Most infants with Rett syndrome seem to grow and behave normally for the first six months. After that, signs and symptoms start to appear. The most pronounced changes generally occur at 12 to 18 months of age, over a period of weeks or months.

How does Rett syndrome occur?

Almost all cases of Rett syndrome are caused by a mutation (a change in the DNA) in the MECP2 gene, which is found on the X chromosome (one of the sex chromosomes). The MECP2 gene contains instructions for producing a particular protein (MeCP2), which is needed for brain development.

Why do girls get Rett syndrome?

Why is Rett syndrome usually only found in girls? Females have two copies of the X chromosome and males have one X and one Y chromosome. The MECP2 gene is found on the X chromosome, so females born with one normal and one changed copy of the MECP2 gene usually develop the symptoms of Rett syndrome.