Hypothesis

Telomere shortening does not merely count divisions; it reflects a rise in genomic informational entropy that leaks into the plasma as altered cell‑free DNA (cfDNA) fragment size heterogeneity, especially at subtelomeric repeats. We propose that the Shannon entropy of cfDNA fragment length distribution (cfDNA‑FE) serves as a quantitative proxy for telomere‑associated entropy and predicts biological age independently of methylation clocks.

Mechanistic Rationale

1. Shelterin loss → chromatin relaxation – Critically short telomeres weaken shelterin binding, permitting ATM‑dependent histone acetylation and loss of heterochromatin at subtelomeric L1HS/AluY repeats (fragment size nucleosome redistribution). This relaxed state makes nucleosomal DNA more accessible to apoptotic nucleases (CAD/DFF40), generating a broader spectrum of fragment lengths.
2. Entropy‑driven fragmentation – As telomeric repeat redundancy declines, the probability of stochastic nuclease cuts increases, raising the variance of fragment sizes. Information theory predicts that the Shannon entropy H = - Σ p_i log₂ p_i of the fragment length distribution will rise with telomere shortening (informational entropy telomere).
3. Neutrophil and colon epithelial bias – Because neutrophils and colon epithelium are the main cfDNA sources in aging (cfDNA methylation patterns), measuring cfDNA‑FE in these cell‑type‑specific fragments (using methylation‑based deconvolution) should amplify the signal.

Testable Predictions

• Prediction 1: In cross‑sectional human plasma, cfDNA‑FE will correlate negatively with leukocyte telomere length (qPCR) and positively with epigenetic age (48‑CpG model) after adjusting for age (48‑CpG methylation model).
• Prediction 2: Experimental telomerase activation in cultured human fibroblasts will reduce cfDNA‑FE released upon induced apoptosis, whereas telomere crisis (TRF2 dominant‑negative) will increase it.
• Prediction 3: Sorting plasma cfDNA by neutrophil‑specific methylation markers will yield a higher cfDNA‑FE signal than total cfDNA, reflecting the cell‑type‑specific source.

Falsification

If cfDNA‑FE shows no significant association with telomere length or epigenetic age, or if telomerase manipulation fails to alter cfDNA‑FE despite verified changes in telomere repeat content, the hypothesis would be refuted.

Implications

A positive result would provide a non‑invasive, entropy‑based readout of telomere informational decay, bridging the gap between molecular clocks and thermodynamic theories of aging.