"20/20? reports on bizarre medical mysteries that stumped even the experts at first. Anchored by Elizabeth Vargas and David Muir, "20/20? airs on FRIDAY, FEBRUARY 7 (10:00 - 11:00 pm ET) on the ABC Television Network. Reports include:

• Selective Eating Disorder: Deborah Roberts reports on a newly diagnosed condition that gives a whole new meaning to the term "picky eater." Amber Scott suffers from Avoidant Restrictive Food Intake Disorder (ARFID), and only eats french fries. Like other adults with this disorder, she suffers excruciatingly painful emotional and physical reactions to certain foods. So what will happen when she agrees to try food outside of her personal diet?

• Allergic to Noise: Joyce Cohen and her husband Ben live in NYC - one of the noisiest cities in the world. But noise is torture for them - so much that Joyce wears industrial strength earmuffs outside, and her husband can barely leave their small apartment. They both suffer from Hyperacusis, which causes terrible, often unbearable, pain in the ear. Elizabeth Vargas reports.

• Dwarf Twin: Sienna 'Sinny' Bernal is one in roughly 200 people in the world with Primordial Dwarfism, a rare genetic condition. On the verge of turning 15, she is just over four feet tall and roughly 50 pounds. Her doctors have said she has reached her maximum height. Aside from the more obvious characteristics that set Sinny apart from other teen girls, there is one thing - or rather, one person - who makes her truly unique: her identical twin sister, Sierra. Sierra is an average sized girl (and now double Sinny's size), making the twins the only known pair in the world with such a combination. Jay Schadler has their unique story.

• Sudden Blindness: One healthy young college student called it his "magical medical mystery tour" when he started loosing his eyesight - and no one knew why. That is, until his mother sprang into action, and saw what the doctors had missed. Chris Connelly reports.

• Hair Loss: Imagine your favorite feature was taken away by a mysterious disease. That is what happened to Georgia Van Cuylenburg. Like five million other Americans she suffers from Alopecia - a condition with sudden and unpredictable hair loss. Making this devastating loss even harder is that Georgia was a professional hair model. Elizabeth Vargas reports on her personal journey to redefine beauty.