Those who are physically mute may have problems with the parts of the human body required for human speech (the throat, vocal cords, lungs, mouth, or tongue, etc.). Being mute is often associated with deafness as people who have been unable to hear from birth may not be able to articulate words correctly (see deaf-mute), but muteness describes people who can hear but cannot talk. Other causes include intellectual disability and autism. A person can be born mute, or become mute later in life as a result of injury or disease. The prevalence of mutism from all causes is on the order of 0.8 persons per 1000.
Trauma or injury to the Broca’s area of the brain can cause muteness.
Muteness may also be caused by a major traumatic incident in a person’s life. However, this is usually temporary.
Akinetic mutism is inability to speak (mutism) and move (akinesia). It is the result of severe frontal lobe injury in which the pattern of inhibitory control is one of increasing passivity and gradually decreasing speech and motion.
(Note: The information above is courtesy of Wikipedia)