Is IgA nephropathy the commonest primary glomerulopathy among young adults in the USA?
2006; Elsevier BV; Volume: 69; Issue: 8 Linguagem: Inglês
10.1038/sj.ki.5000292
ISSN1523-1755
Autores Tópico(s)Vasculitis and related conditions
ResumoOver the past decade, focal segmental glomerulosclerosis (FSGS) has emerged as the most common primary glomerulopathy in adults in the USA. However in our practice, we became aware of increased numbers of patients with IgA nephropathy (IgAN). In order to further examine this, a retrospective analysis of renal biopsy diagnoses from adults was done from our biopsy database. Adult renal biopsies received from 3/1/2001 to 2/28/2005 were analyzed to determine the frequency of common primary glomerulopathies, which included FSGS, IgAN, membranous nephropathy (MN), minimal change disease, and membranoproliferative glomerulonephritis Type I (MPGN). The patients were grouped as all adults (≥20 years) and young adults (20–39 years). The distribution of common primary glomerulopathies among the two age groups, expressed as a percentage of all non-transplant diagnoses (n=4504), was IgAN 6.9/3.4%, FSGS 9.6/3.2%, MN 6.8/1.6%, minimal change disease 2.5/0.9%, MPGN 1.2/0.2%. IgAN was as common as FSGS in young adults in our biopsy population (IgAN/FSGS 154/143 1.08:1). IgAN was the most common primary glomerulopathy in young adult Caucasians (IgAN/FSGS 2.1:1). IgAN was also the most common cause of end-stage renal disease (ESRD) in young adult Caucasians. In contrast, IgAN was rare in African Americans in whom FSGS remains more common (FSGS/IgAN 9.7:1). These findings from a large renal biopsy referral center serving 24 Midwestern and Southern states suggest that IgAN may be the most common primary glomerulopathy and the most common cause of ESRD in young adult Caucasians in the USA. Over the past decade, focal segmental glomerulosclerosis (FSGS) has emerged as the most common primary glomerulopathy in adults in the USA. However in our practice, we became aware of increased numbers of patients with IgA nephropathy (IgAN). In order to further examine this, a retrospective analysis of renal biopsy diagnoses from adults was done from our biopsy database. Adult renal biopsies received from 3/1/2001 to 2/28/2005 were analyzed to determine the frequency of common primary glomerulopathies, which included FSGS, IgAN, membranous nephropathy (MN), minimal change disease, and membranoproliferative glomerulonephritis Type I (MPGN). The patients were grouped as all adults (≥20 years) and young adults (20–39 years). The distribution of common primary glomerulopathies among the two age groups, expressed as a percentage of all non-transplant diagnoses (n=4504), was IgAN 6.9/3.4%, FSGS 9.6/3.2%, MN 6.8/1.6%, minimal change disease 2.5/0.9%, MPGN 1.2/0.2%. IgAN was as common as FSGS in young adults in our biopsy population (IgAN/FSGS 154/143 1.08:1). IgAN was the most common primary glomerulopathy in young adult Caucasians (IgAN/FSGS 2.1:1). IgAN was also the most common cause of end-stage renal disease (ESRD) in young adult Caucasians. In contrast, IgAN was rare in African Americans in whom FSGS remains more common (FSGS/IgAN 9.7:1). These findings from a large renal biopsy referral center serving 24 Midwestern and Southern states suggest that IgAN may be the most common primary glomerulopathy and the most common cause of ESRD in young adult Caucasians in the USA. The most common primary glomerulopathy in the USA is reported to be focal segmental glomerulosclerosis (FSGS).1.D'Agati V. The many masks of focal segmental glomerulosclerosis.Kidney Int. 1994; 46: 1223-1241Abstract Full Text PDF PubMed Scopus (272) Google Scholar, 2.Haas M. Spargo B. Coventry S. Increasing incidence of focal-segmental glomerulosclerosis among adult nephropathies: a 20-year renal biopsy study.Am J Kidney Dis. 1995; 26: 740-750Abstract Full Text PDF PubMed Scopus (188) Google Scholar, 3.Kitiyakara C. Eggers P. Kopp J. Twenty-one-year trend in ESRD due to focal segmental glomerulosclerosis in the United States.Am J Kidney Dis. 2004; 44: 815-825Abstract Full Text Full Text PDF PubMed Scopus (212) Google Scholar, 4.Korbet S. Genchi R. Borok R. et al.The racial prevalence of glomerular lesions in nephrotic adults.Am J Kidney Dis. 1996; 27: 647-651Abstract Full Text PDF PubMed Scopus (187) Google Scholar, 5.Dragovic D. Rosenstock J. Wahl S. et al.Increasing incidence of focal segmental glomerulosclerosis and an examination of demographic patterns.Clin Nephrol. 2005; 63: 1-7Crossref PubMed Scopus (82) Google Scholar, 6.Pontier P. Patel T. Racial differences in the prevalence and presentation of glomerular disease in adults.Clin Nephrol. 