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Bloom syndrome: signs, inheritance and cancer risk | CION Cancer Clinics
Bloom syndrome is a rare inherited condition that happens when a child receives a faulty BLM gene from both parents. It causes small size from before birth, a sun-sensitive facial rash and a greatly raised risk of many cancers, often at a young age. This page explains the signs, how it is inherited, how care is organised and how it differs from being a carrier. 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 is Bloom syndrome, and why does it raise cancer risk?
- What are the signs of Bloom syndrome?
- What does looking after someone with Bloom syndrome involve?
- The terms used about Bloom syndrome, in plain language
- Bloom syndrome or a BLM carrier: what is the difference?
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about Bloom syndrome
The short answer
What is Bloom syndrome, and why does it raise cancer risk?
Bloom syndrome is a rare inherited condition caused by two faulty copies of the BLM gene, one from each parent. BLM helps untangle DNA so it can be copied cleanly. Without it, DNA breaks and swaps pieces far more often than usual, and cancers can appear at a much younger age than in other people.
How a child comes to have it
Bloom syndrome is recessive. Both parents are usually healthy carriers, each with one faulty copy. When two carriers have a child, each pregnancy has a one-in-four chance of the child inheriting both faulty copies and having the syndrome. It is more likely when parents are related by blood, which is why marriage within the family matters here.
Why the cancer risk is so different
People with Bloom syndrome have a greatly raised risk of many types of cancer, often starting in childhood or early adult life. Some people develop more than one cancer over their lifetime. This is very different from the usual picture of cancer as an illness of older age.
Carrying one faulty BLM copy is not the same as having Bloom syndrome. Carriers do not have the condition.What families notice
What are the signs of Bloom syndrome?
The signs usually appear in infancy and early childhood. No single sign proves the diagnosis. It is the combination that makes a doctor think of it.
Small size from before birth
Babies are small in the womb and stay small, but in proportion. The head is often narrow and small. Growth hormone does not usually change final height.
A rash on the face after sun
A red rash often appears across the cheeks and nose after time in the sun, sometimes in a butterfly shape. It can also affect the backs of the hands.
Frequent infections
The immune system is often weaker than normal. Ear and chest infections can be common in childhood and should be treated promptly.
Also seen
- A high-pitched voice
- Patches of lighter or darker skin
- Feeding difficulties in infancy
Later in life
Diabetes can develop earlier than usual. Men are usually unable to father children, and women often have reduced fertility and an early menopause.
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Ask an oncologistHow care is organised
What does looking after someone with Bloom syndrome involve?
Confirming the diagnosis
A blood test looks for the tell-tale pattern of DNA swapping in cells, and a gene test confirms two faulty BLM copies. Both parents are then usually offered carrier testing.
Watching closely in early childhood
Regular abdominal ultrasound is often advised in the early years to look for a kidney tumour. Ultrasound uses no radiation, which is why it is preferred.
Starting bowel checks young
Bowel checks usually begin in late childhood or the early teens, far earlier than for anyone else, because bowel cancer can appear young.
Breast checks in women
Breast MRI is used from early adult life, rather than mammograms, to limit radiation exposure.
Protecting against radiation and harsh treatment
X-rays and CT scans are kept to a minimum. If cancer does develop, chemotherapy and radiotherapy are planned carefully, often at lower doses, because the body is unusually sensitive to them.
Words you will hear
The terms used about Bloom syndrome, in plain language
- BLM gene
- The instruction for a protein that untangles DNA during copying and repair. It belongs to a family called RecQ helicases.
- Recessive
- A condition that appears only when both copies of a gene are faulty. One faulty copy alone does not cause it.
- Carrier
- Someone with one faulty copy and one working copy. Carriers are healthy and do not have Bloom syndrome.
- Biallelic
- Both copies of the gene are faulty. This is what causes the syndrome.
- Sister chromatid exchange test
- A laboratory test that counts how often DNA strands swap pieces. The count is very high in Bloom syndrome.
- Consanguinity
- Parents who are related by blood, such as cousins or an uncle and a niece. It raises the chance of a recessive condition.
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Side by side
Bloom syndrome or a BLM carrier: what is the difference?
