Figure FIG. 3.

Colony‐forming efficiency (CFE) and frequency of mutated clones. (A) Colony‐forming efficiency of single cell suspensions of bone marrow nucleated cells was determined for a series of normal donors (age range, 1–76 yr) from patients in which high levels of mutation were detected (age range, 7–35 yr) and from patients in which low levels of mutation were detected (age range, 35–52 yr). The average CFE was ∼18‐fold higher in samples from patients with a high level of mutation compared with that of normal donors (*p = 0.0001) and significantly higher compared with that of patients with a low level of mutation (^# p = 0.045). There was no statistical difference between samples from normal donors compared with those from patients with a low level of mutation. (B) Clones (∼20 from each patient) isolated from low‐density cultures of single cell suspensions of bone marrow mononuclear cells were genotyped by direct DNA sequencing. The percent of mutated clones (representative of the percent of mutated CFU‐Fs) was compared with the age of the patient by linear regression and was found to have a tight negative correlation.