Stuttering (also referred to as stammering or dysfluency) is an involuntary disturbance in the normal fluency and timing of speech that is not appropriate for the age of the speaker. Various patterns are seen:

  • Prolongation of sounds or syllables
  • Repetition of sounds, syllables, or even whole words
  • Pauses in the middle of words
  • Blocking—either silence or pauses filled with nonsense sounds in the middle of words as if considering what to say next
  • Avoidance—word substitutions that are used to skip known problem words; also called circumlocution
  • Overemphasis of some syllables or words; also called tension
  • Stuttering is significant when it interferes with the patient’s life in academic, occupational, or social arenas. Many children with developmental delays have dysfluencies of speech, but it is not considered stuttering unless the dysfluencies are present more frequently than expected for the level of disability.


  • At least 1% of all studied populations affected
  • Males stutter 3 times more often than females.
  • Stuttering is found in every culture and language. The language spoken in the home does not increase or decrease the amount of stuttering.
  • Stuttering begins between 2 and 7 years of age, with 98% of cases presenting by age 10 years.
  • Girls start stuttering several months earlier on average than boys; however, they also speak, in general, earlier than boys do.

Risk Factors


Stuttering does cluster in families:

  • Monozygotic twins have a higher concordance for stuttering than dizygotic twins.
  • The more closely related one is to a stutterer, the more likely one is to stutter.
  • Identical twins have a concordance for stuttering of ≥30%.

General Prevention

There is no known prevention strategy for stuttering.


Stuttering appears to be associated with an excessive amount of dopamine, or closely related vasoactive compounds, in the brain:

  • Patients with Parkinson disease often develop adult-onset stuttering.
  • PET scans show increased vasoactive substances in the brains of those who stutter.
  • Medications that increase brain dopamine (antidepressants) or are dopaminergic (major tranquilizers) can induce stuttering in nonstutterers; medications that lower dopamine (e.g., clomipramine) may stop stuttering.
  • Many differences exist between the brains of stutterers and nonstutterers in glucose uptake, dopamine release, and metabolic activity of the basal ganglia, but no single physiologic process has been well defined as the cause of stuttering.


  • Specific etiology is not known, but many factors contribute. Stuttering may be more pronounced when a child is fatigued, excited, upset, rushed, or exposed to some other stressor.
  • Environmental factors are thought to have a role. Children adopted by a parent who stutters are more likely to stutter than children adopted by a parent who does not stutter.

Commonly Associated Conditions

  • Other language problems: articulation disorders, phonologic disorders
  • Learning disabilities
  • Dyslexia
  • Attention deficit hyperactivity disorder (ADHD)
  • Students with developmental delay or intellectual impairment are found to stutter up to 25% of the time.

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