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Why MUTYH polyposis needs a faulty copy from both parents | CION Cancer Clinics
MUTYH-associated polyposis appears only when a child inherits a faulty MUTYH copy from each parent. The parents are almost always well, because one working copy is enough. That is why the condition so often surprises a family with no history of it. This page explains how recessive inheritance works, what the one in four chance means, and what it changes for relatives and future children. 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
- Why does MUTYH polyposis need a fault from both parents?
- What can each child inherit from two carrier parents?
- How can a fault stay hidden for generations?
- What do the inheritance words on a report mean?
- How is this different from FAP or Lynch syndrome?
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about how MUTYH polyposis is inherited
The short answer
Why does MUTYH polyposis need a fault from both parents?
Because one working copy of the MUTYH gene is enough to do its job. MUTYH polyposis only appears when a child inherits a faulty copy from the mother and another faulty copy from the father, leaving no working copy at all. That is why two healthy parents can have a child with the condition.
What the MUTYH gene actually does
Every day, ordinary chemical wear damages the DNA inside your cells. MUTYH makes a repair tool that spots one particular kind of damage and fixes it before the cell copies itself. With one working copy, the cell still makes enough of that tool. With none, small errors pile up in the cells lining the bowel, and many of them grow into polyps.
Why the parents are usually well
Each parent has one faulty copy and one working copy. Their repair system still works, so they do not develop polyposis. Most carriers never know they carry anything. The first sign in the family is often a son or daughter with many polyps, and the parents are understandably shocked.
A carrier parent did nothing wrong. Nobody chooses which copy they pass on.When both parents carry it
What can each child inherit from two carrier parents?
Each parent passes on one of their two copies, at random. That gives four equally likely combinations for every pregnancy.
Two faulty copies
About one in four children. This child has MUTYH polyposis and needs regular bowel checks from early adult life.
What it means
- No working MUTYH copy in any cell
- Polyps form more readily in the bowel
- Surveillance for life
One faulty copy
About one in two children. This child is a carrier, just like each parent. They stay well themselves, and can pass the faulty copy on in turn.
No faulty copy
About one in four children. This child inherited both working copies, does not have the condition and cannot pass it on.
Every pregnancy starts fresh
These chances apply to each child separately. Having one affected child does not use up the family's one in four. A couple can have several affected children, or none, purely by chance.
Not sure whether this applies to you?
Ask an oncologistHow it travels
How can a fault stay hidden for generations?
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A carrier passes one copy down
A grandparent carries one faulty copy and stays well. Half of their children, on average, inherit it and are carriers too. Nobody in the family has any reason to suspect anything.
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Carriers marry non-carriers
For many generations a carrier usually marries someone who does not carry a MUTYH fault. Their children can be carriers, but none can have two faulty copies. The fault moves quietly through the family.
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Two carriers have children together
When a carrier happens to marry another carrier, each child now has a one in four chance of inheriting both faults. This is more likely when the two partners are related, because they may share the same fault.
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The condition finally shows
A child with two faulty copies develops polyps in adult life. The family history often looks clear, because every relative before them was a healthy carrier.
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The fault moves on again
That person's own children will almost always inherit one faulty copy from them. Unless their other parent is also a carrier, those children are healthy carriers, and the pattern goes quiet once more.
On your report
What do the inheritance words on a report mean?
- Recessive
- A condition that needs both copies of a gene to be faulty before it appears. MUTYH polyposis works this way.
- Dominant
- A condition where one faulty copy is enough. Most other inherited bowel cancer syndromes work this way.
- Carrier
- Someone with one faulty copy and one working copy. A carrier is well, and is not a patient.
- Biallelic
- Both copies of the gene carry a fault, one from each parent. This is the result that confirms MUTYH polyposis.
- Homozygous
- The two faulty copies are exactly the same fault. This is more common when parents are related to each other.
- Compound heterozygous
- The two faulty copies are different faults in the same gene. The effect is the same as two identical faults.
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Side by side
How is this different from FAP or Lynch syndrome?
