17q21.31 Duplication Syndrome
17q21.31 duplication syndrome is also called 17q21.31 microduplication syndrome. For this webpage, we will be using the name 17q21.31 duplication syndrome to encompass the wide range of variants observed in the people identified.
What is 17q21.31 duplication syndrome?
17q21.31 duplication syndrome happens when a person has an extra piece of chromosome 17, one of the body’s 46 chromosomes. Chromosomes are structures in our cells that house our genes. The extra piece can affect learning and how the body develops.
Key Role
Genes within the 17q21.31 region are important for brain development and function.
Symptoms
Because genes in the 17q21.31 region are important in brain development and function, many people who have 17q21.31 duplication syndrome have:
- Intellectual disability
- Autism
- Speech and language delay
- Learning disability
- Low muscle tone
- Developmental delay
- Schizophrenia
- Alzheimer’s disease around age 60
What causes 17q21.31 duplication syndrome?
17q21.31 duplication 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 17q21.31 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 17q21.31 plays a key role in development, de novo variants in this gene can have a meaningful effect.
Research shows that 17q21.31 duplication syndrome is often the result of a de novo variant in 17q21.31. Many parents who have had their genes tested do not have the 17q21.31 genetic variant found in their child who has the syndrome. In some cases, 17q21.31 duplication syndrome happens because the genetic variant was passed down from a parent.
Autosomal dominant conditions
17q21.31 duplication syndrome is an autosomal dominant genetic condition. This means that when a person has the one damaging variant in 17q21.31 they will likely have symptoms of 17q21.31 duplication 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
What does my child have duplication deletion syndrome?
No parent causes their child’s 17q21.31 duplication syndrome. We know this because no parent has any control over the chromosome 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 or future children will have 17q21.31 duplication 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 17q21.31 deletion 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 17q21.31 duplication syndrome, the sibling’s risk of having a child who has 17q21.31 deletion syndrome depends on the sibling’s genes and their parents’ genes.
- If neither parent has the same genetic variant causing 17q21.31 duplication syndrome, the symptom-free sibling has a nearly 0 percent chance of having a child who would inherit 1721.31 duplication syndrome.
- If one biological parent has the same genetic variant causing 17q21.31 duplication 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 17q21.31 duplication syndrome, the risk of having a child who has the syndrome is about 50 percent.
How many people have 17q21.31 duplication syndrome?
As of 2026, over 13 people with 17q21.31 duplication syndrome have been described in medical research. Some people with a 17q21.31 duplication do not have any symptoms, which makes it difficult to know how common this condition is.
Do people who have 17q21.31 duplication syndrome look different?
People with 17q21.31 duplication syndrome do not look that different. Some people may have more body hair than average.
How is 17q21.31 duplication syndrome treated?
At this point, there are no medicines designed to treat 17q21.31 duplication 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
- Developmental 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 17q21.31 duplication syndrome should begin as early as possible, ideally before a child begins school.
Your doctor can recommend whether to see an endocrinologist to check for kidney and urinary issues.
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: 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 articles, see the Sources and References section of this guide.
Behavior and development concerns linked to 17q21.31 duplication syndrome
Research has suggested that not everyone with a 17q21.31 duplication develops symptoms. In fact, some researchers think that about 3 out of 10 people with a 17q21.31 duplication will not have medical features. This means that the 17q21.31 duplication has incomplete penetrance. It is unclear why some people do or do not develop symptoms.
Learning and speech
Medical research has shown that people with a 17q21.31 duplication had developmental delay or intellectual disability.
- 13 out of 13 people had developmental delay or intellectual disability (100 percent)
Behavior
Some people with a 17q21.31 duplication had behavioral issues, such as autism or features of autism, aggression, and restlessness.
- 6 out of 11 people had behavioral issues (55 percent)
- 3 out of 11 people had autism (27 percent)
Brain
People with a 17q21.31 duplication had neurological medical issues, such as having a small head size (microcephaly), a large head size (macrocephaly), and low muscle tone (hypotonia).
- 6 out of 12 people had microcephaly (50 percent)
- 1 out of 11 people had macrocephaly (9 percent)
- 3 out of 11 people had hypotonia (27 percent)
Medical and physical concerns linked to 17q21.31 duplication syndrome
Other medical features
People with a 17q21.31 duplication had obesity and crossed eyes, also called strabismus.
- 5 out of 13 people had obesity (39 percent)
- 2 out of 12 people had strabismus (17 percent)
Where can I find support and resources?
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 page on 17q21.31 duplication syndrome: www.simonssearchlight.org/research/what-we-study/17q21-31-duplication
- Simons Searchlight 17q21.31 duplication Facebook Community: https://www.facebook.com/groups/17q21-31-duplication
Sources and References
- Goh, S., Thiyagarajan, L., Dudding-Byth, T., Pinese, M., & Kirk, E. P. (2025). A systematic review and pooled analysis of penetrance estimates of copy-number variants associated with neurodevelopment. Genetics in Medicine, 27(1), 101227. doi:10.1016/j.gim.2024.101227
- Saia, F., Prato, A., Florio, C. A., Cutrone, V. P., & Rizzo, R. (2023). 17q21.31 microduplication syndrome in a patient with autism spectrum disorder, macrocephaly, and intellectual disability. Reports (MDPI), 6(3), 30. doi:10.3390/reports6030030
- Tolino, E., Skroza, N., Del Giudice, E., Maddalena, P., Bernardini, N., Proietti, I., Mambrin, A., Marraffa, F., Rossi, G., … & Potenza, C. (2023). A case of psoriatic disease and Hidradenitis Suppurativa in a child with chromosome 17q21.31 microduplication syndrome. Children (Basel), 10(6), 931. doi:10.3390/children10060931