If a gene mutation runs in my family, will I inherit it?

Not necessarily. Most hereditary cancer syndromes give each child of a carrier a 50 percent chance of inheriting the change and a 50 percent chance of not inheriting it. Siblings can land on opposite sides of that coin.

Why the odds are one in two

Most of the gene changes that raise cancer risk in families are passed down in an autosomal dominant pattern. That means one altered copy in each cell is enough to raise risk, and it means a parent who carries the change passes it to each child with a 50 percent chance. BRCA1 and BRCA2 work this way. So does Lynch syndrome, which raises the risk of colorectal, endometrial, stomach, urinary tract, and other cancers.

Two details matter here. The odds reset with each pregnancy, so having three children does not mean one and a half of them will carry it. And the gene can come from either parent. Breast cancer is far more common in women, but a BRCA change is inherited just as readily from a father.

If the change is in your family but was not passed to you, you cannot pass it to your own children. That branch of the family tree ends there.

Testing the right person first

Genetic testing can settle whether you carry the specific change known in your family. NCI recommends that, when possible, counseling and testing start with a relative who has had cancer.

The reason is practical. Testing an affected relative identifies exactly which variant is in the family. Once the lab knows what to look for, your result becomes clean. If they find nothing in you, that is a true negative, meaning you did not inherit the family's change and your cancer risk is probably close to that of the general population.

Without that anchor, a negative result is much weaker. It is called an uninformative negative: nothing was found, but the family history remains unexplained, and you may still need extra screening.

Age matters too. Professional groups do not recommend BRCA1 and BRCA2 testing for children under 18, because there is nothing useful to do about it in childhood and cancer from these changes is very unlikely at that age.

Carrying it is a raised risk, not a diagnosis

Inheriting a harmful change raises the odds. It does not settle them.

The BRCA numbers show the scale. More than 60 percent of women who inherit a harmful BRCA1 or BRCA2 change develop breast cancer in their lifetime, against about 13 percent of women in the general population. For ovarian cancer, the range is about 39 to 58 percent with BRCA1 and 13 to 29 percent with BRCA2, against about 1.1 percent in the general population. High, but not certain, and many carriers never develop cancer.

These changes are also uncommon. Harmful BRCA changes are found in about 0.2 to 0.3 percent of the general population, roughly 1 in 400. In some groups the rate is higher because of founder variants passed down within a population. About 2 percent of people of Ashkenazi Jewish descent carry one, usually one of three specific variants. Norwegian, Dutch, Icelandic, Hispanic, West African, African American, Sephardi Jewish, and Bahamian populations have their own founder variants.

A genetic counselor is the right person to sort out what your family history actually implies, which test to order, and what a result would change about your screening. NCI recommends counseling before testing, not only after a result lands.

Sources

https://www.cancer.gov/about-cancer/causes-prevention/genetics/genetic-testing-fact-sheet

https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet

https://medlineplus.gov/genetics/understanding/inheritance/riskassessment/

https://medlineplus.gov/genetics/condition/lynch-syndrome/