CHD3-Related Syndrome
CHD3-related syndrome is also called Snijders Blok-Campeau syndrome. For this webpage, we will be using the name CHD3-related syndrome to encompass the wide range of variants observed in the people identified.
What is CHD3-related syndrome?
CHD3-related syndrome happens when there are changes in the CHD3 gene. These changes can keep the gene from working as it should.
Key Role
CHD3 plays a key role in the growth of the brain.
Symptoms
Because the CHD3 gene is important for brain activity, many people who have CHD3-related syndrome have:
- Developmental delay
- Intellectual disability
- Impaired language and speech skills
- Large head size
- Low muscle tone
- Unsteady walking
- Seizures
- Features of autism
- A friendly personality
What causes CHD3-related syndrome?
CHD3-related syndrome is a genetic condition, which means that it is caused by variants in genes. Our genes contain the instructions, or code, that tell our cells how to grow, develop, and work. Every child gets two copies of the CHD3 gene: one copy from their mother’s egg, and one copy from their father’s sperm. In most cases, parents pass on exact copies of the gene to their child. But the process of creating the egg or sperm is not perfect. A change in the genetic code can lead to physical issues, developmental issues, or both.
Sometimes a spontaneous variant happens in the sperm, egg or after fertilization. When a brand new genetic variant happens in the genetic code is called a ‘de novo’ genetic variant. The child is usually the first in the family to have the genetic variant.
De novo variants can take place in any gene. We all have some de novo variants, most of which don’t affect our health. But because CHD3 plays a key role in development, de novo variants in this gene can have a meaningful effect.
Research shows that CHD3-related syndrome is often the result of a de novo variant in CHD3. Many parents who have had their genes tested do not have the CHD3 genetic variant found in their child who has the syndrome. In some cases, CHD3-related syndrome happens because the genetic variant was passed down from a parent.
Autosomal dominant conditions
CHD3-related syndrome is an autosomal dominant genetic condition. This means that when a person has the one damaging variant in CHD3 they will likely have symptoms of CHD3-related syndrome. For someone with an autosomal dominant genetic syndrome, every time they have a child there is a 50 percent chance they pass on the same genetic variant and a 50 percent chance they do not pass on the same genetic variant.
Autosomal Dominant Genetic Syndrome
Why does my child have a change in the CHD3 gene?
No parent causes their child’s CHD3-related syndrome. We know this because no parent has any control over the genetic changes that they do or do not pass on to their children. Please keep in mind that nothing a parent does before or during the pregnancy causes this to happen. The genetic change takes place on its own and cannot be predicted or stopped.
What are the chances that other family members of future children will have CHD3-related syndrome?
Each family is different. A geneticist or genetic counselor can give you advice on the chance that this will happen again in your family.
The risk of having another child who has CHD3-related syndrome depends on the genes of both biological parents.
- If neither biological parent has the same genetic variant found in their child, the chance of having another child who has the syndrome is on average 1 percent. This 1 percent chance is higher than the chance of the general population. The increase in risk is due to the very unlikely chance that more of the mother’s egg cells or the father’s sperm cells carry the same genetic variant.
- If one biological parent has the same genetic variant found in their child, the chance of having another child who has the syndrome is 50 percent.
For a symptom-free brother or sister of someone who has CHD3-related syndrome, the sibling’s risk of having a child who has CHD3-related syndrome depends on the sibling’s genes and their parents’ genes.
- If neither parent has the same genetic variant causing CHD3-related syndrome, the symptom-free sibling has a nearly 0 percent chance of having a child who would inherit CHD3-related syndrome.
- If one biological parent has the same genetic variant causing CHD3-related syndrome, the symptom-free sibling has a 50 percent chance of also having the same genetic variant. If the symptom-free sibling has the same genetic variant, their chance of having a child who has the genetic variant is 50 percent.
For a person who has CHD3-related syndrome, the risk of having a child who has the syndrome is about 50 percent.
How many people have CHD3-related syndrome?
As of 2026, over 114 people with CHD3-related syndrome have been identified in a medical clinic. The first person was found in 2018. Scientists expect to find more people who have the syndrome as access to genetic testing improves.
Do people who have CHD3-related syndrome look different?
People with CHD3-related syndrome may look different. Appearance can vary and can include, but is not limited to, these features:
- Wide-set eyes
- Noticeable forehead
- Large head
How is CHD3-related syndrome treated?
Scientists and doctors have only just begun to study CHD3-related syndrome. At this point, there are no medicines designed to treat the syndrome. A genetic diagnosis can help people decide on the best way to track the condition and manage therapies. Doctors can refer people to specialists for:
- Physical exams and brain studies.
- Genetics consults.
- Development and behavior studies.
- Other issues, as needed.
A developmental pediatrician, neurologist, or psychologist can follow progress over time and can help:
- Suggest the right therapies. This can include physical, occupational, speech, or behavioral therapy.
- Guide individualized education plans (IEPs).
Specialists advise that therapies for CHD3-related syndrome should begin as early as possible, ideally before a child begins school.
