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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: JAMA289:1130; 2003). 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. Sci2006;103:14483). 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, p10% monosomy 7 by FISH at presentation, but normal cytogenetics. The two responding patients tested with >6% monosomy 7 prior to IST demonstrated

Telomeres that cap the ends of chromosomes, protect them from recombination, end-to-end fusion, and recognition as damaged DNA. Telomere shorteningmay result in cell cycle arrest and senescence or in genomic instability that precedes malignancy. Maintenance of the integrity of telomeres requires the telomerase ribonucleoprotein complex, mainly the telomerase reverse transcriptase (TERT) and its integral RNA template (TERC). Mutations in TERC and TERT cause progressive telomere shortening; short telomeres are found in constitutional marrow failure syndromes and also in apparently acquired aplastic anemia (Fogarty PF et al, Lancet362:1628, 2003;. Yamaguchi H et al, NEJM352:1413, 2005). Myelodysplasia and acute leukemia are often present in these kindreds and associated with pathogenic mutations. The mechanism resulting in genomic instability in TERT and TERC-deficient individuals is unclear. End-to-end chromosome fusion in TERT-”knock-out” embryonic mouse stem cells are seen after multiple passages in culture and are associated with profound telomere shortening and the development of aneuploidy (Lee HW et al. Nature 9:569–74, 1998). End-to-end fusion of sister chromatids presumably results in disruption of chromosome segregation during metaphase. In the present study, we examined blood and marrow cells from 7 patients with TERT, and TERC gene mutations; 10 healthy young controls; and 2 individuals older than age 60 years of age, as well as 6 umbilical cord bloods. Leukocytes with TERT or TERC mutations had short telomeres as previously measured by flow-fluorescent in situ hybridization (FISH) and confirmed by Southern hybridization (mean telomere shortening in comparison to age-matched controls, 3.4 ± 1.7 kb) and low telomerase enzymatic activity (144±13 vs. 270±56 respectively; P