Familial clustering of IgA nephropathy: further evidence in an Italian population

An Update on the Genetics of IgA Nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN), the most common form of glomerulonephritis, is one of the leading causes of end-stage kidney disease (ESKD). It is widely believed that genetic factors play a significant role in the development of IgAN. Previous studies of IgAN have provided important insights to unravel the genetic architecture of IgAN and its potential pathogenic mechanisms. The genome-wide association studies (GWASs) together have identified over 30 risk loci for IgAN, which emphasizes the importance of IgA production and regulation in the pathogenesis of IgAN. Follow-up fine-mapping studies help to elucidate the candidate causal variant and the potential pathogenic molecular pathway and provide new potential therapeutic targets. With the rapid development of next-generation sequencing technologies, linkage studies based on whole-genome sequencing (WGS)/whole-exome sequencing (WES) also identify rare variants associated with IgAN, accounting for some of the missing heritability. The complexity of pathogenesis and phenotypic variability may be better understood by integrating genetics, epigenetics, and environment. We have compiled a review summarizing the latest advancements in genetic studies on IgAN. We similarly summarized relevant studies examining the involvement of epigenetics in the pathogenesis of IgAN. Future directions and challenges in this field are also proposed.

Candidate Genes for IgA Nephropathy in Pediatric Patients: Exome-Wide Association Study

IgA nephropathy (IgAN) is an autoimmune disorder which is believed to be non-monogenic. We performed an exome-wide association study of 70 children with IgAN and 637 healthy donors. The HLA allele frequencies were compared between the patients and healthy donors from the bone marrow registry of the Pirogov University. We tested 78,020 gene markers for association and performed functional enrichment analysis and transcription factor binding preference detection. We identified 333 genetic variants, employing three inheritance models. The most significant association with the disorder was observed for rs143409664 (PRAG1) in the case of the additive and dominant models (PBONF = 1.808 × 10-15 and PBONF = 1.654 × 10-15, respectively), and for rs13028230 (UBR3) in the case of the recessive model (PBONF = 1.545 × 10-9). Enrichment analysis indicated the strongly overrepresented "immune system" and "kidney development" terms. The HLA-DQA1*01:01:01G allele (p = 0.0076; OR, 2.021 [95% CI, 1.322-3.048]) was significantly the most frequent among IgAN patients. Here, we characterized, for the first time, the genetic background of Russian IgAN patients, identifying the risk alleles typical of the population. The most important signals were detected in previously undescribed loci.

Genome-Wide Association Analysis of Protein-Coding Variants in IgA Nephropathy

SIGNIFICANCE STATEMENT

Genome-wide association studies have identified nearly 20 IgA nephropathy susceptibility loci. However, most nonsynonymous coding variants, particularly ones that occur rarely or at a low frequency, have not been well investigated. The authors performed a chip-based association study of IgA nephropathy in 8529 patients with the disorder and 23,224 controls. They identified a rare variant in the gene encoding vascular endothelial growth factor A (VEGFA) that was significantly associated with a two-fold increased risk of IgA nephropathy, which was further confirmed by sequencing analysis. They also identified a novel common variant in PKD1L3 that was significantly associated with lower haptoglobin protein levels. This study, which was well-powered to detect low-frequency variants with moderate to large effect sizes, helps expand our understanding of the genetic basis of IgA nephropathy susceptibility.

BACKGROUND

Genome-wide association studies have identified nearly 20 susceptibility loci for IgA nephropathy. However, most nonsynonymous coding variants, particularly those occurring rarely or at a low frequency, have not been well investigated.

METHODS

We performed a three-stage exome chip-based association study of coding variants in 8529 patients with IgA nephropathy and 23,224 controls, all of Han Chinese ancestry. Sequencing analysis was conducted to investigate rare coding variants that were not covered by the exome chip. We used molecular dynamic simulation to characterize the effects of mutations of VEGFA on the protein's structure and function. We also explored the relationship between the identified variants and the risk of disease progression.

RESULTS

We discovered a novel rare nonsynonymous risk variant in VEGFA (odds ratio, 1.97; 95% confidence interval [95% CI], 1.61 to 2.41; P = 3.61×10 -11 ). Further sequencing of VEGFA revealed twice as many carriers of other rare variants in 2148 cases compared with 2732 controls. We also identified a common nonsynonymous risk variant in PKD1L3 (odds ratio, 1.16; 95% CI, 1.11 to 1.21; P = 1.43×10 -11 ), which was associated with lower haptoglobin protein levels. The rare VEGFA mutation could cause a conformational change and increase the binding affinity of VEGFA to its receptors. Furthermore, this variant was associated with the increased risk of kidney disease progression in IgA nephropathy (hazard ratio, 2.99; 95% CI, 1.09 to 8.21; P = 0.03).

CONCLUSIONS

Our study identified two novel risk variants for IgA nephropathy in VEGFA and PKD1L3 and helps expand our understanding of the genetic basis of IgA nephropathy susceptibility.

Global Incidence of IgA Nephropathy by Race and Ethnicity: A Systematic Review

Key Points

In 16 studies conducted abroad, IgA nephropathy incidence varied from 0.06 in South Africa to 4.2 per 100,000 in Japan. Globally, the incidence of IgA nephropathy seemed higher in Asians than in non-Asians and higher in male patients than in female patients. Five studies conducted in the United States found no consistent difference in incidence between Black patients and White patients.

Background

The reported incidence of IgA nephropathy varies widely across studies and may vary on the basis of race/ethnicity. This study systematically reviewed the incidence of IgA nephropathy in the United States and other countries and explored variability on the basis of the racial/ethnic composition and other demographic characteristics of different populations.

Methods

This was a systematic review. Studies were eligible for inclusion if they contained data collected from January 1, 1974, to December 31, 2021, and reported IgA nephropathy incidence at a population level (i.e. , cases of IgA nephropathy per 100,000 population).

Results

Five US and 16 international studies were included; three of the US studies reported the race-specific incidence of IgA nephropathy. In the United States, the reported incidence of IgA nephropathy ranged from 0.39 per 100,000 in Tennessee to 1.4 per 100,000 in Minnesota; internationally, IgA nephropathy ranged from 0.06 per 100,000 in South Africa to 4.2 per 100,000 in Japan. Findings regarding the incidence of IgA nephropathy in the United States by race were inconsistent: One study found a higher incidence among White patients compared with Black patients, one study found a lower incidence in White patients, and one study found no difference. Globally, the incidence of IgA nephropathy seemed to be higher in Asian than in non-Asian populations and higher in male patients than in female patients.

Conclusions

Reported incidence of IgA nephropathy varies widely; there is no consensus regarding the relationship between race and IgA nephropathy. Incidence rates seemed to be higher in Asians than non-Asians and in male patients than female patients. We recommend that future studies should report IgA nephropathy incidence rates by race/ethnicity and account for the demographic characteristics of the background population.

Cyclic neutropenia and concomitant IgA nephropathy: a case report

BACKGROUND

IgA nephropathy (IgAN) is universally recognized as one of the most common primary glomerular diseases in all ages. Cyclic neutropenia (CN) is a rare haematologic disorder that is associated with mutations of the ELANE gene. The co-occurrence of IgAN and CN is extremely rare. This is the first case report of a patient with IgAN and genetically confirmed CN.

CASE PRESENTATION

We report a case of a 10-year-old boy who presented with recurrent viral upper respiratory tract infections accompanied by several episodes of febrile neutropenia, haematuria, proteinuria and acute kidney injury. Upon first admission, his physical examination was unremarkable. His kidney function was impaired, whereas his urine microscopy showed evidence of macroscopic haematuria and proteinuria. Further workup showed elevated IgA. The renal histology was consistent with mesangial and endocapillary hypercellularity with mild crescentic lesions, while immunofluorescence microscopy showed IgA-positive staining, which was characteristic of IgAN. Moreover, genetic testing confirmed the clinical diagnosis of CN, therefore Granulocyte colony-stimulating factor (G-CSF) was initiated to stabilize the neutrophil count. Regarding proteinuria control, the patient was initially treated with an Angiotensin-converting-enzyme inhibitor for approximately 28 months. However, due to progressive proteinuria (> 1 g/24 h), Corticosteroids (CS) were added for a period of 6 months according to the revised 2021 KDIGO guidelines with favorable outcome.

