Stuttering, also known as stammering, is a speech disorder characterized externally by involuntary repetitions and prolongations of sounds, syllables, words, or phrases as well as involuntary silent pauses called blocks in which the person who stutters is unable to produce sounds. Almost 80 million people worldwide stutter, about 1% of the world's population, with a prevalence among males at least twice that of females. Persistent stuttering into adulthood often leads to outcomes detrimental to overall mental health, such as social isolation and suicidal thoughts.
Stuttering is not connected to the physical ability to produce phonemes (i.e. it is unrelated to the structure or function of the vocal cords). It is also unconnected to the structuring of thoughts into coherent sentences inside sufferers' brains, meaning that people with a stutter know precisely what they are trying to say (in contrast with alternative disorders like aphasia). Stuttering is purely a neurological disconnect between intent and outcome during the task of expressing each individual sound. While there are rarer neurogenic (e.g. acquired during physical insult) and psychogenic (e.g. acquired after adult-onset mental illness or trauma) variants, the typical etiology, development, and presentation is that of idiopathic stuttering in childhood that then becomes persistent into adulthood.
