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MUTYH-associated polyposis: what it is and how it is inherited | CION Cancer Clinics
MUTYH-associated polyposis, often shortened to MAP, is an inherited condition that causes many polyps in the bowel and a high risk of bowel cancer if they are not removed. Unlike most inherited cancer conditions, a person needs two faulty copies of the gene, one from each parent. This page explains how MAP works, how it differs from other polyp conditions, and what it means for the family. At CION Cancer Clinics, our oncologists plan screening and care for families with an inherited cancer syndrome, explained in plain words.
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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 is MUTYH-associated polyposis?
- How is MAP different from other inherited bowel conditions?
- How do two faulty copies lead to bowel polyps?
- The words you will meet, in plain language
- Two faulty copies or one: what is the difference?
- What this page cannot tell you
- Four things families tell us about MAP, and what is true
- Common questions about MUTYH-associated polyposis
The short answer
What is MUTYH-associated polyposis?
MUTYH-associated polyposis, or MAP, is an inherited condition that causes many polyps to grow in the large bowel. Left alone, some of those polyps can turn into bowel cancer, often earlier in life than usual. With regular colonoscopy and polyp removal, that risk can be brought down a long way.
Why it is called recessive
Most inherited cancer conditions need only one faulty copy of a gene. MAP needs two, one from each parent. The parents usually carry a single faulty copy each and are healthy. This is why MAP often appears in one generation of brothers and sisters, with no bowel polyps in the parents or the grandparents.
How it is usually found
Most people are found to have MAP after a colonoscopy shows more polyps than expected. Tens of polyps is a typical picture, sometimes more. The doctor then arranges a genetic test, because the polyp count alone cannot tell MAP apart from other polyp conditions.
MAP is a statement about risk. It is not a diagnosis of cancer.Telling them apart
How is MAP different from other inherited bowel conditions?
Several conditions cause polyps or early bowel cancer. The difference matters, because it changes who else in the family is at risk.
MAP
Two faulty MUTYH copies, one from each parent. Usually tens to hundreds of polyps, often found in middle age. Brothers and sisters share the risk far more than parents or children do.
Familial adenomatous polyposis
One faulty APC copy is enough. Polyps usually number in the hundreds or thousands and start in the teens. It passes directly from parent to child, so it shows in every generation.
Lynch syndrome
One faulty copy of a repair gene raises the risk of bowel, womb and other cancers. It does not cause large numbers of polyps. A few polyps grow quickly instead.
One MUTYH copy
A single faulty copy makes you a carrier. Carriers do not have MAP. Their own bowel risk is close to average.
What it does mean
- Each child has a one in two chance of being a carrier too
- A partner's test matters when planning children
Not sure whether this applies to you?
Ask an oncologistHow it works
How do two faulty copies lead to bowel polyps?
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MUTYH is a repair gene
Its job is to fix one particular kind of everyday damage to DNA. That damage happens constantly in the lining of the bowel.
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One working copy is enough
A carrier has one faulty copy and one working copy. The working copy does the repair job well, which is why carriers stay healthy.
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Two faulty copies leave no repair
A child who inherits a faulty copy from each parent has no working MUTYH at all. The damage goes unrepaired in every cell of the bowel lining.
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Errors build up and polyps form
Over the years, unrepaired errors pile up in other genes that control growth. Many small polyps form, and each one has some chance of turning into a cancer.
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Which is why removal works
Polyps take time to become cancer. Finding and removing them at regular colonoscopy interrupts that process before it finishes.
On your report
The words you will meet, in plain language
- Biallelic
- Both copies of the gene are faulty. This is what a MAP diagnosis means.
- Monoallelic or heterozygous
- Only one copy is faulty. This means you are a carrier, not that you have MAP.
- Autosomal recessive
- A pattern where the condition appears only when both copies are faulty. Carriers of one copy are usually well.
- Adenoma
- The kind of bowel polyp that can, over time, turn into cancer. MAP polyps are mostly adenomas.
- Polyposis
- Having many polyps, far more than an ordinary colonoscopy would find.
- Duodenum
- The first part of the small bowel, just after the stomach. It is also checked in MAP, because polyps can form there too.
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Side by side
Two faulty copies or one: what is the difference?
