What is Rett syndrome

Rett syndrome is a rare genetic disease that causes neurological (brain) and developmental disorder that occurs almost exclusively in girls. Although very rare, boys can also have Rett Syndrome. Rett syndrome is related to autism spectrum disorder. Infants with Rett syndrome seem to grow and develop normally at first, but then they stop developing and even lose skills in different stages of the disease over a lifetime.

Rett syndrome was identified by Dr. Andreas Rett, an Austrian physician who first described it in a journal article in 1966. It was not until after a second article about the disorder, published in 1983 by Swedish researcher Dr. Bengt Hagberg, that the disorder was generally recognized.

The course of Rett syndrome, including the age of onset and the severity of symptoms, varies from child to child. After birth, girls with classic Rett syndrome have 6 to 18 months of apparently normal development, although there are often subtle abnormalities even in early infancy, such as loss of muscle tone (hypotonia), difficulty feeding, and jerkiness in limb movements, before developing severe problems with language and communication, learning, coordination, and other brain functions. Early in childhood, affected girls lose purposeful use of their hands and begin making repeated hand wringing, washing, or clapping motions. The onset of this period of regression is sometimes sudden. Children with Rett syndrome tend to grow more slowly than other children and have a small head size (microcephaly). Other signs and symptoms that can develop include breathing abnormalities, seizures, an abnormal side-to-side curvature of the spine (scoliosis), and sleep disturbances.

Rett syndrome symptoms include:

• Loss of speech
• Loss of hand movements such as grasping
• Compulsive movements such as hand wringing
• Balance problems
• Breathing problems
• Behavior problems
• Learning problems or intellectual disability

Many children with Rett syndrome are unable to speak, walk or use their hands. Breathing problems, feeding tubes, seizures, anxiety, gastrointestinal and orthopedic issues are common.

Children with Rett syndrome often exhibit autistic-like behaviors in the early stages. Other symptoms may include walking on the toes, sleep problems, a wide-based gait, teeth grinding and difficulty chewing, slowed growth, seizures, cognitive disabilities, and breathing difficulties while awake such as hyperventilation, apnea (breath holding), and air swallowing.

Apraxia — the inability to perform motor functions — is perhaps the most severely disabling feature of Rett syndrome, interfering with every body movement, including eye gaze and speech.

Rett syndrome is estimated to affect one in every 10,000 to 15,000 live female births and in all racial and ethnic groups worldwide. In more than 99 percent of people with Rett syndrome, there is no history of the disorder in their family. Many of these cases result from new mutations in the Methylcytosine-binding protein 2 (MECP2) gene. The MECP2 gene is located on the X chromosome. Between 90% and 95% of girls with Rett syndrome have a mutation in the MECP2 gene ¹. Girls with Rett therefore have two MECP2 genes, one that is mutated and one that is normal. Among families with a child affected by Rett syndrome the chance of having a second child with the syndrome is less than 1% ².

While Rett Syndrome remains a clinical diagnosis based on the child’s symptoms and history, the identification of MECP2 has made DNA testing and confirmation possible for affected individuals and their families. To date, approximately 95% of girls with a clinical diagnosis of Rett have a confirmed MECP2 mutation.

Researchers have described several variant or atypical forms of Rett syndrome, which can be milder or more severe than the classic form.

Rett syndrome has no cure. You can treat some of the symptoms with medicines, surgery, and physical and speech therapy. Most people with Rett syndrome live into middle age and beyond. They will usually need care throughout their lives.

Rett syndrome life expectancy

Despite the difficulties with symptoms, many individuals with Rett syndrome continue to live well into middle age and beyond. Because the disorder is rare, very little is known about long-term prognosis and life expectancy. While there are women in their 40s and 50s with the disorder, currently it is not possible to make reliable estimates about life expectancy beyond age 40.

Patients with Rett syndrome generally survive into their fifth or sixth decade of life and there have been reports of women surviving into their seventies.

Risk factors that decrease life expectancy include epilepsy, loss of mobility, and swallowing difficulties.

It is difficult to predict the neurodevelopmental outcomes in patients with Rett syndrome. Some patients retain some functional ability and 60% of patients with Rett syndrome will continue to walk, however others will have severe disabilities.

With appropriate medical care, physiotherapy, occupational therapy and good nutrition life expectancy is dramatically increased.

