Our genetic code carries the necessary instructions to shape and develop our organism. We inherit a large part of what we are from our ancestors, although the expression or not of part of these instructions will depend on the environment in which we live.

However, sometimes various genetic mutations occur that can result in a disorder in those who carry them. This is the case with Fragile X syndrome , the second most frequent cause of mental retardation for genetic reasons.

Fragile X syndrome: Description and typical symptoms

Fragile X or Martin-Bell syndrome is a genetic X-linked recessive disorder . The symptoms of this syndrome can be seen in different areas.

The most notable are those related to cognition and behavior, although they may present other symptoms such as typical morphological alterations or even metabolic problems. Although it affects both men and women, as a rule it is much more prevalent in the former, also having a more pronounced and serious symptomatology.

Cognitive and behavioral symptoms

One of the most characteristic symptoms is the presence of intellectual disability . In fact, along with Down syndrome, Fragile X syndrome is one of the most frequent genetic causes of mental retardation. This disability can be highly variable.

In the case of women, there is often a level of intelligence on the borderline of intellectual disability, with an IQ between 60 and 80. However, in men the level of disability is usually much higher , with an IQ generally between 35 and 45. In this case we would be facing a moderate disability, which would mean a slower development and with a delay in the main milestones such as speech, with difficulties in abstraction and the need for a certain level of supervision.

Another frequent aspect is the presence of a high level of hyperactivity , presenting motor agitation and impulsive behaviour. In some cases, they may become self-injurious. They also tend to present difficulties in concentrating and maintaining attention

It is also possible that they present typically autistic behaviors , which may involve the presence of severe difficulties in social interaction, phobia of contact with other people, mannerisms such as hand waving and avoidance of eye contact.

Typical morphology

In terms of physical characteristics, one of the most common morphological features in people with Fragile X syndrome is that they have a certain level of macrocephaly from birth, with relatively large and elongated heads. Other common features are the presence of large eyebrows and ears, prominent jaw and forehead.

It is relatively common for them to have hyperlaxed joints, especially in the extremities, as well as hypotonia or a lower than expected muscle tone . Spinal deviations are also frequent. In males, macro-orchidism, or excessive testicular development, may also appear, especially after adolescence.

Medical complications

Regardless of the types of features we have seen, people with Fragile X syndrome may have alterations such as gastrointestinal problems or reduced visual acuity . Unfortunately, many of them have cardiac alterations, with a greater possibility of suffering heart murmurs. A high percentage, between 5 and 25%, also suffer from epileptic or comissional crises, whether localised or generalised.

Despite this, those with Martin-Bell syndrome can have a good quality of life , especially if the diagnosis is made early and there is treatment and education that allows the effects of the syndrome to be limited.

Causes of this disorder

As indicated, Fragile X syndrome is a genetic disorder linked to the X sex chromosome.

In people with this syndrome, the X sex chromosome undergoes a type of mutation that causes a particular set of nucleotides in the FMR1 gene, namely the Cytosine-Guanine (CGG) chain, to appear excessively repeated along the gene.

While subjects without the mutation may have 45-55 repeats of the chain, a subject with Fragile X syndrome may have 200-1300 repeats. This prevents the gene from being expressed correctly, so it does not produce the FMRP protein when it is silenced.

The fact that the X chromosome is the one affected by the mutation is the main reason why the disorder is seen more often and with greater severity in men, by having only one copy of that chromosome . In females, having two copies of the X chromosome has less effect, and the symptoms may not even appear (although they may pass it on to their offspring).

Treatment of Martin-Bell syndrome

Fragile X syndrome currently has no cure . However, the symptoms caused by this disorder can be treated in a palliative manner and in order to improve the quality of life, through a multidisciplinary approach that includes medical, psychological and educational aspects.

Some of the treatments that are used with people with this syndrome in order to improve their quality of life are speech therapy and different language therapies in order to improve their communication skills, as well as occupational therapy that helps them integrate information from different sensory modalities.

Cognitive-behavioral programs and treatments can be used to help them establish basic and more complex behaviors. At the educational level, they need to have individualised plans that take into account their characteristics and difficulties.

At the pharmacological level, SSRIs, anticonvulsants and different anxiolytics are used to reduce the symptoms of anxiety, depression, obsessiveness, psychomotor agitation and seizures. Psychostimulant type drugs are also occasionally used in cases where there is a low level of activation, as well as atypical antipsychotics on those occasions when aggressive or self-destructive behaviour tends to occur.

Bibliographic references:

  • Grau, C.; Fernández, M. & Cuesta, J.M. Fragile X syndrome: behavioral phenotype and learning disabilities. Siglo Cero, vol. 46 (4), nº256. Editions University of Salamanca.