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Biallelic BRCA2: when a child inherits two faulty copies | CION Cancer Clinics
Biallelic BRCA2 means a child has inherited a faulty BRCA2 gene from both parents. It is rare, and it causes a form of Fanconi anaemia, an inherited condition affecting the bone marrow with a high risk of childhood cancers. It is very different from being a BRCA2 carrier. This page explains how it happens, what it involves and what carrier couples can do. 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
- What does biallelic BRCA2 mean?
- How biallelic BRCA2 can affect a child
- How is biallelic BRCA2 diagnosed and managed?
- The words you will meet, in plain language
- One faulty BRCA2 copy compared with two
- Four things families assume, and what is actually true
- What this page cannot tell you
- Common questions about biallelic BRCA2
The short answer
What does biallelic BRCA2 mean?
It means a child has inherited a faulty BRCA2 gene from both parents, so neither copy works. This is rare and serious. It causes a form of Fanconi anaemia, an inherited condition in which the bone marrow struggles to make blood cells and certain cancers appear in early childhood. It is very different from being a BRCA2 carrier.
How it differs from carrying one faulty copy
Most people with a BRCA2 fault have one faulty copy and one working copy. They are usually healthy through childhood and carry raised cancer risks in adult life. A child with two faulty copies has no working BRCA2 at all. Cells cannot repair certain kinds of DNA damage, and problems start much earlier.
Why carrier couples need to know
It can only happen when both parents carry a BRCA2 fault. Each pregnancy then has a one in four chance of a child with two faulty copies. Most couples have no idea they are both carriers until a child is diagnosed, which is why this matters in families where cousins or relatives marry.
Biallelic BRCA2 is rare. Most BRCA2 families will never meet it.What it can involve
How biallelic BRCA2 can affect a child
Not every child has every feature. Doctors look at the whole picture, and some children look entirely well at birth.
Childhood cancers
This is the leading concern with BRCA2 in particular. Cancers can appear young, sometimes before school age.
Cancers reported
- Leukaemia, a cancer of the blood
- Brain tumours
- Kidney tumours, including Wilms tumour
Blood and marrow problems
The marrow may make too few blood cells. That can mean a low haemoglobin, a low platelet count with easy bruising, or a low white cell count with repeated infections.
Signs at birth
Some children are small for their age, or have differences in the thumbs or forearms, or patches of darker skin. Others have none of these, which is why diagnosis is sometimes late.
Sensitivity to treatment
Children with this condition react far more strongly to some chemotherapy medicines and to radiation. Standard doses can cause severe harm.
Treatment must be planned by a team that knows the diagnosis.Not sure whether this applies to you?
Ask an oncologistFrom suspicion to a plan
How is biallelic BRCA2 diagnosed and managed?
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Someone raises the question
Usually a young child has a cancer or a low blood count along with physical signs. Sometimes both parents are already known BRCA2 carriers and a doctor thinks to ask.
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A chromosome breakage test
A blood sample is exposed to a chemical that damages DNA. Cells from a child with Fanconi anaemia show far more broken chromosomes than usual. This test points to the diagnosis.
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Gene testing confirms the cause
A genetic test looks for two faults in BRCA2, one from each parent. Testing both parents then confirms which fault came from whom.
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An expert team takes over care
A paediatric haematologist and oncologist plan checks for blood problems and early tumours. A bone marrow transplant may be discussed, using gentler preparation than usual.
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The wider family is offered testing
Both parents are BRCA2 carriers, with their own adult cancer risks. Their brothers, sisters and other relatives can be offered a test for the family's faults.
On your report
The words you will meet, in plain language
- Biallelic
- Both copies of a gene are faulty, one inherited from each parent. The opposite, one faulty copy, is called monoallelic or heterozygous.
- Fanconi anaemia
- A group of inherited conditions where DNA repair fails, the marrow may not make enough blood and cancers appear early.
- FANCD1
- The name used for the Fanconi anaemia group caused by two faulty copies of BRCA2. It is one of the more severe groups.
- Chromosome breakage test
- A blood test that stresses cells with a chemical and counts the breaks in their chromosomes. It is the usual first test.
- Consanguinity
- A marriage between blood relatives, such as cousins. It raises the chance that both partners carry the same rare fault.
- Preimplantation genetic testing
- Testing embryos made through IVF before one is placed in the womb, so an embryo without two faulty copies can be chosen.