MUTYH polyposis (recessive)
FAP or Lynch syndrome (dominant)
Needs a faulty copy from both parents
One faulty copy from one parent is enough
Parents are usually healthy carriers
One parent is usually affected or at risk
Often seen in brothers and sisters only
Usually seen in every generation
A patient's children are usually carriers only
Each of a patient's children has a one in two chance
Related parents raise the chance noticeably
Related parents make little difference
Being straight with you
What this page cannot tell you
It cannot tell you whether you or your partner is a carrier. Carrying one faulty MUTYH copy is not rare in the populations that have been studied, and Indian data is still limited. Only a blood test answers the question for a particular person.
It cannot read your genetic report
What your specific variant means is a question for the counsellor who ordered the test. Some MUTYH faults are well described. Others are rare, and the laboratory may call them a variant of uncertain significance, which means their effect is not yet known.
Who this does not apply to
Most people reading this do not need a MUTYH test. If nobody in your family has many bowel polyps or bowel cancer at a young age, testing is unlikely to change anything for you. Marriage between relatives is common in many Telangana families, and on its own it is not a reason to test. It becomes one when a recessive condition has already appeared in the family.
A counsellor can tell you whether your family pattern looks recessive, dominant or neither.Commonly believed
Four things families tell us, and what is actually true
"Nobody in our family had it, so it cannot be genetic."
In a recessive condition, an empty family history is the usual picture. Every relative before you may have been a healthy carrier. A clear family tree does not rule MUTYH polyposis out.
"It came from my mother's side, because her father had bowel cancer."
A child with MUTYH polyposis inherited a faulty copy from both parents. Blaming one side is not only unkind, it is also genetically wrong. Both families carry the fault equally.
"We already have one affected child, so the next will be fine."
Each pregnancy has the same one in four chance, whatever happened before. Chance does not balance itself out within one family.
"Being a carrier means I will get polyps later."
A carrier keeps one working copy, which is enough to do the repair job. Some studies suggest a small rise in bowel cancer risk for carriers, but the evidence is mixed and far from the risk in MUTYH polyposis.
Questions we are asked
Common questions about how MUTYH polyposis is inherited
If I have MUTYH polyposis, will my children have it?
Usually not. Each child will inherit one faulty copy from you, but they also need one from their other parent. Unless your partner is a carrier, your children will be healthy carriers. A simple test of your partner answers the question.
Should my husband or wife be tested?
It is often worth considering, especially if you are planning children or your partner is a relative. If your partner is not a carrier, your children cannot have MUTYH polyposis. If they are, each child has a one in two chance.
Are my parents carriers for certain?
Almost always. Very rarely a fault appears new in a child rather than being inherited. Testing parents can confirm that your two faults sit on different copies, which helps the laboratory confirm your diagnosis. Their own health risk is usually small.
Does marrying a relative cause MUTYH polyposis?
No. It does not create a fault. It raises the chance that both partners inherited the same fault from a shared ancestor. Many related couples have no recessive condition in their children at all.
Can a carrier test tell us before we marry?
Yes, if one family already knows its MUTYH fault, the other partner can be tested for carrier status. It is a private choice. A counsellor can explain what each result would mean before you decide whether to test.
Why do my brother and I both have it but my sister does not?
Each child is a separate draw from the same two parents. Your sister happened to receive at least one working copy. She may be a carrier or may carry neither fault, and a test can tell her which.
Is MUTYH testing part of a pregnancy scan?
No. Routine pregnancy tests and scans do not look for MUTYH. Testing in pregnancy is possible when a family fault is known, but for a condition that shows in adult life it is a personal decision best discussed with a counsellor first.
Who can explain this to my whole family?
A genetic counsellor can draw your family tree, explain the pattern in Telugu, and write a letter for relatives. If you are unsure where to begin, call the CION helpline and someone will arrange a counselling appointment.
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
- MedlinePlus Genetics — What are the different ways a genetic condition can be inherited?
- GeneReviews (NCBI Bookshelf) — MUTYH Polyposis
- 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
Testing siblings when MUTYH is recessiveBrothers and sisters are the relatives most at riskConsanguinity and recessive cancer syndromesWhat marriage between relatives does and does not changeMUTYH-associated polyposis explainedThe condition itself, in plain wordsSurveillance in MUTYH-associated polyposisThe checks an affected person needs
Talk to us
Want the inheritance explained for your own family?
A genetic counsellor can draw your family tree and explain who may be a carrier, in Telugu if you prefer. One helpline serves every CION centre.