Medical Oncologist
CION Cancer Clinics
Testing the family for a telomere gene fault | CION Cancer Clinics
Once a telomere gene fault is found, parents, brothers, sisters and children are offered a test for that exact change. Any sibling who might donate bone marrow must be tested before donating, because a well carrier can have weak marrow. This page explains who is tested, in what order, why older relatives can look well, and what the tests cannot tell you. 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. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- Who in the family should be tested for a telomere gene fault?
- Which relatives are offered a test, and why?
- In what order does family testing usually happen?
- The words you will meet, in plain language
- What a sibling's result means if they might donate
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about testing the family
The short answer
Who in the family should be tested for a telomere gene fault?
Test the person with the symptoms first, then parents, brothers, sisters and children. Anyone who might donate bone marrow to the affected person must be tested before donating. The first test finds the family fault. Relatives are then checked for that one change.
Why the pattern in these families is hard to read
Telomere biology disorders, including dyskeratosis congenita, can be caused by several genes. Some are passed on by one parent, some need a faulty copy from both parents, and one is carried on the X chromosome. So the order of testing depends on which gene is involved, and the counsellor works that out first.
Why relatives can look so different
In some families the illness gets earlier and more severe with each generation, because telomeres are passed on already shortened. A child may have bone marrow failure while a parent carrying the same fault has only early grey hair or lung scarring in later life. Those milder signs in older relatives are easy to miss.
A relative who looks well can still carry the fault. Looking well is not the same as testing negative.Circle by circle
Which relatives are offered a test, and why?
Each person is tested for a different reason. The counsellor explains which of these apply to your family.
The person with symptoms
Low blood counts, lung scarring, liver disease or the classic signs on nails, skin and mouth usually lead to testing. Their result tells the family what to look for.
A possible bone marrow donor
A brother or sister being considered as a donor must be tested first. A donor who carries the same fault may have weak marrow, even when they feel completely well.
Tested before
- Tissue matching is finalised
- Any marrow or stem cells are collected
Parents and older relatives
Testing parents shows which side the fault came from. It can also explain a grandparent's unexplained lung scarring, liver disease or low blood counts years earlier.
Brothers, sisters and children
Relatives who carry the fault can have blood counts, lungs and liver watched, and mouth and throat checked, before any problem shows. In families where parents are related by blood, the counsellor also asks about recessive forms.
Not sure whether this applies to you?
Ask an oncologistIn practice
In what order does family testing usually happen?
Draw the family tree
The counsellor asks about low blood counts, lung scarring, liver disease, early grey hair and mouth cancers on both sides, going back several generations.
Measure telomere length
A blood test measures how long the telomeres are in white blood cells. Very short telomeres support the diagnosis and guide the gene test.
Test the affected person's genes
A panel of telomere genes is read. If a fault is found, the family now has an exact change to test for.
Test any possible donor urgently
If a transplant is being planned, sibling donors are tested for the family fault before anything else happens.
Offer testing to the wider family
Parents, remaining siblings and adult children are offered the targeted test, with counselling before and after.
On your report
The words you will meet, in plain language
- Telomere
- A protective cap on the end of each chromosome, like the plastic tip on a shoelace. It shortens each time a cell divides.
- Telomere length test
- A blood test that compares your telomere length with people of the same age. It is often called flow-FISH on the report.
- Anticipation
- The illness appearing earlier or more severely in each new generation of the same family.
- X-linked
- The faulty gene sits on the X chromosome. Boys are usually affected more severely, and mothers can carry it without being ill.
- Recessive
- Illness appears only when both copies of the gene are faulty, one from each parent. The parents are usually well carriers.
- Germline
- Present in every cell from birth, so it can be passed on. The opposite is a change found only in a tumour.
