Medical Oncologist
CION Cancer Clinics
CDH1 in the family: who should be tested, and when | CION Cancer Clinics
When one person is found to carry a CDH1 fault, their parents, brothers, sisters and adult children each have a one in two chance of carrying it too. They are tested for that one known change, which is quick and gives a clear answer. This page explains who is offered a test, in what order, from what age, 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 CDH1?
- Which relatives are offered a test, and why?
- How does family testing actually happen?
- What do the words on a family letter mean?
- What a relative's result changes
- What can this page not tell you?
- What do families assume about testing relatives?
- Common questions about testing the family for CDH1
The short answer
Who in the family should be tested for CDH1?
Start with the closest blood relatives of the person who carries the fault: parents, brothers, sisters and adult children. Each of them has a one in two chance of carrying the same fault. Once you know which side of the family it came from, testing widens to aunts, uncles and cousins on that side.
Relatives are tested for one known change
The first test in the family searched the whole gene. Relatives do not need that again. The lab checks only for the exact fault already found, which gives a clear yes or no and costs far less. This way of moving through a family, one circle of relatives at a time, is called cascade testing.
Why men matter as much as women
Men carry and pass on CDH1 exactly as women do, and the stomach risk applies to both. Families often test only daughters because they have heard about the breast risk. That leaves brothers and sons unaware of the risk that matters most for them.
Testing is always a choice. Every relative decides for themselves, after their own counselling.Relative by relative
Which relatives are offered a test, and why?
The order follows how closely each person is related to the carrier. Closer relatives come first.
Brothers and sisters
Each one has an even chance of carrying the fault, whatever their age and whether or not they feel well. They are usually the first people offered a test.
Parents
Testing a parent shows which side the fault came from. That decides whose brothers, sisters and cousins should be offered testing next. A parent who tests negative spares their whole side of the family.
Sons and daughters
Each child of a carrier has an even chance of inheriting it. Testing usually waits until the late teens, when checks start to matter and the young person can take part in the decision.
Not usually tested
- Young children
- Children of a relative who tested negative
The wider family
Aunts, uncles and cousins on the carrier's side come next. In families where cousins have married, the counsellor will check both sides of the tree, so mention it.
Not sure whether this applies to you?
Ask an oncologistHow it works
How does family testing actually happen?
The carrier shares the result
Your counsellor can give you a family letter that explains the fault in plain words. You decide who receives it. Relatives abroad or in a village can take the letter to any genetics service.
Each relative has their own counselling
Before any sample is taken, each person talks through what a positive or a negative result would mean for them, including marriage, work and insurance. Some decide to wait, and that is allowed.
A sample for the known fault
A blood or saliva sample is tested for the one change on the family report. The lab needs a copy of that report, so keep the original safe and share copies.
The result sets the next plan
A relative who carries the fault is referred for checks and a talk about surgery. A relative who does not carry it needs no special stomach checks for this gene.
On the letter
What do the words on a family letter mean?
- Cascade testing
- Testing relatives step by step, starting with the closest, for a fault already found in the family.
- Predictive test
- A test in someone who is well, to find out whether they carry the family fault before any cancer appears.
- Familial variant
- The exact gene change found in your family. Relatives are tested for this one change only.
- First-degree relative
- A parent, brother, sister or child. Each shares half their genes with you.
- Carrier
- Someone who has the fault but does not have cancer. A carrier is not a patient and needs checks, not treatment.
- True negative
- A relative who does not carry the known family fault. Their risk from this gene is the same as anyone else's.
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Side by side
What a relative's result changes
Carries the family fault
Does not carry it
Offered stomach checks and a talk about surgery
No extra stomach checks needed for this gene
Women are offered breast checks from early adult life
Routine breast screening for age applies
Each child has an even chance of inheriting it
Children cannot inherit it from this person
Their own brothers and sisters may be offered testing
Testing stops on this branch of the family
Being straight with you
What can this page not tell you?