Rett syndrome prognosis

Children with this condition have problems with physical and social development. They generally suffer the loss of many motor, or movement, skills – such as walking and use of their hands – and develop poor coordination. In addition, there is loss of language skills previously acquired.

Rett syndrome generally becomes evident when the patient 2-4 years of age; however, the underlying developmental problems may starts in infants as young as 6 months. The patient goes through a period where development remains static followed by a period of developmental regression. Disease progression stabilizes in many patients once they reach adolescence and although they may regain some function they never fully recover. Death in Rett syndrome patients can occur suddenly and is often secondary to pneumonia.

Many patients with Rett syndrome also have scoliosis. With the progression of disease, muscle tone seems to change from hypotonia to spasticity to rigidity and subsequent wasting, resulting in many patients being wheelchair bound after 10 years.

Rett syndrome complications

Complications of Rett syndrome include:

• Needing lifelong care and assistance with activities of daily living
• Sleep problems, including unusual sleep patterns such as falling asleep during the day or waking up at night
• Difficulty eating, leading to poor nutrition and delayed growth
• Constipation, which can be a severe, ongoing problem, as well as other gastrointestinal (GI) problems, such as gastroesophageal reflux disease (GERD)
• Muscle and joint problems
• Anxiety and problem behavior that may compromise social functioning
• Shortened life span — people with Rett syndrome don’t live as long as most people because of heart problems and other health complications

Rett syndrome causes

In more than 99 percent of people with Rett syndrome, there is no history of the disorder in their family. Many of these cases result from new mutations in the methylcytosine-binding protein 2 (MECP 2) gene. The MECP2 gene is located on the X chromosome. Between 90% and 95% of girls with Rett syndrome have a mutation in the MECP2 gene ³. Among families with a child affected by Rett syndrome the chance of having a second child with the syndrome is less than 1% ².

Not everyone who has an MECP2 mutation has Rett syndrome. Scientists have identified mutations in the CDKL5 and FOXG1 genes in individuals who have atypical or congenital Rett syndrome, but they are still learning how those mutations cause the disorder. Scientists believe the remaining cases may be caused by partial gene deletions, mutations in other parts of the MECP2 gene, or additional genes that have not yet been identified, and they continue to look for other causes.

Classic Rett syndrome and some variant forms of the condition are caused by mutations in the methylcytosine-binding protein 2 (MECP 2) gene. This gene provides instructions for making a protein (MeCP2) that is critical for normal brain function. Although the exact function of the MeCP2 protein is unclear, it is likely involved in maintaining connections (synapses) between nerve cells (neurons). It may also be necessary for the normal function of other types of brain cells.

The MeCP2 protein is thought to help regulate the activity of genes in the brain. This protein may also control the production of different versions of certain proteins in brain cells. Mutations in the MECP2 gene alter the MeCP2 protein or result in the production of less protein, which appears to disrupt the normal function of neurons and other cells in the brain. Specifically, studies suggest that changes in the MeCP2 protein may reduce the activity of certain neurons and impair their ability to communicate with one another. It is unclear how these changes lead to the specific features of Rett syndrome.

Some researchers suggest that the specific type of mutation in the MECP2 gene affects the severity of symptoms of Rett syndrome. Studies are now underway to understand each mutation that may cause the features of Rett syndrome, and how these mutations might change the features of the syndrome.

Several conditions with signs and symptoms overlapping those of Rett syndrome have been found to result from mutations in other genes. These conditions, including FOXG1 syndrome, were previously thought to be variant forms of Rett syndrome. However, doctors and researchers have identified some important differences between the conditions, so they are now usually considered to be separate disorders.

A few families with more than one affected family member have been described. These cases helped researchers determine that classic Rett syndrome and variants caused by MECP2 gene mutations have an X-linked dominant pattern of inheritance. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. The inheritance is dominant if one copy of the altered gene in each cell is sufficient to cause the condition.

Males with mutations in the MECP2 gene often die in infancy. However, a small number of males with a genetic change involving MECP2 have developed signs and symptoms similar to those of Rett syndrome, including intellectual disability, seizures, and movement problems. In males, this condition is described as MECP2-related severe neonatal encephalopathy.

Is Rett syndrome inherited?

