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DNA repair genes, and why they matter most | CION Cancer Clinics
DNA repair genes find and fix the small copying errors every cell makes when it divides. When a repair gene itself is faulty, errors elsewhere build up far faster than normal, which is why several of the best-known inherited cancer genes, including BRCA1, BRCA2 and the Lynch syndrome genes, are repair genes at heart. This page explains what they do and why losing them matters so much. At CION Cancer Clinics in Hyderabad, our oncologists review your family history with you and guide you to the right genetic counselling and testing.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- What do DNA repair genes actually do?
- The main repair systems behind inherited cancer genes
- Why a lost repair gene speeds everything else up
- The words you will meet, in plain language
- A working repair gene compared with a faulty one
- Why repair status can change what treatment is offered
- Two things worth clearing up
- Common questions about DNA repair genes
The short answer
What do DNA repair genes actually do?
DNA repair genes check the body's instructions for copying errors and fix them before they can cause harm. Every cell makes small mistakes every time it divides. Repair genes are the reason most of those mistakes never become permanent. When a repair gene itself is faulty, every other kind of error builds up far faster than normal.
They matter more than almost any other group
A fault in a growth gene or a brake gene affects one instruction. A fault in a repair gene affects the system that catches mistakes across the whole of the DNA, which is why losing repair function tends to have such wide-reaching effects.
Several inherited cancer syndromes trace back to this one group
BRCA1, BRCA2, the Lynch syndrome genes, and several others named on genetic reports are all, at heart, repair genes. Their inherited faults matter because losing repair lets further faults accumulate quickly once the second copy is also lost in a cell.
Not one system, several
The main repair systems behind inherited cancer genes
Different repair genes fix different kinds of damage, which is why they show up in different cancer syndromes.
Homologous recombination repair
Fixes a serious kind of break where both strands of the DNA ladder are cut. BRCA1 and BRCA2 belong to this system, most linked to breast, ovarian, prostate and pancreatic cancer risk.
Mismatch repair
Corrects small spelling errors made when DNA is copied. The genes behind Lynch syndrome, including MLH1 and MSH2, belong to this system.
Base excision repair
Removes and replaces single damaged letters. MUTYH, linked to a polyposis and bowel cancer syndrome, belongs here.
Specialised repair systems
A small number of rare inherited conditions come from faults across a whole group of genes that work together to repair particularly difficult, tangled kinds of DNA damage. These are covered on their own pages, since each has its own pattern of risk.
Not sure whether this applies to you?
Ask an oncologistWhat goes wrong without it
Why a lost repair gene speeds everything else up
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DNA is copied constantly
Every time a cell divides it copies its full set of instructions, and small errors happen even in perfectly healthy people.
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Repair genes normally catch these errors
A working repair system finds most mistakes quickly and corrects them before the cell divides again.
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A fault removes that check
Once both copies of a repair gene fail in one cell, new errors are no longer being caught and corrected there.
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Errors build up far faster in that cell line
Without repair, mistakes accumulate with every division rather than being cleared, including in other genes that control growth.
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The odds of a cancer-causing combination rise
More uncorrected errors mean a much higher chance that, sooner or later, the right combination lands in the same cell.
On your report
The words you will meet, in plain language
- DNA repair gene
- A gene whose job is finding and fixing copying errors in DNA before they become permanent.
- Mismatch repair
- One repair system, correcting small spelling errors made when DNA is copied. Behind Lynch syndrome when faulty.
- Homologous recombination
- A repair system for serious double-strand breaks in DNA. Behind BRCA1 and BRCA2 related risk when faulty.
- Microsatellite instability
- A laboratory sign, found in a tumour sample, that mismatch repair has stopped working properly.
- HRD (homologous recombination deficiency)
- A laboratory finding showing that a tumour's double-strand break repair is not working, which can guide treatment choice.
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Side by side
A working repair gene compared with a faulty one
Working repair gene
Faulty repair gene, both copies lost
Copying errors are found and corrected
routinely
Copying errors are left uncorrected and
accumulate
Other genes stay stable over many
divisions
Faults in other genes appear far more often
No particular pattern on a tumour test
Can show a specific laboratory signature, such
as microsatellite instability or HRD
Why this affects treatment too
Why repair status can change what treatment is offered
A cell that has already lost its repair system is more vulnerable to certain treatments than a normal cell, because it has one less way to cope with further damage. This is part of why some tumours with a confirmed repair fault respond particularly well to specific drug classes, an approach directly built on this biology.
It is also why tumour testing and inherited testing overlap here
Finding a repair-related signature in a tumour, such as microsatellite instability, is one of the more common routes that leads a specialist to recommend inherited testing for the whole family, even when nobody suspected an inherited pattern beforehand.
Not every repair fault is inherited
A tumour can lose its repair function through faults that arose only in that tumour, with nothing inherited at all. Distinguishing the two is exactly why inherited testing is done on a blood sample separately from testing the tumour tissue itself.
Commonly believed
Two things worth clearing up
"A repair gene fault means my DNA is generally
weaker."
A repair gene fault affects that specific repair system, not the strength of DNA in general. The rest of your genes are the same as anyone else's; what has changed is how well one particular kind of error gets caught.
"If my tumour shows a repair problem, my children
automatically carry it too."
A repair fault found only in the tumour, not in a blood sample, is not necessarily inherited. Whether it can be passed on depends on whether the fault is also present in every normal cell, which is exactly what inherited testing checks separately.
"Repair genes only matter for the cancers already
named on this page."
The genes named here are simply the best studied examples. Researchers are still identifying further repair genes and working out which cancers each one is linked to, so this list is not the end of the story, and a counsellor keeps up with additions that a general search will not show you.
Questions we are asked
Common questions about DNA repair genes
Is BRCA a DNA repair gene?
Yes. BRCA1 and BRCA2 both belong to the homologous recombination repair system, which fixes a serious kind of DNA break. Their inherited faults raise cancer risk largely because this repair function is lost.
What is microsatellite instability?
It is a laboratory finding in a tumour sample showing that mismatch repair, the system correcting small copying errors, is not working properly there. It is often the first clue that leads to a Lynch syndrome diagnosis.
Can a repair gene fault be fixed with
medicine?
Not in the sense of restoring the gene itself. Some treatments instead exploit the vulnerability a lost repair system creates in the tumour, which can make certain drug classes more effective specifically because the repair fault is present.
Does losing one repair gene affect all the others
too?
Not directly. Different repair systems work largely independently, so losing one, such as mismatch repair, does not automatically disable another, such as homologous recombination. Testing looks at each system separately.
Why do inherited repair gene faults often affect
several different organs?
A repair gene works the same way in every cell of the body, so an inherited fault raises risk wherever that repair system matters most, which is often more than one organ. This is why several cancer types can appear in the same family history.
Is a repair problem found in my tumour the same as an
inherited fault?
Not necessarily. A tumour can lose repair function through changes that occurred only in that tumour. A separate blood test is needed to find out whether the same fault is present in every cell and could be inherited.
Are repair gene faults more common in certain
families?
Some specific repair gene faults are more common within particular communities, due to a shared ancestor generations back. Your counsellor can tell you whether that applies to your background.
Where can I find out if my cancer is linked to a repair
gene?
This page explains the general biology only. Whether your specific case involves a repair gene, and what that means, is a question for your oncologist or a genetic counsellor. Call the CION helpline if you are unsure who to ask.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- National Cancer Institute — DNA Repair Gene
- Cancer Research UK — Genes and cancer
- GeneReviews (NCBI) — BRCA1/2 Hereditary Breast and Ovarian Cancer
- GeneReviews (NCBI) — Lynch Syndrome
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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