Rare disorder forces a life in darkness

BELLEVILLE, Pennsylvania (CNN) -- Kasey Knauff can't go outside and play today. She can't go to the park or to the mall or to school.

Tonight, however is a different story.

Once the sun goes down, a new world opens up for this spritely 4 1/2-year-old.

Once the sun goes down, Kasey and her family take walks outside, and do things other people do, during the day.

Kasey suffers from an extremely rare genetic disorder called CEP -- congenital erythropoietic porphyria. Exposure to sunlight, fluorescent light, halogen light, any kind of ultraviolet light, can cause burns, blisters and scars.

When Kasey was born, problems developed.

"She was swelling and a little red. They had her under lights to keep her warm," said her father, Kurt Knauff.

They sent her to a trauma center and put her under the blue "bilirubin lamp," commonly used for jaundice.

"She swelled three times her size. She turned red, blue, black and blue from head to toe. Nobody knew what was going on. They thought maybe she had a virus. It took about two-and-a-half-weeks before they came up with a diagnosis," Kurt Knauff said.

By that time, Kasey was burned all over her body. But the Knauffs feel lucky she's alive, lucky that a local dermatologist happened to know about CEP, considering that there are fewer than 100 people in the United States who have it.

Porphyria has eight different manifestations, all resulting from an enzyme deficiency in the production of heme, essential for metabolizing certain proteins. This deficiency causes toxic compounds, or "porphyrins," to build up in bone marrow, red blood cells, certain organs and skin.

And while symptoms vary, reddish-purple urine, purple teeth and abdominal pain are common to all porphyria.

King George III of England suffered from an acute version of this disorder.

Both parents need to carry the rare gene in order for a child to have it.

Kasey's house is protected by UV film on the windows and incandescent lights of no more than 50 watts. The same UV filters are in the van her parents use to take her to her a myriad of doctors.

Among other problems, her scars don't grow with her body. At one point, her thumb was growing inside her arm.

"Mainly," says her mother Brenda Knauff, "we've tracked down doctors ourselves, found plastic surgeons ... and they did the skin graphs and plastic surgery."

Kasey has had seven surgeries so far. She doesn't like to talk about it, but her father is thrilled with the result of the surgeries.

"Now she can touch her thumb and her pinky!" he said.

The only known cure for CEP is a bone marrow transplant. A match for Kasey has not yet been found. And such transplants are risky.

Recent publicity of Kasey's story helped put the Knauffs in touch with another CEP patient who suggested they look into blood transfusions. Her mother is hopeful this might make a difference.

"If she does blood transfusions, she could relatively live a normal life," Brenda Knauff said. "She'd just have to go to the hospital every couple of weeks, get blood work done and then live a normal life. We'd just have to monitor her hemoglobin level."

They have recently been talking to Dr. Robert Desnick, a leading CEP specialist at Mt. Sinai Hospital in New York. He hasn't seen Kasey yet, but thinks she may be a candidate for transfusion. The goal, he said, is to "decrease the toxic compound that causes photosensitivity."

Her parents are also speaking to the local school about making it safe for Kasey to attend, and they are slowly exposing their daughter to a little more light, one day at a time.