CONCLUSIONS

Patients with CN are more susceptible to recurrent viral infections, which can trigger IgAN attacks. In our case CS induced remarkable proteinuria remission. The use of G-CSF contributed to the resolution of severe neutropenic episodes, viral infections and concomitant AKI episodes, contributing to better prognosis of IgAN. Further studies are mandatory to determine whether there is a genetical predisposition for IgAN in children with CN.

IgA nephropathy pathogenesis and therapy: Review & updates

BACKGROUND

IgA nephropathy (IgAN) is the most frequent type of primary glomerulonephritis since the first type was described more than four decades ago. It is the prevalent cause of primary glomerular disease that causes end-stage renal disease. In most patients with IgAN, hematuria is the most common reported symptom, particularly in those with a preceding upper respiratory tract infection. Although the pathogenesis of IgAN is usually multifactorial, autoimmune complex formation and inflammatory processes are the most widely recognized pathogenic mechanisms. Multiple approaches have been trialed as a therapy for IgAN, including tonsillectomy, steroids, other immune-suppressive therapy in different regimens, and kidney transplantation.

AIM AND METHOD

PubMed, Google, Google Scholar, Scopus, and EMBASE were searched by the authors using different texts, keywords, and phrases. A non-systemic clinical review is intended to review the available data and clinical updates about the possible mechanism(s) of IgAN pathogenesis and treatments.

CONCLUSION

IgAN has a heterogeneous pattern worldwide, making it difficult to understand its pathogenesis and treatment. Proteinuria is the best guide to follow up on the IgAN progression and treatment response. Steroids are the cornerstone of IgAN therapy; however, other immune-suppressive and immune-modulative agents are used with a variable response rate. Kidney transplantation is highly advisable for IgAN patients, although the recurrence rate is high. Finally, IgAN management requires collaborative work between patients and their treating physicians for safe long-term outcomes.

Increased retinal drusen in IgA glomerulonephritis are further evidence for complement activation in disease pathogenesis

Drusen are retinal deposits comprising cell debris, immune material and complement that are characteristic of macular degeneration but also found in glomerulonephritis. This was a pilot cross-sectional study to determine how often drusen occurred in IgA glomerulonephritis and their clinical significance. Study participants underwent non-mydriatic retinal photography, and their deidentified retinal images were examined for drusen by two trained graders, who compared central drusen counts, counts ≥ 10 and drusen size with those of matched controls. The cohort comprised 122 individuals with IgA glomerulonephritis including 89 males (73%), 49 individuals (40%) of East Asian or Southern European ancestry, with an overall median age of 54 years (34-64), and median disease duration of 9 years (4-17). Thirty-nine (33%) had an eGFR < 60 ml/min/1.73 m² and 72 had previously reached kidney failure (61%). Overall mean drusen counts were higher in IgA glomerulonephritis (9 ± 27) than controls (2 ± 7, p < 0.001). Central counts ≥ 10 were also more common (OR = 3.31 (1.42-7.73, p = 0.006), and were associated with longer disease duration (p = 0.03) but not kidney failure (p = 0.31). Larger drusen were associated with more mesangial IgA staining (p = 0.004). Increased drusen counts were also present in IgA glomerulonephritis secondary to Crohn's disease but not with Henoch-Schonlein purpura. The finding of retinal drusen in IgA glomerulonephritis is consistent with complement activation and represents a model for better understanding glomerular immune deposition and a supporting argument for treatment with anti-complement therapies.

Case Report: A Pathogenic Missense Variant of WT1 Cosegregates With Proteinuria in a Six-Generation Chinese Family With IgA Nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common type of primary glomerulonephritis worldwide. In addition to hematuria, proteinuria is observed in a considerable proportion of patients with IgAN and has proven to be a strong risk factor for disease progression. Although the exact pathogenesis of IgAN is still unclear, genetic factors are widely considered to play a role in its occurrence and development. Here, we investigated a large IgAN-associated pedigree of 47 members belonging to six generations. Two members of the family who presented with proteinuria and hematuria were diagnosed with IgAN through renal biopsy. Four other members also exhibited proteinuria or hematuria but without renal biopsy. Using whole-exome sequencing, we identified a likely pathogenic variant in WT1 (c.1397C>T; p.Ser466Phe) that cosegregated with proteinuria in the affected family members. In addition, another pathogenic variant in NPHS1 (c.3478C>T; p.Arg1160Ter) was identified; however, it did not cosegregate with abnormal proteinuria. Compared to individuals in the pedigree with only one heterozygous WT1 variant (c.1397C>T; p.Ser466Phe), the proband and her younger brother carried an additional WT1 variant (c.1433-10G>A) and presented with a more severe phenotype and rapid progression to end-stage kidney disease. Our findings suggest the WT1 missense variant (c.1397C>T; p.Ser466Phe)-induced primary podocyte injury might contribute to the proteinuria phenotype and IgAN progression in this pedigree.

The Influence of ACE Insertion/Deletion Gene Polymorphism on the Risk of IgA Nephropathy: A Debatable Topic

Background

The connection between angiotensin-converting enzyme insertion/deletion (ACE I/D) gene polymorphisms and IgA nephropathy (IgAN) was conflicting. This pooled analysis was performed to explore this issue.

Methods

All eligible investigations were identified from various electronic databases, and the pooled analysis was evaluated using Stata software.

Results

27 studies with 2538 IgAN cases and 3592 controls were included. In overall subjects, ACE D allele, DD, and II genotype were associated with IgAN susceptibility (D vs. I: OR = 1.21, 95% CI: 1.10–1.32, P < 0.001; DD vs. ID + II: OR = 1.38, 95% CI: 1.20–1.60, P < 0.001; and II vs. DD + ID: OR = 0.83, 95% CI: 0.73–0.95, P=0.007). In Asian and Chinese patients, ACE I/D gene polymorphism was also correlated with IgAN vulnerability. Moreover, ACE D allele, DD, and II genotype were correlated with the progression of IgAN (D vs. I: OR = 1.37, 95% CI: 1.09–1.73, P=0.008; DD vs. ID + II: OR = 1.57, 95% CI: 1.06–2.31, P=0.024; and II vs. DD + ID: OR = 0.69, 95% CI: 0.49–0.99, P=0.045). Conversely, in Caucasian subjects, there was no link between ACE I/D gene polymorphism and the risk of IgAN.

Conclusion

ACE I/D gene polymorphism was correlated with the vulnerability and progression of IgAN in Asian and Chinese patients, and ACE D allele and DD homozygote genotype could be adverse factors for IgAN, while the II homozygote genotype could be an advantage factor. But, no significant association was found between ACE I/D gene polymorphism and IgAN in Caucasians.

Rare Collagenous Heterozygote Variants in Children With IgA Nephropathy

Introduction

Childhood IgA nephropathy (cIgAN) is a primary glomerulonephritis clinically characterized by microscopic hematuria and proteinuria, the presence of which may potentially overlap with Alport syndrome. Interestingly, earlier studies suggested that familial IgAN could be linked to the chromosome 2q36 region, also the coding region for collagen type 4 alpha 3/4 (COL4A3/A4).

Methods

To investigate a possible relationship or phenocopy between Alport syndrome and cIgAN, COL4A3, COL4A4, and COL4A5 exons were sequenced in 36 cIgAN patients. Clinical data and treatment were collected retrospectively. COL4A3/A4/A5 variants were classified according to American College of Medical Genetics and the Association for Molecular Pathology (ACMG/AMP) guidelines.

Results

Four of 36 cIgAN patients were affected by ACMG class 4/5 COL4A3 heterozygous variants (COL4A3-cIgAN). We found no COL4A4 or COL4A5 variant. Despite having rare and deleterious COL4A3 variants, 3 of 4 COL4A3-cIgAN children developed clinical and biologic features of active IgAN rather than Alport syndrome. Response to intensive immunosuppressive treatment was favorable, leading to a reduction of endocapillary and extracapillary proliferation lesions. High levels of immune immunoglobulin G and A (IgG/IgA) complexes, reduction of proteinuria, and gradual stabilization of estimated glomerular filtration rate (eGFR) argued against Alport syndrome. Nevertheless, COL4A3-cIgAN patients seemed predisposed to a more serious IgAN presentation compared with the non‒COL4A3-cIgAN group, with more glomerulosclerosis and a lower eGFR over time. One of the 4 patients underwent kidney transplant with subsequent IgAN recurrence.