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Side by side
One faulty BRCA2 copy compared with two
One faulty copy (carrier)
Two faulty copies (biallelic)
Usually well through childhood
Serious illness often starts in early childhood
Raised adult risk of breast, ovarian and prostate cancer
Leukaemia, brain and kidney tumours in children
Standard treatment is usually safe
Chemotherapy and radiation must be adapted
Inherited from one parent
Inherited from both parents
Commonly believed
Four things families assume, and what is actually true
"We both carry BRCA2, so all our children will be ill."
Each pregnancy has a one in four chance of two faulty copies. Each also has a one in two chance of one faulty copy, and a one in four chance of none. Every pregnancy is a fresh roll of the dice.
"Nobody in our family was ever ill, so a cousin marriage is safe."
A carrier of one faulty copy is usually healthy for decades, so a fault can pass quietly down both sides. Shared grandparents raise the chance that both partners carry it.
"A child with this condition can have the usual cancer treatment."
Usual doses of some medicines and of radiation can cause severe harm. Doctors treating the child must know the diagnosis before they plan anything.
"Our healthy children must be tested straight away."
Brothers and sisters of an affected child are assessed by the specialist team. A child who may carry just one copy usually waits until adulthood to decide on that test.
Being straight with you
What this page cannot tell you
It cannot tell you how a particular child will do. Biallelic BRCA2 is rare, the studies are small, and children vary widely. Doctors with experience of Fanconi anaemia will explain what the outlook is for your child, and it depends heavily on the exact faults and on early care.
It cannot interpret your family's results
Whether both partners carry a BRCA2 fault, and whether those faults are the kind that cause this condition, is a question for a clinical geneticist. What your specific variants mean is a question for the counsellor who ordered the test.
Who this does not apply to
If only one partner carries a BRCA2 fault, your children cannot have biallelic BRCA2. If you are a carrier asking about your own adult cancer risk, this page is not about you. Our BRCA2 surveillance and family planning pages are the better place to start.
Planning a pregnancy with a partner who is also a relative? Ask for a genetic counselling appointment before trying to conceive.Questions we are asked
Common questions about biallelic BRCA2
Is biallelic BRCA2 the same as being BRCA2 positive?
No. BRCA2 positive usually means one faulty copy and raised adult cancer risks. Biallelic means two faulty copies, one from each parent. It causes a rare childhood condition, a form of Fanconi anaemia, with very different care.
My partner and I both carry BRCA2. What are our options?
See a genetic counsellor together before a pregnancy if you can. Options include testing during pregnancy, testing embryos through IVF, using donor eggs or sperm, or deciding to proceed without testing. The choice is yours, and the counsellor will not push you towards one.
Does cousin marriage cause this condition?
Cousin marriage does not create the fault. It raises the chance that both partners inherited the same rare fault from a shared ancestor. Many couples in related marriages have healthy children. Knowing your family history helps you decide whether testing first is worthwhile.
Can a bone marrow transplant help?
A transplant can replace a failing marrow or treat a leukaemia. It does not correct the gene fault in the rest of the body, so the risk of other tumours remains. Transplants for this condition use gentler preparation and should be done by an experienced team.
What checks does a child with biallelic BRCA2 need?
Regular blood counts, and often scans to look for early brain and kidney tumours. The exact plan depends on the child's age and the specialist team's protocol. Evidence on the best schedule is still limited, so plans vary between centres.
Are the parents at risk too?
Yes. Each parent carries one faulty BRCA2 copy and has the adult risks that come with it. That means checks for breast, ovarian, prostate and pancreatic cancer as advised. Parents are sometimes so focused on the child that their own care slips.
Should our other children be tested?
Brothers and sisters are usually assessed for the two-copy condition, because early care matters. Testing for a single carrier copy is normally left until they are adults. Your specialist team will explain which test is being done and why.
Where can this be looked after in Telangana?
Care usually involves a paediatric haematology and oncology team with transplant experience, typically in Hyderabad. A genetic counsellor can coordinate testing for parents and relatives in the districts, so that city trips are saved for what needs a specialist.
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) — BRCA1- and BRCA2-Associated Hereditary Breast and Ovarian Cancer
- MedlinePlus Genetics — BRCA2 gene
- National Cancer Institute — BRCA Gene Changes: Cancer Risk and Genetic Testing
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
BRCA2 and family planningPregnancy options when one or both partners carry BRCA2Fanconi anaemia genes explainedThe wider group of genes behind Fanconi anaemiaTesting children for inherited faultsWhen a child should be tested and when it can waitSurveillance for BRCA2 carriersThe adult check-up plan for carrier parents
Talk to us
Do you and your partner both carry BRCA2?
A genetic counsellor can explain what it means for a pregnancy and which options exist, with no pressure towards any of them. One helpline serves every CION centre.