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Childhood Cancer — Genetics & Risk Guide for Parents
Hereditary retinoblastoma & the RB1 gene — what a mutation means for your child and family
Medically reviewed by Dr. C. Raghavendra Reddy, DM (Medical Oncology, Gold Medal) · Last reviewed June 2026
If a doctor has mentioned the RB1 gene or told you that your child’s retinoblastoma may be hereditary, it is natural to feel overwhelmed by the questions this raises. What does the gene mutation actually mean? Could other children in the family be affected? What tests are needed, and for whom? This page answers those questions in plain language — honestly and without false reassurance — so that you can have informed conversations with your child’s medical team.
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RB1 gene retinoblastoma
Understanding the RB1 gene — the biology behind hereditary retinoblastoma genetics
Retinoblastoma is a cancer of the retina — the light-sensitive tissue at the back of the eye — that develops almost exclusively in very young children. At the centre of hereditary retinoblastoma is a single gene: RB1, which sits on chromosome 13. The RB1 gene produces a protein called the retinoblastoma protein (pRb). In healthy cells, pRb acts as a molecular brake, controlling when cells are allowed to divide and grow. When both copies of RB1 in a single cell are non-functional, this brake is lost and the cell begins to multiply without limit — forming a tumour.
The two-hit model: why hereditary disease behaves differently
Every person is born with two copies of the RB1 gene — one inherited from each parent. For a retinal cell to become cancerous, both copies must stop working. In the non-hereditary (sporadic) form of retinoblastoma, both of these changes happen by chance in a single retinal cell after birth. Because two independent random events must coincide in the same cell, this is a relatively rare occurrence, and the resulting tumour almost always affects one eye only.
In hereditary retinoblastoma, the child is born with one non-functioning copy of RB1 in every cell of their body — this is the germline mutation. Every retinal cell is therefore already one step away from losing the brake entirely. Only one further random change in any retinal cell is enough to start a tumour. This explains why hereditary retinoblastoma tends to appear earlier, is more likely to affect both eyes, and often results in multiple tumours within each eye.
Did you know?
The RB1 gene was the first tumour suppressor gene to be characterised in human cancer. The two-hit hypothesis that explains hereditary retinoblastoma, first described by Alfred Knudson in 1971 based on mathematical modelling of retinoblastoma cases, became the foundation for understanding hereditary cancer syndromes across oncology. Identifying a germline RB1 mutation in a child today gives clinicians the precise information they need to protect siblings and future family members through planned screening. Source: Knudson AG. Proc Natl Acad Sci USA, 1971
Germline versus somatic RB1 mutations: a distinction that matters
A germline mutation is one that was present from conception — it exists in every cell of the body, including cells that can be tested through a blood sample. A somatic mutation, by contrast, arises only in specific cells (such as a single retinal cell) after birth and is not found in blood or other tissues. When a child’s blood test shows an RB1 mutation, this confirms the hereditary (germline) form. When the blood test is normal but an RB1 mutation is found only in the tumour tissue, this confirms the non-hereditary (somatic) form. The distinction changes the care plan completely: only a germline mutation warrants RB1 family testing of siblings and parents.
Inheritance pattern and what it means for your family
Hereditary retinoblastoma follows an autosomal dominant inheritance pattern. This means that one changed copy of the RB1 gene — inherited from one parent — is sufficient to place a child at elevated risk of the disease. If one parent carries a germline RB1 mutation, each child of that parent has approximately a one-in-two chance of inheriting it. However, inheriting the mutation does not guarantee that retinoblastoma will develop — a small number of carriers never form a tumour (a concept called reduced penetrance). The risk is nonetheless high enough that all mutation carriers require structured surveillance from birth or early infancy.
Sometimes no parent is found to carry the mutation: the change arose for the first time in the egg or sperm that formed the affected child. This is called a de novo mutation. In this situation, the parents themselves are not at elevated risk and their other children are at much lower risk, but the affected child can pass the mutation on to their own children in the future. A clinical genetics team will determine which scenario applies to your family and what this means for each relative.
For a broader overview of retinoblastoma as a disease, see the retinoblastoma overview on the CION pediatric cancer hub, or read our dedicated guide to hereditary retinoblastoma and the RB1 gene. For information about the first warning sign most parents notice, see white glow in a child’s eye.
