Membranous nephropathy remains the commonest primary cause of nephrotic syndrome in a northern European Caucasian population

Dear Sir, We read with interest the paper from Hanko et al. [1] which demonstrates that, between 1976 and 2005, focal segmental glomerulosclerosis (FSGS) was not the commonest adult primary glomerulopathy diagnosed on native renal biopsy in the Northern Irish population, contrary to reports from other parts of the world. The authors allude to the fact that comparing incidence of histological diseases between centres is heavily influenced by ascertainment bias since the tendency to recommend renal biopsy for patients with mild proteinuria or isolated microscopic haematuria varies widely [2]. Most nephrologists recommend renal biopsy for adults with nephrotic syndrome unless the clinical features suggest diabetic nephropathy. Therefore, comparing the incidence of histological causes of nephrotic syndrome is likely to reflect true changes in disease incidence rather than ascertainment bias. The Scottish Renal Biopsy Registry [3] has been recording histological diagnoses prospectively since 2003. The native renal biopsy rate in Scotland between 2003 and 2008 was 126.3 per million population (pmp)/year [2] compared with 70.8 pmp/year in the northern Irish population. In the 6 years between 2003 and 2008, three centres in Glasgow and Dundee, serving a population of 1 956 133 (40% of the Scottish population), performed 1069 native biopsies, of which 209 were performed for nephrotic syndrome (26.5 pmp/year). Of nephrotic patients, 57.9% were male, mean age 56.4 years (SD 18.3), median estimated glomerular filtration rate at time of biopsy 60.2 ml/min/1.73m2 (SD 31.6), mean urinary protein:creatinine ratio 857 mg/mmol (SD 490) and mean serum albumin concentration 22.1 g/l (SD 7.7). One hundred thirty-seven (65.5%) were diagnosed with a primary glomerulopathy. Of these, 54 had idiopathic membranous nephropathy (MGN), 32 had FSGS, 24 had minimal change nephropathy (MCN), 13 IgA nephropathy (IGAN), 9 mesangiocapillary GN (MCGN), 2 post-infectious GN and 1 fibrillary GN (illustrated as incidence pmp per year in Figure 1). The commonest secondary cause of nephrotic syndrome leading to renal biopsy was diabetic nephropathy. In patients <45 years of age minimal change, nephropathy was the commonest diagnosis, and >45 years, membranous nephropathy was commonest.