Fragile X Syndrome

About Fragile X Syndrome

Fragile X Syndrome is a disorder causing abnormalities on the X chromosome and is the most common inherited cause of intellectual disability. Both the prevalence rate and severity of symptoms are higher in males than females. This is because females have two X chromosomes, only one of which is affected by the mutated FMR-1 gene, whilst Fragile X Syndrome affects the only X chromosome that males carry.

It has also been estimated that up to 1 in 50 women and 1 in 800 men are carriers of the faulty gene. In these instances, there is a much higher risk of them passing on the faulty FMR-1 gene to their offspring, leading to them developing Fragile X Syndrome. In addition, carriers of the FMR-1 gene may experience Fragile X-associated disorders. Individuals over the age of 50 may develop Fragile X-Associated Tremor Ataxia Syndrome (FXTAS), which is characterised by tremors, shaking, and dementia, similar to symptoms of Parkinson’s Disease. Female carriers may also experience Fragile X-Associated Primary Ovarian Insufficiency (FXPOI), where menopause-like symptoms emerge before the age of 40.

Individuals may show prominent physical symptoms including a long and narrow face, prominent ears, loose joints, low muscle tone, and large testicles (in males), though these are less common than the behavioural and cognitive issues associated with the syndrome. They may also suffer from other medical conditions including a heart murmur, ear infections and seizures.

Cognitive issues associated with Fragile X Syndrome

Intellectual delays and disabilities are common in individuals with Fragile X Syndrome. In general, these impairments are severe and are accompanied by behavioural and emotional challenges. Typical impairments include speech and developmental delays, aggressive behaviours, and sensory sensitivities.

Up to 25% of individuals with Fragile X Syndrome also have Autism Spectrum Disorder (ASD), making it the most common single-gene cause of Autism Spectrum Disorder (ASD). In many cases, even if clinical diagnosis for ASD is not reached, autistic behaviours are still observed. Compared to children with other developmental delay disorders, children with Fragile X Syndrome, especially those with more severe developmental delays, typically score higher on tests measuring autistic behaviour.

Attention Deficit Hyperactivity Disorder (ADHD) also occurs comorbidly with Fragile X Syndrome, especially in males. These patients lack inhibition, and are especially inattentive, distracted and restless. The symptoms do not improve with age, distinguishing the disorder from other diagnosed ADHD cases.