1q21.1 Deletion Syndrome
1q21.1 deletion syndrome is also called 1q21.1 microdeletion syndrome. For this webpage, we will be using the name 1q21.1 deletion syndrome to encompass the wide range of variants observed in the people identified.
What is 1q21.1 deletion syndrome?
1q21.1 deletion syndrome happens when someone is missing a piece of chromosome 1, one of the body’s 46 chromosomes. Chromosomes are structures in our cells that house our genes.
Key Role
The 1q21.1 deletion region plays a role in brain development.
Symptoms
Because the 1q21.1 deletion region is important in brain development and function, many people who have 1q21.1 deletion syndrome have:
- Low muscle tone
- Global developmental delay
- Intellectual disability
- Small head size
- Poor growth
- Behavioral issues like aggression
- Attention-deficit/hyperactivity disorder, or ADHD
- Sleep issues
- Autism
- Seizures
- Vision issues, such as strabismus (crossed eyes) or nystagmus (repetitive uncontrolled eye movement)
- Hearing loss
- Joint laxity
- Mild but nonspecific dysmorphic facial features
What causes 1q21.1 deletion syndrome?
1q21.1 deletion 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 deletion 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 deletion syndrome happens because the genetic variant was passed down from a parent.
Autosomal dominant conditions
1q21.1 deletion 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 deletion 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 1q21.1 deletion syndrome?
No parent causes their child’s 1q21.1 deletion 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 deletion 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 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 1q21.1 deletion syndrome, the sibling’s risk of having a child who has 1q21.1 deletion syndrome depends on the sibling’s genes and their parents’ genes.
- If neither parent has the same genetic variant causing 1q21.1 deletion syndrome, the symptom-free sibling has a nearly 0 percent chance of having a child who would inherit 1q21.1 deletion syndrome.
- If one biological parent has the same genetic variant causing 1q21.1 deletion 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 deletion syndrome, the risk of having a child who has the syndrome is about 50 percent.
Do all people who have 1q21.1 deletion syndrome have symptoms?
Not necessarily. Some people do not have any symptoms. Some people may not learn that they have this genetic change until it is found in their children.
Will all of the people in a family that have 1q21.1 deletion syndrome have symptoms?
Not necessarily. Family members who have the same chromosome change can have different symptoms.
How many people have 1q21.1 deletion syndrome?
As of 2024, at least 102 people with 1q21.1 deletion syndrome have been identified in medical research. The first case was found in 2008. There are likely many more undiagnosed people who have the syndrome.
Do people who have 1q21.1 deletion syndrome look different?
People who have 1q21.1 deletion syndrome may look different. Some people have a small head, also called microcephaly.
How is 1q21.1 deletion syndrome treated?
At this point, there are no medicines designed to treat 1q21.1 deletion 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 deletion 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. 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 deletion syndrome
The exact breakpoints of the deleted 1q21.1 region can vary. There are usually 7 genes deleted within what is called the recurring deletion. The region could be larger or there could be smaller deletions.
Speech and Learning
Most people with 1q21.1 deletion syndrome had developmental delay, language disorder, learning disabilities, or psychomotor delay.
- 82 out of 112 people had developmental delay or learning difficulties (73 percent)
Behavior
Some people with 1q21.1 deletion syndrome had attention-deficit/hyperactivity disorder (ADHD) and autism.
- 13 out of 112 people had ADHD (12 percent)
- 9 out of 106 people had autism (9 percent)
Brain
Some people with 1q21.1 deletion syndrome had seizures; a smaller than average head size, also called microcephaly; and low muscle tone. In a smaller number of people had brain imaging, about 1 in 3 had changes on magnetic resonance imaging (MRI).
- 15 out of 106 people had seizures (14 percent)
- 50 out of 112 people had microcephaly (45 percent)
- 10 out of 112 people had low muscle tone (9 percent)
- 13 out of 35 people had brain changes on MRI (37 percent)
Medical and physical concerns linked to 1q21.1 deletion syndrome
Feeding and digestion
People with 1q21.1 deletion syndrome had feeding difficulties or gastroesophageal reflux disease (GERD). Inguinal or umbilical hernias were rare. An inguinal hernia is a hernia around the groin area, and an umbilical hernia is a hernia in the umbilical region.
- 19 out of 112 people had feeding difficulties (17 percent)
- 13 out of 112 people had GERD (12 percent)
Eyes and eyesight
Vision issues included but were not limited to strabismus (crossed eyes), visual impairment, and iris or chorioretinal coloboma (when there is a gap or defect in the retina or choroid layers of the eye).
- 20 out of 112 people had strabismus (18 percent)
- 7 out of 46 people had visual impairment (15 percent)
- 3 out of 46 people had iris or chorioretinal coloboma (7 percent)
Other findings
Many people with 1q21.1 deletion syndrome had short height, poor growth, and musculoskeletal defects. In addition, there were various cardiac defects, which were more common in females than males.
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 1q21.1 deletion syndrome: www.simonssearchlight.org/research/what-we-study/1q21-1-deletions
- Simons Searchlight 1q21.1 deletion Facebook community: www.facebook.com/groups/168207334043737
Sources and References
The content in this guide comes from published studies on 1q21.1 deletion syndrome. Below you can find details about each study, as well as links to summaries or, in some cases, the full article.
- Bernier R. et al. Genetics in Medicine: Official Journal of the American College of Medical Genetics, 18, 341-349, (2016). Clinical phenotype of the recurrent 1q21.1 copy-number variant www.nature.com/articles/gim201578
- Buse M. et al. Italian Journal of Pediatrics, 43, 61, (2017). Expanding the phenotype of reciprocal 1q21.1 deletions and duplications: a case series www.ncbi.nlm.nih.gov/pmc/articles/PMC5518118
- Bourgois, A., Bizaoui, V., Colson, C., Vincent-Devulder, A., Molin, A., Gérard, M., & Gruchy, N. (2024). Phenotypic and genotypic characterization of 1q21.1 copy number variants: A report of 34 new individuals and literature review. American Journal of Medical Genetics Part A, 194(3), e63457. https://pubmed.ncbi.nlm.nih.gov/37881147/
- Guo, R., & Haldeman-Englert, C. R. 1q21.1 recurrent deletion. 2024 Feb 1. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from: https://www.ncbi.nlm.nih.gov/books/NBK52787/