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Testing your relatives once an MLH1 fault is found | CION Cancer Clinics
Once one person in a family is found to carry an MLH1 fault, each parent, brother, sister and child has a one in two chance of carrying it too. They are tested for that exact change with a simple blood test. This page explains who is offered testing first, how it works when relatives live far apart, and what a positive or negative 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 once MLH1 is found?
- Which relatives are offered the MLH1 test, and in what order?
- How does testing a relative for MLH1 actually work?
- The words you will meet, in plain language
- What a relative's result changes
- What families often get wrong about testing relatives
- What this page cannot tell you
- Common questions about testing relatives for MLH1
The short answer
Who in the family should be tested once MLH1 is found?
Start with the closest blood relatives: parents, brothers, sisters and adult children. Each of them has a one in two chance of carrying the same MLH1 fault. They are tested for that one exact change, with a simple blood test. Those who carry it can start bowel checks early. Those who do not carry it can usually go back to ordinary screening.
Why the family test is simpler
The first person's test had to search the whole gene. Relatives do not need that. The laboratory already knows the exact spelling change to look for, so the result is usually a clean yes or no. That makes it quicker to explain and much cheaper to run.
Why it matters more with MLH1
Of the genes behind Lynch syndrome, MLH1 is one of the two that carry the highest bowel and womb cancer risks. Checks for carriers tend to start earlier and happen more often. A relative who does not know their status could miss years of useful checks, or sit through years of checks they do not need.
Testing a relative is always their own choice. Nobody should be tested because someone else insisted.Who is offered testing
Which relatives are offered the MLH1 test, and in what order?
Testing moves outwards through the family, one branch at a time. Each positive result tells you which branch to follow next.
Parents
If a parent is alive, testing them shows which side of the family the fault came from. That tells you whose brothers, sisters and cousins need to hear about it next.
Brothers and sisters
Each has a one in two chance of carrying the fault, whatever their age and however healthy they feel. Men need testing as much as women, both for their own bowel risk and for their children.
Adult children
Offered once they are adults and can decide for themselves. Bowel checks for carriers start in adult life, so waiting until then loses nothing.
Usually waits
- Children and teenagers
- Anyone who does not want to know yet
The wider family
Aunts, uncles and cousins on the carrier's side come next. In large families spread across districts and states, a written family letter helps the message travel accurately.
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How does testing a relative for MLH1 actually work?
The family letter
The first person to test positive receives a letter naming the gene and the exact change. Relatives take it to their own counsellor or doctor. Without it, the lab cannot run the cheaper targeted test.
A conversation first
Each relative sees a counsellor before giving a sample. They talk through what a positive result would mean for work, marriage and insurance, and whether they want to know now.
One blood sample
A single blood or saliva sample is taken. It can be collected close to home and sent to the laboratory, so nobody needs to travel to Hyderabad just for this.
A clear answer
The result says whether that person carries the family's MLH1 change. Carriers are referred for a surveillance plan. Non-carriers are told what ordinary screening still applies to them.
On your letter and report
The words you will meet, in plain language
- Cascade testing
- Testing relatives one branch at a time, starting closest to the person who tested positive and moving outwards.
- First-degree relative
- A parent, brother, sister or child. They share half their genes with you, which is why each has a one in two chance.
- Targeted test
- A test that looks only for the change already found in the family. It is sometimes called single-site testing.
- Carrier
- Someone who has the MLH1 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 family's known fault. Their risk from this gene is the same as anyone else's.
- Lynch syndrome
- The name for an inherited fault in MLH1 or one of its partner genes. It raises the risk of bowel, womb and several other cancers.
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Side by side
What a relative's result changes
Carries the MLH1 fault
Does not carry it
Regular colonoscopy from early adult life
Ordinary screening for their age
Women discuss womb and ovary options
No extra womb or ovary checks for this gene
Their own children can be tested later
Their children cannot inherit it from them
Their branch of the family is told next
Testing stops on their branch
Commonly believed
What families often get wrong about testing relatives
"My brother is healthy, so he does not carry it."
