Familial clustering of polymorphic light eruption in relatives of patients with lupus erythematosus: evidence of a shared pathogenesis

Background Abnormal photosensitivity is a common feature of many forms of lupus erythematosus (LE), Objectives To examine the role of polymorphic light eruption (PLE) as a possible predisposing factor for cutaneous forms of LE. Methods Eighty-five patients with well-characterized subacute cutaneous LE (SCLE) and discoid LE (DLE) were recruited from outpatient clinics, and the prevalence of PLE determined by detailed interview and clinical examination, Results Symptoms consistent with PLE were reported in 61% and 55% of SCLE and DLE patients, respectively; this was significantly higher than the overall population prevalence of 13.6% (P < 0.001), giving a relative risk (RR) for PLE in SCLE patients of 3.37 (95% confidence interval, CI 2.46-4.28) and DLE patients of 3.11 (95% CI 2.31-3.91). PLE developed before the onset of LE in 61% of cases (median interval 12 years, range 1-40), concomitantly in 24%, and subsequently in a further 15% (median interval 3.5 years, range 1-25). To delineate the relationship between PLE and LE further, the prevalence of PLE was determined in 103 otherwise unaffected first-degree relatives of SCLE and DLE probands; we had previously demonstrated clustering of PLE in families, reflecting a strong genetic component, We found a significantly higher PLE prevalence in relatives of the LE probands than in the general population (P < 0.001), giving an RR for PLE of 2.29 (95% CT 1.55-3.03) and 2.61 (95% CI 1.32-3.89) for female and male relatives, respectively. Conclusions The high prevalence of PLE in LE patients, together with clustering of PLE among first-degree relatives of SCLE and DLE probands, suggests that there map be a shared pathogenetic basis for PLE and cutaneous LE, We propose that predisposition to PLE may contribute to the LE phenotype in otherwise susceptible individuals.