Lynch syndrome is caused by inherited mutations in one of several "mismatch repair" genes — MLH1, MSH2, MSH6, PMS2, or a related gene called EPCAM. These genes normally function like spell-check for your DNA, catching and fixing small copying errors every time a cell divides. When one of them is broken from birth, those errors accumulate faster than they should, particularly in fast-dividing tissue like the lining of the colon and uterus — which is exactly why Lynch syndrome so sharply raises the risk of colorectal and endometrial cancer specifically, rather than cancer risk broadly.
The Risk Varies Enormously by Which Gene Is Involved
This is one of the more nuanced points about Lynch syndrome: not all four genes carry equal risk, and lumping them together understates how different a management plan should look depending on which one you carry. MLH1 and MSH2 mutations are generally associated with the highest colorectal cancer risk — lifetime estimates for these genes commonly range as high as 70-80% without intervention, dramatically higher than the roughly 4% lifetime risk in the general population. MSH6 and PMS2 mutations, while still meaningfully elevated, tend to carry somewhat lower colorectal cancer risk and a later average age of onset. Endometrial cancer risk follows a different pattern by gene entirely — MSH6 carriers, for instance, can have among the highest endometrial cancer risk of the group, even though their colorectal risk is comparatively lower.
| Gene | Share of Lynch cases | Relative colorectal cancer risk |
|---|---|---|
| MLH1 | ~30–40% | Highest |
| MSH2 | ~35–55% | High |
| MSH6 | ~15–20% | Moderate; higher endometrial cancer risk |
| PMS2 | ~5% | Lower, later onset |
Beyond colorectal and endometrial cancer, Lynch syndrome carriers also face elevated risk for gastric, ovarian, urinary tract, small bowel, and several other cancers, though at lower rates than the two primary associations.
Why Knowing Changes Everything
Lynch syndrome is one of the clearest cases in all of genetics where early knowledge directly and dramatically changes outcomes — not through some future treatment, but through screening that already exists today. Colonoscopy surveillance starting in the mid-20s, done more frequently than average-risk guidelines recommend, has been shown to reduce colorectal cancer incidence and mortality substantially in Lynch syndrome carriers, in large part because it catches and removes precancerous polyps before they become cancer, on a syndrome where polyps can progress to cancer far faster than in the general population — sometimes in as little as two years rather than the decade-long process typical of sporadic colorectal cancer.
Lynch syndrome is inherited in an autosomal dominant pattern — unlike the recessive carrier conditions most family planning content focuses on, a single copy from one parent is enough to confer risk, and each child of a carrier has a 50% chance of inheriting it, regardless of the other parent's status. This also means testing at-risk relatives — not just reproductive partners — is often the more urgent conversation once one family member is identified.
Should You Get Tested?
If you have a personal or family history of colorectal or endometrial cancer, especially at a younger-than-typical age, or multiple relatives across generations with Lynch-associated cancers, talk to your doctor or a genetic counselor about Lynch syndrome testing directly — clinical criteria like the Amsterdam and Bethesda guidelines exist specifically to flag who should be tested. Outside a specific clinical trigger, Lynch-associated genes are also among the genes reliably captured by comprehensive whole genome sequencing.
Hereditary Cancer Risk Doesn't Announce Itself
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Get Sequenced with Dante Labs → 10% off with code GENOMEFor the broader picture of hereditary cancer risk, see our genome testing and cancer risk guide. And because Lynch syndrome's autosomal dominant inheritance pattern differs from the recessive conditions most carrier screening covers, our advanced family planning guide covers dominant and other non-recessive inheritance patterns in more depth.