IgA nephropathy, also known as Berger disease, is the most common primary glomerulonephritis and the most prevalent chronic glomerular disease in the world. It was first described morphologically by Dr. Jean Berger (nephrologist) and Nicole Hinglais (microscopist) in 1968 by electron microscopy. Later, immunofluorescence microscopy was used to show more specific findings associated with the disease, such as deposits of the IgA in the mesangial matrix and its subsequent proliferation, types of immunoglobulins, and complement. The hallmark of the disease is deposition of IgA in the glomerular mesangium, causing progressive kidney disease in a majority of patients. Because gross hematuria often follows an episode of upper tract respiratory infection, IgA nephropathy is also called synpharyngitic glomerulonephritis. Other names used are IgA nephritis, IgA-IgG nephropathy, nephropathy with mesangial IgA and IgG deposits. Major clinical risk factors for progression are hypertension, proteinuria, and reduced GFR; whereas, microscopic hematuria is not a significant risk factor for progressive loss of renal function. The Oxford classification involves scoring based histologic findings, including mesangial hypercellularity, endocapillary proliferation, segmental glomerulosclerosis, tubular atrophy, or interstitial fibrosis. 
It is hypothesized that mucosal infection is the culprit of the disease as most patients develop gross hematuria from IgA nephropathy after upper respiratory tract infections, specifically pharyngitis (synpharyngitic). However, most cases of IgA nephropathy are idiopathic. IgA is mainly produced at mucosal surfaces, and its main role is mucosal defense. After the mucosal injury, the IgA1 monomer undergoes a conformational change of its molecule and thus provides the substrate for antigen-antibody formation in susceptible individuals. Galactose-deficient IgA1 is synthesized as a consequence of the mucosal response to various antigens triggered by infections. Circulating immune complexes made from poorly galactosylated IgA1 bind to mesangial cell plasma membrane causing proliferation of the mesangial cells with the result of podocyte injury and loss of renal function.
IgA nephropathy is the most common glomerulonephritis worldwide and can occur at any age. The peak age onset is in the second and third decades. Review of cohort studies reports 0.2 to 2.9 per 100,000 annual incidences of IgA nephropathy. The disease is more common in Asia and Australia than in other parts of the world. This may be because some Asian countries enforce routine screening with urinalysis, prompting earlier diagnosis. Among the North American and Western European populations, there is 2:1 male to female ratio. IgA nephropathy is rare in all African populations throughout the world.
The main processes leading to the pathogenesis of IgA nephropathy are increased production of IgA1, defective galactosylation of IgA1, binding of antibodies against the galactose-deficient IgA1 with an accumulation of immune complexes in the mesangium, and activation of the mesangial cells. Patients with IgA nephropathy have excess deposits of galactose-deficient IgA1 in their serum and glomerular mesangium. The galactose-deficient immunoglobulin A1 has less galactose in the hinge region of the heavy chains and, subsequently, is recognized as a neo-antigen, triggering the formation of auto-antibodies and circulating immune complexes that accumulate in the mesangial cells. This mesangial deposition causes the release of pro-inflammatory and pro-fibrotic mediators and results in mesangial proliferation, extracellular matrix synthesis, and podocyte damage. These mesangial-induced mediators are also filtered in the urine and activate proximal tubular epithelial cells, causing tubulointerstitial scarring.
Light microscopy findings can range from normal to mesangial proliferation, endocapillary proliferation, focal or segmental necrosis, or crescents in Bowman’s space. However, the most common abnormality is mesangial hypercellularity. Because the light microscopy findings are non-specific, electron and immunofluorescent microscopy are required to confirm the diagnosis of IgA nephropathy by identifying the immune deposits, immunoglobulins (IgA, IgG, IgM), and complements (C3 being the most commonly found) associated with the disease. The immune deposits are most commonly located in the mesangial and paramesangial areas, but can also be observed in the subepithelial and subendothelial areas of the glomerular basement membrane.
Most patients present with asymptomatic microscopic hematuria or proteinuria that can be present for many years. Hypertension is initially found in a minority of patients but becomes common as the disease progresses to chronic kidney disease or end-stage renal disease. IgA nephropathy can present with gross hematuria, nephrotic syndrome, and chronic kidney disease and can escalate to rapidly progressive glomerulonephritis. Episodic gross hematuria is seen commonly in children and young adults after upper respiratory tract infection. Synpharingitic macroscopic hematuria is a classic initial presentation of IgA nephropathy.