Two faulty copies (MAP)
One faulty copy (carrier)
Many bowel polyps and a high bowel cancer risk
Usually no extra polyps, and risk close to average
Regular colonoscopy from early adult life
Screening based on the wider family history
Checks of the stomach and duodenum as well
No extra upper bowel checks as a rule
Every child inherits at least one faulty copy
Each child has a one in two chance of being a carrier
Being straight with you
What this page cannot tell you
It cannot tell you whether you have MAP. That needs a genetic test, and the result has to be read alongside your colonoscopy findings and family history. A polyp count on its own does not settle it.
It cannot interpret a report you are holding
A MUTYH report may list one variant or two, and the difference is everything. Two variants also need to be on opposite copies to count as MAP. What your specific variant means is a question for the counsellor who ordered the test. Most of the larger studies of MAP come from outside India, so Indian data are still limited.
Who this does not apply to
Most people with a few bowel polyps do not have MAP, and do not need a genetic test. Polyps become common with age. Testing is considered when the number is unusually high for your age, or when the family pattern points to an inherited cause.
If you have been told you have many polyps, ask your gastroenterologist whether a genetic referral is worthwhile.Commonly believed
Four things families tell us about MAP, and what is true
"My parents never had polyps, so it cannot be inherited."
In MAP the parents are usually healthy carriers. It often appears only in one set of brothers and sisters. A clear parental history is exactly what a recessive condition looks like.
"I carry one MUTYH variant, so I have the syndrome."
One faulty copy makes you a carrier. MAP needs two. Carriers usually follow screening advice based on their family history, not a MAP schedule.
"My children will definitely have MAP."
Your children each inherit one faulty copy from you, so they will be carriers. They will have MAP only if they also inherit a faulty copy from their other parent. Testing your partner answers this.
"With this many polyps, surgery is the only option."
Many people with MAP are managed with regular colonoscopy and polyp removal. Surgery is considered when polyps are too many to clear safely. It is one option among several.
Questions we are asked
Common questions about MUTYH-associated polyposis
How common is MAP?
It is rare. Being a carrier of one faulty copy is far more common than having MAP. Most studies come from European populations, and good figures for India are not yet available. In families where parents are related by blood, MAP may be more likely.
Should my brothers and sisters be tested?
Yes. Each full brother or sister has a one in four chance of also having MAP, and a one in two chance of being a carrier. A test for the family's two variants gives a clear answer. Those who have MAP need the same colonoscopy schedule.
How often will I need a colonoscopy?
More often than the general population, and for life. The exact interval depends on how many polyps are found each time and how easily they are removed. Your gastroenterologist sets it. Checks of the stomach and duodenum are added too.
Does MAP raise the risk of other cancers?
The bowel risk is the main one. There is a smaller raised risk in the duodenum, which is why it is checked. Some studies suggest other cancers may be slightly more common, but the evidence is less certain. Your team will explain what is watched and why.
Is MAP the same as FAP?
No. Both cause many polyps, but FAP is caused by the APC gene and passes directly from parent to child. MAP is caused by two faulty MUTYH copies. The polyp count, the age polyps appear and the family pattern usually differ.
Is this the same as tumour gene testing?
No. MAP testing looks at the genes you were born with, using a blood sample. Testing a bowel tumour for treatment decisions is a different test and is covered under targeted therapy. Your oncologist may order either, or both.
Does my partner need testing?
If you are planning children, it is worth considering. If your partner does not carry a MUTYH variant, your children will be carriers but will not have MAP. A counsellor can explain how the partner test works.
Where do I start in Hyderabad?
Bring your colonoscopy and polyp reports, and a list of relatives with bowel polyps or cancer. A genetic counsellor can arrange testing and explain the result. Call the CION helpline if you are not sure who to see first.
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
- MedlinePlus Genetics — MUTYH-associated polyposis
- GeneReviews (NCBI) — MUTYH Polyposis
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ) - Health Professional Version
- MedlinePlus Genetics — MUTYH gene
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.
Keep reading
Related pages
Why both parents must be carriersThe recessive pattern, explained step by stepSurveillance in MUTYH-associated polyposisWhat the colonoscopy and upper checks involveTesting siblings when MUTYH is recessiveWhy brothers and sisters come firstFamilial adenomatous polyposis explainedThe other main polyp condition, compared
Talk to us
Told you have more bowel polyps than expected?
Share your colonoscopy reports and a rough family history with us. We will tell you honestly whether a genetic referral makes sense, and arrange it if it does. One helpline serves every CION centre.