Simplex and multiplex families with IgA nephropathy (IgAN) have been reported from several ethnic backgrounds, providing the strongest evidence of a role for genetic factors in pathogenesis of IgAN. From a phenotypic point of view, familial and sporadic IgAN cannot be differentiated, and the main clinical and histological features are similar. Traditionally, the case-control study design was employed to identify associations between particular candidate genes, for example, HLA antigens the uteroglobin gene and IgAN, giving conflicting results. Recently, a different approach, using linkage analysis, was undertaken by geneticists at Yale University. A 10-cM genome-wide screen was performed in 30 multiplex IgAN pedigrees, and one locus was mapped (IGAN-1) on chromosome 6q22-23. Future study will be focused on the identification of the gene underlying IGAN-1. This will enable us to understand the molecular pathogenetic basis of IgAN.