DNMT3A and TET2 in Clonal Haematopoiesis

Two Opposing Methylation Regulators

DNMT3A adds methyl groups to cytosine to establish DNA methylation patterns. TET2 begins the process of removing them by oxidising 5-methylcytosine. Loss-of-function mutations in either gene shift the balance of DNA methylation in blood stem cells and alter which genes they express.

The result is a stem cell that self-renews slightly more efficiently than its neighbours. Over years this modest advantage lets its descendants make up a measurable fraction of circulating blood cells.

What CHIP Is and Is Not

CHIP is defined as a clone driven by a leukaemia-associated mutation at a variant allele fraction of at least 2 percent, in someone with normal blood counts and no blood cancer. About 80 percent of CHIP involves DNMT3A, TET2 or ASXL1.

CHIP is common with age, present in roughly 10 percent or more of people over 70. It carries a small risk of progression to a blood cancer, on the order of half a percent to one percent per year, so most people with CHIP never develop one.

Non-Cancer Associations

CHIP has been linked to a roughly two-fold increase in cardiovascular risk independent of traditional risk factors, thought to act through a pro-inflammatory state driven by the mutant immune cells. Associations with kidney injury, and with outcomes in heart failure and aortic stenosis, have also been reported.

These are population-level associations from epidemiological studies. There is no established treatment for CHIP itself, and it is often an incidental finding on a tumour or germline sequencing test.

Why It Matters for Test Interpretation

Because blood is the usual source of germline DNA, a CHIP mutation can appear on a hereditary-cancer test and be misread as germline, or appear in circulating tumour DNA and be misattributed to the tumour. A low variant allele fraction and a gene typical of CHIP are clues.

Paired testing of a non-blood tissue can resolve the ambiguity when it matters.

CHIP and Cancer Treatment

CHIP intersects with oncology in two practical ways. Cytotoxic chemotherapy and radiotherapy can give a competitive advantage to TP53- or PPM1D-mutant CHIP clones, and therapy-related myeloid neoplasms sometimes trace back to a clone that was detectable before treatment. This is a reason CHIP draws attention when planning treatment in patients who may need years of follow-up.

For a person found to have CHIP incidentally, the usual response is a full blood count and clinical review rather than any specific intervention, with haematology referral reserved for higher-risk features such as a large clone, multiple mutations, or unexplained low blood counts.

Key Takeaways

• ·DNMT3A and TET2 mutations are the commonest drivers of age-related clonal haematopoiesis.
• ·CHIP means a blood-cell clone without blood cancer, with a low annual rate of progression.
• ·CHIP mutations can confound germline and circulating-tumour-DNA testing and are frequently incidental.