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Hereditary retinoblastoma genetics
RB1 family testing — the pathway from your child’s diagnosis to protecting every family member
Once hereditary retinoblastoma is suspected, a structured sequence of genetic and clinical steps ensures that every at-risk family member is identified and protected as early as possible. Here is what that pathway typically looks like.
Retinal examination under anaesthesia
The clinical journey begins with a thorough examination of the retina — in both eyes — under a brief general anaesthetic. This is the only way to see the retina clearly in a young child who cannot keep still for an awake eye examination. The ophthalmologist maps any tumours found: their size, location, and how many are present in each eye. Bilateral disease (tumours in both eyes) is a strong clinical indicator of the hereditary form, as is the presence of multiple separate tumours within a single eye. The findings from this examination inform the decision to pursue genetic testing.
Blood-sample genetic testing for RB1 mutation
A blood sample is taken from your child and sent for genetic testing. The laboratory analyses the RB1 gene to look for a mutation in both copies. If a mutation is found in the blood, this confirms a germline (inherited) mutation — present in every cell of the body. This is the definitive test for confirming hereditary status. In some cases the blood test does not reveal a mutation even when hereditary disease is clinically suspected; in this situation, the tumour tissue itself may be tested directly, and a low-level germline mutation (mosaic mutation) may be detected with more sensitive techniques. The precise mutation found in the child is recorded, because this specific change is the basis for all subsequent family testing.
Clinical genetics consultation for the family
Once a germline RB1 mutation has been characterised, the family is referred to a clinical genetics team. A clinical geneticist or genetic counsellor will explain what the mutation means, how it is inherited, and what the implications are for each family member. This is also the session where the family can ask about future family planning, the specific penetrance of the mutation found, and the logistics of predictive testing for relatives. The genetics team works closely with the oncology team — they are not a separate journey, but an integrated part of your child’s care plan at CION.
Predictive testing for siblings and parents
Predictive testing uses the specific mutation already identified in your child as a target. A blood sample from a sibling or parent is tested for that exact change — a faster and highly accurate process compared to sequencing the entire RB1 gene from scratch. Results are typically unambiguous: a family member either carries the mutation or does not. For siblings, this testing is generally recommended as early as possible — ideally from birth or in the first weeks of life — so that those who carry the mutation can be enrolled in surveillance immediately. Parents who test positive may not have retinoblastoma themselves (reduced penetrance is well recognised) but are important to identify for the broader family tree and for future pregnancy planning.
Surveillance programme for mutation carriers
Any family member found to carry the germline RB1 mutation enters a structured surveillance programme. For infants and young children, this means regular retinal examinations under anaesthesia, with the frequency highest in the first year of life and gradually decreasing as the child grows older and the window of greatest risk for retinoblastoma closes. The goal is to detect any tumour at its smallest, earliest stage — when eye-preserving treatment is most achievable. Adults who are found to carry the mutation have passed the age of retinoblastoma risk, but they and their children may need long-term follow-up for other tumour risks associated with a lifelong germline RB1 mutation. Your child’s oncology team and the genetics team will provide a personalised schedule for each family member.
Long-term follow-up and second tumour surveillance
Children who carry a germline RB1 mutation face a lifelong, elevated risk of developing certain tumours beyond retinoblastoma itself — most notably tumours of the bone and soft tissue. Long-term surveillance extending into adulthood is therefore a recognised part of the recommended care plan. The specific surveillance schedule depends on the type of treatment received for retinoblastoma and the nature of the RB1 mutation. At CION, we coordinate this long-term follow-up and ensure that your child’s care plan evolves as they move from paediatric into adult oncology services. We walk this journey with you and your child — well beyond the initial treatment phase.
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Common questions
Your questions about the RB1 gene and hereditary retinoblastoma — answered
What exactly is the RB1 gene and what does it do in the body?
