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The RUNX1 gene: what it does and why it matters | CION Cancer Clinics
RUNX1 is a gene that works like a master switch in the bone marrow. It tells young blood cells when to mature, and the cells that make platelets depend on it most. An inherited fault in RUNX1 usually causes a mildly low platelet count and easy bleeding, and it raises the lifetime risk of leukaemia. This page explains what the gene normally does and what changes when it is faulty. 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
- What does the RUNX1 gene actually do?
- What changes in someone who inherits a RUNX1 fault?
- Why does a RUNX1 fault not mean leukaemia is certain?
- The words you will meet, in plain language
- Inherited RUNX1 fault or one found only in leukaemia cells?
- Four things families tell us, and what is actually true
- What this page cannot tell you
- Common questions about the RUNX1 gene
The short answer
What does the RUNX1 gene actually do?
RUNX1 is a switch gene in the bone marrow. It does not build any part of a blood cell itself. It turns other genes on and off, so young blood cells mature in the right order and stop dividing when they should.
A switch, not a building block
The RUNX1 protein sits on the cell's DNA and works with a partner protein to decide which instructions get read. Without it, the very first blood-forming stem cells do not develop properly before birth. After birth it keeps guiding those stem cells as they grow into red cells, white cells and platelets.
Why platelets feel it first
Platelets are the small cell fragments that plug a cut. They are made by large bone marrow cells called megakaryocytes, and these cells depend heavily on RUNX1. When one copy of the gene is faulty, the platelets are often fewer than normal and the ones that are made may not stick together well.
Why it matters for leukaemia
RUNX1 also acts as a brake on uncontrolled growth in the marrow. A faulty copy leaves that brake weaker from birth. This is why people who inherit a RUNX1 fault have a raised lifetime risk of leukaemia and related marrow cancers.
An inherited RUNX1 fault is a statement about risk. It is not a diagnosis of leukaemia.When the switch is faulty
What changes in someone who inherits a RUNX1 fault?
Doctors call the inherited condition RUNX1 familial platelet disorder. It shows itself in four ways, and not every carrier has all of them.
Platelets that are too few
The platelet count is usually mildly or moderately low, and it stays that way for life. Doctors call this thrombocytopenia, meaning a low platelet count. Some carriers have a normal count.
Platelets that do not work well
Even when the count looks fine, the platelets may not clump properly. That can mean more bleeding than the count suggests.
Often looks like
- Easy bruising
- Nosebleeds or bleeding gums
- Heavy periods
- Bleeding after a tooth extraction or surgery
A raised risk of blood cancer
The main concern is acute myeloid leukaemia and myelodysplastic syndrome, a marrow cancer that can turn into leukaemia. It can appear in childhood or much later in adult life.
Many carriers feel entirely well
Plenty of carriers have mild bruising they never noticed and never develop leukaemia. Some families also report eczema or other skin problems, but studies so far are small.
Not sure whether this applies to you?
Ask an oncologistFrom fault to leukaemia
Why does a RUNX1 fault not mean leukaemia is certain?
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You start with one working copy
Everyone has two copies of RUNX1. A carrier is born with one faulty copy in every cell. The other copy still works, so the marrow runs, just less smoothly.
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The platelet effect shows early
Because platelet-making cells are sensitive to RUNX1, a low or poorly working platelet count is often present from childhood. Many families simply think they bruise easily.
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Extra faults build up in marrow cells
Over the years, individual marrow cells pick up further faults. In carriers this happens more readily, and often one of the new faults hits the second copy of RUNX1 itself.
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One group of cells can take over
A cell with enough faults can outgrow its neighbours. A sensitive blood test can sometimes spot this growing group before the blood count changes.
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Only some carriers reach leukaemia
Whether that final step happens is partly chance. That is why two brothers with the same fault can have very different lives.
On your report
The words you will meet, in plain language
- Germline
- Present in every cell from birth, and so it can be passed to a child. This is what an inherited RUNX1 fault is.
- Somatic
- Found only inside the leukaemia cells and picked up during life. It cannot be passed on.
- Megakaryocyte
- The large bone marrow cell that breaks up into platelets. It is the cell most affected by a RUNX1 fault.
- Myelodysplastic syndrome
- A marrow cancer where blood cells are made badly. It is often shortened to MDS and can progress to leukaemia.
- Clonal haematopoiesis
- A group of blood cells that all share a new fault and are growing faster than the rest. It is a warning sign, not leukaemia.
- Pathogenic variant
- A spelling change in the gene that is known to break it. This is what a positive result means.
