GENE GUIDE

1q21.1 Duplication Syndrome

This guide is not meant to take the place of medical advice. Please consult with your doctor about your genetic results and health care choices. This Gene Guide was last updated on 2024. As new information comes to light with new research we will update this page. You may find it helpful to share this guide with friends and family members or doctors and teachers of the person who has 1q21.1 Duplication Syndrome.
a doctor sees a patient

1q21.1 duplication syndrome is also called 1q21.1 microduplication. For this webpage, we will be using the name 1q21.1 duplication syndrome to encompass the wide range of variants observed in the people identified.

What is chromosome 1q21.1 duplication syndrome?

1q21.1 duplication syndrome happens when a person has an extra piece of chromosome 1, 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

The 1q21.1 duplication region plays a role in brain development.

Symptoms

1q21.1 duplication syndrome can affect communication, social, and learning skills. People who have 1q21.1 duplication syndrome may have:

  • Developmental delay
  • Intellectual disability
  • Autism or related behavioral issues
  • Larger than average head size
  • Learning disabilities
  • Speech delay
  • Brain changes observed on magnetic resonance imaging (MRI)

What causes 1q21.1 duplication syndrome?

1q21.1 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 1q21.1 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 1q21.1 plays a key role in development, de novo variants in this gene can have a meaningful effect.

Research shows that 1q21.1 duplication syndrome is often the result of a de novo variant in 1q21.1. Many parents who have had their genes tested do not have the 1q21.1 genetic variant found in their child who has the syndrome. In some cases, 1q21.1 duplication syndrome happens because the genetic variant was passed down from a parent.

Autosomal dominant conditions

1q21.1 duplication syndrome is an autosomal dominant genetic condition. This means that when a person has the one damaging variant in 1q21.1 they will likely have symptoms of 1q21.1 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

GENE / gene
GENE / gene
Genetic variant that happens in sperm or egg, or after fertilization
GENE / gene
Child with de novo genetic variant
gene / gene
Non-carrier child
gene / gene
Non-carrier child

Why does my child have 1q21.1 duplication syndrome?

No parent causes their child’s 1q21.1 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 chromosome 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 1q21.1 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 1q21.1 duplication 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 1q21.1 duplication syndrome, the sibling’s risk of having a child who has 1q21.1 duplication syndrome depends on the sibling’s genes and their parents’ genes. 

  • If neither parent has the same genetic variant causing 1q21.1 duplication syndrome, the symptom-free sibling has a nearly 0 percent chance of having a child who would inherit 1q21.1 duplication syndrome. 
  • If one biological parent has the same genetic variant causing 1q21.1 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 1q21.1 duplication syndrome, the risk of having a child who has the syndrome is about 50 percent.

Do all people who have 1q21.1 duplication syndrome have symptoms?

Not necessarily. Some people do not have any symptoms. Some people may not learn that they have this chromosome change until it is found in their children.

Do all the people in a family that has the chromosome change have the same symptoms?

Not necessarily. Family members who have the same chromosome change can have different symptoms.

How many people have 1q21.1 duplication syndrome?

As of 2024, at least 60 people with 1q21.1 duplication syndrome have been identified in a medical clinic. Seventy two people with 1q21.1 duplication syndrome have registered for Simons Searchlight. The first case of 1q21.1 duplication syndrome was described in 2008. Scientists expect to find more people who have the syndrome as access to genetic testing improves.

Do people who have 1q21.1 duplication syndrome look different?

People who have 1q21.1 duplication syndrome may look different. Appearance can vary and can include some but not all of these features:

  • Larger than average head size
  • Widely spaced eyes
  • Noticeable forehead

How is 1q21.1 duplication syndrome treated?

At this point, there are no medicines designed to treat 1q21.1 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 1q21.1 duplication 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: epilepsy.com/learn/types-seizures.

This section includes a summary of information from major published articles and the Simons Searchlight quarterly registry report. 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 1q21.1 duplication syndrome

The typical 1q21.1 duplication region associated with a neurodevelopmental condition is also known as the distal region. Depending on the duplication, breakpoints can have up to about 9 genes duplicated. Some people inherit the 1q21.1 duplication from a parent who may or may not have medical features.

Some of the information below comes from the Simons Searchlight registry.

Speech and Learning

About one-half of people with 1q21.1 duplication syndrome had developmental delay or intellectual disability and speech delay.

  • 31 out of 72 people had developmental delay or intellectual disability (43 percent)
  • 33 out of 72 people had speech delay (46 percent)

Behavior

Behavioral issues occurred in about 1 out of 3 people with 1q21.1 duplication syndrome. Behavioral issues included autism, attention-deficit/hyperactivity disorder (ADHD), and anxiety.

  • 26 out of 72 people had autism (36 percent)
  • 23 out of 72 people had ADHD (32 percent)
  • 25 out of 72 people had anxiety (35 percent)
36%
26 out of 72 people had autism.
32%
23 out of 72 people had ADHD.
35%
25 out of 72 people had anxiety.

Brain

Rarely, people with 1q21.1 duplication syndrome had seizures. Some people had a larger than average head size.

  • 3 out of 72 people had seizures (4 percent)
  • 28 out of 72 people had larger than average head size (39 percent)
Human head showing brain outline
4%
3 out of 72 people had seizures.
39%
28 out of 72 people had larger than average head size.

Medical and physical concerns linked to chromosome 1q21.1 microduplication syndrome

Other findings

Some people with 1q21.1 duplication syndrome had cardiovascular or eye defects.

  • 45 out of 60 people had cardiovascular defects (75 percent)
  • 40 out of 60 people had eye defects (67 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.”

Sources and References

The content in this guide comes from published studies on chromosome 1q21.1 microduplication syndrome. Below you can find details about each study, as well as links to the full articles.

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