Nature and nurture in systemic lupus erythematosus

Nowhere across the spectrum of rheumatic and dermatological disease is the interaction of nature and nurture more relevant than in the connective tissue diseases such as SLE. While genetic and environmental factors are clearly involved in both the triggering of the disease and its expression, the interaction is complex with different combinations of factors contributing in different patients. For example, while genetic factors contribute substantially to susceptibility to lupus, this does not follow a simple Mendelian pattern of inheritance and mathematical models suggest that there may be varying contribution from at least four genes with differing inheritances. A variety of candidate genes and environmental factors have been highlighted in SLE but to dissect out the complexity of how these might interact requires the study of patient groups with a better defined clinical and serological phenotype. For example, studies of patients with subacute cutaneous lupus (SCLE) have shown associations with various genes in the MHC region (including HLA, complement and TNF) and suggest that the biological effect of inheriting an extended MHC region may be greater than its individual parts. One can now speculate on how interaction with an environmental factor such as UV light explains pathogenesis.