MLH1 gene expression is lost as a function of age. (A) Percentage of CFCs that lack detectable MLH1 gene expression by QRT-PCR with age. Solid lines represent the best fit linear regression, and dashed lines represent a 95% confidence interval (P = .0073). (B) Comparison of the percentage of CFUs expressing detectable MLH1 for donor samples ≤ 45 years with donors > 45 years old. Statistical analysis by 2-tailed unpaired t test (P = .029).