Telomere length in peripheral blood leukocytes. (A,B) Telomere length in peripheral blood granulocytes and lymphocytes from patients with acquired aplastic anemia (AA) carrying 258 + 2 T>C SBDS gene mutation (●) and patients with Shwachman-Diamond syndrome (SDS; ■). Telomere lengths were measured by flow fluorescence in situ hybridization analysis. Lines represent the 1st, 10th, 50th, 90th, and 99th percentiles of telomere length in age-matched healthy controls' granulocytes and lymphocytes, based on a reference group of 400 persons. (C) Telomere length of leukocytes also was measured by Southern blot allowing quantification of length heterogeneity by calculating the coefficient of variation (CV). Length heterogeneity was significantly increased in SDS patients compared with healthy controls. Lanes 1 and 2, umbilical cord blood of healthy subjects; lanes 3 and 4, age-matched healthy subjects; lanes 5 to 8, patients with SDS. Bar graphic on the right represents the analysis of variation of optical density (mean ± SEM) in telomere length for controls (1-4) and SDS patients (5-8), indicating the higher variability in telomere length in SDS patients. (D) Cultured lymphocytes from patients with SDS (−/−), with acquired AA heterozygous for SBDS gene 258 + 2 T>C mutation (+/−), and healthy controls (+/+) were assayed for telomerase activity using the fluorescent telomeric repeat-amplification protocol (TRAP). Telomerase activity was measured in quadruplicate and indicated in total product generated (TPG) units. Error bars represent standard deviation.