Variant subtype of xeroderma pigmentosum with multiple basal cell carcinomas diagnosed in a Chinese woman.

As a rare autosomal recessive genetic disease, xeroderma pigmentosum (XP) can be categorized into eight different subtypes (XP-A to XP-G and XP-V) and is caused by mutations in one of eight different genes [1] . The subtypes XP-A to XP-G are genetic disorders caused by mutations in genes involved in the nucleotide excision repair (NER) pathway, making the responses of XP cells to photoproducts induced in DNA by ultraviolet (UV) rays from sunlight defective. Due to this diminished DNA repair activity, patients with this syndrome have a high possibility of developing skin cancers when exposed to sunlight [2-4] . The XP-V subtype has normal NER and is caused by mutations in the XP-V gene, also known as POLH. POLH encodes for Pol η, a member of the Y-DNA polymerase family, which is associated with the synthesis of DNA after injury (translesion synthesis process). In XP-V cells, the ability to replicate DNA after UV exposure is reduced by POLH mutations. As a result, UV lesions are highly mutagenic and lead to skin cancers [5-9] . Classic XP phenotypes include noticeable freckles, acute sunburn, persistent erythema under minimal sun exposure, keratitis, and even nervous abnormities. Compared with the general population, patients with XP develop both non-melanocytic cancer and malignant melanoma at higher frequencies of 10000 and 2000 fold, respectively [10-12] . Among all XP patients worldwide, XP-V patients account for approximately 20% and the number of XP-V patients reported so far is relatively limited [13] . Most patients with a clear diagnosis are older, especially in developing countries. Here we report a Chinese XP-V patient with multiple basal cell carcinomas (BCCs). The application of dermatoscopy was important to early diagnosis and treatment of accompanied skin cancers and then improve the prognosis of this disease.