Fragile X syndrome (FXS) and autism spectrum disorder (ASD) sometimes occur together. While FXS is a known genetic cause of ASD, not everyone who receives an FXS diagnosis is autistic, and not all autistic people have FXS.
FXS is a genetic disorder caused by an alteration in the FMR1 gene. It involves a deficiency in FMRP, a protein essential for neural (brain) development.
FXS is a leading cause of inherited intellectual disability and can lead to challenges across several areas of behavior and physical development.
ASD is a neurodevelopmental disorder that may involve a variety of challenges with communication, social interaction, and restrictive and repetitive behaviors. Genetic causes account for as many as 30% of ASD diagnoses, but not all autistic people live with a genetic disorder.
Many causes of ASD are currently unknown and likely include a complex interplay of genetics, environmental exposures, and changes in the brain’s structure and function.
How is fragile X syndrome related to autism?
FXS and ASD are different conditions that commonly occur together. Overlapping symptoms can make it challenging to tell them apart without genetic testing.
According to a 2017 review, about 60% of people diagnosed with FXS also meet the diagnostic criteria for ASD, but FXS only accounts for up to 6% of ASD diagnoses. This means a high percentage of people with FXS are autistic, but only a small number of autistic people have FXS.
The genetic relationship between FXS and ASD is complex. Experts have determined that FXS is the leading single genetic cause of ASD, but not the only one. Research has linked more than 800 genes and many other genetic disorders to ASD.
Some people with FXS have autistic traits but don’t meet the criteria for a formal ASD diagnosis.
A 2019 review suggests FXS and ASD share symptom similarities due to dysregulation of the protein FMRP. FXS directly affects FMRP levels. FMRP regulates certain genes and neurological pathways associated with ASD. Some experts believe this indicates FMRP dysregulation as an underlying molecular mechanism for overlapping symptoms.
More research is necessary to understand common underlying factors in overlapping symptoms between FXS and ASD.
Can someone have fragile X syndrome without autism?
You can receive a diagnosis of FXS and not have autism, and you can be autistic without having FXS.
While many people living with FXS meet the diagnostic criteria for ASD, around 40% do not. Experts link only a very small percentage of ASD directly to FXS.
What are the symptoms of FXS and ASD?
Genetic testing confirms FXS. If ASD is also suspected, a doctor may look into specific symptoms and experiences to determine a diagnosis.
Every person is different, and unique individual experiences, environment, and developmental factors exist. Not everyone with FXS or ASD will behave, look, feel, or think in the same way.
Among a wide range of possibilities, some symptoms of FXS and ASD that may manifest similarly include:
- social challenges
- hyperactivity
- difficulty focusing
- intellectual disability or learning difficulties (rare in ASD but possible)
- communication and language delays
- repetitive speech (echolalia)
- social anxiety and shyness
- difficulty engaging in or maintaining eye contact
- sensory hypersensitivity (mainly to noises or touch)
- repetitive or restrictive behaviors
- a need to follow routines
Limited interests or hyperfocus on one or a few activities are common behaviors in ASD that may not be present in FXS.
A common difference between FXS and ASD involves physical traits. No particular physical features are associated with ASD, but some children with FXS may develop specific features that become more noticeable with age, such as:
- large head
- large ears
- narrow and long face
- flat feet
- prominent forehead
- hypermobile or flexible joints
Intellectual disability refers to delayed cognitive abilities related to learning, problem solving, and complex reasoning. It’s a primary feature in FXS, though it isn’t always present and can range from mild to severe.
Intellectual disability is not common in autistic children but could co-occur . ASD primarily features challenges with social interactions and restrictive or repetitive behaviors and interests.
According to the National Fragile X Foundation (NFXF) , coinciding symptoms in FXS and ASD may not manifest in the same way and could be a result of different challenges.
For example, a lack of eye contact and challenging social interactions in FXS usually relate to social anxiety. In ASD, a lack of awareness or difficulty understanding social cues tends to underlie social challenges.
Repetitive behaviors are another example where subtle differences can be informative. According to the NFXF, repetitive behaviors in FXS are usually limited to body stiffening and hand-flapping, while repetition in ASD can be more varied.
A doctor may factor in the details of each experience when assessing a dual diagnosis of FXS and ASD.
How is fragile X syndrome treated?
No cure has been found for FXS, but it is possible to manage symptoms with medications, therapeutic interventions, and life skill supports. Because FXS severity may vary and affect each person differently, a doctor may explore treatment plans based on individual needs.
Medications for FXS aim to help address challenges related to mood, hyperactivity, and inattention. Sertraline, for example, is an antidepressant medication widely used to treat symptoms of anxiety in FXS.
A healthcare professional may also prescribe medications for medical challenges commonly seen in FXS, such as :
To support developmental needs and life skill development, a treatment plan for FXS may include:
What support do autistic children need?
Depending on individual needs, autistic children may benefit from:
- educational programs
- classroom modifications
- behavioral therapy
- social skills training
- occupational therapy
- speech therapy
- parental training
- sensory-friendly accommodations
- alternative communication strategies
- regular medical check-ups
- mental health support
Medications are rarely used in ASD but could help if anxiety, hyperactivity, or inattention symptoms are present.
Children diagnosed with FXS and co-occurring ASD may require additional support. One study from 2017 , for example, found that children with both disorders were more likely to experience seizures , sleep disturbances, and disruptive behavior compared to children only living with FXS.
Takeaway
FXS and ASD are separate diagnoses that may occur together. FXS is the most common single-gene cause of ASD. Most children with FXS are autistic, but few children with ASD have FXS.
Healthcare professionals typically reach a differential FXS diagnosis with genetic testing, and details of the overlapping symptoms may help them determine whether ASD is also present.
While no cure exists for FXS, healthcare teams may suggest a combination of medications, therapeutic interventions, and educational support to help manage the condition. Children with ASD who may need additional support could also benefit from these strategies.
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