Background:
Methylation at certain human CpG rich sequences increases with age. The mechanisms underlying such age-related changes are unclear, but methylation may accumulate slowly in a clock-like manner from birth and record lifetime numbers of stem cell divisions. Alternatively, methylation may fluctuate in response to environmental stimuli. The relative stability of methylation patterns may be inferred through serial observations of the same colon.
Case presentation:
A 22 year-old male with attenuated familial adenomatous polyposis received neo-adjuvant chemotherapy and radiation prior to surgery for rectal adenocarcinoma. Colon crypt methylation patterns before and after neo-adjuvant therapy (62 days apart) were essentially identical with respect to percent methylation and diversity. Consistent with previous studies, methylation patterns recorded no evidence for enhanced colon crypt stem cell survival with a germline mutation (codon 215) proximal to the mutation cluster region of APC.
Conclusion:
The inability of neo-adjuvant therapy to significantly alter crypt methylation patterns suggests stem cells are relatively protected from transient environmental changes. Age-related methylation appears to primarily reflect epigenetic errors in stem cells that slowly accumulate in a clock-like manner from birth. Therefore, life-long human stem cell histories are potentially written within and may be read from somatic cell epigenomes.