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The SDHx genes: what they do and why they matter | CION Cancer Clinics
The SDHx genes are five related genes, SDHA, SDHB, SDHC, SDHD and SDHAF2, that together build a machine your cells use to make energy. A fault present from birth raises the risk of rare tumours called paragangliomas and phaeochromocytomas, and a few others. This page explains what the genes do, how a fault leads to a tumour, and what a result means for a family. 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 do the SDHx genes actually do?
- How are the five SDHx genes different from each other?
- How does a faulty SDHx gene lead to a tumour?
- The words you will meet, in plain language
- What does a result change, and what does it not?
- Four things families tell us, and what is actually true
- What this page cannot tell you
- Common questions about the SDHx genes
The short answer
What do the SDHx genes actually do?
The SDHx genes carry the instructions for one small machine inside your cells, called succinate dehydrogenase, or SDH. That machine sits in the mitochondria, the parts of the cell that turn food into energy. When one of the genes is faulty from birth, the risk of certain rare tumours goes up.
Five genes, one machine
SDHA, SDHB, SDHC and SDHD each make one of the four parts of the machine. SDHAF2 makes a helper that fits the SDHA part into place. A fault in any one of the five can stop the whole machine working inside a cell. That is why doctors group them together as the SDHx genes.
Why a broken machine can cause a tumour
When the machine stops, a chemical called succinate builds up inside the cell. High succinate tricks the cell into behaving as if it were short of oxygen. The cell switches on signals that tell it to grow and to build new blood vessels. In certain tissues, that false alarm can slowly lead to a tumour.
Carrying an SDHx fault is not a diagnosis. It is a statement about risk that can be watched.Not all the same
How are the five SDHx genes different from each other?
They build the same machine, but a fault in each one behaves differently. Knowing the exact gene shapes every plan that follows.
SDHB
Tumours are more often found in the abdomen, chest or pelvis than in the neck. They are more likely than other SDHx tumours to spread, which is why SDHB carriers are usually watched most closely.
Also linked with
- A rare kind of kidney cancer
- A rare stomach tumour called GIST
SDHD and SDHAF2
Tumours most often grow in the head and neck, and several can appear in one person. These two genes carry a twist: tumours usually develop only when the fault was inherited from the father.
A fault from the mother can still be passed on to your own children.SDHC
Faults are less common. Tumours are mostly found in the head and neck, and the risk of any tumour appearing is lower than with SDHB or SDHD. Studies so far are smaller, so the picture is less certain.
SDHA
Faults are found more often than people expected, but most carriers never develop a tumour. Many are found in people with no family history at all.
Worth knowing
- Risk estimates are still being refined
- When parents are related by blood, ask the counsellor about a child inheriting two faulty copies
Not sure whether this applies to you?
Ask an oncologistFrom fault to tumour
How does a faulty SDHx gene lead to a tumour?
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You inherit one faulty copy
Everyone has two copies of each SDHx gene, one from each parent. A carrier is born with one faulty copy in every cell of the body.
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One working copy is usually enough
The remaining copy keeps the energy machine running. Most cells behave normally for years, and many carriers never notice anything at all.
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The second copy is lost in one cell
By chance, the working copy can be damaged in a single cell. That cell now has no working machine, and succinate starts to build up inside it.
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The cell grows, and may make hormones
Nerve-related tissue called paraganglia is most sensitive to this. Tumours there can release adrenaline-like hormones that raise the blood pressure and make the heart race.
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Which is why risk is not certainty
The inherited fault only supplies the first step. Whether the second step ever happens is partly chance, which is why relatives with the same fault can have very different lives.
On your report
The words you will meet, in plain language
- Paraganglioma
- A tumour of nerve-related tissue found along the neck, chest, abdomen or pelvis. Most grow slowly and are not cancer, but some can spread.
- Phaeochromocytoma
- The same kind of tumour when it grows inside the adrenal gland, which sits on top of the kidney.
- Succinate
- A natural chemical the SDH machine normally clears. When it builds up, the cell acts as if it is starved of oxygen.
- Metanephrines
- Breakdown products of adrenaline-like hormones. A blood or urine test for them shows whether a tumour is releasing hormones.
- Germline
- Present in every cell from birth, and therefore inheritable. A fault found only inside a tumour is called somatic.
- Parent-of-origin effect
- When the risk depends on which parent passed the fault on. It applies to SDHD and SDHAF2.
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Side by side
What does a result change, and what does it not?
