Rett syndrome is a genetic disorder that almost exclusively affects females. The disease causes problems in nearly every aspect of a person’s life, including the ability to speak, walk, eat, and breathe.

There are two broad types of Rett syndrome: classic and atypical. The classification is based on the type of symptoms and the specific genetic mutations that cause the disease.

Classic Rett syndrome

This is the most common form of the disease, seen in 80-85 percent of all cases, with symptoms usually appearing between ages 6-18 months.

It is caused by mutations in the MECP2 gene located on the X chromosome. This gene encodes for the methyl-CpG binding protein 2, which is essential for brain development.

Atypical Rett syndrome

Nearly 15-20 percent of Rett syndrome patients manifest a non-classic or atypical form of the disease, which is either milder or more severe than the classical form. The different atypical forms are:

Early-onset seizure type

People with early-onset seizure type Rett syndrome, also called Hanefeld variant, usually start having seizures before 6 months of age.

This form of the disease is caused by mutations in a gene called CDKL5, also located on the X chromosome, but mutations in the MECP2 gene are also sometimes observed.

One study described the case of a patient with early seizures who had a translocation (a genetic change where part of a chromosome is moved from its original location to another on the same or different chromosome) involving the NTNG1 gene.

Preserved speech type

Patients with preserved speech type Rett syndrome, also known as the Zappella variant, manifest most symptoms of classic Rett syndrome but later regain some language and motor skills. Patients may have a more normal head size but may be obese, more aggressive, and manifest more autism-like behaviors.

Most patients in this category have mutations in the MECP2 gene.

Congenital type

Congenital Rett syndrome, also called the Rolando variant, is the most severe form of atypical Rett syndrome. Patients show symptoms such as loss of muscle tone and severe developmental delays during the first three months of life.

This form is generally associated with mutations in the FOXG1 gene. Rarely, MECP2 gene mutations are also observed. In some cases, a 14q12 microdeletion is observed. This means that a small piece of chromosome 14 is missing. Patients with this microdeletion also have abnormal facial features.

Late-onset type

Late-onset Rett syndrome, or the forme fruste variant, is a milder form of the disease with early childhood onset. Disease progression occurs later than it does in the classic form. Affected individuals may retain hand use and abnormal hand movements are milder.

Late childhood regression type

Individuals with late childhood regression type Rett syndrome have a normal head circumference and show a more gradual regression of language and motor skills that start later.

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