Many disorders can affect our ability to speak and communicate. They range from saying sounds incorrectly to being completely unable to speak or understand speech. Causes include
Hearing disorders and deafness
Voice problems, such as dysphonia or those caused by cleft lip or palate
Speech problems like stuttering
Developmental disabilities
Learning disabilities
Autism spectrum disorder
Brain injury
Stroke
Some speech and communication problems may be genetic. Often, no one knows the causes. By first grade, about 5 percent of children have noticeable speech disorders. Speech and language therapy can help.
NIH: National Institute on Deafness and Other Communication Disorders