Conclusions

Predisposition factors for developing serious cIgAN flare-up should be considered for cIgAN with COL4A3 pathologic heterozygous variants. COL4A3 variants, usually responsible for Alport syndrome in adults, should not automatically exclude an immunosuppressive regimen in cIgAN. Moreover, evidence of an ACMG class 4/5 COL4A3 variant in early-stage cIgAN could be a helpful tool for stratifying severity of cIgAN beyond the Oxford classification.

Increased Lifetime Risk of ESRD in Familial IgA Nephropathy

Introduction

Familial IgA nephropathy (IgAN) has been widely reported. However, its clinicohistologic characteristics and long-term prognosis are not clear.

Methods

A total of 348 familial IgAN cases from 167 independent families were recruited and their clinicohistologic characteristics as well as lifetime risk of end-stage renal disease (ESRD) were compared to 1116 sporadic IgAN patients from the same geographic region.

Results

Of all familial IgAN patients, 60 (17%) came from 32 single-generation (SG; all affected individuals are siblings) families, whereas 286 (82%) came from 134 multiple-generation (MG; affected individuals were present in at least 2 consecutive generations) families. The lifetime ESRD risk was significantly higher in familial patients than sporadic ones after adjusting by gender (hazard ratio [HR]=1.40, 95% confidence interval [CI]: 1.12–1.74, P = 0.004), with 5 years younger in median ESRD age (60 years vs. 65 years in familial and sporadic cases separately). Interestingly, among familial patients, we found cases from SG families (vs. MG families: HR = 2.62, 95% CI: 1.59–4.31, P < 0.001) or with early onset (onset age <30 years) (vs. late onset: HR = 4.79, 95% CI: 3.16–7.26, P < 0.001) had higher lifetime ESRD risk. Furthermore, among sporadic patients, men had lower estimated glomerular filtration rate (eGFR), higher urine protein, higher Oxford T score, and higher risk for life span ESRD compared with women (male vs. female, 25% vs. 17%, P = 0.003) whereas these gender differences were not seen in familial patients.

Conclusion

Familial IgAN cases had poorer renal outcomes and less gender differences compared with sporadic cases. These findings provide evidence that familial disease represent a distinct subtype of more progressive IgAN. Early diagnosis could improve the prognosis of cases with familial IgAN.

Genome-Wide Meta-Analysis Identifies Three Novel Susceptibility Loci and Reveals Ethnic Heterogeneity of Genetic Susceptibility for IgA Nephropathy

BACKGROUND

Eighteen known susceptibility loci for IgAN account for only a small proportion of IgAN risk.

METHODS

Genome-wide meta-analysis was performed in 2628 patients and 11,563 controls of Chinese ancestry, and a replication analysis was conducted in 6879 patients and 9019 controls of Chinese descent and 1039 patients and 1289 controls of European ancestry. The data were used to assess the association of susceptibility loci with clinical phenotypes for IgAN, and to investigate genetic heterogeneity of IgAN susceptibility between the two populations. Imputation-based analysis of the MHC/HLA region extended the scrutiny.

RESULTS

Identification of three novel loci (rs6427389 on 1q23.1 [P=8.18×10^-9, OR=1.132], rs6942325 on 6p25.3 [P=1.62×10^-11, OR=1.165], and rs2240335 on 1p36.13 [P=5.10×10^-9, OR=1.114]), implicates FCRL3, DUSP22.IRF4, and PADI4 as susceptibility genes for IgAN. Rs2240335 is associated with the expression level of PADI4, and rs6427389 is in high linkage disequilibrium with rs11264799, which showed a strong expression quantitative trail loci effect on FCRL3. Of the 24 confirmed risk SNPs, six showed significant heterogeneity of genetic effects and DEFA showed clear evidence of allelic heterogeneity between the populations. Imputation-based analysis of the MHC region revealed significant associations at three HLA polymorphisms (HLA allele DPB1*02, AA_DRB1_140_32657458_T, and AA_DQA1_34_32717152) and two SNPs (rs9275464 and rs2295119).

CONCLUSIONS

A meta-analysis of GWAS data revealed three novel genetic risk loci for IgAN, and three HLA polymorphisms and two SNPs within the MHC region, and demonstrated the genetic heterogeneity of seven loci out of 24 confirmed risk SNPs.  These variants may explain susceptibility differences between Chinese and European populations.

Complement dysregulation in glomerulonephritis

Glomerulonephritis (GN) refers to a group of renal diseases affecting the glomeruli due to the damage mediated by immunological mechanisms. A large proportion of the disease manifestations are caused by disturbances in the complement system. They can be due to genetic errors, autoimmunity, microbes or abnormal immunoglobulins, like modified IgA or paraproteins. The common denominator in most of the problems is an overactive or misdirected alternative pathway complement activation. An assessment of kidney function, amount of proteinuria and hematuria are crucial elements to evaluate, when glomerulonephritis is suspected. However, the cornerstones of the diagnoses are renal biopsy and careful examination of the complement abnormality. Differential diagnostics between the various forms of GN is not possible based on clinical features, as they may vary greatly. This review describes the known mechanisms of complement dysfunction leading to different forms of primary GN (like IgA glomerulonephritis, dense deposit disease, C3 glomerulonephritis, post-infectious GN, membranous GN) and differences to atypical hemolytic uremic syndrome. It also covers the basic elements of etiology-directed therapy and prognosis of the most common forms of GN. Common principles in the management of GN include treatment of hypertension and reduction of proteinuria, some require immunomodulating treatment. Complement inhibition is an emerging treatment option. A thorough understanding of the basic disease mechanism and a careful follow-up are needed for optimal therapy.

Expert consensus guidelines for the genetic diagnosis of Alport syndrome

Recent expert guidelines recommend genetic testing for the diagnosis of Alport syndrome. Here, we describe current best practice and likely future developments. In individuals with suspected Alport syndrome, all three COL4A5, COL4A3 and COL4A4 genes should be examined for pathogenic variants, probably by high throughput-targeted next generation sequencing (NGS) technologies, with a customised panel for simultaneous testing of the three Alport genes. These techniques identify up to 95% of pathogenic COL4A variants. Where causative pathogenic variants cannot be demonstrated, the DNA should be examined for deletions or insertions by re-examining the NGS sequencing data or with multiplex ligation-dependent probe amplification (MLPA). These techniques identify a further 5% of variants, and the remaining few changes include deep intronic splicing variants or cases of somatic mosaicism. Where no pathogenic variants are found, the basis for the clinical diagnosis should be reviewed. Genes in which mutations produce similar clinical features to Alport syndrome (resulting in focal and segmental glomerulosclerosis, complement pathway disorders, MYH9-related disorders, etc.) should be examined. NGS approaches have identified novel combinations of pathogenic variants in Alport syndrome. Two variants, with one in COL4A3 and another in COL4A4, produce a more severe phenotype than an uncomplicated heterozygous change. NGS may also identify further coincidental pathogenic variants in genes for podocyte-expressed proteins that also modify the phenotype. Our understanding of the genetics of Alport syndrome is evolving rapidly, and both genetic and non-genetic factors are likely to contribute to the observed phenotypic variability.

Genetic Determinants of IgA Nephropathy: Eastern Perspective

IgA nephropathy (IgAN) is one of the most common primary glomerulonephritides throughout the world and a major cause of end-stage renal disease among the East Asian population. It is widely considered that genetic factors play an important role in the pathogenesis of IgAN. This article summarizes the recent achievements in the genetic studies of IgAN, focusing mainly on studies performed in East Asia, from the early association studies of candidate genes and family based designs, to the recent genome-wide association studies. There have been five large genome-wide association studies performed that have identified multiple susceptibility loci for IgAN, especially some novel loci identified in the Chinese population. Genes within these loci have provided important insights into the potential biological mechanisms and pathways that influence genetic risk to IgAN. In susceptibility loci/genes, the study of genetic interaction and structural variants (such as copy number variation) was conducted to identify more variants associated with IgAN and disease progression. Genetic studies of IgAN from East Asia have made great achievements over the years. Most susceptibility loci discovered to date encode genes involved in the response to mucosal pathogens, suggesting that an intestinal-immune network for IgA production may be involved in the pathogenesis of IgAN. Although genetic studies of the complex diseases are challenging, for future genetic studies in IgAN, new genetic techniques and methods of analysis, especially next-generation sequencing, need to be applied to push the genetic studies forward.

