Ethnic differences in immunogenetic features and photosensitivity of cutaneous lupus erythematosus

Genetic differences are involved in the development of lupus erythematosus (LE). Skin lesions are influenced by environmental triggers such as ultraviolet light, temperature, and chemical stresses, and the patterns of skin lesion are variable in cutaneous LE such as systemic LE (SLE), chronic discoid LE (CDLE), subacute cutaneous LE (SCLE), and LE tumidus (LET). Although there are a few conflicting reports, many Japanese dermatologists feel there are photosensitivity differences in lupus erythematosus between Asian and Caucasian subjects with SCLE and LET. HLA studies in Japanese subjects revealed that HLA-DRB1*1501 association was with both CDLE and SLE. The association between HLA-Cw6 and CDLE was first reported in Japanese population, and a HLA-A33-B44-DRB1*1302 haplotype showed a positive association in CDLE. However, these results are not compatible with those from Caucasian subjects. There are no significant associations among HLA studies, photosensitivity, and anti-Ro/SS-A antibodies in Japanese CLE patients. Photosensitivity will be a key factor to dissolve multi-factorial complexes of LE etiopathogenesis. Our present understanding is that an axis of photosensitivity, anti-Ro/SS-A antibodies and apoptosis via TNF are the best (markers) to verify the contribution of genetics in SCLE, LET, and other CLEs. The incidence and photosensitivity of SCLE and LET are much lower in Japanese than in Caucasian subjects. However, this discrepancy may open the window for investigating CLE pathogenesis through global collaborations. For this purpose and goal, a new and more conventional method should be developed for the examination of so-called photosensitivity.