Feeling well says nothing about carrying the fault. Most carriers feel completely normal until a check finds something, and finding it early is the whole point.
"This is a women's problem."
MLH1 raises bowel cancer risk in men and women alike. A father passes it on exactly as a mother does. Leaving men out is one of the most common ways a family misses carriers.
"We should test the children now, to be safe."
Checks for MLH1 carriers start in adult life, so testing a child gains nothing medically. Waiting lets them make the decision themselves. The rare exception is when both parents carry a fault, which is worth raising with the counsellor.
"If I test negative, I never need a colonoscopy."
You drop the extra checks linked to MLH1. You still follow the ordinary screening advice for your age, like anyone else.
Being straight with you
What this page cannot tell you
It cannot tell you which of your relatives carries the fault, or how your family should share the news. Every family has its own history, silences and arguments. A genetic counsellor can help you plan who to tell first and what to say, and can speak to relatives directly if that is easier.
It cannot settle marriage questions
Families often worry about disclosure before a wedding. There is no single right answer, and families decide it in very different ways. Talk it through with a counsellor who understands the family setting, ideally in Telugu if that is easier. If both partners are from the same extended family, mention that too.
Who this does not apply to
If nobody in your family has had a positive MLH1 result, this page is not your starting point. Relatives cannot be tested for a fault nobody has found. The first step then is testing the relative who had cancer, if that is still possible.
What your specific result means is a question for the counsellor who ordered the test.Questions we are asked
Common questions about testing relatives for MLH1
What are the chances my child carries the MLH1 fault?
One in two for each child, whether a son or a daughter. Each pregnancy is a fresh chance, so one child's result does not change the next child's odds. A child who does not inherit the fault cannot pass it on to their own children.
At what age should my children be tested?
Usually once they are adults and can decide for themselves. Bowel checks for MLH1 carriers begin in adult life, so there is no medical reason to test earlier. Your counsellor will advise if anything in your family changes that, such as both parents carrying a fault.
My parents are no longer alive. Can we still find out which side it came from?
Sometimes. Testing their brothers and sisters can show it, and so can a stored tissue block from a parent's old surgery. If neither is possible, both sides of the family may need to be told about the result.
Do relatives in another state need to come to Hyderabad?
No. With the family letter, any genetic service can order the targeted test. Samples can be collected locally and counselling can happen by video. The letter matters more than where the sample is taken.
What if a relative does not want to be tested?
That is their right. Some people prefer to wait, and some prefer regular colonoscopy without knowing their status. Give them the letter and the information, then leave the door open. Many relatives come back to the question later.
Does testing negative mean my children are safe?
From this particular fault, yes. You cannot pass on a change you do not carry. Your children still share the family's other genes and habits, so ordinary screening advice still applies to them like anyone else.
My husband and I are related. Does that matter?
It can. If both partners carry a fault in the same group of genes, a child could inherit two faulty copies. That causes a rare childhood condition that needs early checks. Tell the counsellor if you are related, so both of you can be offered testing.
How do I tell my family without frightening them?
Start with the fact that this is useful news. It tells relatives whether they need extra checks, and many will find they do not. Share the family letter rather than retelling the details. Your counsellor can help you plan the conversation.
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
- GeneReviews (NCBI) — Lynch Syndrome
- MedlinePlus Genetics — Lynch syndrome
- NHS — Predictive genetic tests for cancer risk genes
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ)
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
MLH1 positive: what happens nextWhat a relative who tests positive does nextSurveillance for MLH1 carriersThe checks carriers are offered, and how oftenMLH1 testing cost in HyderabadWhat a relative's targeted test usually costsLiving with Lynch syndrome in a large familySpreading the news through a big extended family
Talk to us
Need help deciding who in the family to tell first?
Bring the family letter and a rough family tree. We will help you work out who should be offered testing and how to arrange it close to where they live. One helpline serves every CION centre.