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One MUTYH copy or two: carrier or MUTYH polyposis | CION Cancer Clinics
A MUTYH carrier has one faulty copy and a bowel cancer risk close to average. Someone with two faulty copies, one from each parent, has MUTYH-associated polyposis and needs regular colonoscopy for life. This page sets the two side by side, explains how doctors tell them apart, and shows what each result means for brothers, sisters, parents and children. At CION Cancer Clinics, our oncologists explain what a gene result means for you and your family, and plan the checks that follow.
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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 the difference between a MUTYH carrier and MUTYH polyposis?
- How do one faulty copy and two faulty copies compare?
- What does each result mean for the people around you?
- How do doctors tell which one you have?
- What do the words on a MUTYH report mean?
- Four things families tell us, and what is actually true
- What this page cannot tell you
- Common questions about MUTYH carriers and MUTYH polyposis
The short answer
What is the difference between a MUTYH carrier and MUTYH polyposis?
A MUTYH carrier has one faulty copy of the gene and a bowel cancer risk close to average. Someone with two faulty copies, one from each parent, has MUTYH-associated polyposis. That condition brings many bowel polyps and a very high bowel cancer risk unless regular colonoscopy removes them.
Same gene, very different meaning
Both results can appear on a report under the same gene name, and both may be called positive. That is where most of the confusion starts. The number of faulty copies is what decides your risk, your checks and what your relatives need. One copy usually changes little. Two copies change a great deal.
Why this is a recessive condition
MUTYH repairs a particular kind of everyday damage to DNA. One working copy is enough to keep that repair running. Only when both copies are faulty does the repair stop, and damage builds up in the lining of the bowel. Conditions that need two faulty copies are called recessive.
Before you read anything else about MUTYH, find out whether your report shows one variant or two.Side by side
How do one faulty copy and two faulty copies compare?
One faulty copy (carrier)
Two faulty copies (MUTYH polyposis)
Bowel cancer risk close to average, or slightly raised
Very high bowel cancer risk without regular checks
Polyps are no more common than usual
Often many polyps, usually from adult life
Screening set mainly by family history
Regular colonoscopy for life, plus a camera check of the duodenum
Children can be carriers, rarely more
Every child will be at least a carrier
Fairly common in many populations
Rare, and more likely when parents are related
Where you sit in the family
What does each result mean for the people around you?
In a recessive condition, the risk falls differently on brothers, sisters, parents and children. Here is how.
Brothers and sisters of someone with two copies
They are the relatives most at risk. Each brother or sister has a one in four chance of having two faulty copies too, even if they feel perfectly well. They should be offered testing first.
Each brother or sister may
- Have two faulty copies
- Be a carrier, like the parents
- Carry neither faulty copy
Parents of someone with two copies
In almost every case, each parent carries one faulty copy. They are usually carriers, not patients, which is why bowel cancer so often appears in brothers and sisters rather than in the generation above.
Children of someone with two copies
Every child inherits one faulty copy and so is at least a carrier. A child could have two only if the other parent is also a carrier, which is why testing the partner is often suggested.
Relatives of a carrier
Each child has a one in two chance of being a carrier. Carriers usually need no special checks, unless a close relative has had bowel cancer or there are two carriers in one marriage.
Not sure whether this applies to you?
Ask an oncologistReading the result
How do doctors tell which one you have?
-
Count the variants on the report
The report lists each MUTYH variant found and how it is classified. Only variants called pathogenic or likely pathogenic count. A variant of uncertain significance should not be counted as a second faulty copy.
-
The same variant twice
If the report says homozygous, you have the same variant on both copies. That means two faulty copies. It is more common when parents are related by blood.
-
Two different variants
Two different variants usually sit on different copies, one from each parent. Occasionally both sit on the same copy, which would make you a carrier. Testing a parent can settle this.
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A colonoscopy adds the picture
Many polyps at a younger age than usual fit two faulty copies. A normal bowel does not rule it out in a young adult, because polyps take time to appear.
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A counsellor puts it together
The counsellor combines the report, the parents' results and the family history, and tells you in plain words which group you are in.
On your report
What do the words on a MUTYH report mean?
- Monoallelic or heterozygous
- One faulty copy of the gene. You are a carrier, and the other copy keeps the repair system working.
- Biallelic
- Both copies faulty. This is the result linked to MUTYH polyposis.
- Homozygous
- The same variant on both copies of the gene, one from each parent.
- Compound heterozygous
- Two different variants, one on each copy. It counts as two faulty copies, just like homozygous.
