Fragile X syndrome is caused by a fragile site at the end of the long arm of X chromosome. Such a
disorder is
1. X-linked
2. all the given options
3. dominant
4. caused by loss -of-function of FMR1 gene

What is Fragile X Syndrome?

Fragile X syndrome is a genetic disorder that causes intellectual disabilities, particularly in males, and is one of the most common forms of inherited intellectual disability.

The condition is caused by a mutation in the FMR1 gene located on the X chromosome. This gene is responsible for producing the fragile X mental retardation protein (FMRP), which plays a role in brain development.

Why Is It Called “Fragile” X?

The term “fragile” refers to a fragile site on the X chromosome, specifically at the end of the long arm (Xq). This site appears as a fragile region under certain conditions, such as folate deficiency.

The mutation is characterized by an expansion of a CGG trinucleotide repeat in the FMR1 gene. When this region becomes too large, it silences the gene, leading to the loss of function of FMRP, which disrupts normal brain development.

Key Features of Fragile X Syndrome

1. X-linked: The FMR1 gene mutation is located on the X chromosome, making this disorder X-linked. Males (XY) are more severely affected than females (XX) because males have only one X chromosome.

2. Dominant: Fragile X syndrome follows a dominant inheritance pattern. One copy of the mutated gene is enough to cause the disorder, which is why both males and females with the mutation exhibit symptoms.

3. Loss-of-function Mutation: The CGG repeat expansion leads to silencing of the FMR1 gene, which in turn results in a loss of function of the FMRP protein, impairing cognitive development.

Symptoms of Fragile X Syndrome

• Intellectual disabilities (more severe in males)

• Social and behavioral challenges, including:

  • Autistic-like behaviors

  • Hyperactivity

  • Anxiety and social withdrawal

• Physical characteristics:

  • Long face, large ears, and a prominent jaw.

Diagnosis and Treatment

• Diagnosis is confirmed by genetic testing to detect the CGG repeat expansion in the FMR1 gene.

• Currently, there is no cure for Fragile X syndrome, but behavioral therapy, speech therapy, and medications can help manage symptoms.

Conclusion

Fragile X syndrome is an X-linked dominant disorder caused by a loss-of-function mutation in the FMR1 gene. This condition highlights the complex interplay of genetics in cognitive and behavioral development.

With early diagnosis and intervention, individuals with Fragile X syndrome can benefit from supportive treatments to manage symptoms.