Glomerular diseases with organized fibrillary deposits are rare entities and more so in children. They can be simply categorized as amyloid or non-amyloid diseases using the Congo red stain. All amyloidogenic proteins as a rule stain positive with Congo red. Non-amyloid diseases can be further classified into organized fibrils with immunoglobulin components (fibrillary glomerulonephritis [FGN] and immunotactoid glomerulopathy [ITG]), and those without immunoglobulin components (fibronectin glomerulopathy and collagenofibrotic glomerulopathy among others). These deposits may have overlapping features that pose a multitude of challenges in making a correct diagnosis. Routine histological features may aid in diagnosis, but electron microscopy and special stains pertaining to each disease are frequently required. Renal prognosis in these conditions remains poor and treatment options are limited.

In general, kidney disease is not a very common feature of mitochondriopathies but tends to be more prevalent in children than adults. Overall, the spectrum of kidney disease in a context of multi-organ mitochondrial disease is quite variable, and diagnostic assessment with a kidney biopsy is indispensable to establish the diagnosis. Clinically, most mitochondrial diseases with renal manifestation will cause tubular dysfunction, ranging from renal tubular acidosis to overt Fanconi syndrome (aminoaciduria, hyperuricemia and electrolyte imbalances); rarely, proteinuria and nephrotic syndrome can be a sign. Chronic kidney disease and end-stage kidney disease are the usual outcomes. The two most common mitochondrial diseases that also have renal involvement are Leigh syndrome and mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome. Notably, CoQ10 deficiency presents with classic FSGS and proteinuria. Other findings include proximal tubulopathy/granular tubular inclusions (large mitochondria found on EM) which clinically correspond to overt De Toni–Debré–Fanconi syndrome.