About fifteen percent of patients with severe aplastic anemia (sAA) who undergo immunosuppression therapy (IST) develop clonal disease in the decade following treatment. Of 122 patients treated with horse ATG/CsA at NIH, 13 developed cytogenetic abnormalities (monosomy 7 in 9 patients, 7p deletion in one, and trisomy 8 in 2) (

Rosenfeld et al:
). Monosomy 7 usually occurs in patients with sAA who are unresponsive to IST. Factors responsible for clonal progression in bone marrow failure are still unclear. We and others have reported that monosomy 7 may be detected by fluorescent in situ hybridization (FISH) months before conventional cytogenetics and that high levels of GCSF foster preferential expansion of the monosomy 7 clone in vitro (
Sloand E et al;
Proc. Natl. Acad. Sci
). We hypothesized that a clone of monsomy 7 cells might indicate an underlying stem cell disorder unlikely to respond to immunosuppression or reflect more severe disease marked by higher endogenous GCSF levels. FISH was undertaken on 40 bone marrow samples obtained from aplastic anemia patients at presentation and before immunosuppressive treatment. Bone marrow mononuclear cells were hybridized with centromeric probes specific for chromosome 7 and chromosome 8 (to control for hybridization efficiency); samples were assessed on duplicate slides by three investigators who were unaware of the diagnoses and outcomes. Twenty-five healthy controls were tested concurrently. The upper limit of normal was set at 6% based on control data. Of twenty-one patients with > 6% monosomy 7 cells, response to IST was observed in 12 (57%), while 6 of 19 (84%) with normal FISH responded to IST (p=0.08). Thirteen patients had monosomy 7 frequencies of >10%. Of these 5 (38%) responded to IST, compared with 23/27 (85%) with ≤10% monosomy 7. The proportion of monosomy 7 cells in the bone marrow correlated with age (R2 =0.6, p<0.001). Two of the 23 non-responding patients later developed clonal progression with monosomy 7 or 7q-; both had >10% monosomy 7 by FISH at presentation, but normal cytogenetics. The two responding patients tested with >6% monosomy 7 prior to IST demonstrated <2% following successful IST, suggesting that the high endogenous levels of G-CSF present before IST response may have facilitated expansion of the clone. Significant monosmy 7 clones may reflect a stem cell disorder in patients not responding to IST.

Author notes

Disclosure: No relevant conflicts of interest to declare.