This form of glomerulonephritis is characterized by the presence of prominent IgA deposits in the mesangial regions, detected by immunoflouorescence microscopy. The disease can be suspected by light microscopic examination, but diagnosis is made only by immunocytochemical techniques. IgA nephropathy is a frequent cause of recurrent gross or microscopic hematuria and is aprobably the most common type of glomerulonephritis worldwide. Mild proteinuria is usually present, and the nephrotic syndrome may occasionally develop. A patient may rarely present with rapidly progressive crescentic glomerulonephritis.

Whereas IgA nephropathy is an isloated renal disease, similar IgA deposits are present in a systemic disorder of children, Henoch-Schonlein purpura. Which has many overlapping features with IgA nephropathy. In addition secondary IgA nephropathy occurs in patients with liver and intestinal disease.

IgA the main immunoglobulin in mucosal secretions is at low levels in normal serum where it is present mostly in monomeric form the polymeric forms being catabolized in the liver. In patients with IgA nephropathy serum polymeric IgA is increased and circulating IgA immune complexes are prsent in some patients. A genetic influence is suggested by the occurance of this condition in families and in HLA identical brothers and the increased frequency of certain HLA and complement phenotypes in some populations. The prominent mesangial deposition of IgA suggests entrapment of IgA immune complexes in the mesangium and the absence of Ciq and C4 in clomeruli points to activation of the alternative complement pathway.

Taken together, these clues suggest a genetic or acquired abnormality of immune regulation leading to increased mucosal IgA synthesis in response to respiratory or gastrointestinal exposure to environmental agents. IgA1 and IgA1 containing complexes are then entrapped in the mesangium where they activate the alternative complement pathway and initiate glomerular injury. In support of this scenario, IgA nephropathy occurs with increased frequency in patients with gluten enteropathy (celiac disease) in whom intestinal muycosal defects are well defined, and in liver disease in which there is defective hepatobiliary clearnce of IgA complexes (secondary IgA nephropathy).

The nature of the antigens is unknown and several infectious agents and food products have been implicated. The deposited IgA appears to be polyclonal and it may be that a variety of antigens are involved in the course of the disease. Alternatively it has been suggested that qualitative alternations in the IgA1 molecule itself make it more likely to bind to mesangial antigens or that IgA antibodies react with mesangial cell autoantigens.

Clinical course

The disease affects children and young patients. More than half the patients present with gross hematuria after an infection of the respiratory or less commonly, gastrointestinal or urinary tract; 30% to 40% have only microscopic hematuria, with or without proteinuria, and 5% to 10% develop a typical acute nephrotic syndrome. The hematuria typically lasts for several days and then subsides only to return every few months. The subsequent course is highly variable. Many patients maintain normal renal function for decades. Slow progression to chronic renal failure occurs in 25 to 50% of cases during a period of 20 years. Onset of old age heavy proteinuria hypertension and extent of glomerulosclerosis on biopsy are clues to an increased risk of progression. Recurence of IgA deposits in transplanted kidneys occurs in 20% to 60% of grafts; the resulting disease most frequently runs the same indolent, slowly progressive course as that of the primary IgA nephropathy.