Fragile X Syndrome

Published April 14, 2020

What is Fragile X Syndrome? 

Fragile X syndrome (FXS) is the second most common chromosomal-based developmental condition after Down Syndrome and is estimated to occur in:

  • 1.4 in 10,000 males (0.014%)
  • 0.9 in 10,000 females (0.009%)

Fragile X syndrome is a genetic disorder characterized by mild-to-moderate intellectual disability.

Physical features of FXS may include a long and narrow face, large ears and flexible fingers. About a third of those affected have features of autism such as problems with social interactions and delayed speech. Hyperactivity is common and seizures occur in about 10 percent of the FXS population.

Fragile X syndrome has an X-linked dominant inheritance, typically caused by an expansion of the CGG triplet repeat within the FMR1 (fragile X mental retardation 1) gene on the X chromosome.

Signs of FXS

Most young children do not show any physical signs of FXS— physical features usually begin to develop around the time puberty begins.  Aside from intellectual disability, prominent characteristics of the syndrome may include:

  • Large, protruding ears
  • Long face (vertical maxillary excess)
  • High-arched palate (related to the above)
  • Hyper-extensible finger joints
  • Hyper-extensible (‘double-jointed’) thumbs
  • Post pubescent macro-orchidism
  • Hypotonia (low muscle tone)
  • Flat feet
  • Soft skin

Behavioral characteristics may include stereotypic movements, such as hand-flapping and atypical social development, particularly:

  • Shyness
  • Limited eye contact
  • Memory problems
  • Difficulty with face recognition

Some individuals with FXS also meet the diagnostic criteria for autism.

Vision and FXS 

Over half of the FXS population suffer from visual problems— most commonly eye turns, lazy eye and poor eye muscle control.

According to a review of ophthalmic findings of 55 patients with FXS, most of the vision problems included:

  • Strabismus (eye turns)
  • Amblyopia (lazy eye)
  • Convergence insufficiency
  • Poor stereopsis (3D vision)
  • Refractive errors
  • Nystagmus

Management of FXS

Medications may be used to treat associated seizures, mood problems, aggressive behavior or ADHD.

Early intervention is highly recommended for children with FXS as it provides the best opportunities for developing a variety of skills and abilities.

These interventions may include:

  • Vision therapy
  • Speech therapy
  • Behavioral therapy
  • Sensory integration therapy
  • Occupational therapy
  • Special education

If your child has been diagnosed with FXS, an eye doctor experienced in vision therapy may be able to offer you solutions and strategies to manage vision problems related to FXS.