Medical Oncologist
CION Cancer Clinics
Testing the family after a rarer polyposis gene result | CION Cancer Clinics
Once a fault in NTHL1, MSH3, AXIN2, GREM1 or RNF43 is confirmed, relatives can be tested for that exact change. Who comes first depends on the gene: brothers and sisters for NTHL1 and MSH3, and parents, siblings and grown children for the other three. This page explains the order, how testing happens, and what each result means for a relative. 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
- Who in the family should be tested after this result?
- Which relatives should be offered a test, and why?
- How does testing the family usually happen?
- What do the family testing terms mean, in plain language?
- What does each result mean for a relative?
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about testing relatives
The short answer
Who in the family should be tested after this result?
It depends on whether the gene needs one faulty copy or two. For NTHL1 and MSH3, brothers and sisters come first, because they are the ones who may also carry two faults. For AXIN2, RNF43 and GREM1, parents, brothers, sisters and grown children each have a one-in-two chance of carrying the same fault.
Testing a relative is simpler than the first test
The first person tested usually has a wide panel of many genes. Once the family's exact fault is known, relatives are tested only for that one change. The test is quicker, cheaper and easier to read, and it can be done on a blood sample taken close to home.
A negative result in a relative actually means something
Because the laboratory knows exactly what it is looking for, a relative who does not carry the family's fault gets a clear answer. That is very different from a first test that finds nothing. It is also why relatives should not be tested before the family's fault is known.
Family testing starts only after a fault is confirmed as harmful. A result of uncertain meaning is not tested in relatives.Who is offered a test
Which relatives should be offered a test, and why?
The order depends on the gene. Your counsellor will draw the family tree and set it out with you.
Brothers and sisters
For NTHL1 and MSH3 they are the priority. Each has a one-in-four chance of carrying two faults, like you. For the other three genes, each has a one-in-two chance of carrying one.
Parents
For AXIN2, RNF43 and GREM1, testing parents shows which side of the family the fault came from. That tells you which aunts, uncles and cousins also need to hear about it. For NTHL1 and MSH3, parents are usually silent carriers and rarely need their own checks.
Grown children
For the one-copy genes, each child has a one-in-two chance of inheriting the fault. For NTHL1 and MSH3, your children receive one faulty copy from you and are usually carriers only.
Usually waits until
- The child is an adult and can decide
- Checks would actually begin soon
A husband or wife
This matters only for NTHL1 and MSH3. If your partner carries a fault in the same gene, a child could inherit two. It is more likely when partners are related by blood.
Not sure whether this applies to you?
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How does testing the family usually happen?
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The first result is confirmed
The counsellor checks that the fault is classified as harmful and gives you a copy of the report. You will also usually get a short letter written for relatives.
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The family tree decides the order
Together you mark who is at risk on each side. Relatives who are older, or who already have symptoms, are often approached first.
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Each relative has their own conversation
Before any sample, each relative is counselled on what a positive or negative result would mean for them. Counselling in Telugu can be arranged.
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A sample is taken, often near home
Usually a small blood sample. Relatives in a district or another state can often give it locally and send it to the same laboratory.
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The result comes with a plan
A relative who carries the fault gets a written colonoscopy schedule. One who does not is told what screening, if any, still applies.
Words you will hear
What do the family testing terms mean, in plain language?
- First person tested
- The relative, usually the one with polyps or cancer, whose test found the family's fault. Reports sometimes call this person the proband.
- Cascade testing
- Offering a test to relatives one step at a time, spreading outward as each new carrier is found.
- Known-variant test
- A test that looks only for the single fault already found in the family. It is simpler than a full panel.
- Carrier
- Someone with one faulty copy of a gene. For NTHL1 and MSH3, a carrier is usually well and needs no extra checks.
- Obligate carrier
- A relative who must carry the fault because of where they sit in the family tree, even without a test.
- True negative
- A clear result in a relative tested for a fault already known in the family. It is much more reassuring than a first test that finds nothing.
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Side by side
What does each result mean for a relative?