Biomarkers and Precision Medicine in IgA Nephropathy

The field of biomarker research in IgA nephropathy has experienced a major boost in recent years with the publication of a large number of scientific reports. Candidate biomarkers from blood, urine, and renal tissue obtained through the use of clinical chemistry, molecular biology, and omics have been proposed for translation in clinical practice. Nevertheless, individual biomarkers often lack sensitivity and specificity with the consequent impairment of disease specificity. This review, moving on from the analysis of the four-hit hypothesis, illustrates the biomarkers linked to the abnormal glycosylation process of IgA1 and the immune complex formation. It also describes other serum and urinary biomarkers. Given the profound insights into the pleiotropic function of a single biomarker that is specific for a pathophysiological mechanism, this review suggests a novel approach based on a panel of biomarkers that covers the entire pathogenic process of the disease. Clinical bioinformatics that integrate genetic, clinical, and bioinformatics data sets could optimize the specific value of each biomarker in a multimarker panel. This is a promising approach for precision medicine and personalized therapy in IgA nephropathy.

Genetic Determinants of IgA Nephropathy: Western Perspective

IgA nephropathy (IgAN) represents a genetically complex multifactorial trait. Its prevalence and clinical features vary geographically, and the disease has a range of clinical presentations that suggest multiple subtypes. Although familial aggregation of IgAN has been reported and prior linkage studies have highlighted significant locus heterogeneity, specific genetic variants underlying familial IgAN have not yet been defined. Population-based genome-wide association studies (GWAS) have discovered nearly 20 IgAN risk loci, providing novel insights into disease epidemiology and molecular mechanisms, shifting old paradigms of the disease pathogenesis. Follow-up fine-mapping studies have identified specific causal variants, and genotype-phenotype correlation studies have begun to delineate clinical consequences of GWAS risk alleles. The association between IgAN and galactose-deficient IgA1 (Gd-IgA1), a validated serum biomarker of IgAN, presented another avenue for genetic discovery because elevated serum levels of Gd-IgA1 are highly heritable. Recent GWAS for serum Gd-IgA1 levels provided novel insights into genetic regulation of this trait, but the genetic link between Gd-IgA1 and IgAN has not yet been established. In this review, we discuss these developments in the broader context of modern genetic approaches to complex traits, and provide our perspective on the critical challenges that need to be addressed to advance the field.

Inflammation in IgA nephropathy

Immunoglobulin A nephropathy (IgAN) is the most frequently occurring primary glomerulonephritis in Caucasian and Asian populations. Nonetheless, therapeutic recommendations are based on weak evidence, large controlled trials are scarce and, in particular, the additional value of immunosuppression beyond comprehensive supportive measures is not well-established. The use of immunosuppressants is supported by experimental insights into IgAN pathogenesis that suggest an autoimmune component in disease development. The so-called "multi-hit" theory comprises multiple steps, starting with defective glycosylation of IgA subclass IgA1 that results in overproduction of galactose-deficient IgA1 (Gd-IgA1), occurrence of anti-Gd-IgA1 autoantibodies, and mesangial deposition of nephritogenic immune complexes. This eventually results in an increased mesangial cell proliferation, inflammatory responses, and complement activation. Recent genome-wide association studies have identified several susceptibility genes, many of which support the "multi-hit" concept. In light of these discoveries, it is astonishing that the vast majority of adult IgAN patients obviously do not need and/or benefit from immunosuppressive therapies in the first place. In fact, a number of supportive measures are highly effective in reducing the risk for disease progression in many patients. These measures need to be optimized before immunosuppression should be considered at all. In this review we focus on the underlying pathogenetic cornerstones and the central question of whether systemic inflammation in adult IgAN patients should be treated. Treatment options in children with IgAN are also discussed.

What Genetics Tells Us About the Pathogenesis of IgA Nephropathy: The Role of Immune Factors and Infection

Immunoglobulin A nephropathy (IgAN) is the most common type of primary glomerulonephritis, which is characterized by IgA1-containing immune-deposits in the glomerular mesangium. The epidemiologic observations of familial clustering as well as ethnic and regional discrepancies indicate a genetic component to IgAN. Large, international, genome-wide association studies have identified several susceptibility genes and loci for IgAN, many of which have been implicated in immune regulation and are shared with other autoimmune diseases. Notably, increasing numbers of genes involved in mucosal immunity have been detected; such genes may impact the susceptibility and progression of IgAN through interaction with environmental stimuli (especially infection). Here, we discuss the innate and adaptive immune mechanisms that drive protective immunity against pathogens. Our goal is to provide a representative overview of the synergistic roles between genetic predisposition and infection in IgAN pathogenesis. We anticipate that these results will provide potential therapeutic agents and advances in precision medicine.

Immunoglobulin A nephropathy: a pathophysiology view

BACKGROUND AND AIM

IgA nephropathy is one of the leading causes of primary glomerulonephritis worldwide and an important etiology of renal disease in young adults. IgA nephropathy is considered an immune complex-mediated disease.

METHODS

This review article summarizes recent evidence on the pathophysiology of IgA nephropathy.

RESULTS

Current studies indicate an ordered sequence of multi-hits as fundamental to disease occurrence. Altered glycan structures in the hinge region of the heavy chains of IgA1 molecules act as auto-antigens, potentially triggering the production of glycan-specific autoantibodies. Recognition of novel epitopes by IgA and IgG antibodies leads to the formation of immune complexes galactose deficient-IgA1/anti-glycan IgG or IgA. Immune complexes of IgA combined with FcαRI/CD89 have also been implicated in disease exacerbation. These nephritogenic immune complexes are formed in the circulation and deposited in renal mesangium. Deposited immune complexes ultimately induce glomerular injury, through the release of pro-inflammatory cytokines, secretion of chemokines and the resultant migration of macrophages into the kidney. The TfR1/CD71 receptor has a pivotal role in mesangial cells. New signaling intracellular mechanisms have also been described.

CONCLUSION

The knowledge of the whole pathophysiology of this disease could provide the rational bases for developing novel approaches for diagnosis, for monitoring disease activity, and for disease-specific treatment.

New developments in the genetics, pathogenesis, and therapy of IgA nephropathy

Recent years have brought notable progress in the field of IgA nephropathy. Here, we highlight important new directions and latest developments, including successful discovery of several genetic susceptibility loci, formulation of the multihit pathogenesis model, introduction of the Oxford pathology scoring system, and formalization of the Kidney Disease Improving Global Outcomes (KDIGO) consensus treatment guidelines. We focus on the latest genetic findings that confirm a strong contribution of inherited factors and explain some of the geoethnic disparities in disease susceptibility. Most IgA nephropathy susceptibility loci discovered to date encode genes involved in the maintenance of the intestinal epithelial barrier and response to mucosal pathogens. The concerted pattern of interpopulation allelic differentiation across all genetic loci parallels the disease prevalence and correlates with variation in local pathogens, suggesting that multilocus adaptation might have shaped the present-day landscape of IgA nephropathy. Importantly, the 'Intestinal Immune Network for IgA Production' emerged as one of the new targets for potential therapeutic intervention. We place these findings in the context of the multihit pathogenesis model and existing knowledge of IgA immunobiology. Lastly, we provide our perspective on the existing treatment options, discuss areas of clinical uncertainty, and outline ongoing clinical trials and translational studies.

UMOD polymorphism rs12917707 is not associated with severe or stable IgA nephropathy in a large Caucasian cohort

Background

Genetic factors are suspected in the pathogenesis of IgA nephropathy, as well as in the course of IgA nephropathy progression towards end stage renal failure. UMOD polymorphism rs12917707 is known to associate with end stage renal failure of mixed aetiologies.

Methods

We tested a large cohort of Caucasian patients for association of rs12917707 with IgA nephropathy showing a benign, stable course and with IgA nephropathy that progressed toward end stage renal failure.

