Fluency disorders include problems such at stuttering.  Stuttering refers to a communication disorder in which the natural flow of speech is disrupted by repetitions of syllables and words, prolongations of sounds and syllables, and stoppages that are considered abnormal.

Stuttering occurs mostly in small children around the ages of  2-6 who are developing language. Boys are three times more likely to stutter than girls. Most children overcome stuttering but some continue to stutter through adulthood.

Stuttering can be considered developmental when it is produced in children that are currently developing language development. Other forms of stuttering are neurological in nature  in which the "relay system" of language has developed difficulties in communication between the brain, nerves and muscles.

It is known that stuttering does run in families but no known gene has been found. Anxiety, low confidence and nervousness do not cause stuttering, although they are very often the result of stuttering.