Medical Oncologist
CION Cancer Clinics
Family testing for SMAD4 and BMPR1A: who, when and why | CION Cancer Clinics
Once a SMAD4 or BMPR1A fault is found in one person, parents, brothers, sisters and children can each be tested for that exact change. Each child of a carrier has a one in two chance of inheriting it. This page explains who is tested first, why children are tested earlier than for most cancer genes, how the process works and what each result changes. 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 SMAD4 or BMPR1A?
- What does testing mean for each relative?
- How does family testing actually happen?
- The words you will meet, in plain language
- What changes after a relative's result?
- What this page cannot tell you
- Four things families believe about testing, and what is true
- Common questions about testing the family
The short answer
Who in the family should be tested for SMAD4 or BMPR1A?
Once a fault is confirmed in one person, their parents, brothers, sisters and children can each be tested for that exact change. Each child of a carrier has a one in two chance of inheriting it. Those who test negative can stop worrying about polyps and need no special checks. Those who test positive can start surveillance before any problem appears.
Why the person with polyps goes first
Testing starts with the relative who has juvenile polyps, because that tells the family which fault to look for. Their test usually covers several polyp genes at once, since different polyp conditions can look alike. If a fault is found, everyone else needs only a simpler, cheaper test for that single change.
Why children are tested earlier here
For many inherited cancer genes, testing waits until a child is an adult. Juvenile polyposis is different. Polyps can bleed in childhood, scheduled checks begin in the early teens, and SMAD4 carriers need blood vessel checks from diagnosis. Testing children lets the family spare the ones who do not carry the fault from years of unnecessary scopes.
A negative test in a relative is a real answer. It closes the question for them and for their children.Relative by relative
What does testing mean for each relative?
The fault travels in a straight line through a family. It helps to think about each group separately.
Parents
Testing both parents shows which side the fault came from. That side of the family, and not the other, then needs to be offered testing.
Worth knowing
- A parent can carry it without ever having had symptoms
- Sometimes neither parent carries it
Brothers and sisters
Each has a one in two chance of carrying the fault if a parent is a carrier. They are usually the next group tested, as many will already be of an age where checks should begin.
Children
Each child of a carrier has a one in two chance. Testing is usually offered in childhood, before scheduled checks would begin, and sooner with SMAD4 or if there is bleeding.
A counsellor will explain the test to the child in a way that suits their age.The wider family
Once the carrier side is known, aunts, uncles and cousins on that side can be offered testing too. In large joint families this is where a single result can help the most people.
Not sure whether this applies to you?
Ask an oncologistHow it works
How does family testing actually happen?
The first result is confirmed
The counsellor checks the report and confirms the fault is classed as disease-causing. A variant of uncertain significance is not used to test relatives.
The family is told
You are given a letter or summary to share. It names the gene and the exact change, so relatives can take it to their own doctor anywhere.
Each relative is counselled first
Before a sample is taken, the relative talks through what a positive or negative result would mean for them, including practical questions about marriage and insurance.
A targeted test and the result
A blood or saliva sample is tested for the single known change. The result is given in person, with a plan for surveillance if it is positive.
On your report
The words you will meet, in plain language
- Cascade testing
- Testing relatives, one step at a time, for a fault already found in the family.
- Targeted test
- A test for one known change only. It is quicker and cheaper than a full gene panel.
- Autosomal dominant
- One faulty copy is enough to raise risk, and it can pass from either parent to a son or a daughter.
- De novo
- A fault that appeared for the first time in one person, so neither parent carries it.
- Carrier
- Someone who has the inherited fault, whether or not they have polyps. A carrier is not a patient.
- Pedigree
- A family tree drawn by the counsellor, showing who had polyps or cancer and who has been tested.
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Side by side
What changes after a relative's result?
