IgA nephropathy and IgA vasculitis nephritis

Overview & Definition

A teenager who notices dark, smoky urine the morning after a sore throat, or a five-year-old who arrives with a purpuric rash on the shins and blood in the urine, both have the same underlying problem: immune complexes built from a defective antibody called IgA are settling in the filtering surface of the kidney and injuring it. When that process is confined to the kidney it is called IgA nephropathy, the most common primary glomerulonephritis in the world. When the same IgA complexes also land in the skin, gut, and joints it is called IgA vasculitis (the modern name for Henoch-Schonlein purpura), and when it scars the kidney it is called IgA vasculitis nephritis. The renal lesion in the two conditions is histologically identical. [8]

The link between the two is the central teaching point. Both are driven by a faulty IgA molecule whose sugar chains are incomplete — galactose-deficient IgA1 (Gd-IgA1). The body makes antibodies against this abnormal molecule, the resulting immune complexes circulate, and they lodge wherever they can, above all in the glomerular mesangium. Whether the child presents with isolated kidney disease or with a full systemic vasculitis depends on where those complexes deposit, not on a different mechanism. [11]

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9. [9]Zhang Y, Hu YT, Lv JC, Zhang H Corticosteroids in the treatment of IgA nephropathy: lessons from the TESTING trial. Pediatr Nephrol, 2023.PMID 36881171
10. [10]Barbour SJ, Coppo R, Er L, Russo ML, Liu ZH, Ding J, et al Application of the updated International IgA Nephropathy Prediction Tool in children one or two years post-biopsy. Kidney Int, 2024.PMID 39094695
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