What is the difference between inherited and acquired gene changes?

An inherited change is in every cell of your body from the day you were born and can be passed to your children. An acquired change happens later, in one cell, and stops with you.

That is the whole distinction, and everything else follows from it. Doctors call inherited changes germline changes, because they were carried in a parent's egg or sperm cell. They call acquired changes somatic changes, from the Greek word for body.

One cell versus every cell

Your genes are sections of DNA that carry instructions for building proteins. Every cell holds a copy of the full set.

If you inherited a change in a gene such as BRCA1, that change sits in your skin cells, your blood cells, and your egg or sperm cells alike. It came with you.

An acquired change starts in a single cell partway through your life. DNA gets copied every time a cell divides, and copying makes mistakes. Carcinogens add more. Tobacco smoke, ultraviolet light from the sun, and human papillomavirus all damage DNA. When that cell divides, its daughters carry the change, so a tumor can be full of it. Your egg or sperm cells are not, so your children do not get it.

The National Cancer Institute is direct about this: cancer itself cannot be passed from parent to child, and genetic changes in tumor cells cannot be passed down either.

How much of cancer is each

Most of it is acquired. NCI says the vast majority of cancers happen by chance as damage piles up over years, and that up to 10% of all cancers may be caused by inherited genetic changes.

That 10% is not spread evenly. It concentrates in family cancer syndromes, which are rare disorders where relatives share a much higher than average risk. Familial adenomatous polyposis is one. It comes from inherited changes in the APC gene, and people who have it face a very high chance of colorectal cancer at an early age.

An inherited change is a head start toward cancer, not a verdict. Scientists think a healthy cell needs more than one DNA change to turn cancerous. Someone born with one of them needs fewer additional hits, which is part of why inherited cancers often appear younger. Many carriers never accumulate the rest and never get cancer.

Different tests, different samples

The two kinds of change are found by two different tests, and mixing them up causes real confusion.

Inherited changes are found by genetic testing on healthy cells. That usually means a blood draw, sometimes saliva, cheek cells, or skin. The result applies to your whole body and carries information for your blood relatives.

Acquired changes are found by biomarker testing, also called tumor testing or somatic testing, done on the cancer itself. That means tissue from surgery or a biopsy, or a blood-based liquid biopsy. Two liquid biopsy tests, Guardant360 CDx and FoundationOne Liquid CDx, have FDA approval. The result guides your treatment. It does not tell your sister anything.

The line does blur in one direction. A tumor test can turn up a change that looks germline. When that happens you need a separate confirmatory genetic test on healthy cells before anyone acts on it, and a genetic counselor should walk you through what it means.

Two federal laws limit what can be done with inherited results. The Genetic Information Nondiscrimination Act of 2008 bars discrimination in health insurance eligibility, health insurance rates, and employment, and the HIPAA Privacy Rule protects the records. GINA has real gaps. It does not cover members of the military, and it does not apply to life insurance, disability insurance, or long-term care insurance. Some states have passed their own laws to close part of that gap.

Sources

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

https://www.cancer.gov/about-cancer/treatment/types/biomarker-testing-cancer-treatment

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