Learn more about some of the rare diseases and conditions featured on Medical Incredible:

Mermaid Baby
Milagros Cerron is currently the only "mermaid" in the world. She has a rare syndrome called sirenomelia; her legs are fused together from trunk to heels.

Her strange, genderless body made Mili and her young parents targets for superstition from the moment she was born. But prejudice can't cloud the image of this beautiful, spirited child who has survived against all the odds. By the time she was 9 months old, Mili was at the center of a media storm. In Peru, there was a growing sense that she was the country's miracle child.

For months, doctors expanded tissue in her legs and abdomen to prepare for her leg-separation surgery. The prognosis was good: Mili had all the bones and structures of normal legs, and she may walk one day. But time was against her. Her internal organs could not grow properly because of her deformity. Moreover, she had only one functioning kidney and the threat of infection loomed constantly.

If the separation surgery to detangle the delicate, shared blood supply for her legs was successful, she'd be separated to the knees and one of the major hurtles — and dangers — to her health would be over. Learn more about Mili's story.

Born With Two Heads
Upon her birth in March 2004, Manar Maged immediately became a media sensation. Born with a parasitic twin, the Egyptian infant was diagnosed with an extremely rare medical condition known as craniopagus parasiticus. Manar's second head has no body of its own and can't live without her. But its existence is putting her life at risk. Learn more about Manar's story.

Born Without a Face
Twenty-one-month-old Juliana Wetmore has no upper jaw, no cheek bones and no eye sockets, and she is missing the corner of her ear. She was born with Treacher Collins syndrome. Doctors say that it is the worst case ever recorded. Learn more about Juliana's story.