There are two main types of Rett syndrome: classic and atypical.1 The two types may differ by their symptoms or by the specific gene mutation.
The majority of Rett syndrome patients have the classic form, which typically develops in four phases. Healthcare providers and researchers, relying on consensus criteria, view the progression of classic Rett syndrome as the following phases2,3
- Early Onset Phase. In this phase, development stalls or stops completely. Sometimes, the syndrome takes hold at such a subtle pace that parents and healthcare providers do not notice it at first. Researchers once thought that this phase began around 6 months of age. However, after analyzing videotapes of Rett individuals taken from birth, they now know4 that some infants with Rett syndrome only seem to develop normally. In fact, these infants show problems with very early development. In one study,5 all of the infants with Rett syndrome showed problems with body movements from birth through age 6 months. Another 42%5 showed stereotyped hand movements during this period.
- Rapid Destructive Phase. The child loses skills (regresses) quickly. Purposeful hand movements and speech are usually the first skills lost. Breathing problems and stereotypic hand movements such as wringing (clasping or squeezing), washing (a movement that resembles washing the hands), and clapping or tapping also tend to start during this stage.
- Plateau Phase. The child's regression slows and other problems may seem to lessen, or there may even be improvement in some areas. Seizures and movement problems are common at this stage. Many people with Rett syndrome spend most of their lives in this stage.
- Late Motor Deterioration Phase. Individuals in this stage may become stiff or lose muscle tone; some become immobile. Scoliosis (an abnormal curvature of the spine) may be present and even become severe enough to require bracing or surgery. Stereotypic hand movements and breathing problems seem to become less common.
There are currently five known variants of atypical Rett syndrome, defined by characteristic symptoms, age at which the symptoms present, or genetic makeup.
Forms of atypical Rett syndrome that have been identified to date include:
- Congenital Rett Syndrome (Rolando Variant)6
- Early-Onset Rett Syndrome (Hanefeld Variant)6
- Late-Childhood Rett Syndrome
- Forme Fruste Rett Syndrome
- Preserved-Speech Variant of Rett Syndrome (Zappella Variant)6
For more information on the specific types of atypical Rett syndrome, visit https://rarediseases.info.nih.gov/diseases/5696/rett-syndrome.