Although Rett syndrome is a genetic disorder, less than 1 percent of recorded cases are inherited or passed from one generation to the next. Most cases are spontaneous, which means the mutation occurs randomly. However, in some families of individuals affected by Rett syndrome, there are other female family members who have a mutation of their MECP2 gene but do not show clinical symptoms. These females are known as “asymptomatic female carriers.”

Can I Predict my Child’s Symptoms From the Mutation?

One variable that plays a role in symptom severity is X inactivation. Females have two X chromosomes, while males have one. In order for males and females to have the same amount of genetic material, females must silence one of their X chromosomes in every cell. Most females have a random inactivation pattern which activates roughly 50% of one X and 50% of the other. However, for reasons unknown it can happen that a female will skew one X over the other.

If a girl with Rett syndrome favors inactivation of the X chromosome with the mutated MECP2 she will have less severe symptoms. If the reverse happens the child may have more severe symptoms. Although it is possible to have your daughter’s X inactivation pattern in her blood tested this will not tell you what the pattern is in her brain, so the clinical usefulness of this test at this point in time is limited.

Another variable is the child’s own genetic make-up. There are individuals with mutations in MECP2 and normal X chromosome skewing who do not have Rett symptoms. It is likely that these individuals have mutations in other genes that confer protection against their mutated MECP2 gene.

Rett Syndrome in Boys

Although rare, males can have mutations in MECP2. Because males have a different chromosome combination from females, boys who have the genetic mutation that causes Rett syndrome are affected in devastating ways. Most of them die before birth or in early infancy.

A very small number of boys have a different mutation that results in a less destructive form of Rett syndrome. Similar to girls with Rett syndrome, these boys will likely live to adulthood, but they’re still at risk of a number of intellectual and developmental problems.

There are three scenarios which may lead to males with Rett syndrome:

1. A boy has Klinefelter Syndrome (which happens in 1 in 1,000 male births) and is born with an extra X chromosome (XXY). One of the X’s has the mutation and the other does not. These boys will have symptoms similar to girls with Rett syndrome.
2. A mutation derives not from the sperm or the egg but rather at a slightly later stage, such as the 20-cell stage (blastula). If one cell becomes mutated, every cell downstream to it will also mutate, while the remaining 19 cells and all cells that originate from them will not. This is called somatic mosaicism and the phenotype will resemble a girl with Rett syndrome, since the somatic mosaicism will function similarly to X inactivation patterns in girls.
3. A boy is born with a typical XY karotype and has mutations in MECP2 on all of his X chromosomes. Since he has no healthy copy to mitigate the mutated gene his symptoms are typically more severe than in girls. However, for reasons not yet understood, there are some boys with “milder” mutations.

MECP2 Duplication Syndrome

Unlike Rett Syndrome, which is caused by mutations or deletions in the MECP2 gene, the symptoms that arise from the duplication syndrome are caused, as the name suggests, by having an area of the X chromosome (Xq28), which includes the MECP2 gene, erroneously duplicated. The section duplicated may vary from individual to individual and may also contribute to the severity of the disease.

The syndrome has been diagnosed mostly in boys. The majority inherits the duplication from their mothers who are typically asymptomatic due to favorable X chromosome inactivation (the moms have inactivated the X chromosome that harbors the duplication). Carrier mothers have a 50% chance of passing on the duplication to their children.

The MECP2 Duplication Syndrome may be quite prevalent. Preliminary studies suggest that 1% of cases of X-linked intellectual disability may be due to this syndrome. The core phenotypes in boys include infantile hypotonia, mild dysmorphic features, developmental delay, absent to minimal speech, recurrent infections, progressive spasticity especially of the lower limbs, ataxia, autistic features, and seizures. Females with MECP2 duplication without X chromosome inactivation skewing have been reported and present similarly to boys.

Who gets Rett syndrome?

Rett syndrome is estimated to affect one in every 10,000 to 15,000 live female births and in all racial and ethnic groups worldwide. Prenatal testing is available for families with an affected daughter who has an identified MECP2 mutation. Since the disorder occurs spontaneously in most affected individuals, however, the risk of a family having a second child with the disorder is less than 1 percent.

Genetic testing is also available for sisters of girls with Rett syndrome who have an identified MECP2 mutation to determine if they are asymptomatic carriers of the disorder, which is an extremely rare possibility.

