Gm phenotype linkage to subsets of juvenile chronic arthritis (JCA) with influence on IgG subclass response

The serum hyper IgG of 76 JCA patients of different clinical subsets, 8 systemic, 37 polyarticular and 31 oligoarticular, were investigated by IgG subclass quantitation and Gm allotype determination. The well known increased serum IgG in JCA was confirmed as increased IgG1, IgG2 and IgG3 in the whole group. Investigating the clinical subsets IgG1 was significantly increased in all subsets while IgG2 and IgG3 increased only in the polyarticular form. In search of a genetic linkage for the clinical JCA subsets and the different IgG subclass patterns found, the alternative Gm allotypes G1m(a), G1m(f) for IgG1, G2m(n), G2m(") for IgG2 and G3m(g) , G3m(b) for IgG3 gene loci were investigated. The Gm (a,",g) haplotype was significantly increased in the whole JCA group and in the polyarticular subset. In the systemic subset the Gm (a,",g/a",g) phenotype was significantly increased, but the Gm (a,'h,g/f,n,b) phenotype was increased in the oligoarticular subset. The number of JCA patients with G1m(f,f)-,G3m(b,b)-phenotypes were significantly decreased. In such phenotypes, remission was more common. The susceptibility of JCA, its different clinical subsets and outcome of the disease is determined by Gm allotypes, affecting characteristic IgG subclass patterns.