the loss of ability to speak is known as Aphasia
caused by damage to the related regions of the brain.It is mainly caused by a stroke or brain injury with damage to one or more parts of the brain .
people who survive a stroke have highly chances to get aphasia.
Aphasia may also be caused by a brain tumor, brain infection, or dementia auch as Alzheimer's disease In some cases, aphasia is a symptom of epilpsy or other neurological disorder.