It cannot tell you who in your own family should be tested next. That depends on who is alive, who has already been tested and which side the fault came from. A genetic counsellor works this out from your family tree and your relative's report.
It cannot read the family report
Cascade testing only makes sense when the family fault is clearly harmful. What your specific variant means is a question for the counsellor who ordered the test.
Who this does not apply to
If the family result was a variant of uncertain significance, meaning the lab could not say whether it matters, relatives are usually not tested for it. The same applies when the first test found no fault at all. In those families, checks are planned from the family history instead. Testing of a tumour to choose treatment is a separate question, covered under targeted therapy.
Sharing a result is hard in close families. Your counsellor can help you plan who to tell and how.Commonly believed
What do families assume about testing relatives?
"Only the daughters need testing, because it is a breast gene."
The main risk with CDH1 is to the stomach, and it affects men and women alike. Sons and brothers need the same offer of testing as daughters and sisters.
"My brother tested negative, so I must be negative too."
Each person's result is their own. Brothers and sisters inherit genes separately, so one sibling's result says nothing about another's. Each needs their own test.
"We should test the children now, while they are small."
Nothing is done for a CDH1 carrier in early childhood, so testing usually waits until the late teens. That lets the young person take part in a decision about their own body.
"Keeping quiet protects the family's marriage prospects."
A relative who is never told cannot choose checks that could find a cancer early. How and when to share is personal, and a counsellor can help you find words that protect privacy.
Questions we are asked
Common questions about testing the family for CDH1
If I test negative, are my children safe from this gene?
Yes, as far as the known family fault is concerned. You cannot pass on a fault you do not carry, so your children do not need testing for it. Their ordinary risk of stomach and breast cancer, shared with everyone, stays the same.
At what age can a child be tested for CDH1?
Usually from the late teens. Checks and decisions about surgery are not needed in childhood, so there is no benefit to testing earlier. Waiting lets the young person understand the result and choose for themselves. Your counsellor will advise if a family pattern suggests otherwise.
What if a relative refuses to be tested?
That is their right. Some people need time, and some never want to know. Give them the family letter so they can decide later. A relative who declines testing can still be offered checks based on the family history.
My relatives live abroad. Do they need to come here?
No. A test for a known family fault can be done by a genetics service in their own country. They will need a copy of the original family report so the lab knows exactly which change to look for.
Should we tell the family of a prospective bride or groom?
There is no single right answer, and it is one of the most common questions we hear. A counsellor can help you think through timing and wording. Remember that a carrier also has choices about checks, surgery and family planning that affect a future spouse.
Can relatives be tested if our result was uncertain?
Usually not. A variant of uncertain significance is not treated as a fault, so testing relatives for it would not guide their care. If the lab later reclassifies it as harmful, family testing can start then.
Can carriers have children who do not inherit the fault?
There are options, including testing during pregnancy and testing embryos during IVF. Each raises practical and personal questions, and they are not right for everyone. Ask for a separate conversation with the counsellor before planning a pregnancy.
Will a relative's result affect their insurance?
India has no dedicated law on genetic discrimination in insurance, and the position has been argued in court rather than settled. It is a fair question to raise before testing, not afterwards, and it is one reason some relatives arrange cover first.
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) — Hereditary Diffuse Gastric Cancer
- MedlinePlus Genetics — Hereditary diffuse gastric cancer
- NHS — Predictive genetic tests for cancer risk genes
- 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
CDH1 positive: what happens nextThe checks and choices for a relative who tests positiveCDH1 testing cost in HyderabadWhat a relative's test usually costsCDH1 mutation: which cancers and what riskThe size of the risk a carrier facesSurveillance for CDH1 carriersThe checks a carrier relative is offered
Talk to us
Not sure which relatives to tell first?
Bring your family report and a rough family tree. A counsellor will help you work out who to offer testing, in what order, and how to share the news. One helpline serves every CION centre.