Bloom syndrome
BLM carrier
Two faulty copies of BLM
One faulty copy and one working copy
Small size, sun rash and infections from childhood
No signs, usually healthy
Greatly raised risk of many cancers at young ages
Any raised risk is unclear, studies disagree
Specialist surveillance from infancy
Screening guided by the family history
Being straight with you
What this page cannot tell you
It cannot diagnose Bloom syndrome in your child. A small baby with a rash is far more likely to have something common. The diagnosis needs a paediatrician or clinical geneticist, and a specific test. What your specific variant means is a question for the counsellor who ordered the test.
It cannot give a surveillance timetable
Bloom syndrome is rare, and the guidance comes from a small number of families followed over many years, mostly outside India. Studies so far are small. A specialist team sets the timing for each child, and it changes as the child grows.
Who this does not apply to
Most families do not need to think about Bloom syndrome at all. It is rare, and it is recognised by its signs in childhood. If you are a healthy adult carrier of one BLM fault, this page describes your relative's condition, not your own. Tumour testing to guide treatment is a different test, covered under targeted therapy.
Commonly believed
Four things families tell us, and what is actually true
"Nobody in our family has this, so it cannot be genetic."
Carriers are healthy, so the fault can pass silently through many generations. It often appears for the first time when two carriers have a child together.
"Our child is small because we did not feed her well."
The small size in Bloom syndrome starts before birth and is part of the condition. It is not caused by feeding or anything the parents did.
"More scans are always safer."
In Bloom syndrome, X-rays and CT scans carry extra risk because the cells repair radiation damage poorly. Ultrasound and MRI are preferred wherever they can do the job.
"If we have one affected child, the next will be affected too."
Each pregnancy has the same one-in-four chance. Many brothers and sisters of an affected child are unaffected, and some are healthy carriers.
Questions we are asked
Common questions about Bloom syndrome
Which cancers are linked to Bloom syndrome?
Many types. Leukaemia and lymphoma can appear in childhood and early adult life. Cancers of the bowel, breast, skin, mouth and throat can appear decades earlier than usual. Some children develop a kidney tumour. A specialist team explains the pattern for each person.
How is Bloom syndrome diagnosed?
A doctor usually suspects it from the combination of small size, a sun-sensitive facial rash and frequent infections. A blood test showing very frequent DNA swapping supports it, and a gene test finding two faulty BLM copies confirms it. Parents are then offered carrier testing.
We are cousins. Should we be tested before having children?
Being related raises the chance of any recessive condition, not Bloom syndrome in particular. Testing for BLM alone is not routine unless it is already known in the family. A counsellor can look at your family tree and explain which tests, if any, make sense.
If we already have an affected child, what are our options next time?
Once both parents' faults are known, testing is possible during a future pregnancy, or embryos can be tested through IVF. These choices are personal and sometimes difficult. A genetic counsellor can explain each option in Telugu, with no pressure either way.
Is Bloom syndrome treatable?
The gene fault cannot be corrected or reversed. Care focuses on growth, nutrition, treating infections, checking for diabetes and finding cancer early. If cancer develops, it is treated, with doses adjusted for the body's sensitivity to chemotherapy and radiation.
Do BLM carriers need extra cancer screening?
Usually not on the basis of the gene alone. Some studies suggested a small raised bowel cancer risk in carriers and others did not. Carriers are generally screened according to their family history. Your counsellor can say whether anything extra applies to you.
Why are X-rays and CT scans avoided?
Cells in Bloom syndrome cannot repair radiation damage well, so each dose may add to cancer risk. That does not mean a needed X-ray should be refused in an emergency. It means doctors choose ultrasound or MRI whenever either can answer the question.
Who should look after a child with Bloom syndrome?
A team, usually led by a paediatrician or clinical geneticist, with input from oncology, endocrinology and dermatology. Families from districts often travel to Hyderabad for the specialist reviews and keep routine care close to home.
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) — Bloom Syndrome
- MedlinePlus Genetics — Bloom syndrome
- MedlinePlus Genetics — BLM gene
- 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
BLM, WRN and RECQL4: which cancers and what riskHow Bloom compares with the two related syndromesRothmund-Thomson syndrome and osteosarcoma riskThe RECQL4 condition, explained the same wayTesting the family for BLM, WRN and RECQL4Carrier testing for parents and siblingsConsanguinity and cancer riskWhy marriage between relatives matters for recessive genes
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Worried about Bloom syndrome in your family?
Tell us about the signs and the family history. We will help you reach a genetics team who can explain what testing would and would not show. One helpline serves every CION centre.