The RB1 gene is a tumour suppressor gene — its job is to produce a protein, known as the retinoblastoma protein or pRb, that acts as a brake on cell division. In healthy cells, pRb helps regulate the cycle of growth and division so that cells multiply only when the body needs them to. Every person inherits two copies of the RB1 gene — one from each parent. Both copies need to be non-functioning before the brake is lost entirely. When that happens in a retinal cell, the cell can begin to divide without limit, eventually forming a retinoblastoma tumour. The RB1 gene was the first tumour suppressor gene to be identified in human cancer, and understanding how it works has shaped our knowledge of hereditary cancer more broadly.
What does it mean when a doctor says my child has an RB1 gene mutation?
An RB1 gene mutation means that one or both copies of the RB1 gene in your child's cells carry a change that prevents the gene from working correctly. In the context of retinoblastoma, a germline RB1 mutation — one that is present in every cell of the body, including blood cells — indicates the hereditary form of the disease. This matters for two reasons. First, your child's other eye (and certain other tissues) remains at elevated risk of developing tumours until early childhood is complete, so structured surveillance is essential. Second, the mutation can potentially be passed on to your child's own children in the future. A non-germline (somatic) mutation, by contrast, is limited to the tumour itself and does not carry the same inherited risk. Genetic testing of a blood sample is the standard way to determine which situation your child is in.
How is RB1 family testing done, and who in the family should be tested?
Once a germline RB1 mutation has been identified in your child, a blood sample from that child is used to characterise the exact mutation. That information is then used to offer predictive testing to other family members — parents, siblings, and in time, the affected child's own children. Predictive testing is a straightforward blood test: it looks for the specific mutation already identified in the child, rather than scanning the entire gene. This means results are highly accurate. Testing is generally recommended for siblings from birth, so that those who inherit the mutation can begin early eye examinations before any tumour has a chance to grow. Parents may also be tested to understand how the mutation entered the family and to clarify future family planning. A clinical genetics team coordinates this process alongside your child's oncology team.
If the RB1 mutation is found in a sibling who has no eye symptoms, what happens next?
A sibling who carries the RB1 germline mutation but has no current eye symptoms is at elevated risk of developing retinoblastoma, typically within the first few years of life. The appropriate response is structured, planned screening — not waiting for symptoms to appear. Screening usually involves examination of the retina under a brief general anaesthetic, so that the ophthalmologist can see the retina clearly in a young child who cannot cooperate with an awake eye examination. The frequency of these examinations is highest in infancy and early toddlerhood, then gradually reduces as the child moves through early childhood and the window of greatest risk passes. The advantage of catching a tumour this way — before it causes any visible symptoms — is that treatment at an early stage offers the best chance of preserving the eye and vision. Your genetics and oncology team will set out a personalised screening schedule for each family member found to carry the mutation.
Does carrying the RB1 mutation mean my child will definitely develop retinoblastoma?
Carrying a germline RB1 mutation places a child at significantly elevated risk of retinoblastoma, but it does not guarantee that a tumour will form. The risk is high — in families with hereditary retinoblastoma, the great majority of children who carry the mutation do develop at least one tumour — but a small proportion of carriers never develop retinoblastoma. This is referred to as reduced penetrance and is influenced by the specific type of RB1 mutation involved. Because risk is high but not absolute, the practical approach is planned surveillance rather than preventive eye removal. Structured screening catches any tumour at its earliest stage, when treatment options are widest and vision preservation is most achievable. Your oncology and genetics team will explain the penetrance associated with your family's specific mutation, so you can understand the level of risk and what the surveillance schedule is designed to do.
Are children with hereditary retinoblastoma at risk of other cancers later in life?
Yes — individuals with a germline RB1 mutation carry a lifelong, elevated risk of developing certain cancers beyond retinoblastoma itself, even after their retinoblastoma has been successfully treated. These second tumours can involve the bone, soft tissue, skin, and other sites. The risk is influenced by the type of treatment the child received for their retinoblastoma — in particular, radiation therapy to the eye area in early childhood can increase the risk of certain tumours in the radiation field later in life. For this reason, long-term surveillance extending into adulthood is an accepted part of care for individuals with hereditary retinoblastoma. This lifelong follow-up is coordinated between oncology and genetics services and is designed to detect any second tumour early. Your child's oncology team will provide a personalised long-term surveillance plan as part of the overall care programme.
For more information on childhood cancers with a genetic component, visit the Pediatric Cancer hub or read our guide on is childhood cancer hereditary?
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