Fragile X Syndrome is a genetic disease that is inherited in a dominant pattern and is linked to the X chromosome. It is a mutation that occurs in the FRM-1 gene on the X chromosome, so not enough FRMP-1 protein is produced, leading to delays in normal brain development.
Within the FMR-1 gene, there is a specific segment characterized by the repetition of a sequence of three nucleotides: CGG. Therefore, Fragile X Syndrome is defined by the number of CGG triplets in the gene. For this reason, it can be said that there are three levels:
- when the number of repetitions of the CGG triplet is between 5 and 44 there is no risk of Fragile X Syndrome.
- Gray or intermediate zone
- when the number of repetitions of the CGG triplet is between 44 and 55, they represent the interval between normal and premutated alleles. In these situations the disease does not manifest itself but some characteristic manifestation of the syndrome may appear.
- if there are between 55 and 200 CGG triplets in the patient, it is said that he does not manifest Fragile X Syndrome, but is a carrier of it.
- corresponds to a number greater than 200 CGG triplets. In this case, patients with more than 200 repetitions are affected by the syndrome.