Fragile X syndrome (FXS) is a genetic condition that causes intellectual disability, behavioral and learning challenges, and various physical characteristics. Although FXS occurs in both genders, males are more frequently affected than females, and generally with greater severity. Life expectancy is not affected in people with FXS, because typically no life-threatening health concerns are associated with the condition.
FXS, also known as Martin-Bell syndrome, results in a spectrum of intellectual disabilities ranging from mild to severe, as well as physical characteristics such as an elongated face, large or protruding ears, large testicles, and behavioral characteristics such as stereotypic movements (eg, hand-flapping) and social anxiety.
In approximately half of all children with FXS, the criteria for a diagnosis of autism can be made. FXS is associated with mutations of the X chromosome and affect the fragile X mental retardation (FMR1) gene on the X chromosome. The condition results in the failure to express the fragile X mental retardation protein (FMRP), which is needed for normal neural development.
Whereas ASD is typically diagnosed using a behavioral approach, the diagnosis of FXS is typically made using genetic analysis. When associated with FXS, ASD is caused by the genetic change or mutation in the fragile X gene. If a child is diagnosed with ASD and then diagnosed with FXS, he or she still has ASD, but the cause of the ASD is known. Over the past decade, many studies have evaluated the FXS-ASD link. Moreover, autism is much more common in boys with FXS than in girls with FXS. According to the CDC, surveys have found that 46% of males and 16% of females with FXS have been diagnosed or treated for ASD. On the other hand, about 10% of children with ASD are identified as having another genetic and chromosomal disorder, such as FXS. Moreover, individuals with FXS who have autism can have a more significant intellectual disability (lower IQ) than those with FXS who do not have autism. Given the possibility of a link, it is recommended that all children with ASD, both male and female, be referred for genetic evaluation and testing for FXS and any other genetic cause of ASD.
