6 to 18 months
In this stage the first signs of the syndrome may become apparent.
May show a lack of interest in toys. May be calm and placid.
Development of motor skills may be slow. Head growth may slow.
1 to 4 years
In this stage, the greatest changes occurs, often rapid, though it may also be gradual.
May show lack of interest in social interaction and development of communication skills may be poor. May be quite irritable.
Repetitive hand motions may become apparent and purposeful hand skills may be lost.
Growth of head circumferance may be slow.
Breathing problems may arise.
2 to 10 years
In this stage, the rapid regression of stage 2 will slow and improvements may be seen in behaviour, particularly in irritability. Should show more alertness and be communicative.
Motor control may still deteriorate. Loss of muscle tone may become apparent. May start having seizures.
10+ years (though very variable, may occur anywhere from about 5 to 25 years)
This stage is characterised by loss of mobility. The ability to walk may be lost, if it had been acquired. Stiffness and curving of the spine (scoliosis) may occur.
Communication abilities and cognition should not decrease however and repetitive hand motions may decrease.