Clinical Characteristics

Mutations in MFF may cause the following health conditions:

Central Nervous System

  • Delayed psychomotor development (delay in acquiring motor and cognitive skills)
  • Developmental regression (loss of previously acquired skills)
  • Poor head and trunk control
  • Absent speech
  • Spasticity (stiffness or rightness of the muscles that can interfere with normal movement)
  • Hyperreflexia (overactive or overresponsive reflexes)
  • Seizures
  • Abnormalities detected on EEG
  • Abnormalities detected on MRI (especially common are abnormalities in the basal ganglia, a structure in the brain responsible for motor control and motor learning)
  • Peripheral neuropathy (impairment of the nerves that carry signals to and from the brain and spinal cord to and from the rest of the body)
  • Severely reduced muscle tone

Head and Neck

  • Abnormally small head
  • Visual impairment


  • Difficulty swallowing
  • Abnormal laboratory findings, including increased lactate levels