KMT5B-Related 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 KMT5B-Related Syndrome.
a doctor sees a patient

KMT5B-related syndrome happens when there are changes to the KMT5B gene. These changes can keep the gene from working as it should.

Key Role

The KMT5B gene plays a key role in brain development.


Because the KMT5B gene is important in the development and function of brain cells, many people who have KMT5B-related syndrome have:

  • Intellectual disability
  • Autism

Our genes contain the instructions, or code, that tell our cells how to grow, develop, and work. Every child gets two copies of the KMT5B gene: one copy from their mother, from the egg, and one copy from their father, from the sperm. In most cases, parents pass on exact copies of the gene to their child. But the process of copying genes is not perfect. A change in the genetic code can lead to physical issues, developmental issues, or both.

Sometimes a random change happens in the sperm or egg. This change to the genetic code is called a ‘de novo’, or new, change. The child can be the first in the family to have the gene change.

De novo changes can take place in any gene. We all have some de novo changes, most of which don’t affect our health. But because KMT5B plays a key role in development, de novo changes in this gene can have a meaningful effect.

Research shows that KMT5B-related syndrome is often the result of a de novo change in KMT5B. Many parents who have had their genes tested do not have the KMT5B gene change found in their child who has the syndrome. In some cases, KMT5B-related syndrome happens because the gene change was passed down from a parent.

Dominant Inheritance

Children have a 50% chance of inheriting the genetic change.

Child who has genetic change in KMT5B gene

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

Why does my child have a change in the KMT5B gene?

No parent causes their child’s KMT5B-related syndrome. We know this because no parent has any control over the gene 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 gene change takes place on its own and cannot be predicted or stopped.

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 KMT5B-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 KMT5B-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 KMT5B-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 KMT5B-related syndrome is 50 percent.

For a person who has KMT5B-related syndrome, the risk of having a child who has the syndrome is about 50 percent.

As of 2019, doctors had found about a dozen people in the world with changes in the KMT5B gene. The first case of KMT5B-related syndrome was described in 2012. Scientists expect to find more people who have the syndrome as access to genetic testing improves.

People who have KMT5B-related syndrome may look different. Appearance can vary and can include some but not all of these features:

  • Broad forehead
  • Long, oval face

Scientists and doctors have only just begun to study KMT5B-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 KMT5B-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:

This section includes a summary of information from a published article describing four people who have the syndrome. To learn more about the article, see the Sources and references section of this guide.


  • All four people in the study had some level of intellectual disability.


  • Two out of four people had autism.

Eyes and eyesight

  • 2 out of 4 people had crossed eyes.


  • 2 out of 4 people in the study had seizures.

Joints and spine

  • 2 out of 4 people had very flexible joints.

Muscle tone

  • 1 out of 4 people had low muscle tone.

Birth defects

  • 2 out of 4 people had a condition in which the ring and pinky fingers are permanently bent.

Where can I find support and resources?

KMT5B Gene Facebook Group

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 and click “Join Us.”

Sources and References

The content in this guide comes from a published study about KMT5B-related syndrome. Below you can find details about the study, as well as a link to a summary and the full article.

  • Faundes V. et al. American Journal of Human Genetics, 102, 175-187, (2018). Histone lysine methylases and demethylases in the landscape of human developmental disorders