CHD3-related syndrome happens when there are changes to the CHD3 gene. These changes can keep the gene from working as it should.

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 birth parents.

• If neither birth parent has the same gene change 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 change in the gene.
• If one birth parent has the same gene change found in their child, the chance of having another child who has the syndrome is 50 percent.

For a symptom-free sibling, a brother or sister, of someone who has CHD3-related syndrome, the risk of having a child who has the syndrome depends on the symptom-free sibling’s genes and their parents’ genes.

• If neither parent has the same gene change found in their child who has the syndrome, the symptom-free sibling has a nearly 0 percent chance of having a child who has CHD3-related syndrome.
• If one birth parent has the same gene change found in their child who has the syndrome, the symptom-free sibling has a small chance of also having the same gene change. If the symptom-free sibling has the same gene change as their sibling who has the syndrome, the symptom-free sibling’s chance of having a child who has CHD3-related syndrome 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.

As of 2019, about 35 people in the world with changes in the CHD3 gene had been described in the medical literature. The first case of CHD3- related syndrome was described in 2018. Scientists expect to find more people who have the syndrome as access to genetic testing improves.

People who have CHD3-related syndrome may look different. Appearance can vary and can include some but not all of these features:

• More than half of those who have the syndrome have a large head.
• They may also have widely-spaced eyes, a broad forehead, sparse eyebrows, low-set ears, and a pointed chin.

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.

Learning

People who have CHD3-related syndrome often have developmental delays, intellectual disability, or both. IQ ranges from 70–85 (just below or within the typical range), to below 35 (severe intellectual disability).

Muscle tone

About 75 percent of people who have the syndrome had low muscle tone.