Dysregulation of apoptosis leading to reduced DNA repair capacity, increased DNA mutation, and chromosomal instability is one of the pathological mechanisms associated with aging. Rothmund-Thomson syndrome (RTS) is a human genetic disease characterized by several features of premature aging. Although the genetic defect has not been identified, defects in DNA repair capacity have been implicated in the pathogenesis of this disease. To determine whether dysregulation of apoptosis is associated with the pathogenesis of RTS symptoms, we investigated the sensitivity of a lymphoblastoid cell line--derived from a young (10-year-old) individual with RTS--to cell death induced by anti-Fas antibody (clone: CH-11). Cell lines derived from a normal young (14-year-old) individual and a normal aged (79-year-old) individual were used as controls. Treatment with CH-11 (500 ng/ml) resulted in significantly decreased cell viability in the RTS cell line (42.4% +/- 4.2%) and that derived from the aged individual (47.3% +/- 9.2%) as compared to the normal young cell line (66.9% +/- 7.0%). The concentrations of CH-11 required to induce 50% cell death in the RTS (IC50, 890 ng/ml) and that derived from the aged individual (IC50, 3640 ng/ml) were lower than that of the control young cell line (IC50 > 10(5) ng/ml). The lower viability was due to increased susceptibility to apoptosis to CH-11 in the RTS (59.0% +/- 2.0%) compared to that in the normal young cell line (40.9% +/- 0.9%) as shown by 7-amino-actinomycin D (7-AAD) staining (p < .005). Treatment of the RTS cell line with acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO), a specific inhibitor of caspase-3, significantly increased the cell viability after CH-11 treatment (75.9% +/- 2.2%). Taken together, these results provide the first evidence to show that RTS lymphoblastoid has an increased sensitivity to cell death mediated by Fas and that inhibition of caspase-3 activity may be a potential target in reversing the sensitivity of RTS cells to Fas-mediated apoptosis in vitro.