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Fragile X Syndrome

Fragile X syndrome (FXS) is a rare genetic disorder and the most common inherited cause of intellectual disability and autism spectrum disorder

Prevalence

1-9 / 10 000

1 in 4,000

US Estimated

1 in 6,000–8,000

Europe Estimated

Age of Onset

Childhood

ICD-10

Q99.2

Inheritance Pattern

Autosomal dominant

Autosomal recessive

Mitochondrial/Multigenic

X-linked dominant

X-linked recessive

5 Facts you should know

FACT

Fragile X syndrome is the most common inherited cause of intellectual disability and autism spectrum disorder, caused by a CGG trinucleotide repeat expansion in the FMR1 gene on the X chromosome

FACT

The mutation leads to silencing of the FMR1 gene and deficiency of fragile X mental retardation protein (FMRP), which is critical for synaptic development and neuronal function

FACT

Affected individuals often present with developmental delay, intellectual disability, autism features, anxiety, and behavioral challenges, with males typically more severely affected than females

FACT

Physical features may include long face, large ears, hyperextensible joints, and macroorchidism (post-puberty), though these findings can be subtle in early childhood

FACT

Fragile X is associated with related conditions such as fragile X–associated tremor/ataxia syndrome (FXTAS) and fragile X–associated primary ovarian insufficiency (FXPOI) in premutation carriers

Interest over time

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