Tests positive
Tests negative
Colonoscopy and stomach checks are planned
Ordinary screening for age applies
HHT checks if the gene is SMAD4
No blood vessel checks needed
Their own children can be offered testing
Their children cannot inherit it from them
Family planning choices can be discussed
Nothing further to plan for this fault
Being straight with you
What this page cannot tell you
It cannot tell you who in your family carries the fault, or how to raise the subject with a relative who does not want to know. Every family is different, and a counsellor can help you plan those conversations, including in Telugu if that is easier for older relatives.
It cannot read your result
What your specific variant means is a question for the counsellor who ordered the test. If the first person's result was a variant of uncertain significance, relatives should not be tested for it, and nobody's screening should change because of it.
Who this does not apply to
In a sizeable share of families with juvenile polyposis, no gene fault is found at all. Cascade testing is not possible then, and relatives are offered checks based on the family history instead. Relatives on the side of the family that does not carry the fault do not need testing. Most people with a single bowel polyp do not need this test either.
Commonly believed
Four things families believe about testing, and what is true
"My brother tested negative, so I must be negative too."
Each child's chance is separate, like a coin toss every time. One sibling's result tells you nothing about another's. Each person needs their own test.
"We should wait until the children are adults."
For juvenile polyposis, polyps can bleed in childhood and checks begin in the early teens. Testing children usually helps, and it spares those who do not carry the fault from unnecessary scopes.
"Neither parent has polyps, so it cannot be inherited."
A parent can carry the fault and never have symptoms. The fault can also appear for the first time in one person. Testing the parents is the only way to know.
"A negative result means we did the wrong test."
When the family's fault is already known, a negative targeted test is reliable. It means that person did not inherit it and cannot pass it on.
Questions we are asked
Common questions about testing the family
Is a relative's test cheaper than the first one?
Usually yes. The first person needs a broader test that searches several genes. Relatives need only a targeted test for the one change already found, which is simpler and typically costs less. Ask the laboratory for the family rate and bring the original report.
Can relatives in another city or abroad be tested?
Yes. They need the family letter or a copy of the original report, which names the exact change. Any accredited genetics laboratory can then run the targeted test, and a local counsellor can give the result.
What if the person with polyps has died?
Stored tissue from an old operation or biopsy can sometimes be tested. If that is not possible, a living relative who has had polyps may be tested instead. A counsellor can advise on the best starting point for your family.
Does a relative have to be tested?
No. Testing is always a personal choice. A relative who chooses not to be tested can still be offered surveillance as if they might be a carrier, which keeps them safe without a result. Their decision should be respected.
Should we disclose the result before a marriage?
This is a family decision, and a common worry in India. There is no legal requirement, and no dedicated law on genetic discrimination. A counsellor can help you think through who needs to know, when, and how to explain that the risk can be managed.
Can we avoid passing it to our children?
There are options, including testing during pregnancy and IVF with embryo testing. Each raises its own practical and personal questions, and costs vary. A counsellor can explain them before you plan a pregnancy, so you have time to decide.
How long does a family test take?
A targeted test for a known change is usually faster than the first broad test, but turnaround varies by laboratory. Ask when the sample is taken, and plan the result appointment with a counsellor rather than reading the report alone.
Where do we start?
Bring the first person's report to a genetic counsellor, along with a list of relatives on both sides. Call the CION helpline if you are not sure who to approach, and someone will point you to the right clinic.
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
Medical Oncologist
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Sources
- GeneReviews (NCBI) — Juvenile Polyposis Syndrome
- MedlinePlus Genetics — Juvenile polyposis syndrome
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ®)–Health Professional Version
- National Cancer Institute — Genetic Testing for Inherited Cancer Susceptibility Syndromes
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
SMAD4 and BMPR1A positive: what happens nextThe first steps after a positive resultSurveillance for SMAD4 and BMPR1A carriersWhat relatives who test positive will be offeredSMAD4 and BMPR1A cancer risksWhat carrying the fault means for cancer riskSMAD4 and hereditary haemorrhagic telangiectasiaWhy SMAD4 relatives also need blood vessel checks
Talk to us
Has one person in your family tested positive?
Tell us which gene was found and who else is in the family. We will help you plan who to test first and arrange counselling for each relative. One helpline serves every CION centre.