Medical Oncologist
CION Cancer Clinics
Testing your family after an NBN result | CION Cancer Clinics
Once an NBN fault is found in you, your parents, brothers, sisters and adult children can be tested for that exact fault. Each has a one in two chance of carrying it. If you are planning a family, testing your partner is often the most useful step. This page explains who to test, in what order, how it works, and when children should wait until they are adults. 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 for NBN?
- What does testing mean for each person in the family?
- How does testing a relative actually work?
- What do the family-testing words mean?
- What does a relative's result change?
- What can this page not tell you?
- What do families get wrong about testing relatives?
- Common questions about testing the family for NBN
The short answer
Who in the family should be tested for NBN?
Your closest relatives come first: parents, brothers, sisters and adult children. Each has a one in two chance of carrying the same NBN fault as you. If you are planning a family, your partner may also be offered a test, which is the most useful step for many couples.
Why testing relatives is simpler than your test was
Your own test searched the whole gene, often along with many others. Relatives do not need that. The laboratory looks only for the exact fault already found in you. This is quicker, usually cheaper, and gives a clearer yes or no answer.
Why the stakes are lower than with some genes
For most NBN faults, carrying one faulty copy raises cancer risk only modestly, if at all. So a relative who tests positive will not usually face big decisions. The main reasons to test are to guide screening where the family history is strong, and to protect future children from inheriting two faults.
Bring a copy of your own report. The laboratory needs the exact fault to test your relatives.Relative by relative
What does testing mean for each person in the family?
The reason to test is different for each relative. So is the right time.
Parents
Testing a parent can show which side of the family the fault came from. That tells you which aunts, uncles and cousins might also want to know.
Brothers and sisters
Each has a one in two chance of carrying the fault. Sisters with a strong family history of breast cancer may gain the most from a clear answer.
Children
For a fault that only affects adult risk, testing usually waits until the child is an adult and can choose.
The exception
- A child with signs of Nijmegen breakage syndrome
- A brother or sister of a child who has it
Your partner
If both partners carry an NBN fault, each child has a one in four chance of inheriting two. Testing the partner, before or early in a pregnancy, tells a couple whether this is possible at all.
Not sure whether this applies to you?
Ask an oncologistStep by step
How does testing a relative actually work?
You tell your relatives
Your counsellor can give you a short family letter explaining the result in plain words. Many families find this easier than explaining it themselves.
Each relative sees a counsellor
Before testing, each adult has their own conversation about what a result would mean for them. Nobody should be tested because the family insisted.
A sample is taken
A blood or saliva sample is sent to the laboratory with your report. Relatives in district towns can often give a sample locally, without travelling to Hyderabad.
The result comes back as yes or no
The relative either carries the family's fault or does not. The counsellor then explains what, if anything, changes for them.
Words you will hear
What do the family-testing words mean?
- Cascade testing
- Testing relatives one circle at a time, starting with the closest, and moving outwards as each new carrier is found.
- First-degree relative
- A parent, brother, sister or child. Each shares half of your genes.
- Targeted testing
- A test that looks only for the one fault already known in the family, rather than reading the whole gene.
- Carrier testing
- Testing a partner to see whether they also carry a fault in the same gene. It matters for family planning.
- Predictive testing
- Testing someone who is well, to see whether they carry the family's fault before any illness appears.
- Consanguinity
- Partners who are related by blood, such as cousins. It raises the chance both carry the same rare fault.
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Side by side
What does a relative's result change?
Relative carries the fault
Relative does not carry it
Screening reviewed against their own family history
Screening follows their family history as before
Their own children can be offered testing as adults
Their children cannot inherit this fault from them
Their partner may be offered carrier testing
No partner testing is needed for this fault
They join the family tree of known carriers
Their branch of the family can stop here
Being straight with you
What can this page not tell you?
It cannot tell you which relatives to approach first in your own family, or how. What your specific variant means is a question for the counsellor who ordered the test. That person can help you decide who needs to know and in what order.
It cannot settle worries about marriage or insurance
Many families worry that a result will affect a marriage proposal or an insurance policy. India has no dedicated law on genetic discrimination. Raise these worries with your counsellor before relatives are tested, not afterwards, so each person can decide with their eyes open.
Who this does not apply to
If your report calls the NBN change a variant of uncertain significance, relatives should not be tested for it. The result would mean nothing either way. And if the finding came from a tumour test, it may not be inherited at all. That is covered under targeted therapy.
Every adult relative has the right not to be tested. That choice deserves respect.Commonly believed
What do families get wrong about testing relatives?
"If I carry it, all my children will carry it too."
Each child has a one in two chance, and each pregnancy is separate. Some families have several carriers, others have none among the children.
"Only the women in the family need testing."
Men carry and pass on NBN faults just as often. A father or brother may be the link to a whole branch of the family.
"We should test the children now, to be safe."
For adult carrier risk, testing a child brings no medical benefit and takes away their own choice. The exception is a child with signs of the childhood syndrome.
"A carrier result will ruin a marriage proposal."
Carrying one NBN fault usually changes little for your own health, and many carriers never know. What matters most for future children is whether the partner also carries a fault, which a test can answer.
Questions we are asked
Common questions about testing the family for NBN
Who should be tested first?
Your parents, brothers, sisters and adult children, as each has a one in two chance of carrying the fault. If one parent is tested and found to carry it, that side of the family becomes the focus. Your counsellor can help you plan the order.
Does my relative need the same big panel test I had?
No. They need a targeted test for your exact fault, which is simpler and usually cheaper. The laboratory needs a copy of your report to know what to look for. A full panel is only needed if the relative has their own strong history of cancer.
Should my partner be tested before we have children?
It is often worth it. If your partner carries no NBN fault, your children cannot inherit two faulty copies. If your partner also carries one, a counsellor will explain the options before or during a pregnancy. Partners who are related by blood gain the most from testing.
My sister does not want to be tested. What should I do?
Share the information, then respect her choice. Some people prefer to rely on screening based on family history, and that is a reasonable decision. She can change her mind later, and the test will still be available when she is ready.
Can relatives abroad be tested?
Yes. Give them a copy of your report so a laboratory near them can test for the exact fault. Genetic services in most countries can do targeted testing. Your counsellor's family letter helps their doctor understand the request quickly.
Is family testing covered by insurance or schemes?
Coverage varies, and predictive testing in a well relative is often not covered by private policies. Aarogyasri and Ayushman Bharat cover is limited for genetic tests. Ask the helpline to check the current position for your family before sending samples.
What if a relative tests negative but has cancer in their family branch?
Their screening then follows their family history, just as it would for anyone. A negative result for the NBN fault does not rule out other causes. A counsellor may suggest a wider test if their own branch has a strong pattern.
Where do we start?
Ask your counsellor for a family letter and keep copies of your report. Make a list of relatives who might want testing. Call the CION helpline if you need help arranging counselling or sample collection for relatives in the districts.
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
- NHS — Predictive genetic tests for cancer risk genes
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
- MedlinePlus Genetics — NBN gene
- GeneReviews (NCBI) — Nijmegen Breakage 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.
Keep reading
Related pages
NBN positive: what happens nextYour own next steps, before you reach out to relativesBiallelic NBN and Nijmegen breakage syndromeWhy partner testing matters for future childrenNBN mutation: which cancers and what riskWhat a positive result means for a relativeThe NBN gene: what it doesA plain explanation to share with the family
Talk to us
Need help arranging tests for relatives?
Tell us who in the family wants testing and where they live. We can help arrange counselling and sample collection, including in the districts. One helpline serves every CION centre.