Tonight on ER, doctors debated the fate of a 14-year-old girl with a rare fatal disorder called Sanfilippo Syndrome.

The program hit especially close to home for five Utah families who are among a select group across the country - dealing everyday with the emotions of what are called the MPS diseases. Science Specialist Ed Yeates was with them including one of the oldest survivors of the disorder.

Ali Smith, Brigham Raneer, Nathon Thomas, and Shauna Taylor. These kids share a common bond, and unfortunately, a common fate.

Because they're missing one of the enzymes which helps the body break down and get rid of certain compounds - growth is stunted. They face mental and physical handicaps - and at an early age - vegetation and death!

Among the family of MPS diseases, there's Hurler and Hunter Syndromes, and Sanfilippo.

ED YEATES, SCIENCE SPECIALIST: "AT AGE 22, SHAUNA IS ONE OF THE OLDEST SURVIVORS OF SANFILIPPO. THE AVERAGE LIFESPAN IS AGE 15."

So far only 11 kids in the United States have survived past their 15th year. Jeanette Taylor says her family expected to say goodbye to Shauna many times. ER was especially difficult to watch because the parents of these kids deal with severe complications and the issue of life OR death all the time.

JEANETTE TAYLOR, SHAUNA'S MOTHER: "IT'S HARD TO BE THE JUDGE OF THAT. AND I'VE ALSO SEPARATED MYSELF FROM THINKING THAT I AM IN CONTROL OF HER LIFE BECAUSE I HAD NO IDEA THAT SHE WOULD LIVE THIS LONG."

"ALL I DO IS TRY TO GIVE HER THE BEST QUALITY OF LIFE. HER LIFE HAS BEEN ENRICHED BY MANY, MANY PEOPLE AND IN RETURN I THINK SHE GIVES SO MUCH IN HER OWN QUIET, UNASSUMING WAY."

Sanfilippo and its cousin diseases are often hard to diagnose at an early age because many, like Nathon, look quite normal.

Parents often call these children their unspoken angels. Though the body fails and falls apart, they draw you deep inside the heart. Families say even after death - like Brook here - that warmth never goes away.