The MECP2 gene is found on a person’s X chromosome, one of the two sex chromosomes. Girls have two X chromosomes, but only one is active in any given cell. This means that in a girl with Rett syndrome only a portion of the cells in the nervous system will use the defective gene. Some of the child’s brain cells use the healthy gene and express normal amounts of the protein.

The severity of Rett syndrome in girls is in part a function of the percentage of their cells that express a normal copy of the MECP2 gene. If the active X chromosome that is carrying the defective gene is turned off in a large proportion of cells, the symptoms will be mild, but if a larger percentage of cells have the X chromosome with the normal MECP2 gene turned off, onset of the disorder may occur earlier and the symptoms may be more severe.

The story is different for boys who have a MECP2 mutation known to cause Rett syndrome in girls. Because boys have only one X chromosome (and one Y chromosome) they lack a back-up copy that could compensate for the defective one, and they have no protection from the harmful effects of the disorder. Boys with such a defect frequently do not show clinical features of Rett syndrome but experience severe problems when they are first born and die shortly after birth. A very small number of boys may have a different mutation in the MECP2 gene or a sporadic mutation after conception that can cause some degree of intellectual disability and developmental problems.

Rett syndrome stages

Scientists generally describe four stages of Rett syndrome.

Stage I, called early onset, typically begins between 6 and 18 months of age. This stage is often overlooked because symptoms of the disorder may be somewhat vague, and parents and doctors may not notice the subtle slowing of development at first. The infant may begin to show less eye contact and have reduced interest in toys. There may be delays in gross motor skills such as sitting or crawling. Hand-wringing and decreasing head growth may occur, but not enough to draw attention. This stage usually lasts for a few months but can continue for more than a year.

Stage II, or the rapid destructive stage, usually begins between ages 1 and 4 and may last for weeks or months. Its onset may be rapid or gradual as the child loses purposeful hand skills and spoken language. Characteristic hand movements such as wringing, washing, clapping, or tapping, as well as repeatedly moving the hands to the mouth often begin during this stage. The child may hold the hands clasped behind the back or held at the sides, with random touching, grasping, and releasing. The movements continue while the child is awake but disappear during sleep. Breathing irregularities such as episodes of apnea and hyperventilation may occur, although breathing usually improves during sleep. Some girls also display autistic-like symptoms such as loss of social interaction and communication. Walking may be unsteady and initiating motor movements can be difficult. Slowed head growth is usually noticed during this stage.

Stage III, or the plateau or pseudo-stationary stage, usually begins between ages 2 and 10 and can last for years. Apraxia, motor problems, and seizures are prominent during this stage. However, there may be improvement in behavior, with less irritability, crying, and autistic-like features. A girl in stage III may show more interest in her surroundings and her alertness, attention span, and communication skills may improve. Many girls remain in this stage for most of their lives.

Stage IV, or the late motor deterioration stage, can last for years or decades. Prominent features include reduced mobility, curvature of the spine (scoliosis) and muscle weakness, rigidity, spasticity, and increased muscle tone with abnormal posturing of an arm, leg, or top part of the body. Girls who were previously able to walk may stop walking. Cognition, communication, or hand skills generally do not decline in stage IV. Repetitive hand movements may decrease and eye gaze usually improves.

Rett syndrome symptoms

Babies with Rett syndrome are generally born after a normal pregnancy and delivery. The age at which symptoms begin and their severity and associated disability varies widely among individuals. However, most babies with Rett syndrome seem to grow and behave normally for the first six months. After that, signs and symptoms start to appear.

The most pronounced changes generally occur at 12 to 18 months of age, suddenly, or over a period of weeks or months.

Rett syndrome signs and symptoms include:

