In stage III there may be more interest in the surroundings and alertness, attention span, and communication skills may improve. Many girls remain in this stage for most of their lives. Stage IV
Stage IV, or the late motor deterioration stage, can last for years or decades. Prominent features include reduced mobility, curvature of the spine, and muscle weakness, rigidity, spasticity, and increased muscle tone with abnormal posturing of an arm or leg. 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. Variants
The signs and symptoms of the typical form of the Rett syndrome are well described. In addition to the classical form of Rett syndrome, several atypical forms have been described over the years; the main groups are:

Congenital variant (Rolando variant): in this severe subtype of Rett syndrome, the development of the patients and their head circumference are abnormal from birth. The typical gaze of Rett syndrome patients is usually absent;
Zappella variant of Rett Syndrome or preserved speech variant: in this subtype of Rett syndrome the patients acquire some manual skills and language is partially recovered around the age of 5 years (that is after the regression phase). Height, weight and head circumference are often in the normal range, and a good gross motor function can be observed. The Zappella variant is a milder form of Rett syndrome;
Hanefeld variant or early epilepsy variant.
Conditions with similar symptoms must first be ruled out.There is a certain criteria that must be met for the diagnosis. A blood test can rule in or rule out the presence of the MECP2 mutation, however, this mutation is present in other conditions as well.For a classic diagnosis, all four criteria for ruling in a diagnosis must be met, as well as the two criteria for ruling out a diagnosis. Supportive criteria may also be present, but are not required for diagnosis. For an atypical or variant diagnosis, at least two of the four criteria for ruling in the diagnosis must be met, as well as five of the eleven supportive criteria. A period of symptom regression followed by recovery or symptom stabilization must also occur. Children are often misdiagnosed as having autism, cerebral palsy, or another form of developmental delay.