Fragile X Syndrome (FXS) is an X chromosome-linked dominant disorder caused by the amplification of a CGG repeat in the 5′ untranslated region of the fragile X mental retardation gene 1 (FMR1). It is the most common inherited cause of intellectual disability, after Down syndrome.[1]
X
tra large testes, jaws, and ears” can be used to remember the features of Fragile X
Syndrome.
FXS can overlap with other disorders, such as autism, Prader-Willi syndrome, and attention-deficit/hyperactivity disorder (ADHD).
On physical exam, individuals with FXS typically have: