What is fragile X chromosome syndrome?
All parents-to-be care about the health of the unborn child. Therefore, even before pregnancy, they may decide to undergo a preconception genetic test to assess the likelihood of conceiving children with recessive genetic diseases such as the Fragile X chromosome syndrome (FXS).
It is a hereditary syndrome
It is an inherited syndrome, correlated with genetic inheritance, and can occur in both males (1 in 4000 cases) and females (1 in 7000 cases).
I disease symptoms, most prominent in males, are mild-to-severe mental retardation associated with behavioral disturbances and characteristic physical signs.
As of 2001, X-fragile syndrome falls under “rare diseases,” as it occurs in less than 5 cases per 10 thousand normal births. 1
X-chromosome-fragile syndrome is also known as Martin-Bell syndrome and is a form of mental disability due to the gene mutation FMR1 (Fragile X Mental Retardation 1), located on the long arm of the X chromosome. In patients with FXS, there is a break in this arm, hence the term “X-Fragile”. 1,2
The FMR1 gene contains the CGG trinucleotide triplet
The FMR1 gene contains the CGG trinucleotide triplet, which can be highly variable repeats in the population. Based on its expansion, four case histories can be distinguished:
- normal (5-45 CGG repeats in the FMR1 gene);
- intermediate (45-55 repeats);
- pre-mutation (55 to 200 triplet repeats);
- complete mutation (more than 200 repeats) causing the syndrome.
Intermediate and pre-mutated repeats tend to expand during transmission to the next generation. Therefore, if a couple already has repeats these can expand to lead to the onset of the disease in the child’s. 3
The FMR1 gene encodes for the FMRP protein (Fragile X Mental RetardationProtein) that has “regulatory” function in many cellular processes, such as messenger RNA transport and protein synthesis at the synapses of neurons. In individuals with fragile X-chromosome syndrome, the FMR1 gene is no longer able to produce the FMRP 1 protein .
Cognitive, behavioral, physical disabilities are thus generated. 1
Regarding the disability at the cognitive level, one has learning and speech, motor and balance difficulties.
Regarding disabilities at the behavioral level, there is hyperactivity, aggression, shyness, anxiety, and difficulty paying attention. Children manifest autistic-like behaviors.
As for the disability at the physical level, you have poor muscle tone, hypersensitivity of the joints, narrow and elongated face, prominent forehead and jaws, large and protruding ears, flat feet, mitral valve prolapse and macroorchidism in males 1,4 .
There is still no cure for fragile X syndrome; one can only try to improve or alleviate symptoms 5 .
Therefore, it is important to know one’s reproductive risk with a genetic test, such as the Igea preconception test: is performed on a simple blood draw and identifies the most common and severe genetic recessive, autosomal or X sex chromosome-related diseases.