Results

No association was observed between either groups, and a non-significant trend was observed for more severe IgA nephropathy with the allele reported to protect against end stage renal failure of mixed aetiologies.

Conclusion

We conclude that UMOD is unlikely to play a role in IgA nephropathy pathogenesis nor progression to end stage renal failure, and suggest that UMOD effects are restricted to some causes of renal disease, e.g. diabetes or hypertension.

How benign is hematuria? Using genetics to predict prognosis

Hematuria is a common presenting feature of glomerular disease and is sometimes associated with kidney failure later in life. Where isolated microscopic hematuria occurs in children and young adults, an underlying monogenic disorder, such as Alport syndrome or thin basement membrane nephropathy, is frequently responsible. In this review, these and other diseases, which often present with isolated microscopic hematuria, including hereditary angiopathy, nephropathy, aneurysms, and muscle cramps (HANAC) syndrome, IgA nephropathy, and CFHR5 nephropathy, are discussed together with the associated molecular pathology, clinical features, and prognosis. Genetic testing for these conditions used in clinical practice can provide important diagnostic and prognostic information that is relevant to the patient and their family, particularly when kidney transplantation is considered.

Genetic evidence for involvement of adaptive immunity in the development of IgA nephropathy: MHC class II alleles are protective in a Caucasian population

There is evidence suggesting that IgA nephropathy (IgAN) is an immunological disease. The role of HLA class II DR beta 1 (DRB1) has previously not been well studied. The aim of our study was to investigate the association of HLA-DRB1 variants with IgAN in a Swedish Caucasian cohort. Our study consisted of 213 patients with biopsy proven IgAN, all of self-reported Caucasian ancestry. As a control cohort, 1569 healthy subjects from the same population in Sweden were included. HLA-DRB1 low-resolution genotyping was performed and odds ratios were calculated to assess the risk. In an allelic model the HLA-DRB1(*)03 and (*)10, demonstrated association for IgAN after correction for multiple comparison, with subsequent OR=0.54 (95% CI 0.37-0.78) and 3.44 (95% CI 1.67-7.07). When the influence of risk allelic groups was adjusted for protective allelic groups and vice versa, only a protective effect of HLA-DRB1(*)03 remained significant. In conclusion, the variants of HLA-DRB1 were associated with IgAN of which the HLA-DRB1(*)03 revealed a strong protective effect for IgAN. Our data replicates finding from other Caucasian populations and suggest that involvement of adaptive immunity may be of importance in the development of the disease.

Geographic differences in genetic susceptibility to IgA nephropathy: GWAS replication study and geospatial risk analysis

IgA nephropathy (IgAN), major cause of kidney failure worldwide, is common in Asians, moderately prevalent in Europeans, and rare in Africans. It is not known if these differences represent variation in genes, environment, or ascertainment. In a recent GWAS, we localized 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). These IgAN loci are associated with risk of other immune-mediated disorders such as type I diabetes, multiple sclerosis, or inflammatory bowel disease. We tested association of these loci in eight new independent cohorts of Asian, European, and African-American ancestry (N = 4,789), followed by meta-analysis with risk-score modeling in 12 cohorts (N = 10,755) and geospatial analysis in 85 world populations. Four susceptibility loci robustly replicated and all five loci were genome-wide significant in the combined cohort (P = 5×10⁻³²–3×10⁻¹⁰), with heterogeneity detected only at the PSMB9/TAP1 locus (I² = 0.60). Conditional analyses identified two new independent risk alleles within the HLA-DQB1/DRB1 locus, defining multiple risk and protective haplotypes within this interval. We also detected a significant genetic interaction, whereby the odds ratio for the HORMAD2 protective allele was reversed in homozygotes for a CFHR3/R1 deletion (P = 2.5×10⁻⁴). A seven–SNP genetic risk score, which explained 4.7% of overall IgAN risk, increased sharply with Eastward and Northward distance from Africa (r = 0.30, P = 3×10⁻¹²⁸). This model paralleled the known East–West gradient in disease risk. Moreover, the prediction of a South–North axis was confirmed by registry data showing that the prevalence of IgAN–attributable kidney failure is increased in Northern Europe, similar to multiple sclerosis and type I diabetes. Variation at IgAN susceptibility loci correlates with differences in disease prevalence among world populations. These findings inform genetic, biological, and epidemiological investigations of IgAN and permit cross-comparison with other complex traits that share genetic risk loci and geographic patterns with IgAN.

IgA nephropathy (IgAN) is the most common cause of kidney failure in Asia, has lower prevalence in Europe, and is very infrequent among populations of African ancestry. A long-standing question in the field is whether these differences represent variation in genes, environment, or ascertainment. In a recent genome-wide association study of 5,966 individuals, we identified five susceptibility loci for this trait. In this paper, we study the largest IgAN case-control cohort reported to date, composed of 10,775 individuals of European, Asian, and African-American ancestry. We confirm that all five loci are significant contributors to disease risk across this multi-ethnic cohort. In addition, we identify two novel independent susceptibility alleles within the HLA-DQB1/DRB1 locus and a new genetic interaction between loci on Chr.1p36 and Chr.22q22. We develop a seven–SNP genetic risk score that explains nearly 5% of variation in disease risk. In geospatial analysis of 85 world populations, the genetic risk score closely parallels worldwide patterns of disease prevalence. The genetic risk score also predicts an unsuspected Northward risk gradient in Europe. This genetic prediction is verified by examination of registry data demonstrating, similarly to other immune-mediated diseases such as multiple sclerosis and type I diabetes, a previously unrecognized increase in IgAN–attributable kidney failure in Northern European countries.

The genetic variants at the HLA-DRB1 gene are associated with primary IgA nephropathy in Han Chinese

Background

Immunoglobulin A nephropathy (IgAN), an immune-complex-mediated glomerulonephritis defined immunohistologically by the presence of glomerular IgA deposits, is the most common primary glomerular disease worldwide and a significant cause of end-stage renal disease. Familial clustering of patients with IgAN suggests a genetic predisposition.

Methods

In this study, 192 patients with IgAN and 192 normal controls in the Sichuan cohort and 935 patients with IgAN and 2,103 normal controls in the Beijing cohort were investigated. HLA-DRB1*01–DRB1*10 specificities were genotyped by the PCR–SSP technique in both cohorts. Based on the HLA-DRB1*04-positive results, the subtypes of HLA-DRB1*04 were analyzed using sequencing-based typing (SBT) in 291 IgAN cases and 420 matched controls.

Results

The frequency of HLA-DRB1*04 in the IgAN group was significantly higher than that in the control group (0.129 vs. 0.092, P = 8.29 × 10^-5, odds ratio (OR) =1.381, 95% confidence interval (CI) 1.178–1.619). Other alleles at the HLA-DRB1 locus were observed with no significant differences between the case and control groups. The dominant alleles of the HLA-DRB1*04 subtypes were DRB1*0405 in both cohorts. The frequencies of HLA-DRB1*0405 and 0403 were significantly increased in the patients compared to healthy subjects.

Conclusion

HLA-DRB1*04 was significantly associated with primary IgAN in Chinese population. This result implies that HLA-DRB1 gene plays a major role in primary IgAN.

Pathogenesis of IgA nephropathy

Since its first description in 1968, IgA nephropathy has remained the most common form of idiopathic glomerulonephritis leading to chronic kidney disease in developed countries. The exact pathogenesis of IgA nephropathy is still not well defined. Current data implicate an important genetic factor, especially in promoting the overproduction of an aberrant form of IgA1. The immunochemical aberrancy of IgA nephropathy is characterized by the undergalactosylation of O-glycans in the hinge region of IgA1. However, such aberrant glycosylation alone does not cause renal injury. The next stage of disease development requires the formation of glycan-specific IgG and IgA antibodies that recognize the undergalactosylated IgA1 molecule. These antibodies often have reactivity against antigens from extrinsic microorganisms and might arise from recurrent mucosal infection. B cells that respond to mucosal infections, particularly tonsillitis, might produce the nephritogenic IgA1 molecule. With increased immune-complex formation and decreased clearance owing to reduced uptake by the liver, IgA1 binds to the glomerular mesangium via an as yet unidentified receptor. Glomerular IgA1 deposits trigger the local production of cytokines and growth factors, leading to the activation of mesangial cells and the complement system. Emerging data suggest that mesangial-derived mediators following glomerular deposition of IgA1 lead to podocyte and tubulointerstitial injury via mesangio-podocytic-tubular crosstalk. This Review summarizes the latest findings in the pathogenesis of IgA nephropathy.

