Brooke Greenberg looks like any other 10-month-old baby. However, the big difference is Brooke is actually 20-years old. She suffers from a rare syndrome that has halted her aging, physically and mentally. It’s so rare, in fact, that Brooke is the only-known diagnosed case of Syndrome X.

Appearing on a medical mysteries-themed episode of Katie, Brooke’s parents and younger sister discussed life with Brooke. “It hasn’t been easy,” her mother says, “but each day you get better at your job.” Her father added, “She comes first and we try to do whatever we can to make her happy.”

Brooke attends a special school that includes music and art classes, along with physical therapy. Experts who have studied Brooke’s DNA have not been able to determine what has caused the syndrome or how it might be cured. Until the secret of Syndrome X can be unlocked, Brooke’s mother says her family, “just takes each day as it is to make her healthy and happy.”