Stage I 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 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 which is called mouthing. 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 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. 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. thumb Variants thumb The signs and symptoms of the typical form of the<unk>  are well described. In addition to the classical form of<unk> , several atypical forms have been described over the years; the main groups are: * Congenital variant (Rolando variant): in this severe subtype of<unk> , the development of the patients and their head circumference are abnormal from birth. The typical gaze of<unk>  patients is usually absent; * Zappella variant of<unk>  or preserved speech variant: in this subtype of<unk>  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<unk> ; * Hanefeld variant or early epilepsy variant. In this form of<unk> , the patients have epilepsy before 5 months of age. The definition itself of the<unk>  has been refined over the years: as the atypical forms subsist near to the classical form (Hagberg & Gillgerg, 1993), the "Rett Complex" terminology has been introduced.
Rett syndrome
1p36 deletion syndrome
Fragile X syndrome
Angelman syndrome
Poland syndrome
Childhood disintegrative disorder
Fragile X-associated tremor/ataxia syndrome
Snyder–Robinson syndrome