Prosopagnosia is a neurological disorder characterized by the inability to recognize faces. Prosopagnosia is also known as face blindness or facial agnosia. The term "prosopagnosia" comes from the Greek words for "face" and "lack of knowledge." Depending on the degree of impairment, some people with prosopagnosia may only have difficulty recognizing a familiar face, others will be unable to discriminate between unknown faces, and some may not even be able to distinguish a face as being different from an object. Some people with the disorder are unable to recognize their own face. Prosopagnosia is not related to memory dysfunction, memory loss, impaired vision, or learning disabilities. It is thought to be the result of abnormalities, damage, or impairment in the right fusiform gyrus, which is a fold in the brain that appears to coordinate the neural systems that control facial perception and memory. Prosopagnosia can result from a stroke, a traumatic brain injury, or certain neurodegenerative diseases. In some cases, prosopagnosia is a congenital disorder, present at birth in the absence of any brain damage. Congenital prosopagnosia appears to run in families, which makes it likely to be the result of a genetic mutation or deletion. Some degree of prosopagnosia is often present in children with autism and Asperger's syndrome and may be the cause of their impaired social development.
This answer is based on source information from the National Institute of Neurological Disorders and Stroke.