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Side by side
Inherited RUNX1 fault or one found only in leukaemia cells?
Inherited fault
Fault in leukaemia cells only
In every cell, from birth
Only in the cancer cells
Children and siblings may carry it
Relatives are not affected
Confirmed on a skin or hair sample
Found on a marrow or blood sample
Changes which relative can donate stem cells
Guides the treatment of this leukaemia
Commonly believed
Four things families tell us, and what is actually true
"Low platelets run in our family, so it is nothing serious."
A lifelong low platelet count shared by several relatives is exactly the pattern that should prompt a RUNX1 question. It is often labelled as an immune platelet problem and treated with steroids that do not help.
"If my leukaemia report mentions RUNX1, my children are at risk."
Not necessarily. RUNX1 faults are common inside leukaemia cells and are usually not inherited. Only a test on a non-blood sample, such as skin, can tell the two apart.
"A carrier will certainly get leukaemia."
The risk is raised, well above the general population, but it is not certain. Many carriers never develop a blood cancer.
"Nobody else had leukaemia, so this cannot be inherited."
Relatives may carry the fault and show only bruising or a slightly low count. A fault can also appear for the first time in one person.
Being straight with you
What this page cannot tell you
It cannot tell you whether your family carries a RUNX1 fault, or what a specific variant on your report means. What your specific variant means is a question for the counsellor who ordered the test, working with a haematologist who knows this condition.
It cannot give you a personal risk figure
Leukaemia risk differs between families and between variants. Studies so far are small, and published figures come from a limited number of families, most of them outside India. Your haematologist will explain what is known for your situation and what is still uncertain.
Who this does not apply to
Most people with a low platelet count do not have a RUNX1 fault. Infections, medicines, immune causes and liver disease are far more common reasons. Most people do not need this test. It is usually considered when low platelets or bleeding run through a family, or when leukaemia appears alongside that pattern.
If your family has bruising, low platelets and a blood cancer on one side, write down who and at what age before your appointment.Questions we are asked
Common questions about the RUNX1 gene
Is RUNX1 a cancer gene?
It is a normal gene that everyone has. It guides blood cell development and helps keep growth in check. It becomes linked to cancer only when it is faulty, either inherited from birth or picked up inside leukaemia cells during life.
How is an inherited RUNX1 fault passed on?
It follows a dominant pattern. Each child of a carrier has a one in two chance of inheriting it, whether the carrier is the mother or the father. Sons and daughters are equally likely to inherit it.
What kind of leukaemia is linked to RUNX1?
Mostly acute myeloid leukaemia and myelodysplastic syndrome, both of which start in the bone marrow cells that make red cells, platelets and some white cells. A smaller number of families have had lymphoid leukaemia or lymphoma.
Can a normal platelet count rule it out?
No. Some carriers have a normal count but platelets that do not work properly. Special platelet function tests can show this, but only a genetic test settles the question. Your haematologist will decide whether testing makes sense.
Why does my leukaemia report mention RUNX1?
Leukaemia panels look for faults inside the cancer cells, and RUNX1 is one of the genes they check. Most such faults are not inherited. Tumour testing of this kind is covered on our targeted therapy pages rather than here.
Does RUNX1 affect any organ other than blood?
The main effects are on platelets and the bone marrow. Some families report eczema or other skin conditions, and a few studies suggest other links. The evidence is still thin, so ask your doctor before assuming any symptom is related.
Can anything be done to fix the gene?
An inherited fault cannot be corrected or reversed today. What helps is knowing about it. Bleeding can be planned for, blood counts can be watched, and early marrow changes can be acted on before leukaemia is advanced.
Is counselling available in Telugu?
Yes. The family history conversation and the explanation of results can be done in Telugu, and relatives can join the call from their districts. Bring any old blood count reports you have, especially from other family members.
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) — RUNX1 Familial Platelet Disorder with Associated Myeloid Malignancies
- MedlinePlus Genetics — RUNX1 gene
- National Cancer Institute (PDQ) — RUNX1-Familial Platelet Disorder (PDQ)
- 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
RUNX1 mutation: which cancers and what riskWhat a carrier's leukaemia risk actually looks likeFamilial platelet disorder with leukaemia riskThe condition a RUNX1 fault causes, explained in fullTesting the family for RUNX1Who should be tested once a fault is foundLow platelets running in a familyWhen a family pattern of low platelets is worth checking
Talk to us
Low platelets or leukaemia running in your family?
Tell us who was affected and at what age, and we will tell you honestly whether a genetic referral makes sense. If it does, we will arrange it with a haematologist. One helpline serves every CION centre.