‘Midnight sun’ and what it means to have XP

I just finished watching Midnight Sun (based on the hit Japanese film No Uta), a romantic tearjerker about 17-year-old Katie Price (Bella Thorne), whose mother died when she was four.  Katie has been sheltered at home since childhood with a rare genetic condition (xeroderma pigmentosum, or XP), a life-threatening sensitivity to sunlight with accompanying neurodegeneration. Having only her father Jack (Rob Riggle) for company, Katie’s world opens up after dark when she risks going outside to sing and play her guitar.

One night, her dreams come true when she’s noticed by her longtime crush Charlie (Patrick Schwarzenegger), whom she’s secretly watched from her bedroom window (an ultraviolet-protected glass window, of course) for years since she was a child. In panic mode, Katie leaves suddenly and forgets her notebook, which Charlie keeps.  He returns the next day and gives it to Katie when she shows up to retrieve it. They ultimately become friends and start dating. As they embark on nightly ventures, their love for each other grows more. 

Katie, however, doesn’t tell Charlie about her condition. On one of their dates he mentions watching the sunrise and Katie freaks out, running home in fear. Charlie picks her up and quickly drives her there, but she does not make it in time, and is exposed to sunlight for a couple of seconds. While Charlie stands confused at the front door, a friend of Katie’s explains that she has xeroderma pigmentosum.

What exactly is xeroderma pigmentosum? XP is a rare, recessive disorder of DNA repair. Affected individuals are unable to repair ultraviolet radiation (UVR)-induced DNA damage, leading to a variety of clinical manifestations: a dramatic increase in skin cancers and small, pigmented spots on the skin with clearly defined edges, an exaggerated response to sun exposure and neurodegeneration (degeneration of the nervous system, especially the neurons in the brain) in approximately 30 percent of affected individuals. 

Its incidence in Western Europe is recorded at 2.3 per million live births. Those with XP are classified into eight different groups corresponding to eight affected genes. Classically, XP patients were identified by clinicians for their tendency to develop  severe and exaggerated sunburn after minimal sun exposure; however, recently it has been shown that  three XP groups have normal sunburn reactions compared to the other groups, who suffer not only from severe, exaggerated sunburn but also have an increased incidence  of neurodegeneration (what Katie had) . 

A diagnosis of XP should be considered in a child with either severe sunburn, increasing pigmented spots at sun-exposed sites, or development of multiple skin cancers at an early age. A skin biopsy and subsequent testing in cell cultures for defective DNA repair will confirm or exclude the diagnosis.  Average life expectancy is reduced, the two main causes of mortality being skin cancer and neurodegeneration. These clinical features distinguish XP from other disorders of DNA repair, namely Trichothiodystrophy and Cockayne syndrome, although overlapping syndromes do occur.

Protecting XP patients from the sun (photoprotection) has been shown to reduce both the pigmented spots and skin cancers dramatically and is presumed to increase life expectancy. Compliance with photoprotection is a recognized problem among XP patients, particularly those without easy sunburn. This is further accentuated by lack of social acceptance for people who wear UVR-protective visors. Increased awareness of XP, both within the medical and media spheres, will benefit current and future XP patients. It will aid in earlier diagnosis and timely photoprotection with better compliance, and therefore result in an improved prognosis. 

It is so rare that in my 27 years of practice I only had one case: a young male brought to me by a TV station for assessment.  But when I was a student in London, I encountered a few cases of XP, which is why I am familiar with what their skin looks like.  It is actually easy to spot in its late stages, but the neurodegeneration is not evident until the symptoms set in.

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