20/20: MEDICAL MYSTERIES" REPORTS ON SOME OF THE STRANGEST CASES KNOWN TO MEDICINE

Airing on a Special Edition of "20/20," Friday, March 14 at 9:00 p.m.

From unstoppable hair-pulling to a man who hears everything, including his own heartbeat and even the sounds of his eyes moving back and forth in his head, "20/20" reports on rare medical cases and conditions on a special edition of the show, FRIDAY, MARCH 14, from 9:00-10:00 p.m., ET on the ABC Television Network.

"20/20: Medical Mysteries" reports include:

* Hair pulling: What could cause a beauty queen or a chic Hollywood stylist to pull out their own hair-repeatedly, uncontrollably, even as they fight the urge to do it? It's called "trichotilomania" and it's a compulsion that doctors still don't understand. Somehow the wiring in their brains makes them pull out the hair on their heads, their eyebrows, even their eyelashes. JuJu Chang reports.

* No Fingerprints: Imagine going through life without leaving a trace - literally having no fingerprints. To a thief it might sound like a dream-but it's reality for people living with a rare form of what's called Ectodermal Dysplasia. Deborah Roberts reports on the syndrome that leaves people with not only fingertips as smooth as porcelain, but no sweat glands and varying effects on hair and teeth. (OAD: 1/10/2007)

* Hearing Everything: He's a talented musician, First French Horn in the orchestra. But he's not just hearing the music-he's hearing EVERYTHING. From his heartbeat, his chewing, the pounding of his feet hitting the pavement, to the sounds of his own eyes moving back and forth in his head, he hears the internal "symphony" of his body. Can the doctors at Johns Hopkins end the cacophony? Chris Cuomo reports.

* Selective Mutism: Everyone knows what it is to be shy. But what if your child went beyond that? It's not that they don't want to talk - they can't... not to children in their kindergarten class, nor to the waitress in the restaurant. It's even more puzzling when the parents say their silent child talks up a storm at home. Believe it or not, seven in every 1000 children suffer with "selective mutism." Nobody is certain what causes it, but doctors are finding ways to overcome it. JuJu Chang profiles two children-one who is still suffering with his mutism and one who has found her voice again-and reports on their unprecedented meeting.

"20/20" is anchored by Elizabeth Vargas and John Stossel. David Sloan is executive producer.