Introduction

Clinical characteristics of fragile X syndrome (FXS) may include developmental effects, behavioural characteristics and physical characteristics. Typical features of fragile X syndrome vary in severity and are not always present.

Fragile X syndrome is usually recognised in young children (eg around age 3), but diagnosis may be later in girls because they tend to externalise their behaviour less than boys.

Females may appear to be less affected by fragile X syndrome than males, but 30 to 50% of females with fragile X syndrome have intellectual disability; the remainder tend to have anxiety or behavioural problems, and executive function deficits.