• Slowed growth. Brain growth slows after birth. Smaller than normal head size (microcephaly) is usually the first sign that a child has Rett syndrome. As children get older, delayed growth in other parts of the body becomes evident.
• Loss of normal movement and coordination. The first signs often include reduced hand control and a decreasing ability to crawl or walk normally. At first, this loss of abilities occurs rapidly and then it continues more gradually. Eventually muscles become weak or may become rigid or spastic with abnormal movement and positioning.
• Loss of communication abilities. Children with Rett syndrome typically begin to lose the ability to speak, to make eye contact and to communicate in other ways. They may become disinterested in other people, toys and their surroundings. Some children have rapid changes, such as a sudden loss of speech. Over time, most children gradually regain eye contact and develop nonverbal communication skills.
• Abnormal hand movements. Children with Rett syndrome typically develop repetitive, purposeless hand movements that may differ for each person. Hand movements may include hand wringing, squeezing, clapping, tapping or rubbing.
• Unusual eye movements. Children with Rett syndrome tend to have unusual eye movements, such as intense staring, blinking, crossed eyes or closing one eye at a time.
• Breathing problems. These include breath-holding, abnormally rapid breathing (hyperventilation), forceful exhalation of air or saliva, and swallowing air. These problems tend to occur during waking hours, but not during sleep.
• Agitation and irritability. Children with Rett syndrome become increasingly agitated and irritable as they get older. Periods of crying or screaming may begin suddenly, for no apparent reason, and last for hours.
• Other abnormal behaviors. These may include, for example, sudden, odd facial expressions and long bouts of laughter, hand licking, and grasping of hair or clothing.
• Cognitive disabilities. Loss of skills can be accompanied by a loss of intellectual functioning.
• Seizures. Most people who have Rett syndrome experience seizures at some time during their lives.
• Abnormal curvature of the spine (scoliosis). Scoliosis is common with Rett syndrome. It typically begins between 8 and 11 years of age and increases with age. Surgery may be required if the curvature is severe.
• Irregular heartbeat. This is a life-threatening problem for many children and adults with Rett syndrome and can result in sudden death.
• Pain. Because of health problems, people with Rett syndrome may have an increased risk of pain. But communication problems may prevent others from recognizing these pain issues. In one small study, one-fourth of the parents estimated that their daughters have more than a week of pain each month.
• Other symptoms. A variety of other symptoms can occur, such as thin, fragile bones prone to fractures; small hands and feet that are usually cold; problems with chewing and swallowing; and teeth grinding. Symptoms can vary greatly from child to child.

Rett syndrome diagnosis

Doctors clinically diagnose Rett syndrome by observing signs and symptoms during the child’s early growth and development, and conducting ongoing evaluations of the child’s physical and neurological status. Scientists have developed a genetic test to complement the clinical diagnosis, which involves searching for the MECP2 mutation on the child’s X chromosome.

A pediatric neurologist, clinical geneticist, or developmental pediatrician should be consulted to confirm the clinical diagnosis of Rett syndrome. The physician will use a highly specific set of guidelines that are divided into three types of clinical criteria: main, supportive, and exclusion. The presence of any of the exclusion criteria negates a diagnosis of classic Rett syndrome.

Examples of main diagnostic criteria or symptoms include partial or complete loss of acquired purposeful hand skills, partial or complete loss of acquired spoken language, repetitive hand movements (such has hand wringing or squeezing, clapping or rubbing), and gait abnormalities, including toe-walking or an unsteady, wide-based, stiff-legged walk.

Diagnostic criteria

A diagnosis of classic Rett syndrome includes these core symptoms:

• Partial or complete loss of purposeful hand skills
• Partial or complete loss of spoken language
• Walking abnormalities, such as problems walking or not being able to walk
• Repetitive purposeless hand movements, such as hand wringing, squeezing, clapping or tapping, putting hands in the mouth, or washing and rubbing movements

Additional typical symptoms can support the diagnosis.

Diagnostic criteria for atypical or variant Rett syndromes may vary slightly, but the symptoms are the same, with varying degrees of severity.

Supportive criteria are not required for a diagnosis of Rett syndrome but may occur in some individuals. In addition, these symptoms — which vary in severity from child to child — may not be observed in very young girls but may develop with age. A child with supportive criteria but none of the essential criteria does not have Rett syndrome.

Supportive criteria include:

• scoliosis
• teeth-grinding
• small cold hands and feet in relation to height
• abnormal sleep patterns
• abnormal muscle tone
• inappropriate laughing or screaming
• intense eye communication, and
• diminished response to pain.

In addition to the main diagnostic criteria, a number of specific conditions enable physicians to rule out a diagnosis of Rett syndrome. These are referred to as exclusion criteria.

Children with any one of the following criteria do not have Rett syndrome:

• brain injury secondary to trauma,
• neurometabolic disease,
• severe infection that causes neurological problems and
• grossly abnormal psychomotor development in the first 6 months of life.

Genetic testing

If your child’s doctor suspects Rett syndrome after evaluation, he or she may recommend a genetic test (DNA analysis) to confirm the diagnosis. The test requires drawing a small amount of blood from a vein in the arm. The blood is then sent to a lab, where technicians examine your child’s DNA for abnormalities and clues as to the cause and severity of the disorder.

