What Is Snijders Blok Campeau Syndrome? Essential Guide

Snijders Blok-Campeau syndrome is a rare genetic condition caused by changes in a single gene called CHD3. It was first described in 2018 by a team of researchers led by Lot Snijders Blok and Philippe Campeau, which is where the name comes from. The condition affects brain development and typically causes intellectual disability, speech and language difficulties, and distinctive facial features. Because it was only identified in 2018, many people — including some doctors — are still learning about it.

What Is Snijders Blok Campeau Syndrome?

Snijders Blok-Campeau syndrome (often shortened to SBCS) is a neurodevelopmental disorder with a genetic cause. It happens when there is a change — called a variant or mutation — in the CHD3 gene.

CHD3 stands for chromodomain helicase DNA-binding protein 3. This gene plays a role in how DNA is packaged and read inside cells. When CHD3 doesn’t work the way it should, it affects how genes are turned on and off during brain development. That disruption is what leads to the features of the syndrome.

The condition is not something a person develops over time. It is present from conception. It is not caused by anything a parent did or didn’t do during pregnancy.

SBCS is considered extremely rare. Because it was only identified in 2018, and because genetic testing for it is not routine, the number of diagnosed cases is likely lower than the actual number of people who have it. Some researchers estimate that the true prevalence is unknown at this point.

What Causes Snijders Blok-Campeau Syndrome?

The cause is a variant in the CHD3 gene. That gene provides instructions for making a protein that helps regulate chromatin — the structure that DNA wraps around inside cells. When the CHD3 protein is altered, it can affect how other genes are expressed, particularly in the developing brain.

Most known cases are caused by what geneticists call de novo variants. That means the gene change happened spontaneously — it was not inherited from either parent. In these cases, neither parent carries the variant.

In some cases, the variant can be inherited from a parent. This happens when a parent also carries the CHD3 variant. The pattern of inheritance depends on the specific situation, and a genetic counselor can explain what applies to a particular family.

It’s important to understand that a de novo variant is not anyone’s fault. Nothing during pregnancy causes this kind of gene change. It is a random event that occurs when cells are dividing and copying DNA.

What Are the Symptoms of Snijders Blok-Campeau Syndrome?

The symptoms vary from person to person. Some people are more affected than others. That said, certain features appear consistently in the medical literature.

The most common symptoms include:

• Intellectual disability, ranging from mild to severe
• Speech and language delays, which are often significant
• Motor delays, such as sitting, crawling, or walking later than expected
• Distinctive facial features, which can include a broad forehead, widely spaced eyes, and a wide mouth
• Behavioral differences, which may include features associated with autism spectrum disorder
• Low muscle tone (hypotonia) in infancy
• Feeding difficulties early in life

Some people with SBCS may have seizures, vision problems, or other medical issues. Others may not. The range of severity is broad, which is common in genetic neurodevelopmental conditions.

Because the condition was only described in 2018, the full range of symptoms is still being studied. What researchers know today may expand as more cases are identified and followed over time.

How Is Snijders Blok-Campeau Syndrome Diagnosed?

Diagnosis is made through genetic testing. Specifically, a test that reads the CHD3 gene and identifies whether a disease-causing variant is present.

This kind of testing is usually done as part of a broader genetic panel or through whole exome sequencing — a test that looks at the protein-coding regions of many genes at once. A doctor may order this type of testing when a child has developmental delays, intellectual disability, or other features that suggest a genetic cause.

There is no blood test, imaging scan, or physical exam that can diagnose SBCS on its own. The facial features and developmental pattern may raise suspicion, but confirmation requires finding a CHD3 variant through genetic testing.

One challenge is that not all CHD3 variants cause the same effects. Some variants are clearly linked to the syndrome. Others are classified as “variants of uncertain significance,” meaning researchers aren’t sure yet whether they cause disease. This can make diagnosis complicated and sometimes inconclusive.

Is There a Treatment for Snijders Blok-Campeau Syndrome?

There is no cure for SBCS, and no treatment that targets the underlying genetic cause. This is true for most genetic neurodevelopmental conditions.

What exists instead is supportive care. That means addressing the specific symptoms and challenges a person faces. This can include:

• Speech therapy for language delays
• Occupational therapy for motor skills and daily living tasks
• Physical therapy for movement and strength
• Educational support tailored to the person’s needs
• Behavioral support if needed
• Medical management of seizures, feeding issues, or other health problems

The goal of supportive care is to help the person function as well as possible and improve quality of life. Early intervention is generally recommended for children with developmental delays, though the specific outcomes for SBCS are not yet well studied.

It’s important not to overstate what any therapy can achieve. The evidence base for specific interventions in SBCS is very limited because the condition is so newly described and so rare. Most recommendations are based on what works for children with similar neurodevelopmental conditions, not on studies specific to SBCS.

What Is the Outlook for Someone With SBCS?

The outlook varies widely. Some people with SBCS will need lifelong support. Others may achieve more independence than expected.

Because the condition was only identified in 2018, long-term data is limited. Most of what is known comes from case reports and small case series. That means researchers cannot yet say with confidence what the typical trajectory looks like over a full lifetime.

What is clear is that the severity of the CHD3 variant and the specific symptoms a person has will shape their needs. Some individuals have significant intellectual disability and require substantial support. Others may have milder delays.

Families often find it helpful to connect with other families affected by the same condition. Support organizations for rare genetic conditions can provide information, community, and sometimes access to research opportunities.

How Common Is Snijders Blok-Campeau Syndrome?

SBCS is very rare. As of now, only a small number of cases have been reported in the medical literature since the condition was first described in 2018.

However, the true number of people with SBCS is likely higher than what has been documented. Many people with developmental delays never receive a specific genetic diagnosis. Genetic testing is not universal, and testing for CHD3 variants specifically is not routine.

As genetic testing becomes more common and more affordable, more cases are likely to be identified. That may change what researchers understand about how common the condition actually is.

There is no known geographic, ethnic, or sex-based pattern to SBCS. It appears to affect people worldwide.

What Should Families Know About Genetic Counseling?

Genetic counseling is an important part of the process for families affected by SBCS. A genetic counselor can explain how the condition was inherited, what the risk is for future children, and what testing options exist for family members.

In cases where the CHD3 variant is de novo — meaning neither parent carries it — the chance of having another child with the same condition is generally low. But that risk is not zero, and a genetic counselor can give a more precise estimate based on the specific situation.

If a parent does carry the variant, the inheritance pattern and risk to future children will be different. This is why testing parents is often recommended when a child is diagnosed.

Genetic counseling also helps families understand what is known and what is not known. For a condition as newly described as SBCS, that distinction matters.