If seizures happen, consult a neurologist. There are many types of seizures, and not all types are easy to spot. To learn more, you can refer to resources such as the Epilepsy Foundation’s website: www.epilepsy.com/learn/types-seizures.
This section includes a summary of information from major published articles. It highlights how many people have different symptoms. To learn more about the article, see the Sources and references section of this guide.
Behavior and development concerns linked to CHD3-related syndrome
Some people inherit a CHD3 variant from a parent. Research suggests that every parent carrying the same CHD3 variant as their child with CHD3-related syndrome has at least one medical feature associated with the syndrome. The information below includes dependents with CHD3-related syndrome. Additional information on parents is given at the end of the guide.
Learning and speech
People with CHD3-related syndrome had developmental delay or intellectual disability, and speech delay or impairment.
- 81 out of 83 people had developmental delay (98 percent)
- 61 out of 83 people had intellectual disability (73 percent)
- 76 out of 83 people had speech delay or impairment (92 percent)
Behavior
Some people with CHD3-related syndrome had behavioral issues, such as autism or features of autism, attention-deficit/hyperactivity disorder (ADHD), repetitive behaviors (stereotypic behavior), or a happy personality. One person had autism and high cognitive abilities.
- 23 out of 83 people had autism (28 percent)
- 7 out of 83 people had ADHD (8 percent)
- 5 out of 83 people had stereotypic behavior (6 percent)
Brain
People with CHD3-related syndrome had neurological medical issues, including a small head size (microcephaly); a large head size (macrocephaly); low muscle tone (hypotonia); seizures; and brain changes seen on magnetic resonance imaging (MRI), such as ventriculomegaly.
- 3 out of 83 people had microcephaly (4 percent)
- 46 out of 83 people had macrocephaly (55 percent)
- 59 out of 83 people had hypotonia (71 percent)
- 11 out of 83 people had seizures (13 percent)
- 4 out of 83 people had ventriculomegaly (5 percent)
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Medical and physical concerns linked to CHD3-related syndrome
Vision and hearing
People with CHD3-related syndrome had vision issues, such as wide-set eyes and crossed eyes, also called strabismus. Some had hearing loss.
- 46 out of 83 people had vision issues (55 percent)
- 59 out of 83 people had wide-set eyes (71 percent)
- 23 out of 83 people had strabismus (28 percent)
- 3 out of 83 people had hearing loss (4 percent)
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Growth issues
Some people with CHD3-related syndrome had issues with growth and development, such as heart structure defects, teeth changes, and joint flexibility.
- 11 out of 83 people had heart structure defects (13 percent)
- 6 out of 83 people had teeth changes (7 percent)
- 25 out of 83 people had joint flexibility (30 percent)
Parents with medical features
All 19 parents who carried the same CHD3 variant as their child with CHD3-related syndrome had at least one medical feature associated with the syndrome.
These features included a noticeable forehead, deep-set eyes, large head size, autism or features of autism, vision issues, and in a few instances, mild or borderline intellectual disability (4 out of 19 people, 21 percent). But, most parents had no history of intellectual disability.
Genetic sequencing efforts on the general population have identified some people in the general population who have problematic CHD3 genetic variations.
Where can I find support and resources?
CHD3 Foundation
CHD3 Foundation connects families, funds research, and advocates for those living with Snijders Blok-Campeau Syndrome worldwide.
Simons Searchlight
Simons Searchlight is an online international research program, building an ever growing natural history database, biorepository, and resource network of over 175 rare genetic neurodevelopmental disorders. By joining their community and sharing your experiences, you contribute to a growing database used by scientists worldwide to advance the understanding of your genetic condition. Through online surveys and optional blood sample collection, they gather valuable information to improve lives and drive scientific progress. Families like yours are the key to making meaningful progress. To register for Simons Searchlight, go to the Simons Searchlight website at www.simonssearchlight.org and click “Join Us.”
Learn more about Simons Searchlight: www.simonssearchlight.org/frequently-asked-questions
Simons Searchlight webpage with more information on CHD3: www.simonssearchlight.org/research/what-we-study/chd3
Simons Searchlight CHD3 Facebook community: www.facebook.com/groups/2252498664847936
Sources and References
The content in this guide comes from a published study about CHD3-related syndrome. Below you can find details about this study, as well as a link to a summary and the full article.
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- Pascual, P., Tenorio-Castano, J., Mignot, C., Afenjar, A., Arias, P., Gallego-Zazo, N., Parra, A., Miranda, L., Cazalla, M., … & Lapunzina, P. (2023). Snijders Blok-Campeau syndrome: Description of 20 additional individuals with variants in CHD3 and literature review. Genes (Basel), 14(9), 1664. doi:10.3390/genes14091664
- van der Spek, J., den Hoed, J., Snijders Blok, L., Dingemans, A. J. M., Schijven, D., Nellaker, C., Venselaar, H., Astuti, G. D. N., Barakat, T. S., … & Kleefstra, T. (2022). Inherited variants in CHD3 show variable expressivity in Snijders Blok-Campeau syndrome. Genetics in Medicine, 24(6), 1283-1296. doi:10.1016/j.gim.2022.02.014