AUSTIN, TEX. – If a child presents with acute (XP), a rare autosomal recessive disorder.
Doug Brunk/MDedge News
Dr. John J. DiGiovanna
Other telltale symptoms of XP include the presence of skin cancer at an early age and a large number of skin cancers.
At the annual meeting of the Society for Pediatric Dermatology, John J. DiGiovanna, MD, described XP as a disorder of genomic instability, which has no cure. It’s caused by a mutation in genes XPA through XPG and the XP variant (XPV) gene. “The genome controls our genes, and UV rays damage DNA,” said Dr. DiGiovanna, who is a senior research physician at the National Cancer Institute’s Laboratory of Cancer and Biology and Genetics, Bethesda, Md. “This damage from UV radiation is similar to damage from chemical agents that form DNA adducts, such as cigarette smoke and certain chemotherapy agents such as cisplatinum.”
XP patients present with or without acute burning after minimal sun exposure, while children with both subtypes develop “freckling” by the time they reach 2 years of age. Dr. DiGiovanna pointed out that lentigo maligna lesions associated with XP resemble freckles at first glance, yet they vary in size, intensity, and border. Meanwhile, freckles in healthy patients are similar in size, are light tan in color, and have a regular border.
“The burning with minimal sun exposure that occurs during childhood leads to pigmentary changes, atrophy, xerosis, and telangiectasias,” he said. A follow-up analysis of 106 XP patients admitted to the National Institutes of Health between 1971 and 2009 found that patients were diagnosed with their first nonmelanoma skin cancer at a median age of 9 years, compared with age 67 among those in the general population (J Med Genet 2011 Mar;48[3]:168-76). “This is a 58-year decrease in age at risk, which is a 10,000-fold increase in skin cancer,” said Dr. DiGiovanna, who was one of the study authors.
Melanoma also occurs at an earlier age among XP patients – a median age of 22 years, compared with a median of 55 years in the general population. “In the general population, melanoma occurs at a younger age than nonmelanoma skin cancer, while in the XP population, melanoma occurs at an older age,” he said. “This is giving us a good biologic lesson that the melanoma induction mechanism must be different from nonmelanoma skin cancer.”
He recalled one XP patient who was followed by NIH researchers for 4 decades. She worked in a doctor’s office and drove a car, but developed progressive neurologic degeneration and died at the age of 40. “This was not due to unrepaired UV damage, but there are other agents which damage other neurons,” Dr. DiGiovanna explained. “Over time, what you get is a decrease in brain volume, an increase in the brain ventricles, and a loss of brain tissue. At postmortem examination, her brain was of infantile size, compared with that of an equivalent 40-year-old. This is a disease of neuronal loss, and it’s progressive. Only about 20%-25% of XP patients experience neural degeneration.”
Management of XP involves strict sun avoidance, including use of a portable UV meter and many layers of UV protection, including application of sunscreen, wearing protective clothing, sunglasses, hats, and face shields, and the use of UV-blocking window film, LED lights, and a vitamin D diet or oral supplementation. Affected individuals also require frequent skin monitoring by the patients and their family members, frequent dermatologic exams by clinicians, biopsy of suspicious lesions, removal of any skin cancers found, field treatments with agents such as 5-fluorouracil and imiquimod, and chemoprevention with oral retinoids for patients who are actively developing large numbers of new lesions (N Engl J Med. 1988 Jun23;318[25]:1633-7).
“Probably the most important thing you can do is refer them to patient support groups,” Dr. DiGiovanna said. “They are present in many countries and can help them manage the day-to-day issues of their condition.” Support groups based in North America include the XP Family Support Group, XP Society, and XP Grupo Luz De Esperanza.
Dr. DiGiovanna reported having no financial disclosures.