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Side by side
What a sibling's result means if they might donate
Sibling carries the fault
Sibling does not carry it
Usually not used as a donor
Can be considered if the tissue match is right
Offered their own checks of blood, lungs and liver
Needs no telomere-related checks
Their own children may need testing later
Cannot pass the family fault on
Team looks for another donor if needed
Transplant planning can continue
Being straight with you
What this page cannot tell you
It cannot tell you what your family's result means. The same gene can be inherited in different ways, and the exact change matters. What your specific variant means is a question for the counsellor who ordered the test, working with your haematologist.
It cannot promise a clear answer
In some families with very short telomeres and clear symptoms, no gene fault is found. Several telomere genes are still being studied, and studies so far are small. A negative gene test in that situation does not mean the illness is not inherited, and relatives are then watched using the family history.
Who this does not apply to
Most people with early grey hair, or one older relative with lung scarring, do not have a telomere biology disorder. Both are common on their own. Testing is worth discussing when several features appear together, when blood counts fail young, or when a relative already has a confirmed fault. A counsellor will say honestly if testing is not needed.
Commonly believed
Four things families tell us, and what is actually true
"My brother is healthy, so he is the perfect donor."
A healthy-looking sibling can carry the same fault and have weak marrow. That is why every sibling donor is tested for the family fault before donating.
"Our parents are fine, so it cannot be inherited."
In some families the illness gets milder going back up the generations. A parent can carry the fault and show only small signs, or none, until later in life.
"Grey hair at a young age means we have it."
Early greying is common in healthy families. It counts only alongside other features, such as low blood counts or lung scarring in relatives.
"Only boys are affected in our family."
That fits the X-linked form, where mothers and sisters can carry the fault. Women carriers are usually well, but they are still offered testing and a talk about their children.
Questions we are asked
Common questions about testing the family
Should children who look well be tested?
Often, yes, especially if a sibling might donate marrow or a parent carries a dominant fault. Knowing early means blood counts can be watched. Your counsellor and haematologist will talk through the timing with you and the child.
Does being related by marriage within the family matter?
It can. When parents are related by blood, the recessive forms are more likely, because both may carry the same fault. Tell the counsellor openly. It changes which relatives are tested, not how the family is treated.
Can the telomere length test replace the gene test?
No. The length test shows whether telomeres are very short, which supports the diagnosis. The gene test finds the exact fault that relatives can be tested for. Most families need both, usually in that order.
Is the telomere length test available in India?
Only a few laboratories offer it, and samples are sometimes sent out. The haematology team will arrange the sample and advise where it goes, so the family does not have to organise shipping themselves.
What if an unrelated donor is needed?
If no suitable sibling is free of the fault, the transplant team searches donor registries. Testing siblings early helps this search start sooner rather than after a sibling has already been prepared.
Will a relative who carries the fault get cancer?
Not necessarily. Carriers have a raised risk of some blood cancers and mouth and throat cancers, but many never develop them. Regular checks and avoiding tobacco and alcohol are the steps that matter most.
Will relatives be told without our permission?
No. Results are confidential. The counsellor can help you decide how to tell relatives and can give you a letter to share. Who is told, and when, stays with your family.
Where do we start in Hyderabad?
Write down who in the family had low blood counts, lung or liver disease, or mouth cancers, and at roughly what age. Call the CION helpline, and someone will point you to a haematologist and genetic counsellor.
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
- GeneReviews (NCBI) — Dyskeratosis Congenita and Related Telomere Biology Disorders
- MedlinePlus Genetics — Dyskeratosis congenita
- MedlinePlus Genetics — What are the different ways a genetic condition can be inherited?
- MedlinePlus Genetics — TERT gene
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
Telomere gene positive: what happens nextThe checks a relative who tests positive would haveShort telomere syndromes and cancer riskThe conditions these genes cause, beyond cancerTelomere genes: which cancers and what riskWhat a carrier relative is being watched forWhat the telomere biology genes doHow telomeres work, in plain language
Talk to us
Is a brother or sister being considered as a donor?
Tell us what the report says and who in the family might be tested. We will help you reach a haematologist and genetic counsellor who can plan the order. One helpline serves every CION centre.