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.
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What is chromosome 1q21.1 duplication syndrome?

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 behavior issues

What causes 1q21.1 duplication syndrome?

1q21.1 duplication syndrome is caused when someone has an extra piece of chromosome 1, one of the body’s 46 chromosomes.

Our cells contain genes that instruct the body on how to grow and function. The genes are arranged in long threads called chromosomes.

We inherit chromosomes from our parents. When the sperm from the father joins the egg from the mother, they form a single cell with 46 chromosomes — 23 from the mother and 23 from the father. This cell then makes many copies of itself.

Dominant inheritance

Children have a 50% chance of inheriting the genetic change

Some people inherit a gene change from a parent. In other people, small mistakes can occur when genes are copied. Parts of the chromosomes can break off, make extra copies, or end up in a different order than expected. When this happens, it is called a “de novo”, or new, change. The child can be the first in the family to have the gene change.

People who have 1q21.1 duplication syndrome have an extra piece of chromosome 1. The extra piece can affect learning and how the body develops. Researchers are trying to learn more about what the genes in this extra piece do.

Child who has genetic change in 1q21.1 gene

Genetic change occurs in egg or sperm after fertilization
Child with de novo genetic change in autism gene

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 chromosomes of both birth parents.

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

For a symptom-free sibling, a brother or sister, of someone who has 1q21.1 duplication 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 chromosome 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 the syndrome.
  • If one birth parent has the same chromosome 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 chromosome change as the child who has the syndrome, the symptom-free sibling’s chance of having a child who has 1q21.1 duplication syndrome is about 50 percent.

For a person who has 1q21.1 duplication syndrome, their 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?

About 3 in 10,000 people have 1q21.1 duplication syndrome. The first case was found in 2008. There are likely many more undiagnosed people who have the syndrome. 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?

In general, people who have 1q21.1 duplication syndrome do not look very different.

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 published articles. It highlights how many people have different symptoms. See the Sources and references section of this guide for a list of articles.

Behavior and development concerns linked to 1q21.1 duplication syndrome

Learning

Many people have learning issues. But most do not have intellectual disability.

Many people have some level of developmental delay. This often includes issues with fine motor skills, such as using the hands to write.

  • 20% have an intellectual disability.

Behavior

Some people who have the syndrome have attention deficit hyperactivity disorder (ADHD) or autism.

  • 40% have autism.
  • 30% have ADHD.

Speech

Some people have some trouble understanding and forming words.

  • 38% have trouble forming words.
20%
20% of people have an intellectual disability.
40%
40% of people have autism.
30%
30% of people have ADHD.
38%
38% of people have trouble forming words.

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

Sitting and walking

4 out of 10 people (39%) have trouble walking.

Joints and spine

About a third (36%) have a curved spine, also called scoliosis.

Growth

More than a quarter (27%) are short.

Eating and gastrointestinal issues

About a quarter of people (27%) have stomach ulcers.

Head

About a quarter (26%) have larger than average head size.

Muscle tone

Almost 2 out of 10 (16%) have low muscle tone.

39%
4 out of 10 people have trouble walking.
36%
About a third have a curved spine, also called scoliosis.
27%
More than a quarter are short.
27%
About a quarter of people have stomach ulcers.
26%
About a quarter have larger than average head size.
16%
Almost 2 out of 10 have low muscle tone.

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.

  • Bernier R. et al. Genetics in Medicine, 18, 341-349 (2016). Clinical phenotype of the recurrent 1q21.1 copy-number variant
    www.nature.com/articles/gim201578
  • Brunetti-Pierri N. et al. Nature Genetics, 40, 1466-1471 (2008). Recurrent reciprocal 1q21.1 deletions and duplications associated with microcephaly or macrocephaly and developmental and behavioral abnormalities
    www.ncbi.nlm.nih.gov/pmc/articles/PMC2680128
  • Mefford H.C. et al. New England Journal of Medicine, 359, 1685-1699 (2008). Recurrent rearrangements of chromosome 1q21.1 and variable pediatric phenotypes www.ncbi.nlm.nih.gov/pmc/articles/PMC2703742

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