Medical Oncologist
CION Cancer Clinics
The xeroderma pigmentosum genes: what they do and why it matters | CION Cancer Clinics
The xeroderma pigmentosum genes repair the damage sunlight does to DNA in skin and eye cells. A child who inherits a faulty copy of the same gene from both parents cannot make that repair, so sun damage builds up and skin cancers can start in childhood. This page explains what the genes do, how the different ones compare, and why early sun protection matters so much. At CION Cancer Clinics, our oncologists explain what a gene result means for you and your family, and plan the checks that follow.
NG
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
17+specialists on panel
15,000+patients treated
35+centres across Telangana & AP
4.8★ / 800+Google rating
On this page
- What do the xeroderma pigmentosum genes actually do?
- Which genes cause XP, and how do they differ?
- How does sun damage turn into cancer when repair fails?
- The words you will meet, in plain language
- Working repair genes compared with XP
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about the XP genes
The short answer
What do the xeroderma pigmentosum genes actually do?
The xeroderma pigmentosum genes, usually shortened to XP genes, repair the damage that sunlight does to DNA in skin cells. Every time skin is out in daylight, ultraviolet light bends and kinks small stretches of DNA. These genes find the kink, cut it out and patch the gap.
What happens when the repair team is missing
A child who inherits a faulty copy of the same XP gene from both parents cannot repair that damage properly. The kinks stay in the DNA. Each one can become a spelling mistake the next time the cell divides, and those mistakes build up far faster than in other children. That is why skin cancers can appear in childhood rather than in old age.
Why this matters to the family
Knowing which gene is faulty explains what the child is facing, whether the nerves and hearing may also be affected, and which relatives can be tested for the same fault. It also means brothers and sisters can be checked early, while sun protection can still make the biggest difference.
One faulty copy does not cause XP. It takes two, one from each parent.One condition, several genes
Which genes cause XP, and how do they differ?
XP is not one gene. Several genes share the repair job, and a fault in any one of them can cause the condition. Which one it is shapes the picture.
The damage spotters
XPC and DDB2, also called XPE, scan the whole of the DNA looking for kinks and flag them for repair. Children with faults here often freckle early but may not burn badly, so the condition can be missed for a while.
The unwinders and cutters
XPA, ERCC3, ERCC2, ERCC4 and ERCC5 open up the damaged stretch and snip it out. Some of these genes also protect nerve cells, which is why certain groups develop problems with nerves and hearing.
On a report these may appear as
- XPA, XPB, XPD, XPF or XPG
- Or their ERCC gene names
The copier
POLH lets a cell copy its DNA accurately past damage that has not yet been fixed. A fault here causes the XP variant form, which often shows itself later in childhood or even in adult life.
Same genes, other conditions
A few of these genes can cause different conditions, such as Cockayne syndrome or trichothiodystrophy, depending on the exact fault. These bring sun sensitivity without the same skin cancer risk. The report names which one applies.
Not sure whether this applies to you?
Ask an oncologistFrom daylight to a skin cancer
How does sun damage turn into cancer when repair fails?
-
Ultraviolet light reaches a skin cell
This happens to everyone, every day, including through window glass and on cloudy days. The light causes small kinks in the DNA of exposed skin and the surface of the eyes.
-
Normally, the kink is found and removed
In most people the XP genes cut out the damaged stretch and rebuild it, usually before the cell next divides. The cell carries on as normal and no mistake is left behind.
-
With XP, the kink stays put
When both copies of one XP gene are faulty, the repair is slow or does not happen. The damage sits in the DNA and builds up with every hour outdoors.
-
Copying errors become permanent mistakes
When the cell divides, it misreads the kinked stretch. The mistake is passed to every daughter cell. Some mistakes land in genes that control growth.
-
Which is why protection works
Every hour of ultraviolet light that is blocked is damage that never has to be repaired. This is why strict sun protection is the main treatment, and why starting it early matters so much.
On your report
The words you will meet, in plain language
- Xeroderma pigmentosum
- The name of the condition. It roughly means dry, freckled skin, which describes how it often first looks in a young child.
- Nucleotide excision repair
- The cut-and-patch repair system the XP genes run. It removes a damaged stretch of DNA and rebuilds it using the healthy strand.
- Complementation group
- An older way of sorting XP by which part of the repair team is missing. Group A matches the XPA gene, group C the XPC gene, and so on.
- Autosomal recessive
- A pattern where a person is affected only if both copies of the gene are faulty. Parents are usually healthy carriers.
- Carrier
- Someone with one faulty copy and one working copy. A carrier does not have XP and does not need sun protection beyond the ordinary.
- Biallelic
- Both copies of the gene carry a fault. This is the finding that confirms XP on a genetic report.
Leave a number, we will call you
One field. No form to fill in, and no charge for the call.