CRP polymorphisms and chronic kidney disease in the third national health and nutrition examination survey

BACKGROUND

CRP gene polymorphisms are associated with serum C-reactive protein concentrations and may play a role in chronic kidney disease (CKD) progression. We recently reported an association between the gene variant rs2808630 and CKD progression in African Americans with hypertensive kidney disease. This association has not been studied in other ethnic groups.

METHODS

We used data from 5955 participants from Phase 2 of The Third National Health and Nutrition Examination Survey (1991-1994) to study the association between CRP polymorphisms and CKD prevalence in a population-based sample. The primary outcome was CKD defined as estimated glomerular filtration rate (eGFR) <60 ml/min or the presence of albuminuria. Secondary outcomes were the presence of albuminuria (any degree) and continuous eGFR. Six single nucleotide polymorphisms (SNPs) from the CRP gene, rs2808630, rs1205, rs3093066, rs1417938, rs3093058, and rs1800947, were evaluated.

RESULTS

CRP rs2808630 AG compared to the referent AA genotype was associated with CKD in non-Hispanic blacks (n = 1649, 293 of whom had CKD) with an adjusted odds ratio (OR) of 3.09 (95% CI 1.65-5.8; p = 0.001). For the secondary outcomes, rs2808630 AG compared to the referent AA genotype was associated with albuminuria with an adjusted OR of 3.07 (95% CI 1.59-5.94; p = 0.002), however not with eGFR. There was no association between the SNPs and CKD, albuminuria or eGFR in non-Hispanic whites or Mexicans Americans.

CONCLUSIONS

In this cross-sectional study, the 3' flanking CRP gene variant rs2808630 was associated with CKD, mainly through its association with albuminuria in the non-Hispanic blacks. Despite not finding an association with eGFR, our results support our previous study demonstrating an association between CRP gene variant rs2808630 and CKD progression in a longitudinal cohort of African American with hypertensive kidney disease.

Genetic studies of IgA nephropathy: past, present, and future

Immunoglobulin A nephropathy (IgAN) is the most common form of primary glomerulonephritis worldwide and an important cause of kidney disease in young adults. Highly variable clinical presentation and outcome of IgAN suggest that this diagnosis may encompass multiple subsets of disease that are not distinguishable by currently available clinical tools. Marked differences in disease prevalence between individuals of European, Asian, and African ancestry suggest the existence of susceptibility genes that are present at variable frequencies in these populations. Familial forms of IgAN have also been reported throughout the world but are probably underrecognized because associated urinary abnormalities are often intermittent in affected family members. Of the many pathogenic mechanisms reported, defects in IgA1 glycosylation that lead to formation of immune complexes have been consistently demonstrated. Recent data indicates that these IgA1 glycosylation defects are inherited and constitute a heritable risk factor for IgAN. Because of the complex genetic architecture of IgAN, the efforts to map disease susceptibility genes have been difficult, and no causative mutations have yet been identified. Linkage-based approaches have been hindered by disease heterogeneity and lack of a reliable noninvasive diagnostic test for screening family members at risk of IgAN. Many candidate-gene association studies have been published, but most suffer from small sample size and methodological problems, and none of the results have been convincingly validated. New genomic approaches, including genome-wide association studies currently under way, offer promising tools for elucidating the genetic basis of IgAN.

Genetic contribution and associated pathophysiology in end-stage renal disease

End-stage renal disease (ESRD) or chronic kidney disease (CKD) is the terminal state of the kidney when its function has been permanently and irreversibly damaged. A wide variety of etiologies and pathological processes culminate in ESRD, and both environmental and genetic factors contribute to its development and progression. Various reports suggest that susceptibility to develop ESRD has a significant genetic component. These studies include familial aggregation studies, comparisons of incidence rates between different racial or ethnic populations, and segregation analysis. Genetic approaches have been used to identify genes that contribute to genetic susceptibility. Many studies have now been carried out assessing the contribution of specific “candidate genes”, which correlate with different functions that are involved in the renal pathogenesis. Independent studies for specific associated genes have frequently provided contradictory results. This may be due, in part, to the modest contribution to genetic susceptibility which these genes impart. With the availability of different genomewide association studies, chromosomal regions harboring novel, previously unrecognized, genes that may contribute to renal diseases have been recently reported. We have focused on different genetic studies conducted on ESRD and have discussed the strength and weaknesses of these studies. The nonmuscle myosin heavy chain 9 gene (MYH9) and renin–angiotensin system (RAS) have been discussed in detail.

Familial IgA nephropathy in southeastern Kentucky

BACKGROUND

Two decades ago, pedigrees of patients with IgA nephropathy (IgAN) from Pike County, KY, USA, provided evidence for a role of genetic factors in the pathogenesis of this disorder. Subsequently additional pedigrees were described for several communities from northern Italy. Recently, we found another cluster of patients in the Clay County, KY area, about 100 miles southwest of Pike County.

AIM

The purpose of this study was to evaluate and expand the pedigrees of patients with IgAN from Clay County, KY to provide additional insight into the mechanisms of inheritance of IgAN and assess the possible influence of a founder effect on the prevalence of IgAN in the region.

METHOD

Since 1980, most patients with IgAN and their relatives in eastern KY have provided personal genealogic data. These data were used to construct pedigrees that included the patients born in Clay County. Nine of 11 patients with IgAN born in Clay County, KY, USA were members of 1 or more of 5 pedigrees, each with 3 - 11 patients with IgAN.

CONCLUSION

Our findings suggest the possibility of a low-penetrance ancestral mutation in the IgAN kindreds from Clay County.

Rare association of immunoglobulin A nephropathy and lymphedema-distichiasis syndrome

Immunoglobulin A nephropathy is the most common primary glomerulonephritis worldwide. The pathogenesis is still unknown and newer treatments are being researched. Rarely, it can be associated with other disorders. Its association with hereditary lymphedema has been reported on one occasion but never with lymphedema-distichiasis syndrome. We report a patient with hereditary lymphedema-distichiasis syndrome and immunoglobulin A nephropathy occurring simultaneously.

CRP polymorphisms and progression of chronic kidney disease in African Americans

BACKGROUND AND OBJECTIVES

Chronic inflammation may play a role in chronic kidney disease (CKD) progression. CRP gene polymorphisms are associated with serum C-reactive protein (CRP) concentrations. It is unknown if CRP polymorphisms are associated with CKD progression or modify the effectiveness of anti-hypertensive therapy in delaying CKD progression.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We genotyped 642 participants with CKD from the African American Study of Kidney Disease and Hypertension (AASK), selecting five tag polymorphisms: rs2808630, rs1205, rs3093066, rs1417938, and rs3093058. We compared the minor allele frequencies (MAF) of single nucleotide polymorphisms (SNPs) in AASK to MAFs of African Americans from NHANES III. Among AASK participants, we evaluated the association of SNPs with CRP levels and prospectively with a composite: halving the GFR, ESRD, or death.

RESULTS

The MAF was higher for the rs2808630_G allele (P = 0.03) and lower for the rs1205_A allele (P = 0.03) in the AASK compared with NHANES III. Among AASK participants, the rs3093058_T allele predicted higher CRP concentrations (P < 0.0001) but not CKD progression. The rs2808630_GG genotype was associated with higher risk of the composite endpoint compared with the AA genotype (P = 0.002). Participants with the rs2808630_GG genotype on angiotensin converting enzyme inhibitors (ACEIs) versus beta blockers had increased risk of progression (P = 0.03).

CONCLUSION

CRP SNPs that were associated with higher levels of CRP did not predict CKD progression. The rs2808630_GG genotype was associated with higher risk of CKD progression, and in patients with this genotype, ACEIs did not slow progression.

Aberrant galactosylation of IgA1 is involved in the genetic susceptibility of Chinese patients with IgA nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is associated with genetic and environmental factors, and undergalactosylation of IgA1 in the serum is considered to be a contributor to pathogenesis of IgAN. The present study was conducted to detect the galactose- (Gal) deficient IgA1 level in Chinese IgAN patients and their family members.

