Glomerulomegaly in Australian Aborigines

Summary: Idiopathic glomerular enlargement has previously been described in a number of indigenous populations, including Australian Aborigines. This study had three aims: (1) evaluate three methods for estimating mean glomerular tuft and renal corpuscle volume; (2) assess the effects of fixation on glomerular dimensions; and (3) estimate glomerular tuft and renal corpuscle volume in clinical biopsies from Australian non‐Aboriginals, Aboriginals and Aboriginal inhabitants of the Tiwi Islands (Bathurst Island and Melville Island, Northern Territory, Australia). First, glomerular volume was determined in initial transplant biopsies from 17 non‐Aboriginal males (30–50 years) using three methods: the Cavalieri method, a stereological method that requires serial sectioning of glomeruli and knowledge of section thickness, but requires no knowledge or assumptions of glomerular size or shape (the gold‐standard method); the stereological method of Weibel and Gomez that employs a single section but requires assumptions of glomerular size distribution and shape; and the maximal profile method, with which the largest glomerular profile in a single section is identified, and used to calculate the volume of the parent glomerulus (assuming glomerular sphericity). Estimates for glomerular tuft volume were (mean ± SD): Cavalieri method (2.08 ± 0.37 × 10 6 μm 3 ); Weibel and Gomez (2.55 ± 0.63 × 10 6 μ 3 ); maximal profile method (3.09 + 0.6610 6 μ 3 ). Taking the Cavalieri estimate to be accurate, the maximal profile method is seen to grossly overestimate mean glomerular tuft volume, whereas the Weibel and Gomez method overestimated tuft volume by 23%. Both methods considerably overestimated mean renal corpuscle volume. In the study of fixation and glomerular dimensions, we found that glomeruli in clinical biopsies fixed in formalin were larger (47% for glomerular tuft and 25% for renal corpuscle) than the glomeruli in biopsies fixed in formol mercury/Dubosq Brazil. This result emphasizes the importance of standardizing the histological technique in quantitative studies of glomeruli. Finally, the Weibel and Gomez method was used to estimate mean glomerular volume in formalin‐fixed clinical biopsies from 80 non‐Aboriginal Australians, 78 non‐Tiwi Aboriginals and 72 Tiwi Aboriginals. Mean glomerular tuft volumes were: 3.12 ± 1.46 × 10 6 μm 3 , 4.91 ± 2.59 × 10 6 μm 3 and 4.79 ± 2.08 × 10 6 μm 3 , respectively, (for biopsies with four or more profiles). Mean glomerular tuft volume in the two Aboriginal populations was significantly ( P < 0.001 in each case) greater than that in the non‐Aboriginals. These data indicate that there is pronounced glomerulomegaly in Australian Aborigines.