The relative's result
What usually follows
Carries the family's fault in a one-copy gene
Regular colonoscopy on a schedule the specialist sets
Carries two faults in NTHL1 or MSH3
The same regular colonoscopy as the first person tested
Carries one fault in NTHL1 or MSH3
Usually no extra checks, though a partner test may matter
Does not carry the family's fault
Usually routine screening, unless the family history says otherwise
Chooses not to be tested
Can still be offered colonoscopy as if they might carry it
Being straight with you
What this page cannot tell you
It cannot tell you which of your relatives carries the fault. Only a test can do that. It also cannot tell you what your family's particular variant means. That is a question for the counsellor who ordered the test, who knows the exact change and how firmly it is linked to polyps.
It cannot decide for a relative
Every adult relative has the right to be tested or to decline. You can pass on the information, and the counsellor can help with how to say it. What each person does next is their choice. Some relatives need time, and some come back to it years later.
Who this does not apply to
If the first test in your family found nothing, or found only a variant of uncertain meaning, there is nothing specific for relatives to be tested for. Those families are guided by the history and the polyp count instead. Most people with a relative who had bowel cancer are in this group.
Commonly believed
Four things families tell us, and what is actually true
"My sister tested negative, so I must be negative too."
Each child inherits their genes separately. One sibling's result says nothing about another's. Every brother and sister needs their own test.
"I feel perfectly well, so I do not need testing."
Polyps rarely cause symptoms until they are large or have turned into cancer. Feeling well is exactly when finding them is most useful.
"I carry one NTHL1 fault, so my children will get polyps."
With NTHL1 and MSH3, a child needs a faulty copy from both parents. If your partner does not carry a fault in the same gene, your children can be carriers at most. A partner test answers this.
"If we test, word will spread and marriages will suffer."
Results are confidential, and you decide who is told and when. Many families find a known result easier to discuss than an unexplained worry. A counsellor can help you plan those conversations.
Questions we are asked
Common questions about testing relatives
Should my young children be tested now?
Usually not yet. Polyps from these genes tend to appear in adult life, so testing normally waits until checks would actually start and the young person can decide. Your counsellor will tell you if your family's gene needs a different plan.
Can relatives in a district or another state be tested?
Yes. A blood sample can often be taken locally and sent to the laboratory that found the family's fault. Counselling can be done by video. Give relatives a copy of the original report so the lab knows exactly what to look for.
Does my husband or wife need a test?
Only for NTHL1 and MSH3, and only if you are thinking about children or have them. If your partner carries a fault in the same gene, a child could inherit two. The chance is higher when partners are related by blood.
What if a relative does not want to know?
That is their right. You can share the family letter and leave the door open. If they are not tested but may be at risk, they can still be offered colonoscopy as though they might carry the fault.
Is testing a relative as expensive as the first test?
No. A test for one known fault is usually far cheaper than the first panel, because the lab looks at one change instead of many genes. Ask for a written estimate, including counselling, before the sample is taken.
Can a relative who has died still be tested?
Sometimes. If they had surgery or a biopsy, a stored tissue block may still be held by the hospital. It can sometimes be tested for the family's fault. Ask early, because blocks are not kept forever.
My brother tested negative. Can he skip colonoscopy?
Often he can return to routine screening for his age. If the family has other bowel cancers the fault does not explain, his doctor may still suggest earlier checks. That decision belongs with his counsellor, based on the whole family tree.
Does the relative need the same laboratory?
It helps. For GREM1 especially, the test must be able to find an extra stretch of DNA, not only spelling mistakes. Using the same lab, or sending the original report to a new one, avoids a false all-clear.
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)
Medical Oncologist
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Sources
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ®)–Health Professional Version
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- NCCN — Genetic/Familial High-Risk Assessment: Colorectal, Endometrial, and Gastric
- 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
What the rarer polyposis genes doWhy some need one faulty copy and others twoRarer polyposis genes: which cancers and what riskWhat a relative who carries the fault is facingHow cascade testing worksThe general method, step by stepGenetic testing in consanguineous familiesWhy marriage within the family matters for NTHL1 and MSH3
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Not sure which relative to approach first?
Bring the original report and a rough family tree, and we will help you plan who to test and in what order. One helpline serves every CION centre.