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March 8, 2019

Disase Week: Collagen Type III Glomerulopathy

Collagen type III glomerulopathy is an ultra-rare kidney disease of unknown etiology and pathogenesis with only rare cases reported in the literature, the vast majority being case reports. A few non-controlled, small case series exist that shed light on differences in pediatric and adult presentations and specific geographic patient populations.

Type III collagen is typically absent in normal glomeruli, although small amounts have been reported in some advanced glomerular diseases. In patients with collagen type III glomerulopathy, abundant type III collagen is seen within the mesangium and lamina rara interna of the capillary loops and typically occurs in a flocculent mesangial/capillary wall matrix.

Exactly how the type III collagen gets into the mesangium and capillary wall is unknown. Some authors believe this is a systemic disease with circulating procollagen leading to the accumulation of type III collagen. This hypothesis comes from evidence in humans and canines of increased amounts of the serum aminoterminal propeptide of type III procollagen in those with collagen type III glomerulopathy and rare case reports of multi-organ identification of type III collagen deposition. However, the aminoterminal propeptide of type III procollagen is not a specific biomarker and most patients with collagen type III glomerulopathy do not develop symptoms of multi-organ injury in the course of their disease. Conversely, some authors believe that the collagen type III is locally produced in the glomerulus as small amounts of collagen type III can be seen in some advanced glomerular disorders implying the mechanism for production may exist in the injured glomerulus. Also, mesangial cell activation has been identified in at least one report of collagen type III glomerulopathy.

While no genetic etiology has been identified in humans, pediatric forms of the disease can display an autosomal recessive pattern of inheritance. And, a naturally occurring canine equivalent disease displays the same inheritance pattern but without the hypocomplementemia seen in some pediatric patients. Importantly, when diagnosed in adulthood, the disease appears to be sporadic with no inheritance pattern identified and does not typically co-occur with hemolytic uremic syndrome as has also been seen in pediatric patients.

In adult patients, progressive chronic kidney disease usually occurs and some patients progress to end-stage kidney disease while in the pediatric presentation, renal outcomes are generally poor. To date, no controlled trials evaluating different treatment strategies and outcomes exist and there is no general consensus on treatment although treatment to reduce hypertension and proteinuria are generally accepted. Finally, while only a few patients with this disease have received a renal allograft, to date recurrence of the disease in the allograft has not been reported.