Sirenomelia, also called "mermaid syndrome", is a rare disorder. It happens when a child is born with his or her legs grown together and little or no genitalia. This, however, is as rare as conjoined twins, and only happens to one out of every 100,000 live births. It is usually very bad for the kidney and bladder, and only about four survivors were known to be alive as of July 2003.