RESUMO
Asthma is a common, heterogeneous, complex disease accompanied by raised total and specific immunoglobulin-E (IgE) antibody levels. Despite numerous previous reports of linkage and association of asthma, atopy and serum IgE levels to genes within the 5q21-33 region, definitive, replicable results are still not available. We used the classical twin design to (i) estimate the relative contributions of genes and environment to variation in total IgE levels, (ii) assess genetic linkage, and (iii) examine allelic association of 11 microsatellite markers spanning the 5q21-33 region to total IgE. Variation in total IgE level was shown to be highly heritable (65%). Although evidence for linkage of the 11 microsatellites to IgE was not observed, the omnibus test of association, not confounded by population substructure, showed positive association of D5S393 and D5S673 to IgE. Genes in the vicinity of D5S673 include hepatitis A virus receptor (HAVCR-1) and IL-12B. Recently, the mouse orthologue of HAVCR-1, the T-cell membrane family of proteins, have been shown to be in strong association with expression of airway hyperactivity in a mouse model of human asthma and atopy. IL-12B subserves many proinflammatory functions and also induces B cells proliferation.