MEDICAL MYSTERIES, ON ABC NEWS� �PRIMETIME,� THURSDAY, APRIL 6

-- A Disturbing Disorder Where People Want to Remove Their Own Limbs--

-- An Irregular and Lethal Heart Abnormality Killing Teenagers --

-- A Rare Syndrome Where People Wake Up With a Foreign Accent --

Why would people freeze their legs in dry ice, so that doctors would be forced to amputate? �Primetime� explores a rare condition called Body Integrity Identity Disorder (BIID), whose sufferers obsess over losing one or more of their limbs because they say they don�t feel �whole� with these limbs and that their body image is that of an amputee. �Primetime� talks with three BIID patients, including a man who freezes his legs, ultimately forcing doctors to have to amputate; a woman who has tried twice and failed; and an intensely physically active man who -- despite his love of hiking and skiing -- wants his left leg cut off. Jay Schadler reports on �Primetime,� THURSDAY, APRIL 6 (10:01-11:00 p.m., ET) on the ABC Television Network.

Also: Sixteen-year-old Casey Shockley had never been seriously ill, but could an alarm clock have triggered her death? Chris Cuomo reports on an abnormality of the heart, known as Long QT Syndrome, that can trigger a fast, irregular and lethal heartbeat. One doctor interviewed believes the syndrome may be to blame for more than half of the sudden, unexplained deaths in teenagers and young adults, killing as many as 4,000 young people a year. But just this week a new test has emerged that may be able to detect the mysterious syndrome that affects one in 3,000 people.

Then: Imagine a person goes to bed one night and wakes up the next morning speaking with an entirely different accent, from a country the or she has never even been to. �Primetime� investigates Foreign Accent Syndrome, where a people find themselves speaking their native language but � out of the blue -- with a distinctly different accent. John Qui�ones reports on the phenomenon, including how a woman awoke one day with Russian accent � having never even been to Russia or Europe � and no idea where it came from, and a second man who, after a stroke, finds he has a German accent. After much testing and hypothesizing, doctors diagnose both people with the rare syndrome, but much mystery remains as to how and why this happens.

And: Cynthia McFadden reports on National Geographic's press conference tomorrow, which is expected to detail the only known surviving copy of what experts believe is the Gospel of Judas.

DIANE SAWYER, CHRIS CUOMO, CYNTHIA McFADDEN and JOHN QUI�ONES are the anchors of �Primetime.� DAVID SLOAN is the executive producer.