Fas-induced T-cell death in patients with ALPS or DALD and several of their parents. Data from ALPS patients' families are marked with squares, those from DALD patients' families with circles; gray symbols mark patients; black symbols, the fathers; and white symbols, the mothers. Numbers correspond to the code assigned to each patient. Long-term T-cell lines were treated with anti-Fas Mab, and survival was assessed after 18 hours. Results are expressed as relative cell-survival percent. The horizontal lines indicate the upper limit of the normal range, calculated as the 95th percentile of data obtained from 200 healthy donors (median cell survival of controls was 60%; the 5th-95th percentile range was 38%-82%). In the control wells (ie, in the absence of apoptotic stimuli), spontaneous cell loss was always less than 10% of the seeded cells and similar in cultures from the patients and healthy donors. ALPS patients 1 to 7 carried heterozygous mutations of the Fas gene.