- Recessive
- A condition that appears only when both copies of a gene are faulty. Carriers of one copy are usually well.
- MAP
- Short for MUTYH-associated polyposis, the condition caused by two faulty copies. Some reports simply say MUTYH polyposis.
Commonly believed
Four things families tell us, and what is actually true
"The report says MUTYH positive, so I have polyposis."
Positive can mean one faulty copy or two. Most people told they are MUTYH positive have one copy, and they are carriers with a risk close to average.
"My parents are healthy, so it cannot be inherited."
In a recessive condition, healthy parents are the usual picture. Each one carries a single faulty copy without any effect, and the problem appears only in a child who inherits both.
"As a carrier, I need a colonoscopy every year."
Most guidelines do not ask this of carriers. Screening is usually based on your family history. If a close relative had bowel cancer, checks may start earlier.
"Marrying within the family makes no difference here."
It can. Relatives are more likely to carry the same variant, so a child is more likely to inherit two copies. If your families are related, mention it to the counsellor.
Being straight with you
What this page cannot tell you
It cannot tell you which group you are in. That depends on the exact variants on your report, how each is classified and sometimes on a parent's test. What your specific variant means is a question for the counsellor who ordered the test.
Where the evidence is still thin
The risk for people with two faulty copies is well described. The risk for carriers is less certain. Some studies find a small rise in bowel cancer risk and others find none, and guidelines differ slightly as a result. Very little of this research comes from Indian families, and how common MUTYH carriers are in India is not well known.
Who this does not apply to
If your MUTYH result came from a test on tumour tissue alone, it may be a change inside the cancer rather than an inherited one. That is covered on our targeted therapy pages. Most people with a single ordinary polyp do not need MUTYH testing at all.
Bring the full report, not a photo of one page. The second variant is sometimes listed further down.Questions we are asked
Common questions about MUTYH carriers and MUTYH polyposis
How do I know if I have one faulty copy or two?
Look for the number of pathogenic or likely pathogenic MUTYH variants on your report, and for words such as heterozygous, homozygous or biallelic. If you are unsure, ask the person who ordered the test. Sometimes a parent's test is needed to be certain.
Is a MUTYH carrier at risk of bowel cancer?
At most, only slightly more than average, and some studies find no rise at all. Most carriers follow routine bowel screening, with earlier checks if a close relative had bowel cancer. Your gastroenterologist will set the plan.
What checks does MUTYH polyposis need?
Regular colonoscopy from early adult life, with polyps removed at each test. An upper endoscopy looks at the duodenum, the first part of the small bowel. If polyps become too many to clear, bowel surgery is discussed as one option among several.
Should my brothers and sisters be tested?
If you have two faulty copies, yes, and soon. Each brother or sister has a one in four chance of the same result. If you are a carrier, testing them matters less, unless there is bowel cancer or many polyps in the family.
Will my children get MUTYH polyposis?
Only if they inherit a faulty copy from both parents. That can happen only when both parents carry one. Testing your partner answers the question for your children, and it matters more if your families are related.
Can a carrier become biallelic later in life?
No. The copies you inherited do not change over your life. A result can be updated only if a variant is reclassified, or if a second variant was missed and is found on a fuller test.
Does MUTYH raise breast cancer risk?
The evidence that one faulty copy raises breast cancer risk is weak and disputed. A carrier result found on a breast cancer panel should not change breast screening on its own. Your screening is set by your wider family history.
Does marriage within the family matter?
It can. Cousins or an uncle and niece are more likely to carry the same variant, which makes two faulty copies in a child more likely. Tell the counsellor if your families are related. It is asked without judgement and changes the advice.
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
- GeneReviews (NCBI Bookshelf) — MUTYH Polyposis
- MedlinePlus Genetics — MUTYH gene
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ®)–Health Professional Version
- MedlinePlus Genetics — What are the different ways a genetic condition can be inherited?
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 one MUTYH variant usually changes very littleIf your report shows a single variant, start hereSurveillance for MUTYH carriersThe checks for one copy and for two, set out plainlyWhy both parents must be carriersHow a recessive condition passes through a familyTesting siblings when MUTYH is recessiveWhy brothers and sisters are tested first
Talk to us
Not sure whether your report shows one copy or two?
Bring your MUTYH report and we will arrange a counsellor to go through it with you, in Telugu if you prefer. If a colonoscopy or a parent's test is needed, we can help arrange it. One helpline serves every CION centre.