Fragile X Syndrome

Fragile X Syndrome results from expanded CGG trinucleotide repeats in the FMR1 gene on the X chromosome, leading to gene silencing and absence of the fragile X mental retardation protein. This protein plays a critical role in regulating synaptic plasticity and dendritic spine development in the brain. Males with full mutations typically have moderate to severe intellectual disability, with IQ scores ranging from 20 to 70. Speech is often cluttered and difficult to understand, with echolalia (repeating words or phrases) common. Many individuals develop autism spectrum disorder characteristics. Physical features include a long, narrow face; prominent ears; and distinctive hand features including soft hands with hyperextensible joints. Behavioral issues include hyperactivity, impulsivity, anxiety, and sometimes aggression. Females with full mutations show variable severity, from normal intelligence to moderate disability, depending on X-inactivation patterns.