With Midnight Sun hitting theaters on Friday, a spotlight is being put on the rare genetic disorder xeroderma pigmentosa, or XP, that makes Bella Thorne’s character, Katie, hypersensitive to the sun.
But it’s not the first time this story is being told. The 1994 film Children of the Dark features two young girls, Jaime and Sherry Harrison, living with XP. Four years earlier, the real-life Harrison sisters that inspired the movie covered the May 14, 1990 issue of PEOPLE.
Back in 1990, Jaime and Sherry were 5 and 3 years old, respectively, and living in Northern California with their parents, Kim and Jim, and 12-year-old stepbrother Bobby. Unlike other kids their age, the only time they were allowed outside to play was during nightfall as any exposure to the sun or ultraviolet rays, no matter how brief, could leave them acutely vulnerable to skin and eye cancers because of XP.
“ patients don’t have the repair mechanism in their DNA,” Debra Jaliman, assistant dermatology professor at the Icahn School of Medicine at Mount Sinai, tells PEOPLE. “When they get damaged by sunlight, they can’t repair that damage and so a lot of these individuals really can’t go out in the sun at all. A lot of people call them ‘moon children.'”
According to Jaliman, people with XP have a high risk of developing every type of skin cancer — from basal cell and squamous cell skin cancers to melanoma.
Kim and Jim first noticed signs of trouble when Jaime was only 2 months old while on vacation in Montana.
“She hated to go outside. She would scream and thrash and fight,” Kim said at the time. “We loved the outdoors, but in her baby pictures she is always closing her eyes real tight.”
During the vacation, Jaime developed burns and blisters. Doctors didn’t know that it had to do with being outside, and so they diagnosed Jaime’s condition as a rash, then changed the diagnosis to impetigo, then allergies.
Jaliman says there are symptoms of XP to look out for in babies, including pigmentary problems, wrinkling of the skin and rough patches.
“Their skin is like a thousand times more sun sensitive than the average person,” she says. “When they’re very young, you see the changes that you wouldn’t see for many, many years. You see the changes much earlier than you would in somebody with just regular skin.”
In 1986, a skin biopsy revealed Jaime had XP, and like most victims, would have a high chance of dying of melanoma cancer at a young age. Kim and Jim dreaded the idea of testing Sherry, who was 3 months old when they got Jaime’s diagnosis, but gave in to pressure from their doctors.
Sherry’s test results came back positive, but neither of them had any idea that they both carried the abnormal gene that causes XP.
“It’s recessive, and it’s carried in genes that can be passed in families.” Bruce Katz, director of the JUVA Skin and Laser Center in New York, tells PEOPLE. Even when both parents carry the recessive mutation of the same gene, there’s still only a 1 in 4 chance they’ll be affected.
Katz says those with XP can also develop neurological complications, including seizures. The only noticeable impairment Jaime and Sherry had at the time was a slurring of speech, though they didn’t know for sure if it was due to XP.
Kim and Jim tried to make life as normal as possible for their girls, and when they had to take them out in daylight to see a doctor, they would slather them in No. 50 sun block, cover them up in all types of clothing and would give them ultraviolet-proof glasses. Their van, as well as their home, had protective film on all the windows.
“Windows block UV light but not UVA ,” Katz says. “So they can still get sunburn. They really have to be completely in dark areas that have no sunlight.”
Even some fluorescent light bulbs can pose a risk, but those living with XP can use UV meters to test UV levels in different environments. Though it’s been decades, Katz says these techniques haven’t changed much for those living with XP.
“Unfortunately, we have not progressed since the 1990s,” he says. “XP is very rare so it’s not one of the diseases that are getting attention.”
Currently, it’s estimated that 1 in 1 million people in the U.S. suffers from the disorder, according to the U.S. National Library of Medicine’s Genetics Home Reference. So far, Thorne has been “relieved” at the positive response Midnight Sun has received for putting a focus on the rare disease.
“The awareness that we’ve spread about XP such an enormous difference,” Thorne told PEOPLE. “We have tweets from the XP organization saying, ‘Thank you so much, with all the commercials and stuff we’ve had like 100,000 clicks in less than 24 hours overnight on their site.’ There’s another girl that tweeted us like, ‘Finally people are starting to understand and ask questions’ about her disease.”
“So many people have reached out to me with other terminal illnesses, not XP specifically, but other things and they’re just like ‘this movie is so touching, this is really beautiful, I feel good walking out of this movie,'” she continues. “I’m like, ‘Oh thank God.'”
When it comes to treatment, Jaliman says XP patients go through the same processes as anybody with skin cancer would.
“You can treat the individual skin cancers with surgery, of course,” she says. “You can treat the sun damage with laser, and there’s special prescription medications that you can treat pre-malignancies. We also treat pre-malignancies with freezing, with cryotherapy.”
Now in their 30s, Jaime and Sherry have beaten the odds.
“Less than 40% of people survive the young age of 20,” Jaliman says. “But some people, no matter what bad genes they’re dealt in their life, are so good at managing it.”
Read the rest of PEOPLE’s May 1990 cover story here.