10 July 2006
Face Blindness Caused By Single Gene
by Kate Melville
Imagine how debilitating and awkward it would be if you could not differentiate faces in a crowd. It sounds like a nightmare, but this is the reality that sufferers of prosopagnosia (PA) - otherwise known as face blindness - have to contend with everyday. The condition can be caused by a brain injury, but studies have shown that it can also come in the form hereditary prosopagnosia (HPA). Now a landmark study, published in the American Journal of Medical Genetics, has not only demonstrated that HPA exists, but also revealed that the condition can be attributed to a defect in a single gene.
To understand HPA and its prevalence, a team of researchers at the Institute of Human Genetics at the University of Muenster, in Germany, studied 689 students from local secondary and medical schools. The team, led by Ingo Kennerknecht, identified 17 sufferers of HPA among this cohort by way of a questionnaire. Fourteen students from this group consented to further tests, which revealed that all of them had at least one first degree relative who also had HPA. "This study provides epidemiological evidence that congenital PA is a very common cognitive disorder which almost always runs in families," say the authors.
There are some common identifiers of those who have the condition. "Nearly all affected persons report a problem in deciding immediately whether a face is known," the authors state. This leads to great indecision and doubt for the subjects when in social situations, stemming from the inability to identify all but the closest of relatives. Following television programs and movies is also problematic, as they cannot distinguish between the actors.
PA subjects deal with challenging situations by employing up to 3 different coping mechanisms, which include compensation, explanation and avoidance strategies. Compensation involves identifying people by markers other than their face, such as hair color, gait or voice. Explanation strategies often include excuses as to why they cannot recognize someone that they know, or PA subjects may avoid large gatherings altogether. The use of such strategies from an early age may explain why HPA is not as widely recognized as other cognitive disorders, or why it is not recognized within families where the condition exists. "This could explain why this kind of cognitive impairment is largely unknown to lay persons or even to physicians other than neurologists and psychiatrists," the authors state, adding that there are no established diagnostic tools for PA.
But researchers explain that the HPA subject's ability to identify other characteristics about a person presents some clues about the nature of the condition. If there is a capacity to differentiate gender, age and emotional expression, then it means that these characteristics are processed independently. The authors also note that if it is solely facial recognition that sufferers have trouble with, HPA is among a select number of conditions where only one symptom is inherited.
"Neurophysiological studies of people with this highly selective dysfunction might fundamentally improve our understanding of face recognition," the authors conclude. "As soon as gene mapping/mutation mapping [is] successful, the genotype/phenotype correlations should widen our knowledge of the development of higher cerebral functions."
Source: American Journal of Medical Genetics