METHODS

Sixty-three IgAN patients were enrolled, where 32 first-degree relatives of 19 patients and 44 spouses of 44 patients were recruited. Healthy blood donors (n = 39) were used as normal controls. Biotinylated HAA (Helix aspersa) was utilized to detect the Gal-deficient IgA1 in enzyme-linked immunosorbent assay (ELISA). All the results were corrected by serum IgA1 concentration.

RESULTS

Compared with normal controls, the sera IgA1 of patients and their first-degree relatives demonstrated increased Gal-deficient IgAl level (0.17 +/- 0.09 versus 0.10 +/- 0.04, P = 0.001; 0.14 +/- 0.07 versus 0.10 +/- 0.04, P = 0.028); no significant difference between patients and their first-degree relatives was detected (0.17 +/- 0.09 versus 0.14 +/- 0.07, P = 0.127). In contrast, serum Gal-deficient IgA1 level of IgAN patients was higher than their counterpart spouses and normal controls (0.18 +/- 0.13 versus 0.14 +/- 0.09, P = 0.009; 0.18 +/- 0.13 versus 0.10 +/- 0.04, P = 0.001), while that of patients' spouses was comparable with normal controls (0.14 +/- 0.09 versus 0.10 +/- 0.04, P = 0.075). There was no correlation between clinicopathological data and serum Gal-deficient IgA1 level.

CONCLUSION

The patients with IgAN and their first relatives showed significant higher Gal-deficient IgA1 level than healthy controls, whereas patients' spouses were the same as healthy controls. It can be suggested that the Gal-deficient IgA1 might be inherited in Chinese patients with IgAN.

Human leukocyte antigen DRB1 alleles predict risk and disease progression of immunoglobulin A nephropathy in Han Chinese

The role of human leukocyte antigen (HLA) class II polymorphisms in the pathogenesis and progression of primary immunoglobulin A nephropathy (pIgAN) is unclear. This study aimed to explore the relationship of HLA-DRB1 alleles with the susceptibility and disease progression of pIgAN in Han Chinese. A PCR-based genotyping technique was used to detect HLA-DRB1 alleles in 139 patients with pIgAN and 143 healthy subjects. A total of 37 HLA-DRB1 alleles were detected, of which 30 were found in pIgAN patients and 29 in healthy subjects. In pIgAN patients, the frequencies of HLA-DRB1*140501 (belonging to DR*14) were significantly increased, while the frequencies of HLA-DRB1*070101 (belonging to DR*7) were significantly reduced compared with the healthy individuals. Further stratification analysis revealed that the frequencies of HLA-DRB1*030101 in pIgAN patients with normal renal function were significantly higher than those in patients with renal dysfunction. These findings suggest that HLA-DRB1 polymorphisms are related to the occurrence and disease progression of pIgAN patients in Han Chinese, with HLA-DRB1*140501 being a susceptible allele and HLA-DRB1*070101 a resistant allele. HLA-DRB1*030101 may serve as a predictor of disease progression and renal damage of pIgAN in Han Chinese. Further studies are warranted to explore the immunological mechanisms for the genotype-disease phenotype relationship.

IL5RA and TNFRSF6B gene variants are associated with sporadic IgA nephropathy

Familial clustering and genome-wide linkage scans strongly support a genetic susceptibility to familial IgA nephropathy (IgAN), but genetic factors that predispose to sporadic IgAN are unknown. A high-throughput single nucleotide polymorphism (SNP) association study was conducted using a customized Illumina BeadChip in 732 white patients with biopsy-proven IgAN and 503 control subjects from Canada, France, and Finland. Approximately 93% of 1536 SNPs on the array were tag SNPs from Phase I+II of the HapMap with a minor allele frequency > or =5%, designed to capture the common variants of genes within the critical interval of IGAN1 on chromosome 6q22 and 69 biologic candidate genes for IgAN. SNPs of suggestive or significant association were identified by using logistic regression to adjust for age, gender, study site, and population stratification. Despite using a dense marker set that covered an average interval of 6.5 kb between SNPs, there was no strong and consistent association signal within the IGAN1 critical interval. Among the biologic candidate genes examined, two significant association signals were found at IL5RA and TNFRSF6B, the latter being particularly interesting because this gene encodes a decoy receptor for a TNF family ligand that causes IgAN in mice when overexpressed. Pending replication, these data suggest that variants of IL5RA and TNFRSF6B may predispose to sporadic IgAN.

The genetics of IgA nephropathy

IgA nephropathy is the most common form of primary glomerulonephritis. Variations in clinical manifestations indicate that a diagnosis of IgA nephropathy encompasses multiple disease subsets that cannot be distinguished on the basis of renal pathology or clinical variables alone. Familial forms of the disease have been reported throughout the world, but are probably under-recognized because associated urinary abnormalities are often intermittent in affected family members. IgA nephropathy has complex determination, with different genes probably causing disease in different patient subgroups. Of the many pathogenic mechanisms reported, defects in IgA1 glycosylation that lead to formation of immune complexes have been consistently implicated. Here, we present the evidence for genetic contributions to the disease, review clinical patterns of familial disease, and summarize some of the most promising genetic studies conducted to date. Linkage-based approaches to the study of familial forms of the disease have identified significant or suggestive loci on chromosomes 6q22-23, 2q36, 4q26-31, 17q12-22 and 3p24-23, but no causal gene has yet been identified. Many interesting, but poorly replicated, genetic association studies have also been reported. We discuss recent developments in analytic tools that should enable genetic studies of sporadic forms of disease by the genome-wide association approach.

Genome-wide linkage scan of a large family with IgA nephropathy localizes a novel susceptibility locus to chromosome 2q36

IgA nephropathy (IgAN) is the most common glomerulonephritis worldwide and an important cause of ESRD. Familial clustering of cases suggests genetic predisposition to this disease. Two recent genome-wide studies in IgAN have identified a major susceptibility locus on chromosome 6q22 (IGAN1) and two additional loci with suggestive linkage signals on chromosomes 4q26-31 and 17q12-22. A large four-generation family with 14 affected individuals has been clinically ascertained and excluded from linkage to these loci. A genome-wide linkage scan was performed on this family with GeneChip Mapping 10K 2.0 Arrays using an "affected-only" strategy. By nonparametric analysis, two regions of suggestive linkage (multipoint logarithm of odds [LOD] scores >2) were identified on chromosomes 2q36 and 13p12.3. By parametric analysis (assuming an autosomal dominant inheritance, a disease allele frequency of 0.001, phenocopy rate of 0.01, and penetrance of 75%), a significant linkage to chromosome 2q36 (maximum multipoint LOD score 3.47) was found. Nine simple sequence repeat markers then were genotyped in 21 members (included all of the affected individuals), and significant linkage to chromosome 2q36 over a region of 12.2 cM (maximum multipoint LOD score 3.46) was confirmed. Recombination events in two affected individuals, as detected by haplotype analysis, delineated a critical interval of approximately 9 cM (equivalent to approximately 7 Mb) between D2S1323 and D2S362. Taken together, these data provide strong evidence for a novel disease susceptibility locus for familial IgAN.

Familial Clustering of Chronic Kidney Disease

The incidence and prevalence rates of most forms of chronic kidney disease (CKD) had steadily been increasing for the past 30 years, although these rates now appear to have reached a plateau. It is clear that an individual's likelihood of developing progressive CKD results from complex interactions between multiple genetic and environmental factors. Familial clustering of CKD and end-stage renal disease (ESRD) is observed among all the common etiologies of nephropathy. This article reviews the epidemiology of the familial clustering of kidney disease, as well as potential environmental and genetic contributors. The related impact of familial clustering of cardiovascular disease (CVD) and the impact of CVD on the current epidemic of ESRD is also discussed. It is imperative that nephrologists and primary care physicians recognize that individuals who have relatives with advanced nephropathy are themselves at high risk for subsequent kidney disease, proteinuria, and atherosclerotic cardiovascular complications. Until kidney failure genes are identified, it is reasonable to use "family history" (FH) as a surrogate marker for risk of future nephropathy. The detection of kidney disease genes holds great promise for detecting novel pathways that initiate renal fibrosis and lead to progressive loss of renal function. These pathways are likely to offer new therapies that may slow or halt development of chronic kidney failure.

