Fragile X syndrome is a genetic disease caused by the expansion of a chromosomal region present on the X chromosome that repeats over and over again in an excessive manner. In fact, all of us, in a physiological and normal way, have repetitions of the genetic code in this area.
Basically, we could say that our genome at this point stutters physiologically, repeating over and over again the same thing. In Fragile X syndrome this stuttering is greater than normal, which causes a syndrome that produces mental retardation and a characteristic appearance in those affected.
It is interesting to note that this syndrome is not related to the breakage of the X chromosome at some point, as its name suggests. It is so named because when it was discovered, before we could read a person's genetic sequence, it was possible to detect in most affected cases, under an optical microscope, a small notch in the X chromosome that gave it a fragile appearance. Today we know that this notch is caused by the aforementioned codon repetition.
In fact, as we have already mentioned, every person has repeated in the Fragile X area. The appearance or not of symptoms and signs of the disease actually depends on the number of times that sequence repeats occur in this area. Thus we can classify people, depending on this number of repetitions as normal, mutated or permuted.
Normal persons will not show any symptoms.
Mutated individuals will have a high probability of having the disease. However, this will depend on other factors, such as the presence of another X chromosome to compensate for the defect (which usually occurs in females).
Permutated individuals will be people with a high number of repeats in this area of the X chromosome, but not enough to generate disease. These are people at risk of having sick children since they tend to increase the number of repeats in their offspring, i.e. they tend to have sick children.
This last group of patients is usually asymptomatic, but in them, it is classic to describe the presence of low ovarian reserve. That is why in the presence of low ovarian reserve in a young woman we should always investigate a possible Fragile X pre-mutation, before carrying out fertility treatment with our own oocytes, since this situation could have direct consequences on the health of the future baby, (Fragile X syndrome, with frequent mental retardation) which could also be avoided if we diagnose this situation by means of genetic diagnostic techniques.