rs555607708 — CHEK2 1100delC

CHEK2 1100delC — The Cell Cycle Guardian with a Broken Sword

Every time your cells divide, they face a dangerous moment: the entire genome must be copied without error, and any double-strand breaks in DNA must be repaired before the cell commits to division. CHEK2 (checkpoint kinase 2) is one of the critical sentries in this process. When the upstream kinase ATM¹¹ ATM
Ataxia telangiectasia mutated — a kinase that detects double-strand DNA breaks and activates downstream repair and cell cycle arrest pathways detects a double-strand break, it phosphorylates and activates CHEK2, which then halts the cell cycle by phosphorylating p53, BRCA1, and CDC25 phosphatases. The 1100delC variant — a single-nucleotide deletion in exon 10 — destroys this checkpoint function entirely, leaving carriers with reduced capacity to arrest damaged cells before they become cancerous.

The Mechanism

The 1100delC deletion removes a single cytosine from position 1100 of the coding sequence, shifting the reading frame and creating a premature stop codon 15 amino acids downstream (p.Thr367MetfsTer15). The truncated protein lacks the entire kinase domain²² kinase domain
The catalytic domain of CHEK2 that phosphorylates downstream targets including p53, BRCA1, and CDC25C; without it, CHEK2 cannot transmit the DNA damage signal, rendering it completely non-functional. The truncated mRNA is also partly degraded by nonsense-mediated decay³³ nonsense-mediated decay
A cellular surveillance mechanism that destroys mRNA transcripts containing premature stop codons, reducing the amount of abnormal protein produced, further reducing functional CHEK2 protein in carriers.

In heterozygous carriers (one normal copy, one 1100delC copy), total CHEK2 kinase activity is reduced by roughly 50%. This is enough for normal cell cycle regulation under most circumstances, but under conditions of increased DNA damage — from ionizing radiation, certain chemicals, or the cumulative DNA replication errors of aging — the reduced checkpoint capacity allows more damaged cells to slip through into division rather than being arrested for repair or directed to apoptosis⁴⁴ apoptosis
Programmed cell death — the cell's self-destruct mechanism that eliminates damaged cells before they can become cancerous.

Importantly, CHEK2 operates in the same pathway as BRCA1 and BRCA2. ATM detects the break, phosphorylates CHEK2, and CHEK2 in turn phosphorylates BRCA1 to initiate homologous recombination repair. This explains a key finding: the 1100delC variant does not further increase cancer risk in individuals who already carry pathogenic BRCA1 or BRCA2 mutations, because the downstream pathway is already compromised.

The Evidence

The landmark 2002 discovery⁵⁵ landmark 2002 discovery
Meijers-Heijboer H et al. Low-penetrance susceptibility to breast cancer due to CHEK2*1100delC in noncarriers of BRCA1 or BRCA2 mutations. Nat Genet, 2002 by the CHEK2-Breast Cancer Consortium identified 1100delC in 5.1% of breast cancer patients from families without BRCA1/2 mutations, compared with 1.1% in healthy controls. The study estimated approximately a twofold increase in breast cancer risk for women and a striking tenfold increase for men carrying the variant.

A large collaborative analysis⁶⁶ large collaborative analysis
CHEK2 Breast Cancer Case-Control Consortium. CHEK2*1100delC and susceptibility to breast cancer. Am J Hum Genet, 2004 pooling 10,860 breast cancer cases and 9,065 controls from 10 studies across five countries confirmed the association, reporting an odds ratio of 2.34 (95% CI 1.72-3.20). The variant was present in 1.9% of cases versus 0.7% of controls, with some evidence of higher prevalence among women with a first-degree relative affected by breast cancer.

Beyond breast cancer, the colorectal cancer meta-analysis⁷⁷ colorectal cancer meta-analysis
Xiang HP et al. Meta-analysis of CHEK2 1100delC variant and colorectal cancer susceptibility. Eur J Cancer, 2011 analyzed 4,194 colorectal cancer cases and 10,010 controls, finding a significant association with unselected colorectal cancer. A prostate cancer meta-analysis⁸⁸ prostate cancer meta-analysis
Wang Y et al. CHEK2 mutation and risk of prostate cancer: a systematic review and meta-analysis. Int J Clin Exp Med, 2015 reported an odds ratio of 3.29 (95% CI 1.85-5.85) for prostate cancer.

The rare homozygous state has been studied in a Dutch cohort⁹⁹ Dutch cohort
Huijts PEA et al. CHEK2*1100delC homozygosity in the Netherlands. Eur J Hum Genet, 2014, where three of five tracked homozygous women developed contralateral breast cancer, suggesting a considerably higher risk than heterozygosity alone.

Practical Actions

For DG carriers: this is a moderate-penetrance cancer susceptibility variant — meaningfully higher risk than the general population, but far lower penetrance than pathogenic BRCA1/2 mutations. The appropriate response is enhanced surveillance, not panic. Women should begin breast cancer screening earlier than the general population, with breast MRI added for those with additional family history. Colorectal cancer screening should start earlier as well. Men should be aware of both the elevated prostate cancer risk and the rare but real risk of male breast cancer.

For DD homozygotes: this extremely rare genotype (roughly 1 in 10,000 in Europeans) carries substantially higher cancer risk. Intensified surveillance across multiple cancer types is warranted, and discussion with a cancer genetics specialist is appropriate.

Interactions

CHEK2 sits at a critical node in the DNA damage response pathway, directly downstream of ATM (rs1801516)¹⁰¹⁰ ATM (rs1801516)
The ATM kinase detects double-strand breaks and activates CHEK2; reduced ATM function combined with reduced CHEK2 could compound DNA repair deficiency and upstream of BRCA1. A carrier of both CHEK2 1100delC and the ATM D1853N variant (rs1801516 AG or AA) could theoretically have impaired signaling at two sequential steps in the double-strand break response, though clinical data on this specific combination are limited. If a user carries CHEK2 1100delC heterozygous (DG) plus ATM D1853N heterozygous (AG at rs1801516), the combined effect on DNA repair checkpoint efficiency may warrant earlier and more intensive cancer screening than either variant alone would indicate.

The TP53 codon 72 polymorphism (rs1042522)¹¹¹¹ TP53 codon 72 polymorphism (rs1042522)
TP53 Pro72Arg affects apoptotic efficiency; since CHEK2 phosphorylates and stabilizes p53, reduced CHEK2 combined with altered p53 function could further impair the damage response is also relevant, as CHEK2 directly phosphorylates p53 at Ser20 to stabilize it. The combination of reduced CHEK2 kinase activity and the less apoptotically efficient Pro72 variant could theoretically compound the defect in eliminating damaged cells.