Diagnosing Rett Syndrome: How Doctors Identify the Condition

When a child stops acting in ways they used to — no longer babbling, reaching for toys, or looking at the people around them — it can be deeply concerning for families. These changes, especially after months of what seemed like normal growth, often lead caregivers to look for answers. For some families, the answer is Rett syndrome.

Rett syndrome is a rare genetic disorder that affects brain development. It happens mostly in females, according to University of Michigan Health-Sparrow. Babies with Rett syndrome usually seem to grow and learn normally for the first six to 18 months of life. After that, they start to lose skills they once had — like crawling, walking, talking, or using their hands on purpose.

This article explains how doctors determine if a child has Rett syndrome, covering the early warning signs, how clinicians watch development over time, the role of genetic testing, and how other conditions are ruled out.

Recognizing the Early Signs

The path to a Rett syndrome diagnosis often starts when caregivers or healthcare providers notice that a child has stopped making progress — or has started going backward. Knowing what to look for can help families make sense of what they are seeing.

Understanding Developmental Regression

Losing skills, called developmental regression, is the main sign of Rett syndrome. To be diagnosed with typical Rett syndrome, a child must go through a period of losing skills, followed by a leveling off or some recovery. Clinicians also look for four key features: loss of purposeful hand use, loss of spoken language, walking problems, and repetitive hand movements.

This regression doesn’t always look the same from child to child. Sometimes it happens fast — caregivers may feel like their child changed almost overnight. More often, the changes happen slowly over weeks or months. Families may notice less interest in surroundings, less eye contact, or hands that no longer reach and grab. These changes are usually most noticeable between 12 and 18 months of age.

Identifying Physical and Behavioral Changes

Along with losing skills, children with Rett syndrome often show certain physical and behavioral signs. Repetitive hand movements are one of the most common features, including hand wringing, clasping, squeezing, flapping, mouthing, tapping, or rubbing the hands together. These actions take the place of purposeful hand use.

Breathing abnormalities are also common. A child may hold their breath, breathe very fast, blow out air or saliva forcefully, or swallow air. Healthcare providers may also notice unusual eye movements. Some children develop a strong way of communicating with their eyes, sometimes called eye pointing.

Slowed head growth is another distinct sign. Over time, the rate of head growth often decreases, leading to acquired microcephaly (a head size that is smaller than expected for the child’s age).

Many children with Rett syndrome develop hypotonia, which means their muscles feel loose or floppy. This can make it harder to sit up straight, move around, or keep balance.

Changes in motor skills are another key sign. Walking often becomes wide-based and unsteady, with shorter steps and a slower speed. Some children lose the ability to walk entirely, while others can still get around but with clear difficulty.

Observing Development Over Time

Unlike many conditions that show up on a single test, Rett syndrome is mainly diagnosed by watching how a child grows and changes. Clinicians pay close attention to patterns of skill loss and the appearance of certain signs over time.

There’s no single lab test or brain scan that can confirm Rett syndrome on its own. Instead, healthcare providers look at early growth patterns, ask detailed questions about development, and do regular physical and neurological checkups. This process often takes time as doctors gather information and track how symptoms change.

This step-by-step approach matters because many early signs of Rett syndrome — like delays in learning or less interest in people — can look like other conditions. Watching how these signs change over time helps clinicians tell Rett syndrome apart from other possibilities.

Confirming the Diagnosis With Genetic Testing

While watching development is the main way to diagnose Rett syndrome, genetic testing also plays a helpful role. Knowing what genetic testing can and cannot show helps caregivers understand what to expect.

Understanding the MECP2 Gene

Most cases of classic Rett syndrome are linked to a mutation (change) in the MECP2 gene on the X chromosome. The MECP2 gene is important for brain development. When it doesn’t work properly, it affects how the brain grows and functions. Between 80 percent and 97 percent of people with a diagnosis of Rett syndrome have a detectable MECP2 mutation, which is found through a blood test. Some children with Rett-like symptoms may have changes in other genes, so doctors may sometimes look beyond MECP2.

A positive result can give families a clearer answer after what is often a confusing and uncertain time. It can also help them connect with clinical trials, support groups, and other families going through similar experiences.

Interpreting Genetic Test Results

Genetic testing helps support a diagnosis, but it doesn’t give a final answer on its own. Finding an MECP2 mutation points toward Rett syndrome, but a child still needs to show the right signs to be diagnosed. If a genetic change is found but the child doesn’t meet the clinical criteria for Rett syndrome, they may not receive that diagnosis.

The opposite can also happen. Some children clearly have Rett syndrome based on their symptoms, but testing doesn’t find an MECP2 mutation. In these cases, clinicians rely on what they observe — the pattern of skill loss, the hand movements, how development unfolds — to make the diagnosis.

Test results also cannot predict how mild or severe symptoms will be. Two people with the same genetic change can be affected very differently. This means genetic information is useful, but it cannot tell the whole story.

Ruling Out Other Conditions

Because several conditions look similar to Rett syndrome, healthcare providers usually do extra checks to make sure nothing else explains the symptoms. This helps ensure the right diagnosis and the right care.

Gathering Developmental History

A detailed history of how a child has developed is one of the most helpful tools. Clinicians ask about when the child reached developmental milestones like sitting, walking, and first words of spoken language. They ask about any skill loss, when it happened, and family health history. Caregivers often know details that don’t show up during a short office visit, making their input very valuable.

Conducting Physical and Neurological Exams

A physical exam helps healthcare providers spot signs that fit with Rett syndrome. Measurements may show slower-than-expected growth. Neurological exams check movement, reflexes, muscle tone, and coordination — all areas that Rett syndrome can affect.

Clinicians also look for signs of epilepsy, which affects many people with Rett syndrome. Seizures can start at different ages and range from mild to severe. Catching epilepsy early helps ensure the right treatment and monitoring are in place.

Ordering Additional Tests When Needed

Sometimes doctors order extra tests to rule out other conditions. These tests might include brain scans like MRIs or CT scans, brain wave tests called electroencephalograms (EEGs), or blood and urine tests that check for metabolic problems.

These tests don’t diagnose Rett syndrome directly. Instead, they help rule out conditions — like autism spectrum disorder, cerebral palsy, or metabolic disorders — that can look similar at first. Once other causes have been ruled out and the signs match the known pattern, healthcare providers can move forward with a Rett syndrome diagnosis.

Taking the Next Steps

Diagnosing Rett syndrome takes time. It combines careful watching of how a child develops, thorough medical exams, and often genetic testing. While no single test confirms the condition, the combination of key signs — skill loss, changes in hand use, repetitive hand movements, and other brain-related symptoms — allows healthcare providers to make a confident diagnosis. Finding Rett syndrome early may help families get answers and support sooner, including physical therapy for movement and strength, occupational therapy to support everyday tasks, and other services matched to a child’s needs.

Caregivers who are worried about a child’s development can take simple steps to prepare for doctor visits. Writing down developmental milestones and any changes over time gives healthcare providers useful information. Recording short videos of unusual movements or behaviors can show behaviors that are hard to describe in words. Making a list of questions ahead of time helps ensure nothing important is forgotten.

Talking with a pediatric neurologist, developmental specialist, or other child healthcare provider is an important first step for families who notice signs of skill loss or other worrying changes. A healthcare team can walk families through the process and discuss next steps based on each child’s situation.

Join the Conversation

On MyRettTeam, people share their experiences with Rett syndrome, get advice, and find support from others who understand.

Which early sign of Rett syndrome do you think is the hardest to spot? Let others know in the comments below.