Evaluation involves urinalysis and renal biopsy. The urinalysis demonstrates hematuria, dysmorphic red blood cells, and proteinuria. Renal biopsy and immunohistologic examination confirm the diagnosis. Light microscopy can show focal or diffuse mesangial proliferation and increased mesangial matrix and cellularity. In advanced disease, interstitial fibrosis with tubular atrophy can be found. Electron microscopy shows the electron dense deposits of IgA in the mesangium. Immunofluorescence microscopy shows the types of immunoglobulins deposits (mainly IgA1, but also IgG and IgM) in mesangium and capillary walls. C3 and C4 are commonly detected with C4d indicating poor prognosis with progression to end-stage renal disease. Serum IgA level is of no clinical utility.
Treatment options are patient dependent based on clinical findings and disease evolution. Conservative therapy with angiotensin-converting enzyme inhibitor or angiotensin receptor blocker to slow proteinuria is recommended in all patients. If no response, trial of corticosteroids can be started for 3 to 6 months. Immunosuppressants (mycophenolate, azathioprine, cyclophosphamide) are reserved for patients with progressive crescentic IgA nephropathy and avoided if the biopsy shows advanced interstitial fibrosis or tubular atrophy. Aggressive treatment of blood pressure with the goal of blood pressure of less than 130/80 mm Hg is highly encouraged. Although rituximab is used in many other glomerular diseases, it did not show beneficial effects on renal function or proteinuria of patients with IgA nephropathy. Tonsillectomy is not supported by current Kidney Disease Improvement Global Outcomes guidelines. Diet should consist of adequate protein and avoidance of increased salt intake. Fish oil therapy did not show a delay in disease progression and is not supported by current treatment guidelines. Renal transplantation is the preferred treatment for patients who require renal replacement therapy, but IgA nephropathy recurrence rate is high after transplantation.
Risk factors for disease progression include clinical factors such as hypertension, reduced glomerular filtration rate at the time of renal biopsy, or persistent proteinuria on follow-up) and pathological risk factors as based on the Oxford classification. According to Oxford classification, the following parameters provide prognostic information: mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, and tubular atrophy. Poor prognosis is associated with a glomerular filtration rate of less than 60 mL per minute, proteinuria greater than 0.5 g per day, hypertension greater than 140/90 mm Hg, more than 50% glomeruli affected by mesangial hypercellularity. Other prognostic histologic factors indicative of progression to end-stage renal disease are the presence of segmental glomerulosclerosis, interstitial fibrosis, and endocapillary proliferation. It is estimated that about half of all patients eventually develop the end-stage renal disease within 20 years after diagnosis. In fact, IgA nephropathy is the main cause of end-stage renal disease secondary to primary glomerular disease.
Many diseases have IgA glomerular deposition but do not have the clinical findings of the IgA nephropathy. Some of the conditions that have secondary causes of mesangial IgA deposition include liver diseases (alcoholic, cryptogenic or primary biliary cirrhosis), inflammatory bowel disease (ulcerative colitis, Crohn's disease), infections (HIV, leprosy, tuberculosis), skin disorders (psoriasis, dermatitis herpetiformis), malignancy (lung, pancreas,larynx), sarcoidosis, cystic fibrosis, among others.
Even though IgA nephropathy is a benign disorder, it does worsen in about 20% of patients leading to end-stage renal failure, which may require dialysis. Today, the focus on management is to prevent the kidney disease from progressing. Besides the nephrologist and pediatrician, the nurse and pharmacist play a critical role in patient education. The patient must be educated about the importance of blood pressure control and compliance with antihypertensive medications. A dietitian should educate the patient on a low salt diet and eating foods that are low in fat and carbohydrates. The patient should be encouraged to join a rehab program and maintain a healthy body weight. Finally, smoking cessation is vital to prevent progression of the disease. Those patients managed with corticosteroids must be monitored for side effects. Only through such an approach can be morbidity of the disease be lowered. (Level V)
In the majority of patients, Berger disease has a benign course, but about 10-20% will develop end-stage renal failure within ten years. Predictors of poor outcomes include hypertension, ongoing proteinuria, high serum creatinine and CD4 staining on biopsy. (Level V)