Accumulation of very short telomeres precedes development of –7 MDS in SAA patients. (A) Mean telomere content for clonal evolution group (red line, n = 13) and SAA stable controls (blue line, n = 30) measured by qPCR. For each patient in both groups, mean telomere content at each available time point was normalized to mean telomere content at presentation. (B) Examples of XpYp STELA profile of serial peripheral blood leukocytes for patients from the time of diagnosis of SAA until progression to −7 MDS (left) or SAA controls (right). (C) Quantification of telomere length measured by XpYp STELA. For each of the 2 groups, all available samples at various time points after IST were assayed by both qPCR and STELA. For the clonal evolution group, samples up to the time of −7 diagnosis were used; thus for each time point, at least 4 patients samples were used. Similarly for the SAA control group, 30 patients’ samples were available to 24 months after initial IST; each time point included more than 15 patient samples. For serial blood samples’ telomere length measured by XpYp STELA, average lengths were mean-centered by patient. Discrete bands lengths were quantified using ImageQuant TL software (GE Healthcare Life Sciences, Piscataway, NJ). Bands were quantified based on a standard DNA ladder. A 1-way Wilcoxon test on equal length of the telomeres of the patients over all time points was statistically significant (P = .0027) for the clonal evolution group but not for controls (P = .62).