CD40LG and rheumatoid arthritis: Moreover, the average proportion of trait loci detected by either the multiple-marker or single-marker two-step strategy was close to 55%: the DR, C, D, and E loci affecting RA risk directly and the F locus as a QTL for IgM were detected in at least 98% of the replicates, while the influence of Loci G and H on disease severity and the involvement of Loci A and B in more complex gene × gene (G × G) and gene × environment interactions (G × E) were almost never revealed.