NEPHROLOGY 2004; 9, 52 Blackwell Science, LtdOxford, UKNEPNephrology1320-53582004 Asian Pacific Society of NephrologyApril 2004925252Editorial Thin basement membrane nephropathyJ Savige Correspondence: Professor Judy Savige, The Northern Hospital, Epping, Victoria 3076, Australia. Email: jasavige@unimelb.edu.au Accepted for publication 25 February 2004. Editorial Thin basement membrane nephropathy and coincidental renal biopsy lesions JUDY SAVIGE The Northern Hospital, Epping, Victoria, Australia Thin basement membrane nephropathy (TBMN) is the commonest cause of persistent haematuria in both children and adults, and affects at least 1% of the popu- lation. 1 Previous reports have focused on TBMN in Caucasians, and there are only occasional descriptions of it in Chinese, Indian and African individuals. The article by Sue et al. in the previous issue of the Journal (Nephrology 2004; 9: 14–18), 2 represents the first study of TBMN in the Chinese race in Western medical literature. Recent reports have helped in our understanding of the nature of TBMN. 3 We now know that at least 40% of affected individuals have single mutations in the COL4A3 or COL4A4 genes, which code for the a3(IV) or a4(IV) collagen chains. These genes are also affected in autosomal recessive Alport syndrome, and TBMN sometimes represents the carrier state for this condition. Thin basement membrane nephropathy is usually diagnosed when the typical clinical features are present. Affected individuals have persistent microscopic haema- turia, minimal proteinuria and normal kidney function. 1 Two-thirds have another family member with haema- turia. The prognosis is usually excellent and no treat- ment is required. Despite the usually benign prognosis of TBMN, approximately 40% of our patients with biopsy-proven disease develop proteinuria and 7% have some degree of renal impairment. 1 This contrasts with their unbiopsied but affected family members who have the more typical clinical features. 1 Why does renal impairment occur in TBMN? In most cases, the cause is unknown, 4,5 but sometimes IgA disease or X-linked Alport syndrome have been misdiagnosed, and in other cases, there are coincidental glomerular or tubulointerstitial lesions. Sue et al. found an additional histological diagnosis in 38 of the 52 patients (73%) with TBMN who were examined. 2 This is more often than we have found, and may reflect the frequency of the atypical clinical features in the patients studied. The commonest additional lesion identified in Sue’s study was focal glomerulosclerosis, 2 but tubulointerstitial nephritis, immunoglobulin A (IgA) disease, membrano- proliferative, lupus and membranous glomerulonephritis were also described. The non-IgA mesangial proliferative changes do not represent a distinct pathological entity because they correspond to the light microscopic changes normally seen in TBMN. 1 Likewise, the associ- ation with minimal change glomerulonephritis should be disregarded because the membrane thinning seen in this condition is artefactual. 1 Nevertheless, the study by Sue et al. is important for two reasons. First, the diverse nature of the additional diagnoses suggests that coincidental glomerular or tubu- lointerstitial lesions occur by chance and not because TBMN predisposes to their pathogeneses. Second, this study indicates that coincidental glomerular and tubu- lointerstitial lesions are common in patients with TBMN and nephrotic range proteinuria or impaired renal func- tion. Thus, patients who are suspected of having TBMN, because of a positive family history, and who also have marked proteinuria or renal impairment, warrant a kid- ney biopsy to demonstrate these lesions which, unlike TBMN, often require treatment. REFERENCES 1. Savige J, Rana K, Tonna S, Buzza M, Dagher H, Wang YY. Thin basement membrane nephropathy. Kidney Int. 2003; 64: 1169– 78. 2. Sue Y-M, Huang J-J, Hsieh R-Y, Chen F-F. Clincal features of thin basement membrane disease and associated glomerulopathies. Nephrology 2004; 9: 14–18. 3. Buzza M, Wilson D, Savige J. Segrgation of haematuria in thin basement membrane disease with haplotypes at the loci for Alport syndrome. Kidney Int. 2001; 59: 1670–6. 4. Monga G, Mazzucca G, Roccatello D. The association of IgA glom- erulonephritis and thin basement membrane disease in a hematuric patient: Light, electron microscopic and immunofluorescence in- vestigation. Am. J. Kidney Dis. 1991; 18: 409–12. 5. Cosio FG, Falkenhain ME, Sedmak DD. Association of thin glo- merular basement membrane with other glomerulopathies. Kidney Int. 1994; 46: 471–4.