What Causes Rett Syndrome? Genetics and Risk Factors

Because Rett syndrome is uncommon and complex, caregivers often have questions about why it happens and whether it could have been prevented. Some people may also wonder whether the condition can affect other family members. Researchers now understand that Rett syndrome has a clear genetic cause, but there are very few known risk factors.

This article explains what causes Rett syndrome, the role of genetics, and what this means for families with the condition.

Rett Syndrome Is a Genetic Condition

According to BMJ Paediatrics Open, Rett syndrome affects up to 1 in 10,000 girls under age 12. This rare genetic disorder affects brain development and leads to challenges with movement, communication, and daily functioning. Early signs can be subtle in the first year or two of life. Later, often between about 18 and 30 months, some children begin to lose skills they had gained, such as speech, purposeful hand use, or the ability to walk. Over time, they may also develop seizures, breathing problems, scoliosis, and heart rhythm changes.

Rett syndrome is caused by mutations, or changes, to a gene known as MECP2. This gene provides instructions for making a protein that helps control how other genes are turned on and off, especially in brain cells. The MECP2 protein plays a key role in neurological (brain) development and in how nerve cells communicate with each other.

When the MECP2 gene doesn’t work as it should, brain cells may not develop or function normally. This leads to the symptoms seen in Rett syndrome, including loss of development, trouble with movement, and problems with breathing or heart rhythm.

Changes in the MECP2 gene disrupt brain development and how brain cells connect with each other over time. This helps explain why many children with Rett syndrome appear to develop typically in early infancy, before symptoms become noticeable later on.

What Is the MECP2 Gene?

The MECP2 gene is on the X chromosome, one of the two sex chromosomes. Females typically have two X chromosomes, while males usually have one X and one Y chromosome, according to Cleveland Clinic. Because MECP2 is on the X chromosome, Rett syndrome mostly affects females.

The MECP2 protein helps control gene activity in the brain. It’s especially important after birth, when the brain is rapidly forming new connections. When MECP2 doesn’t work properly, these processes are disrupted. This helps explain the developmental differences in Rett syndrome.

Different mutations in the MECP2 gene can affect people in different ways. Some lead to more severe symptoms, while others cause milder or less typical forms of Rett syndrome.

Most Cases Happen by Chance

One of the most important facts about Rett syndrome is that most cases are not inherited. Instead, the MECP2 genetic change usually happens randomly before birth, either in the egg or the sperm or very early after fertilization. These are called de novo changes, meaning they’re new and not passed down from either parent.

Because the genetic change happens by chance, caregivers don’t cause Rett syndrome. Parenting choices, environmental exposures, or pregnancy behaviors don’t lead to Rett syndrome.

Can Rett Syndrome Be Passed Down?

According to the National Institute of Neurological Disorders and Stroke, in extremely rare cases, a woman may have no symptoms of Rett syndrome. This can happen when the MECP2 mutation is mild, and the healthy X chromosome is used more often in the cells. In that situation, there is a 50 percent chance that the MECP2 gene mutation will be passed to each child.

However, these inherited cases are uncommon. Most families that have one child with Rett syndrome won’t have another affected child.

Why Rett Syndrome Mostly Affects Girls

Rett syndrome primarily affects girls because of the way the X chromosome works. Since females have two X chromosomes, they usually have one normal copy of the MECP2 gene and one altered copy. This means some cells can still use the working gene, which supports survival and can lead to the classic form of Rett syndrome.

In contrast, males typically have only one X chromosome, according to Cleveland Clinic. If that single copy of MECP2 has a severe mutation, the effects are often much more serious. Many male fetuses with classic MECP2 changes don’t survive past pregnancy or die shortly after birth.

Rett Syndrome in Boys

Although rare, Rett syndrome can occur in boys, according to the International Rett Syndrome Foundation. When it does, it often looks different and may be more severe. Boys with MECP2 genetic changes may experience:

• Symptoms starting at birth
• Significant developmental impairment
• Life-threatening complications early in life

In some cases, male infants survive because of:

• A less severe MECP2 mutation
• An extra X chromosome (a condition known as Klinefelter syndrome)
• Mosaicism, in which only some cells carry the genetic change

These situations allow some normal MECP2 function, which may allow survival beyond pregnancy.

Known Risk Factors for Rett Syndrome

Because Rett syndrome usually occurs randomly, there are very few known risk factors. Researchers have identified the following factors associated with the condition:

• Spontaneous MECP2 change — The biggest risk factor is having a random change in the MECP2 gene, which can’t currently be prevented.
• Being female — Female infants have the highest likelihood of developing Rett syndrome.

What Doesn’t Cause Rett Syndrome?

Clear evidence shows that this neurodevelopmental disorder is not caused by:

• Parenting style or caregiving practices
• Environmental exposures during infancy
• Older parental age
• Vaccines
• Diet or nutrition
• Pregnancy stress or routine illness

These factors don’t cause MECP2 mutations and therefore don’t lead to Rett syndrome. Understanding this can help reduce guilt or self-blame, which is common among caregivers after diagnosis.

Can Rett Syndrome Be Prevented?

At this time, Rett syndrome can’t be prevented. Because almost all cases result from spontaneous genetic changes that occur before birth, there’s no known way to stop the mutation from happening.

If someone has one child with Rett syndrome, the chance of another child developing it is less than 1 percent. If someone’s concerned about this risk in future pregnancies, genetic counseling may help them discuss testing options for future pregnancies.

Why Understanding the Cause Matters

Knowing that Rett syndrome is caused by a gene change can help doctors confirm a diagnosis. Testing for MECP2 gene changes can help confirm Rett syndrome when someone has symptoms. However, having a MECP2 mutation alone is not enough to diagnose Rett syndrome.

This knowledge has also helped scientists work on treatments that focus on the specific problems caused by Rett syndrome. It’s also helped researchers figure out how different types of mutations affect health outcomes in people with Rett syndrome.

Caregivers should talk with healthcare providers about genetic testing and long-term care plans. A medical team for Rett syndrome may include doctors who specialize in the brain, genetics, and heart health, as well as therapists who help with movement, speech, and daily skills.

Rett syndrome is a lifelong condition, but new research and better care are helping people with Rett syndrome live fuller lives and improve their long-term health. With the right medical care, therapy, and support at home and school, many people can build skills, stay connected, and take part in daily life in meaningful ways. If you think you or a loved one may have Rett syndrome, talk with a specialist about genetic testing and care options.

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