The study, “Ten novel insertion/deletion variants in MECP2 identified in Japanese patients with Rett syndrome,” was published in the journal Human Genome Variation.
Almost all cases of Rett syndrome are caused by a mutation in the MECP2 gene, which provides instructions to make a protein that regulates the activity of other genes, particularly in the brain.
Each person inherits two copies of each gene, one from the mother and one from the father. Because females have two X chromosomes, but males only one, having a mutated MECP2 gene copy leads to worse outcomes in males.
In most cases, these mutations occur spontaneously. However, in less than 1% of cases, Rett syndrome can be inherited from the parents.
More than 900 mutations in MECP2 have been identified, with their locations associated with the course and severity of the disease. Variants in other genes, including CDKL5 and FOXG1, also have been linked with clinical features of Rett syndrome.
A team from Japan’s National Center of Neurology and Psychiatry used a database of MECP2 variants called RettBASE (among other sources) to conduct genetic testing in blood samples of 49 children and adults diagnosed with Rett syndrome.
Results revealed 10 novel insertion/deletion variants, eight known insertion/deletion variants, and 31 other mutations already known to cause Rett syndrome. (An insertion/deletion variant is a mutation in which a DNA piece is inserted or eliminated from the gene.)
The novel mutations were found in 10 females ranging from 2 to 36 years old. One patient had a complex rearrangement where a large stretch of the MECP2 gene had been eliminated.
A more detailed analysis of the exact locations where DNA deletions occurred suggested that certain deletions in MECP2 can be unique to families and are not always related to a so-called deletion-prone region in the gene.
“The list of MECP2 variants found in 49 Japanese patients with [Rett syndrome] should provide a useful resource to further examine the correlation between genotypes [genetic background] and disease phenotypes [clinical manifestations],” the researchers wrote.