HLA–Gm/κm interaction in sarcoidosis. 
Suggestions for a complex genetic structure

The aetiology of sarcoidosis is still unknown. Environmental exposures are believed to interact with genetic factors in determining the pattern of sarcoidosis presentation, progression and prognosis. The frequency of serological polymorphism of immunoglobulin G heavy chain (Gm) and κ light chain (κm) markers in 107 patients with biopsy‐proven sarcoidosis and in 227 controls, and their interactions with histocompatibility leukocyte antigen (HLA) class I, II, and III markers, were studied. A “protective” effect of the Gm(3 5*) phenotype in the sarcoid group versus controls (p‐value for number of specificities tested (pc)=0.05, odds ratio 0.15) and a reduced frequency of Gm(3 23 5*) in patients with advanced chest radiographic stage (Chi‐squared (two degrees of freedom)(χ2(2df) 17.61, pc=0.0058) were observed. With reference to epistatic interactions, the combination Gm(3 23 5*)/BfS had a “protective” effect towards stage II (χ2(2df) 13.86, pc=0.043). Finally, correspondence analysis defined two clusters: HLA‐DR4, C4BQ0, Gm(1, 3, 17 23 5*, 21, 28) and BfF associated with stage II, and HLA‐DR3, C4AQ0, κm(1) and Gm(3 23 5*) associated with stage I. These data further support the hypothesis that sarcoidosis results from an interplay of environmental factors and genes, each contributing to the susceptibility/resistance to and/or the clinical heterogeneity of the disease. In addition, these data provide the first evidence of an interaction between immunoglobulin G heavy chain/κ light chain markers and histocompatibility leukocyte antigen class III genes in a disease.