Medical Oncologist
CION Cancer Clinics
Testing the family after a TSC1 or TSC2 result | CION Cancer Clinics
When someone is diagnosed with tuberous sclerosis, the parents and the brothers and sisters are usually offered a check, even if they seem completely well. Many cases arise new in the child, but mild signs in a parent are easily missed. Where the exact TSC1 or TSC2 fault is known, relatives can have a simple blood test for it. This page explains who is tested, in what order, and what each answer means. 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
- Who in the family should be checked for tuberous sclerosis?
- Who is offered a check, and what does it involve?
- In what order does the family get tested?
- The words you will meet, in plain language
- What the parents' result means for everyone else
- Four things families tell us, and what is actually true
- What this page cannot tell you
- Common questions about testing the family for TSC1 and TSC2
The short answer
Who in the family should be checked for tuberous sclerosis?
Start with the parents of the person who has tuberous sclerosis, even if they seem completely well. If a parent turns out to carry the TSC1 or TSC2 fault, their other children should be checked next. Anyone who carries it has a one in two chance of passing it to each of their own children.
Why parents who seem well are still checked
Tuberous sclerosis can be so mild that an adult has never been told they have it. A few pale patches on the skin, small bumps near the nails or quiet kidney growths are easy to miss for a lifetime. Finding them in a parent changes the answer for every brother and sister, and gives that parent their own kidney checks.
Why most children have no affected parent
In about two in every three families, the fault appeared for the first time in the child. Nobody passed it on and nobody did anything to cause it. In those families, the parents do not carry it and the brothers and sisters are very unlikely to have it.
Checking the parents is not about blame. It is the quickest way to find out who else needs care.Relative by relative
Who is offered a check, and what does it involve?
The check depends on whether the exact gene fault has been found in the person with tuberous sclerosis.
Parents
A blood test for the family's exact fault if it is known. Doctors also look for mild signs, because a parent can carry the fault in only some cells.
The check may include
- A skin examination under an ultraviolet lamp
- An eye examination
- A kidney scan
- Sometimes a brain MRI
Brothers and sisters
If a parent carries the fault, each sibling has a one in two chance. They are tested for the exact fault, usually in childhood, because early knowledge helps with seizures and scans.
Children of an affected adult
Each child has a one in two chance, with every pregnancy. A baby can be tested soon after birth, and some signs show on scans before birth.
Wider relatives
Aunts, uncles and cousins only need checking if a parent is found to carry the fault. Testing then moves out along that side of the family, one branch at a time.
Not sure whether this applies to you?
Ask an oncologistStep by step
In what order does the family get tested?
Find the fault in the person affected
The first test looks at both TSC1 and TSC2 in the person with tuberous sclerosis. Knowing their exact fault makes every later test simpler and cheaper.
Check both parents
Each parent has a blood test for that one fault, plus an examination for mild signs. Both parents are checked, not only the mother.
Test siblings if a parent carries it
Brothers and sisters are offered the same single-fault test. Those who test negative need no tuberous sclerosis checks.
Plan ahead for future pregnancies
Once the family fault is known, testing in pregnancy or before pregnancy can be discussed. This applies even when both parents test negative.
On your report
The words you will meet, in plain language
- De novo
- A gene fault that appeared for the first time in this person. It was not inherited from either parent.
- Mosaicism
- When a fault is present in only some of a person's cells. A mosaic parent may have very mild signs, or none, and a blood test can miss it.
- Cascade testing
- Testing relatives one step at a time, starting closest to the person affected and moving outward.
- Targeted test
- A test that looks only for the one fault already found in the family. It is quicker and cheaper than testing the whole gene.
- No mutation identified
- Someone clearly has tuberous sclerosis, but no fault was found in TSC1 or TSC2. Relatives are then checked by examination and scans instead.
- Preimplantation testing
- Testing embryos made by IVF for the family fault before one is placed in the womb.
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Side by side
What the parents' result means for everyone else
A parent carries the fault
Neither parent carries it
Each child has a one in two chance
The fault most likely arose new in the child
Siblings should be tested
Siblings' chance is small, though not zero
That side of the wider family can be offered testing
Wider relatives do not usually need testing
That parent needs their own kidney checks
Parents need no tuberous sclerosis checks
Testing in future pregnancies can be offered
Testing can still be offered, for reassurance
Commonly believed
Four things families tell us, and what is actually true
"It must have come from the mother's side."