Evaluating other causes for the symptoms

Because Rett syndrome is rare, your child may have certain tests to identify if other conditions are causing some of the same symptoms as Rett syndrome. Some of these conditions include:

• Other genetic disorders
• Autism
• Cerebral palsy
• Hearing or vision problems
• Metabolic disorders, such as phenylketonuria (PKU)
• Disorders that cause the brain or body to break down (degenerative disorders)
• Brain disorders caused by trauma or infection
• Brain damage before birth (prenatal)

What tests your child needs depends on specific signs and symptoms. Tests may include:

• Blood tests
• Urine tests
• Imaging tests such as magnetic resonance imaging (MRI) or computerized tomography (CT) scans
• Hearing tests
• Eye and vision exams
• Brain activity tests (electroencephalograms, also called EEGs)

Rett syndrome treatment

There is no cure for Rett syndrome. Treatment for the disorder is symptomatic — focusing on the management of symptoms — and supportive, requiring a multidisciplinary approach.

Treatments that can help children and adults with Rett syndrome include:

• Regular medical care. Management of symptoms and health problems may require a multispecialty team. Regular monitoring of physical changes such as scoliosis and GI and heart problems is needed.
• Medications. Though medications can’t cure Rett syndrome, they may help control some signs and symptoms associated with the disorder, such as seizures, muscle stiffness, or problems with breathing, sleep, the GI tract or the heart.
• Physical therapy. Physical therapy and the use of braces or casts can help children who have scoliosis or require hand or joint support. In some cases, physical therapy can also help maintain movement, create a proper sitting position, and improve walking skills, balance and flexibility. Assistive devices may be helpful.
• Occupational therapy. Occupational therapy can help children develop skills needed for performing self-directed activities (such as dressing, feeding, and practicing arts and crafts), while physical therapy and hydrotherapy may prolong mobility. If repetitive arm and hand movements are a problem, splints that restrict elbow or wrist motion may be helpful.
• Speech-language therapy. Speech-language therapy can help improve a child’s life by teaching nonverbal ways of communicating and helping with social interaction.
• Nutritional support. Proper nutrition is extremely important for normal growth and for improved mental and social abilities. A high-calorie, well-balanced diet may be recommended. Feeding strategies to prevent choking or vomiting are important. Some children and adults may need to be fed through a tube placed directly into the stomach (gastrostomy).
• Behavioral intervention. Practicing and developing good sleep habits may be helpful for sleep disturbances.
• Support services. Academic, social and job training services may help with integration into school, work and social activities. Special adaptations may make participation possible.

Coping and support

Children with Rett syndrome need help with most daily tasks, such as eating, walking and using the bathroom. This constant care can be exhausting and stressful for families. And in one study, for example, seizures were linked to higher levels of stress for parents whose daughters have Rett syndrome.

To better cope with the challenge:

• Find ways to relieve stress. It’s natural to feel overwhelmed at times. Talk about your problems with a trusted friend or family member to help relieve your stress. Take some time for yourself doing something you like to recharge your battery.
• Arrange for outside help. If you care for your child at home, seek the help of outside caregivers who can give you a break from time to time. Or you may consider residential care at some point, especially when your child becomes an adult.
• Connect with others. Getting to know other families facing problems similar to yours can help you feel less alone. Look for online support and information from organizations such as the International Rett Syndrome Foundation ⁴.

Alternative medicine

A few examples of complementary therapies that have been tried in children with Rett syndrome include:

• Music therapy
• Hydrotherapy, which involves swimming or moving in water
• Animal-assisted therapy, such as using therapy dogs or therapeutic horseback riding

Although there’s not much evidence that these approaches are effective, some parents who have used them report good results.

If you think alternative or complementary therapies might help your child, talk to your doctor or therapist about the possible benefits and risks, and how the approach might fit into the medical treatment plan.

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3. Amir, R. E., Van den Veyver, I. B., Wan, M., Tran, C. Q., Francke, U., & Zoghbi, H. Y. (1999). Rett syndrome is caused by mutations in X-linked MECP2. Nature Genetics, Oct;23(2), 185–188.[↩]
4. International Rett Syndrome Foundation. https://www.rettsyndrome.org/[↩]