The FISH analysis determined that the first sample, taken 19 months earlier, had 8 of 200 cells (4%) with monosomy 7 and the second sample, taken 7 months later, contained 43 of 200 cells (21.5%) with monosomy 7. These results indicate a slow evolution toward monosomy 7 in the patient’s bone marrow. Standard metaphase chromosome analysis represents only spontaneously dividing cells, leading us to hypothesize that FISH was detecting monosomy 7 in nondividing cells and that it might be useful in the early detection of abnormal clones. To test this hypothesis, FISH was performed on 13 bone marrow samples from nine patients with FA who did not exhibit monosomy 7 by cytogenetic analysis. Monosomy 7 was detected in 3.44% of nuclei in FA patients and in 3% of nuclei in normal controls. To date, none of these nine FA patients have developed monosomy 7 or leukemia. They are being monitored by standard cytogenetics and by FISH to determine whether monosomy 7 develops and whether it can be detected by FISH prior to its detection by standard cytogenetics. As standard practice, we have adopted FISH analysis for monosomy 7 in all patients with FA.