The frequency of risk alleles was highest in East Asians and most affordable in Blacks (17), mimicking the distribution maps discussed before

The frequency of risk alleles was highest in East Asians and most affordable in Blacks (17), mimicking the distribution maps discussed before. system and IgAN. Herein, we review the evidence supporting the role of gut inflammation in IgAN pathogenesis. Keywords:glomerular and tubulointerstitial diseases, gut-associated lymphoid tissue, IgA nephropathy, immunoglobulin A, inflammatory bowel disease, microbiome, Peyers patches == Introduction == Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis worldwide (1). Clinical presentation generally involves episodic macrohematuria intercurrent with mucosal infections and a varying degree of proteinuria. Disease progression is variable: some patients have a mild presentation with normal kidney function, sometimes achieving complete remission of proteinuria with supportive care alone, whereas up to 50% of patients progress to irreversible kidney damage and ESKD (2). Histologically, the disease is characterized by mesangial and paramesangial Lactitol deposition of immune complexes with dominance or co-dominance of IgA by immunofluorescence microscopy. Since its initial description by Berger and Hinglais in 1968 (3), significant advances have been made in understanding the pathogenesis of this disease, and evidence now points toward a multihit autoimmune process also known as the four-hit hypothesis, which starts with the Lactitol production of a galactose-deficient and polymeric immunoglobulin A-1 (gd-IgA1) and then formation of gd-IgA1 immune complexes in the circulation that ultimately deposit in the glomerular mesangium, leading to inflammation and progressive glomerular injury (4). The mechanisms behind the production of gd-IgA1 are not entirely clear, but studies have revealed that the origin of gd-IgA1 is likely mucosal (58). Interactions between commensal bacteria and the intestinal mucosa seem to be essential in regulating IgA production in the gut, although it is not clear how this interaction may influenceO-glycosylation and production of gd-IgA1. Importantly, these findings formed the basis for the development of drugs that target the gut mucosa to treat patients with IgAN. Recently, a novel targeted release form of the corticosteroid budesonide that has been engineered to target the Peyers patches in the distal ileum (911) was approved by the US Food and Drug Administration (FDA) to become the first disease-specific therapy for IgAN (12). Herein, we review the processes that regulate IgA production in the gut mucosa and the evidence that links gut mucosal alterations to IgAN. We also explore the relationship between this disease and other gastrointestinal conditions such as inflammatory bowel disease (IBD) and celiac disease (CD). Lactitol == IgAN: Epidemiology, Genetic Susceptibility, and Clinical Presentation == == Epidemiology and Genetic Susceptibility == IgAN is the most common cause of kidney failure secondary to a primary glomerular disease worldwide. It is common in Asia, has lower prevalence in Europe, and is very infrequent among populations of African ancestry (13). In Eastern Asia, IgAN is diagnosed in 40%50% of native kidney Lactitol biopsies, which Lactitol Prkwnk1 heavily contrasts with African registries that show prevalence as low as 3% (14). Differences in screening policies may partially explain such disproportion. In Japan, screening for IgAN by assessment of proteinuria and hematuria with urine dipstick has been used since 1972 (15). This aids to capture and prompts kidney biopsies in asymptomatic patients with isolated microscopic hematuria with or without proteinuria that would have otherwise passed unnoticed. However, differences in screening practices do not fully explain the geographic variability of the disease. IgAN can present sporadically or in familial form. For the latter, autosomal dominant transmission with incomplete penetrance or a combined model where the activation of genes is dependent on environmental factors represent reasonable explanations (16). Genome-wide association studies (GWAS) have identified several susceptibility and protective genetic loci. Using seven single nucleotide polymorphisms, a genetic risk score detected significant differences in the distributions of risk alleles among different ethnicities. The frequency of risk alleles was highest in East Asians and lowest in Blacks (17), mimicking the distribution maps discussed before. The genetic risk score was based on a previous GWAS, which identified five IgAN susceptibility loci on Chr.6p21 (HLA-DQB1/DRB1, PSMB9/TAP1, and DPA1/DPB2 loci), Chr.1q32 (CFHR3/R1 locus), and Chr.22q12 (HORMAD2 locus) (18). Intriguingly, these loci have been associated with other autoimmune diseases, including IBD. Several other GWAS have identified various susceptibility loci that link IgAN to potential environmental and alimentary hits (1921). These loci, which include, among others, TLR9, DEFA, and TNFSF13, that encode for genes implicated in the immunogenic response to antigens in the intestinal mucosa. DNA methylation studies suggest that environmental and alimentary changes in IgAN may induce aberrant methylation of the DNA, leading to an abnormal expression.