Fragile-X syndrome

Fragile X syndrome (FXS) is a genetic disorder characterized by mild-to-moderate intellectual disability. The syndrome is also associated with anxiety, hyperactivity, features of autism spectrum disorders, and, in some cases, seizure disorders. FXS is the most common form of inherited intellectual disability in males and a significant cause of intellectual disability in females. The condition is caused by a mutation on the FMR1 gene located on the X chromosome, which leads to the body producing insufficient amounts of the protein FMRP. This protein plays a crucial role in the development of synapses, which are critical for the transmission of nerve impulses.

Causes

Fragile X syndrome is caused by a mutation in the FMR1 gene on the X chromosome. This mutation involves an expansion of the CGG trinucleotide repeat in the FMR1 gene. In individuals without FXS, the CGG sequence is repeated approximately 5 to 40 times. However, in individuals with FXS, the CGG sequence is repeated more than 200 times, leading to a full mutation of the gene and significant reduction or absence of the production of FMRP.

Symptoms

The symptoms of Fragile X syndrome can vary widely among affected individuals. Common symptoms include:

• Intellectual disability or learning disabilities
• Behavioral challenges such as ADHD, anxiety, and features of autism spectrum disorders
• Physical features such as a long face, large ears, and flexible fingers
• Connective tissue problems such as joint hypermobility
• Seizures in about 15% of affected males and 5% of affected females

Diagnosis

Diagnosis of Fragile X syndrome is based on clinical findings and confirmed by genetic testing. The test involves analyzing the number of CGG repeats in the FMR1 gene. A full mutation, indicative of FXS, is present when an individual has over 200 CGG repeats.

Treatment

There is no cure for Fragile X syndrome, but treatments are available to manage symptoms. Treatment strategies may include:

• Educational interventions tailored to the individual's needs
• Behavioral therapy to address issues such as social skills and anxiety
• Medications to treat symptoms such as ADHD, seizures, and mood disorders
• Occupational and speech therapy to improve daily functioning and communication skills

Prognosis

The prognosis for individuals with Fragile X syndrome varies. While most affected individuals live normal life spans, they may require support for learning disabilities and health issues throughout their lives. Early intervention and tailored treatments can improve quality of life.

Epidemiology

Fragile X syndrome affects approximately 1 in 4,000 males and 1 in 8,000 females. It is the most common inherited cause of intellectual disability worldwide.

See also

• Genetic disorder
• X-linked dominant inheritance
• Intellectual disability

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