The Genetics of IgA Nephropathy: An Overview from Western Countries.

BACKGROUND: IgA nephropathy (IgAN) is the commonest primary glomerulonephritis worldwide and a significant cause of chronic kidney disease and end-stage renal disease. It is widely accepted that genetic factors play a role in the pathogenesis of IgAN. However, the identity of these genetic factors remains uncertain.
SUMMARY: Critical to all genetic studies is a precise phenotypic definition of the disease. It is well recognised that IgAN displays striking phenotypic variation, raising the possibility that it may not be a single disease and it may not be the same disease in different parts of the world. In this review, we discuss the challenges that this phenotypic variation poses to interpreting genetic data and the current evidence for specific gene involvement in IgAN, focusing particularly on data from European IgAN cohorts. KEY MESSAGE: With advances in genetic techniques, in particular next-generation sequencing, and an increased understanding of the importance of copy number variations, epigenetics and transcriptomics, it is likely that we will gain a greater understanding of the genetic basis for IgAN. However, due to the lack of consistency in epidemiological clinicopathological studies both within and between continents, this will only be achieved if we are able to more precisely phenotype IgAN populations. FACTS FROM EAST AND WEST: The reported prevalence of IgAN is higher in Asia than in Europe and North America. However, differences in use of biopsy for the diagnosis of IgAN should be taken into account in analysing data from both East and West. In Europe, IgAN affects men more frequently than women; this is not the case in Asia. Familial IgAN has been more frequently reported in Europe than in Asia. Within Europe, familial IgAN is more evident in southern than in northern populations. Changes in the pattern of serum IgA1 O-glycosylation is a common finding in IgAN patients in the East and West. SNPs within the gene coding for the enzyme C1GALT1 have been reported in Chinese and European patients. However, there is no evidence for a role of gene polymorphism of the C1GALT1 chaperone cosmc in Europeans. Genetic variants in the HLA gene family have been observed in populations from the East and West. Associations between IgAN and variants of the TAP1/PSMB and DEFA genes were observed in Asian but not in Western patients. Association with the angiotensin-converting enzyme gene was seen only in Asian patients.