The present status of xeroderma pigmentosum in Japan and a tentative severity classification scale.

Xeroderma pigmentosum (XP) is a rare autosomal recessive hereditary disease. Patients with XP have severe hypersensitivity to sunlight, resulting in skin cancers, and some patients have neurological symptoms. In Japan, XP complementation group A (XP-A) is the most common form, and it is associated with severe neurological symptoms. We performed a nationwide survey on XP to determine the present status of XP in Japan. The distribution of complementation groups in Japan was considerably different from that in other countries, but there was a higher frequency in group A and the variant type, which is similar to previous reports in Japan. Basal cell carcinoma was the most frequent skin cancer that patients with XP developed, followed by squamous cell carcinoma and malignant melanoma. The frequency of these skin cancers in patients with XP-A has decreased, and these skin cancers have been occurring in much older people than those previously observed. Diagnosing XP in patients at younger ages seems to encourage patients and their parents to use sun protection, which helps prevent skin cancer. We also created a tentative scale for classifying the severity of XP, and we evaluated the neurological symptoms of XP-A using this severity scale. Our classification correlated well with patients' age, suggesting that it may be useful and feasible in clinical practice to assess the progression of symptoms of each patient with XP and evaluate the effects of treatment in the future.