Rett syndrome is a rare genetic disorder that affects females mostly. The disease is characterized by normal early development, followed by slowed growth and a loss of motor control. As the disease progresses, patients may display symptoms such as repetitive motions, difficulty walking, and seizures.
What causes Rett syndrome?
Almost all cases of Rett syndrome are caused by mutations in the MECP2 (methyl CpG binding protein 2) gene. The MECP2 protein, for which this gene encodes, is involved in regulating the activity of other genes by modifying the structure of chromatin, the bundle of protein and DNA that makes up chromosomes. By making changes to the chromatin, MECP2 controls which genes are turned on or off in the genome.
The MECP2 protein is present in most cells, but it plays a particularly important role in the brain. There, it is thought to help maintain connections between nerve cells by making sure the right genes are active at the right time.
The MECP2 protein also may be involved in processing molecules called mRNA. mRNA is a temporary copy of a gene that is used as a template by the protein-making machinery of the cell. Sometimes different proteins can be made from the same gene through a process called alternative splicing. The MECP2 protein may be involved in cutting and rearranging mRNA, so having a faulty MECP2 may mean that some proteins are not made. Alternative splicing is thought to play a crucial role in nerve-cell communication and also may be important for the function of other brain cells.
Other genetic causes of Rett syndrome
Scientists have identified mutations in CDKL5 and FOXG1 genes in individuals who have atypical or congenital Rett syndrome, but it is not yet clear how these mutations cause the disease. It is likely there are other mutations in other genes that can cause Rett syndrome.
Inheritance of Rett syndrome
Although Rett syndrome is a genetic disease, less than 1 percent of cases are inherited. The remainder of cases is caused by de novo (new) mutations. MECP2 is located on the X-chromosome (the female sex-determining chromosome).
Females have two copies of the X-chromosome, so girls who have one faulty copy of the MECP2 gene survive because they have a second normal copy of the gene.
Males, who have only one X-chromosome, do not survive if they have a mutation in the MECP2 gene.
Rett syndrome in males
Most males with Rett syndrome die in utero (before birth). There are a few reported cases, however, of males with Rett syndrome. These individuals have one of the rarer disease-causing mutations that are not located on the X-chromosome. These males have symptoms and disease progression similar to what is seen in females with Rett syndrome.
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