An SDHx fault is found
No fault is found
Regular hormone tests and scans are planned
Routine care for age and background applies
Relatives can be tested for that exact fault
Relatives are guided by the family history
Checks may start in childhood
Children need no special checks for this
Surgeons plan with hormone levels in mind
Any tumour is planned on its own features
Commonly believed
Four things families tell us, and what is actually true
"It is an energy gene, so eating better will fix it."
The fault is written into the gene and cannot be corrected by diet, tonics or supplements. What helps is finding any tumour early through planned checks.
"My father has no tumour, so it cannot have come from him."
Many carriers never develop a tumour. With SDHD, a father may have inherited the fault from his own mother and stayed well, yet his children who inherit it carry the full risk.
"A paraganglioma is always cancer."
Most are slow-growing and do not spread. Some do, especially with SDHB. That uncertainty is exactly why carriers are watched rather than left alone.
"A fault in the tumour means the whole family carries it."
A change found only in the tumour may not be inherited at all. A separate blood test answers that question, and it is the only one relatives should rely on.
Being straight with you
What this page cannot tell you
It cannot tell you what your own result means. The exact gene, the exact spelling change, which parent it came from and whether you have already had a tumour all change the picture. What your specific variant means is a question for the counsellor who ordered the test.
The evidence is still growing
These tumours are rare, so studies are small and risk figures differ between them. Estimates for SDHA and SDHC in particular are still shifting. A good counsellor will say plainly where the evidence is thin rather than quote a confident number.
Who this does not apply to
Most people do not need SDHx testing. It is usually offered after a paraganglioma, a phaeochromocytoma, a certain type of stomach or kidney tumour, or a known fault in a relative. Testing a tumour to choose a treatment is a different test, covered under targeted therapy.
If you are unsure whether your family history counts, call the helpline and describe it before paying for any test.Questions we are asked
Common questions about the SDHx genes
Is a paraganglioma a cancer?
Most paragangliomas are slow-growing and stay in one place. A minority spread to other parts of the body, and there is no reliable way to tell from a first scan which ones will. That is why they are treated seriously and followed up for life.
Can I pass an SDHx fault to my children?
Yes. Each child has an even chance of inheriting it, whether you are the mother or the father. With SDHD and SDHAF2, a child who inherits it from the mother is at much lower risk, but can still pass it on later.
Why was I tested after only one tumour?
A meaningful share of paragangliomas and phaeochromocytomas are linked to an inherited fault, even in people with no family history. For that reason, many guidelines suggest offering genetic testing to everyone diagnosed with one.
What symptoms should a carrier watch for?
Attacks of pounding heartbeat, sweating and headache, or blood pressure that is high and hard to control. A lump in the neck, ringing in one ear or a change in the voice can come from a head and neck tumour. Report any of these to your team promptly.
Are the SDHx genes the same as VHL or RET?
No. VHL, RET, NF1, MAX and TMEM127 are other genes that can also cause these tumours. Most laboratories test them together in one panel, because the tumour type alone rarely points to a single gene.
Does a fault found in my tumour mean I carry it?
Not always. A tumour can lose its SDH machine through changes that arose only inside it. A blood test for the inherited fault is needed before relatives are told they may be at risk.
Can lifestyle changes lower the risk?
No habit is known to prevent these tumours. Keeping blood pressure checked, attending every planned test and telling any doctor who treats you that you carry the fault are the things that genuinely make a difference.
Where can this testing be done in Hyderabad?
Testing is ordered through a genetic counsellor or an oncologist and sent to an accredited laboratory. The sample is a simple blood draw. Call the CION helpline and someone will explain how to arrange counselling, including in Telugu.
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) — Hereditary Paraganglioma-Pheochromocytoma Syndromes
- MedlinePlus Genetics — Hereditary paraganglioma-pheochromocytoma
- MedlinePlus Genetics — SDHB gene
- National Cancer Institute — Pheochromocytoma and Paraganglioma Treatment (PDQ) – Patient Version
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
SDHx faults: which cancers and what riskWhich tumours each gene is linked withWhy SDHB carries the highest risk of spreadWhy one gene is watched more closely than the restMaternal imprinting in SDHDWhy the parent it came from changes the riskTesting the family for SDHxWho should be tested, and in what order
Talk to us
Have you been told an SDHx gene is involved?
Tell us what the report says and who in your family has had a tumour. We will help you reach a genetic counsellor who can explain it properly. One helpline serves every CION centre.