A fault can come from either parent, and most often it comes from neither. Blaming one side is unfair and usually wrong. It can also stop the right person being checked.
"Both of us tested negative, so the next baby is completely safe."
The chance is much lower, but not zero. Rarely, a parent carries the fault only in some egg or sperm cells, which a blood test cannot see. Testing in a later pregnancy can be discussed for this reason.
"A test will tell us how badly our other child will be affected."
It will not. Two siblings with the same fault can be affected very differently. The test tells you who needs surveillance, not how severe it will be.
"Because we are cousins who married, our risk is higher."
Tuberous sclerosis needs only one faulty copy, from one parent. A cousin marriage does not change the chance of passing it on, though it can matter for other inherited conditions.
Being straight with you
What this page cannot tell you
It cannot tell you whether a particular relative is affected, or what a result in your family means. What your specific variant means is a question for the counsellor who ordered the test. They can also help you decide how to tell each relative.
Who this does not apply to
If a TSC1 or TSC2 change was found only in a tumour sample, for example in bladder or kidney cancer, that is not tuberous sclerosis and relatives do not need testing. That kind of result is covered under targeted therapy. A variant of uncertain significance is also not a reason to test relatives.
The conversations that are hard in India
Families often worry about marriage prospects, or about a daughter-in-law being blamed. Keeping a diagnosis from a brother or sister means they may miss checks they need. How and when to tell them is your decision, and a counsellor can help find the words, in Telugu if you prefer.
Insurance
India has no specific law protecting people from genetic discrimination. Raise it with your counsellor before relatives are tested.
Questions we are asked
Common questions about testing the family for TSC1 and TSC2
Should our other children be tested even if they seem well?
If a parent carries the fault, yes, and usually in childhood. Unlike many inherited cancer genes, tuberous sclerosis can cause problems early, such as seizures, and knowing helps you act quickly. If neither parent carries it, the chance for siblings is small.
What if no gene fault was found in our child?
Some people clearly have tuberous sclerosis but no fault is found by standard tests. Relatives are then checked by examination and scans rather than a blood test. Ask whether a more detailed test on another tissue, such as a skin growth, might find it.
Is the test for a relative cheaper than the first test?
Usually, yes. Once the exact fault is known, a relative can have a targeted test for that one change, which is simpler than reading both genes. Ask the laboratory for a family variant test and bring a copy of the original report.
Can tuberous sclerosis be tested for in pregnancy?
If the family fault is known, a sample can be tested during pregnancy. Some signs, such as heart growths, can also show on a pregnancy scan. Testing embryos made by IVF is another option. Discuss these before pregnancy if you can, so there is time to decide.
Why is my husband being examined when our child's test was positive?
Because the fault can come from either parent. Checking only the mother is a common mistake and can miss a father who carries it. Both parents are examined and tested in the same way, without blame on either.
Does a positive parent need treatment?
Not treatment, but checks. An adult found to carry the fault through their child needs the adult surveillance plan, especially kidney scans and blood pressure checks. Women are also offered lung checks. Many such adults have been well all their lives.
Do grandparents need to be tested?
Only if a parent is found to carry the fault. Then the grandparents on that side, and their other children, can be offered testing to find where the fault came from. If neither parent carries it, grandparents do not need testing.
Who should tell relatives about the result?
Usually the person tested or their parents, since doctors cannot contact relatives without permission. A counsellor can write a short family letter explaining the fault and what testing involves. Relatives can then take it to their own doctor.
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) — Tuberous Sclerosis Complex
- MedlinePlus Genetics — Tuberous sclerosis complex
- NHS — Tuberous sclerosis
- 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
TSC1 and TSC2 positive: what happens nextWhat a relative who tests positive should expectSurveillance for TSC1 and TSC2 carriersThe checks a positive relative will needTSC1 and TSC2 mutation: which cancers and what riskWhat a positive result actually means for healthThe TSC1 and TSC2 genes explainedHow the genes work and how faults are passed on
Talk to us
Not sure who in the family should be checked?
Tell us who has been diagnosed and what the report says. We will help you work out which relatives to check first and arrange counselling, in Telugu if you prefer. One helpline serves every CION centre.