Rett syndrome is a neurodevelopmental condition that almost always appears in girls. A baby is born after a typical pregnancy and meets early milestones, then, somewhere between about 6 and 18 months of age, development stalls and skills already in place start to fade.
This page gives a plain overview of what Rett syndrome is, its genetic cause, how it tends to unfold, and the general approach to managing it. It is educational only, not a tool for diagnosis. A suspected case belongs with a pediatrician, neurologist, or genetic counselor who can order the right testing and follow the child over time.
What is Rett syndrome?
Rett syndrome is a brain disorder affecting language, movement, coordination, and other nervous-system functions. In the classic form, infants have 6 to 18 months of apparently normal development before problems with communication, learning, and coordination appear. Children often lose purposeful hand use around this time and replace it with repeated, involuntary motions such as wringing, washing, or clapping.
Growth tends to slow, and roughly three-quarters of affected girls develop a smaller-than-average head size (microcephaly). Other features that can appear include breathing irregularities, drooling, unusual eye movements, cold hands and feet, sleep disturbance, seizures, and scoliosis, a sideways curve of the spine. Milder and more severe atypical forms, which do not follow the classic pattern exactly, have also been described.
The genetic basis: MECP2 and X-linked inheritance
Classic Rett syndrome, and several variant forms, is caused by changes (mutations) in a gene called MECP2, located on the X chromosome. This gene carries instructions for a protein important for normal brain function, likely by helping maintain connections between nerve cells. When the gene is altered, the resulting protein does not work properly, or there is not enough of it, which appears to disrupt communication between neurons. Researchers are still working out exactly how that disruption produces the specific features of Rett syndrome.
Because MECP2 sits on the X chromosome, the condition follows an X-linked inheritance pattern, and it behaves as dominant: a single altered copy is generally enough to cause it. This is a large part of why Rett syndrome occurs almost exclusively in females, who carry two X chromosomes. Males with a disease-causing MECP2 change often do not survive infancy, though a small number of boys with certain MECP2 changes have developed a related, typically more severe, picture described separately as a severe neonatal encephalopathy.
In more than 99 percent of cases, there is no family history of Rett syndrome. The overwhelming majority arise from a de novo variant, a change that is new in the child and was not inherited from either parent. A de novo finding generally does not mean a parent carries the same change, which affects how recurrence risk for future children is discussed with a genetic counselor. Rett syndrome is estimated to affect roughly 1 in 9,000 to 10,000 females.
The typical clinical course
What makes Rett syndrome distinctive, and often disorienting for families, is the apparently typical start. There is no obvious early sign that anything is different. Then, over weeks to a few months, previously acquired skills, hand use, babbling or early words, social engagement, begin to recede. This regression is usually followed by a phase where the picture stabilizes, and hallmark features such as hand stereotypies, gait disturbance, and loss of spoken language tend to persist through childhood and adult life rather than continuing to worsen indefinitely. The course varies from child to child: some girls retain a degree of purposeful hand use or mobility, while others develop more pronounced impairment. Seizures, scoliosis, sleep disruption, and feeding difficulties commonly need their own ongoing attention well beyond the regression period itself.
General approach to management
There is no cure for Rett syndrome, and care is built around managing specific symptoms rather than reversing the underlying cause. In 2023, the FDA approved trofinetide to treat Rett syndrome in children age two and older; it addresses some of the condition's features rather than the gene itself. Other medications help manage seizures and specific movement or behavioral symptoms. Regular monitoring for scoliosis and cardiac issues is standard, occupational and physical therapy support everyday skills and mobility, and some children benefit from spinal braces, splints, or nutritional support. Because the picture spans neurology, orthopedics, and developmental therapy, care is usually coordinated across a small team rather than managed by one clinician alone.
Families weighing a possible Rett syndrome diagnosis may also find it useful to look at how it compares with Angelman syndrome, another neurodevelopmental condition with a distinct genetic basis and some overlapping features. Other conditions in the same general neurogenetic space, including tuberous sclerosis complex, fragile X syndrome, and the broader topic of genetic epilepsies, share overlapping features such as seizures or developmental differences but have their own distinct causes and courses.
When to talk to a clinician
A pattern of normal early development followed by loss of hand skills, language, or social engagement is a reason to see a pediatrician promptly, not to wait and watch. Genetic testing for MECP2 and related genes, paired with a clinical evaluation, is how a diagnosis gets made. A genetic counselor can help a family understand what a de novo finding does, and does not, mean for siblings and future pregnancies. This page is an educational overview, not a substitute for that kind of evaluation. For related inherited and developmental conditions, see the full conditions index.