Prosopagnosia is a disorder where suffers have trouble identifying the faces of others. Some people learn to cope with the disorder by simply using other features like voice, build, and hair color to identify people. Although these useful coping skills can make the problem virtually undetectable it is important to undergo a neuropsychological assessment, especially if the problem develops overtime. Prosopagnosia can be a symptom of other problems, like degenerative neurological illness or brain injury.
Prosopagnosia is part of a larger family of visual agnosia. These are problems in the brain in identifying objects such as people, colors or places. Certain delusional disorders have similar systems and may affect the same part of the brain, the frontal cortex. In some cases the problem is only in the frontal cortext while in other cases the problem may be in the way the frontal cortex communicates with the limbic system, which is responsible for emotional responses. In such cases people can have issues making the emotional connection between themselves and other people.
Genetics is a big factor in such disorders, as they often run in a family. Treatment is limited to learning coping skills to help identify people, though sometimes a neuropsychological assessment can explain the underlying issue. If the underlying issue, like neurological disorder, is identified and treated, the problem often goes away.