Signs of fragile X syndrome (FXS) can range from mild to severe, and some symptoms may not appear at all in children with FXS. For example, most males with FXS have mental retardation, whereas about half of all females with FXS have mental retardation. In general, females tend to have milder symptoms than males – such as learning disabilities and behavioral problems (e.g., social anxiety, mild attention-deficit hyperactivity disorder) rather than the profound cognitive impairment in mental retardation.

Many children with FXS also have autistic-like symptoms (e.g., little eye contact, repetitive movements, poor social skills). Estimates vary, but it appears that as many as one-third of all children with FXS are also diagnosed with autism, according to the National Fragile X Foundation (NFF). Of the various physical signs that may indicate FXS, prominent ears, an elongated face and enlarged testicles (after puberty) occur in 60 percent of all cases of FXS, according to the NFF.

FXS may be difficult to identify in infants. Very few signs are apparent during the first year of life, with the exception of a large head circumference in some patients. For parents, the most noticeable indication that something may be wrong with their child occurs when they notice delays in basic development (e.g., taking longer than normal to walk and talk).  

Cognitive signs of FXS may include:

• Learning disabilities
  
• Delayed speech or language development
• Mental retardation

Behavioral signs of FXS may include:

• Autistic-like behaviors
  
• • Avoids eye contact
    
  • Odd, repetitive movements (e.g., hand-flapping, hand-biting)
    
  • Tactile defensiveness (negative response to touch)
    
  • Sensitivity to sound or light
    
  • Temper tantrums
    
  • Speech disturbances such as perseverative speech (continued repetition of words or phrases) or cluttering (abnormal rate of speech combined with attention deficits)
    
    
• Hyperactivity
  
• Inability to concentrate
  
• Shyness
  
• Social anxiety

Physical signs of FXS may include:

• Prominent ears
  
• Enlarged testicles (macroorchidism) after puberty
  
• Elongated face
  
• Large body size
  
• Large head (macrocephaly)
  
• Prominent jaw
  
• Finger joints that can extend beyond the normal range (e.g., double-jointed)
  
• Flat feet
  
• Mitral valve prolapse (heart deformity characterized by heart murmurs)

Parents who believe their child has FXS should consult their child’s pediatrician. Anyone with a family history of unexplained mental retardation should see a physician for FXS screening, especially if they are considering having children.