Genetic heterogeneity in Italian families with IgA nephropathy: suggestive linkage for two novel IgA nephropathy loci

IgA nephropathy (IgAN) is the most common glomerulonephritis worldwide, but its etiologic mechanisms are still poorly understood. Different prevalences among ethnic groups and familial aggregation, together with an increased familial risk, suggest important genetic influences on its pathogenesis. A locus for familial IgAN, called "IGAN1," on chromosome 6q22-23 has been described, without the identification of any responsible gene. The partners of the European IgAN Consortium organized a second genomewide scan in 22 new informative Italian multiplex families. A total of 186 subjects (59 affected and 127 unaffected) were genotyped and were included in a two-stage genomewide linkage analysis. The regions 4q26-31 and 17q12-22 exhibited the strongest evidence of linkage by nonparametric analysis (best P=.0025 and .0045, respectively). These localizations were also supported by multipoint parametric analysis, in which peak LOD scores of 1.83 ( alpha =0.50) and 2.56 ( alpha =0.65) were obtained using the affected-only dominant model, and by allowance for the presence of genetic heterogeneity. Our results provide further evidence for genetic heterogeneity among families with IgAN. Evidence of linkage to multiple chromosomal regions is consistent with both an oligo/polygenic and a multiple-susceptibility-gene model for familial IgAN, with small or moderate effects in determining the pathological phenotype. Although we identified new candidate regions, replication studies are required to confirm the genetic contribution to familial IgAN.

Familial aggregation of primary glomerulonephritis in an Italian population isolate: Valtrompia study

Hereditary factors are suspected to contribute to the pathogenesis of sporadic primary glomerulonephritis, but their contribution is difficult to delineate in the general population. We studied the prevalence of primary glomerulonephritis in an isolated population from the extreme northern Valtrompia valley, Northern Italy. Investigation of medical records, community urinary screening program and molecular characterization of the population's ancestry were performed; genealogies of affected individuals were researched. Forty-three patients with primary glomerulonephritis were identified: 25 had biopsy-proven disease (11 immunoglobulin A (IgA) nephropathy; eight mesangial proliferative glomerulonephritis without IgA deposits; four focal segmental glomerular sclerosis; two membranous nephropathy), and 18 had clinical glomerulonephritis. All 43 patients originated from three mountain villages (Collio, San Colombano, and Bovegno). In contrast, we found only four cases of primary glomerulonephritis in two nearby villages (Pezzaze and Tavernole) that shared similar population histories and lifestyles, demonstrating heterogeneity of risk factors for glomerulonephritis (P=3 x 10(-5)). All 43 affected individuals could be traced back to common ancestors (XVI-XVII centuries), enabling the construction of three large pedigree including three parent-child affected pairs and five affected siblings pairs. Molecular data showed lower genetic diversity and increased inbreeding in the Valtrompia population compared to the control population. Molecular and genealogical evidence of limited set of founders and the absence of shared nephritogenic environmental factors suggest that our patients share a common genetic susceptibility to the development of primary glomerulonephritis. Further molecular study of our families will offer the possibility to shed light on the genetic background underlying these glomerular disorders.

IgA Nephropathy: The Presence of Familial Disease Does Not Confer an Increased Risk for Progression

BACKGROUND

Immunoglobulin A (IgA) nephropathy is the most common form of glomerulonephritis worldwide. Familial and sporadic cases are recognized, and a locus associated with the familial form of the disease was mapped to chromosome 6. Recent data suggest the familial IgA nephropathy form may have a poorer outcome than the sporadic form.

METHODS

We tested the hypothesis of unequal survival rates between the 2 forms of disease by analyzing time from biopsy to end-stage renal disease in patients of Italian ancestry; 589 patients with sporadic and 96 patients with familial IgA nephropathy.

RESULTS

Overall 10- and 20-year renal survival probabilities of the cohort as a whole were 71% and 50%, respectively. Macroscopic hematuria was the modality of clinical presentation in 51% of patients with familial IgA nephropathy and 39% of patients with sporadic IgA nephropathy. At univariable analysis, the sporadic form of IgA nephropathy was associated significantly with increased risk for renal death. However, patients with the sporadic form tended to be more hypertensive and diagnosed later, with signs of more advanced renal disease than those with familial disease at baseline. In the regression model, form of disease lost any independent effect. Only male sex, lower baseline glomerular filtration rate, greater proteinuria, and histopathologic score proved to be independent predictors of disease progression. Treatment with steroids or angiotensin-converting enzyme inhibitors was associated with improved outcomes.

CONCLUSION

Our study does not confirm that familial IgA nephropathy has a worse prognosis than the sporadic form. The similar renal phenotype may support a common pathogenic mechanism underlying familial and sporadic IgA nephropathy.

The IgA nephropathy Biobank. An important starting point for the genetic dissection of a complex trait

Background

IgA nephropathy (IgAN) or Berger's disease, is the most common glomerulonephritis in the world diagnosed in renal biopsied patients. The involvement of genetic factors in the pathogenesis of the IgAN is evidenced by ethnic and geographic variations in prevalence, familial clustering in isolated populations, familial aggregation and by the identification of a genetic linkage to locus IGAN1 mapped on 6q22–23. This study seems to imply a single major locus, but the hypothesis of multiple interacting loci or genetic heterogeneity cannot be ruled out. The organization of a multi-centre Biobank for the collection of biological samples and clinical data from IgAN patients and relatives is an important starting point for the identification of the disease susceptibility genes.

Description

The IgAN Consortium organized a Biobank, recruiting IgAN patients and relatives following a common protocol. A website was constructed to allow scientific information to be shared between partners and to divulge obtained data (URL: ). The electronic database, the core of the website includes data concerning the subjects enrolled. A search page gives open access to the database and allows groups of patients to be selected according to their clinical characteristics. DNA samples of IgAN patients and relatives belonging to 72 multiplex extended pedigrees were collected. Moreover, 159 trios (sons/daughters affected and healthy parents), 1068 patients with biopsy-proven IgAN and 1040 healthy subjects were included in the IgAN Consortium Biobank. Some valuable and statistically productive genetic studies have been launched within the 5^th Framework Programme 1998–2002 of the European project No. QLG1-2000-00464 and preliminary data have been published in "Technology Marketplace" website: .

Conclusion

The first world IgAN Biobank with a readily accessible database has been constituted. The knowledge gained from the study of Mendelian diseases has shown that the genetic dissection of a complex trait is more powerful when combined linkage-based, association-based, and sequence-based approaches are performed. This Biobank continuously expanded contains a sample size of adequately matched IgAN patients and healthy subjects, extended multiplex pedigrees, parent-child trios, thus permitting the combined genetic approaches with collaborative studies.

Épidermolyse bulleuse dystrophique récessive d’Hallopeau-Siemens associée à une glomérulonéphrite à dépôts mésangiaux d’IgA : 4 cas

BACKGROUND

The Hallopeau-Siemens type of recessive dystrophic epidermolysis bullosa (HS-RDEB) is a severe hereditary dermatosis, associated with a collagen VII deficiency. A chronic inflammatory syndrome, secondary to recurrent cutaneous infections, may be the cause of AA amyloidosis, with chronic renal failure, involving life prognosis. Less frequently, an IgA glomerulonephritis may occur and induce renal failure. Only two cases have been previously described. We report herein four new cases.

CASE REPORT

We report four cases of HS-RDEB associated with IgA glomerulonephritis. A renal biopsy confirmed the diagnosis in all four cases. Later on, two patients had a second renal biopsy, indicated for deterioration of renal function. One of these patients showed AA type renal amyloidosis on the second biopsy. None of these six biopsies, conducted in our four patients led to local cutaneous complications. Subsequently three patients presented with terminal renal failure. Hemodialysis was set up, with good tolerance and improvement in quality of life.

DISCUSSION

IgA glomerulonephritis should be suspected if a patient with HS-RDEB presents with hematuria. Renal biopsy is not contraindicated, confirms the diagnosis and helps to specify the prognosis. Hemodialysis is possible and well tolerated in the terminal stage of renal failure. There is not enough evidence for a genetic link between HS-RDEB and IgA glomerulonephritis, but repeated skin infections may be involved in the pathophysiology of the renal disease.