Side by side
Working repair genes compared with XP
Repair genes working
Both copies faulty (XP)
Sun damage is cleared from skin cells
Sun damage stays and builds up
Skin cancer is mostly a disease of later life
Skin cancer can begin in childhood
Eyes tolerate ordinary daylight
Eyes are light-sensitive and need shielding
Nerve cells are unaffected
Some gene groups also affect nerves and hearing
Being straight with you
What this page cannot tell you
It cannot tell you what your child's particular result means. The same gene can cause mild or severe disease depending on the exact fault, and whether nerves are likely to be affected depends on the gene and the variant together. What your specific variant means is a question for the counsellor who ordered the test.
It cannot predict the future of one child
XP is rare, and much of what is known comes from small groups of patients followed abroad. Studies from India are few. Two children with the same gene can do very differently, largely because of how early and how strictly sun protection began.
Who this does not apply to
Most people who burn easily, freckle, or develop a skin cancer in later life do not have XP. Parents and relatives who carry one faulty copy do not have it either. XP is a rare childhood condition, and a dermatologist or clinical geneticist can usually tell quickly whether it is worth testing for.
Somatic testing of a skin tumour is a different question. It looks at the cancer, not at what was inherited.Commonly believed
Four things families tell us, and what is actually true
"Neither of us has any skin problem, so it cannot be inherited."
Parents of a child with XP are almost always healthy carriers. Each has one faulty copy and one working copy, which is enough. The condition only appears when a child inherits the faulty copy from both.
"Dark skin protects against XP."
Darker skin blocks some light, but it cannot replace a missing repair gene. Children with XP in India develop freckling, eye damage and skin cancers too, and need the same strict protection.
"Staying indoors is enough protection."
Some ultraviolet light passes through ordinary window glass, and some indoor lamps give it off. Protection at home, in school and in the car all matter, not just time spent outside.
"It is a skin disease, so a skin cream will fix it."
The fault is in the DNA of every cell and cannot be corrected or reversed. Creams and procedures treat damage and early cancers. Blocking ultraviolet light is what prevents new damage.
Questions we are asked
Common questions about the XP genes
Is xeroderma pigmentosum a type of cancer?
No. It is an inherited condition that makes the skin and eyes unable to repair sunlight damage. That raises the chance of skin cancer sharply, often from childhood, but a child with XP does not have cancer simply because they have the condition. Close skin checks are how early cancers are caught.
Why did our child get XP when we are both healthy?
Because each of you most likely carries one faulty copy of the same gene, which causes no illness. Your child inherited the faulty copy from both of you. Nobody did anything to cause this, and it could not have been seen or prevented without testing beforehand.
Does it matter which XP gene is faulty?
Yes. The gene helps predict whether the child is likely to burn badly, whether nerves and hearing may be affected, and how early problems may begin. It also tells the laboratory exactly what to look for when brothers, sisters and other relatives are tested.
Are marriages within the family linked to XP?
They can be. When parents are related by blood, they are more likely to carry the same rare faulty gene inherited from a shared ancestor. This is why recessive conditions such as XP are seen more often in such families. It is a pattern of chance, not blame.
Can adults be diagnosed with XP?
Occasionally. The XP variant form and some milder types may not be recognised until several skin cancers appear in early adult life. Anyone with many skin cancers at an unusually young age should ask a dermatologist or geneticist whether an inherited repair problem has been considered.
Does XP only affect the skin?
No. The eyes are sensitive to light and the surface of the eye can be damaged, so eye checks matter. Some gene groups also affect nerves, hearing and development. A small raised risk of some cancers inside the body has also been reported, though the evidence is limited.
How is the diagnosis confirmed?
Usually with a genetic test on a blood sample, looking at the XP genes together as a panel. In some centres a skin sample is also tested to see how well the cells repair damage in the laboratory. A clinical geneticist will explain which test suits your child.
Where do we start if we think our child may have XP?
Start with a dermatologist who can look at the skin and eyes, and ask for a referral to a clinical geneticist. Begin strict sun protection now rather than waiting for a result. Call the CION helpline if you are unsure who to approach first.
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)
Medical Oncologist
Medical Oncologist
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
Sources
- GeneReviews (NCBI) — Xeroderma Pigmentosum
- MedlinePlus Genetics — Xeroderma pigmentosum
- National Cancer Institute — Genetics of Skin Cancer (PDQ) - Health Professional Version
- MedlinePlus Genetics — What are the different ways a genetic condition can be inherited?
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
XP genes: which cancers and what riskWhat the skin and eyes are watched forXeroderma pigmentosum: sun protection as treatmentThe daily routine that makes the biggest differenceTesting the family for the XP genesWhich brothers, sisters and relatives to testXP positive: what happens nextThe plan after the result comes back
Talk to us
Has a doctor mentioned XP for your child?
Tell us what the doctor said and what, if anything, the report shows. We will help you reach a genetics team who can explain it and plan the next steps. One helpline serves every CION centre.