Is Lynch syndrome passed down in families?

Yes. Lynch syndrome is inherited. The gene change that causes it is present in every cell of the body from birth, so a parent can pass it to a child.

The National Cancer Institute also calls it "hereditary nonpolyposis colorectal cancer." NCI says it is "caused by germline pathogenic variants in DNA MMR genes (MLH1, MSH2, MSH6, and PMS2) and EPCAM."

Germline is the key word. It means the change was there from conception, in every cell. It did not appear later inside a tumor. That is why it can travel down a family tree.

What those genes normally do

MMR stands for mismatch repair. Every time a cell divides, it copies its whole DNA, and it makes mistakes. Mismatch repair is the proofreading crew that catches them.

When one of those genes is faulty, errors go uncorrected and pile up over a lifetime. Cells take on damage faster than they should. Cancer becomes more likely, and it tends to arrive earlier.

How it passes down

Lynch syndrome follows autosomal dominant inheritance. That means one altered copy of the gene is enough. It can come from either parent. Each child of a carrier has a one in two chance of inheriting it.

Two things follow. Sons and daughters are equally affected, so a father can pass it on just as a mother can. And it does not skip generations. Someone who does not carry the variant cannot pass it on.

Not every relative inherits it. In any family, some do and some do not, which is why testing individuals matters rather than assuming.

How families usually find out

This is the practical part, and it surprises people.

The discovery often starts with the tumor, not the patient. NCI notes that "a universal screening approach to tumor testing is supported, in which all CRC cases are evaluated." Two methods are used. One is "immunohistochemistry testing for the expression of the MMR proteins." The other is "microsatellite instability (MSI) testing." Both hunt for fingerprints of broken repair in the cancer itself.

If the tumor shows those fingerprints, a blood or saliva test can confirm whether the person carries an inherited variant. So if you or a relative has colorectal cancer, ask whether the tumor had MMR or MSI testing.

Lynch syndrome accounts for roughly 2% to 3% of colorectal cancers. A family pattern of colorectal and endometrial cancer, particularly at younger ages, is one of the classic clues.

Why the answer changes what happens next

Knowing has proven value. NCI reports that "surveillance of Lynch syndrome patients with colonoscopy every 1 to 2 years, and in one study up to 3 years, has been shown to reduce CRC incidence and mortality."

Every one to two years, against the far longer gap used for average-risk adults. That is not a small change. The benefit shows up as cases prevented and lives saved, not just cancers found sooner.

When testing a family, it usually helps to start with a relative who has already had cancer. NCI explains that a true negative result only exists once a specific family variant is known. Without that anchor, a relative's negative result is much harder to read.

If Lynch syndrome runs in your family, ask for a referral to a genetic counselor. Bring a written family history, with ages at diagnosis.