1994; 42: 79-84PubMed Google Scholar, 7.Braden G. Mulhern J. O'Shea M. et al.Changing incidence of glomerular diseases in adults.Am J Kidney Dis. 2000; 35: 878-883Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar This is in contrast to reports from other parts of the world where IgA nephropathy (IgAN) is the most common primary glomerulopathy among all races from Europe, Asia, and Australia with the exception of the black race.8.Research Group on progressive chronic renal disease Nationwide and long-term survey of primary glomerulonephritis in Japan as observed in1850 biopsied cases.Nephron. 1999; 82: 205-213Crossref PubMed Scopus (103) Google Scholar, 9.Ballardie F.W. O'Donnaghue D.J. Peehally J. Increasing frequency of adult IgA nephropathy in the UK?.Lancet. 1987; 2: 1205Abstract PubMed Scopus (16) Google Scholar, 10.Briganti E. Dowling J. Finlay M. et al.The incidence of biopsy-proven glomerulonephritis in Australia.Nephrol Dial Transplant. 2001; 16: 1364-1367Crossref PubMed Scopus (168) Google Scholar, 11.Floege J. Grone H. IgA nephropathy: frequent, but rarely diagnosed.Internist (Berlin). 2003; 44: 1131-1139Crossref PubMed Scopus (3) Google Scholar, 12.Jennette J. Wall S. Wilkman A. Low incidence of IgA nephropathy in blacks.Kidney Int. 1985; 28: 944-950Abstract Full Text PDF PubMed Scopus (84) Google Scholar, 13.Li L. Liu Z. Epidemiologic data of renal diseases from a single unit in China: analysis based on 13, 519 renal biopsies.Kidney Int. 2004; 66: 920-923Abstract Full Text Full Text PDF PubMed Scopus (344) Google Scholar, 14.Pettersson E. von Bonsdorff M. Tornroth T. et al.Nephritis among young Finnish men.Clin Nephrol. 1984; 22: 217-222PubMed Google Scholar, 15.Rivera F. Lopez-Gomez J. Perez-Garcia R. Frequency of renal pathology in Spain, 1994–1999.Nephrol Dial Transplant. 2002; 17: 1594-1602Crossref PubMed Scopus (152) Google Scholar, 16.Schena F. Survey of Italian Registry of renal biopsies. Frequency of renal diseases for 7 consecutive years.Nephrol Dial Transplant. 1997; 12: 418-426Crossref PubMed Scopus (191) Google Scholar, 17.Seedat Y. Nathoo B. Parag K. et al.IgA nephropathy in blacks and Indians of Natal.Nephron. 1988; 50: 137-141Crossref PubMed Scopus (40) Google Scholar, 18.Simon P. Ramee M. Boulahrouz R. et al.Epidemiologic data of primary glomerular diseases in western France.Kidney Int. 2004; 66: 905-908Abstract Full Text Full Text PDF PubMed Scopus (141) Google Scholar, 19.Sinniah R. Javier A.R. Ku G. The pathology of mesangial IgA nephritis with clinical correlation.Histopathology. 1981; 5: 469-490Crossref PubMed Scopus (51) Google Scholar, 20.Stratta P. Segoloni G. Canavese C. et al.Incidence of biopsy-proven primary glomerulonephritis in an Italian province.Am J Kidney Dis. 1996; 27: 631-639Abstract Full Text PDF PubMed Scopus (71) Google Scholar, 21.Tiebosch A. Wolters J. Frederik P. et al.Epidemiology of idiopathic glomerular disease: a prospective study.Kidney Int. 1987; 32: 112-116Abstract Full Text PDF PubMed Scopus (87) Google Scholar, 22.Tojo S. Narita M. Koyama A. Natural history and treatment of IgA nephropathy in Japan.J Nephrol ROC. 1987; 1: 305-318Google Scholar, 23.Woo K. Chiang G. Pall A. et al.The changing pattern of glomerulonephritis in Singapore over the past two decades.Clin Nephrol. 1999; 52: 96-102PubMed Google Scholar The racial makeup of the North American population is predominantly of European descent with a smaller mixture of other races. So the apparently lower incidence of IgAN seen here is not easily explained. We noticed in our renal biopsy practice that IgAN is frequent in all age groups, but particularly common in younger individuals. We became increasingly aware that patients in the third and fourth decades of life, who present with hitherto undetected chronic renal failure, often have a diagnosis of IgAN. Review of the literature on the incidence of various glomerulopathies led us to suspect that FSGS cases might be over-represented in series from metropolitan hospitals serving large African American populations. The number of patients with FSGS might also be inflated due to the presence of secondary FSGS in older individuals in some studies. Based on the above, we analyzed our renal biopsy database, stratifying the diagnoses by age and race and comparing the frequency of IgAN with other common primary glomerulopathies, including FSGS, membranous nephropathy (MN), minimal change disease, and membranoproliferative glomerulonephritis Type I (MPGN). If indeed IgAN is more common as our data suggest, then new strategies in detection and therapy may be justified since this disease is not as benign as once considered.24.Berger J. Yaneva H. Crosnier J. Mesangial IgA glomerulonephritis: a frequent cause of terminal renal failure.Nouv Presse Med. 1980; 9: 219-221PubMed Google Scholar Out of the 4504 non-transplant renal biopsies in all adults aged 20 years and above, 1228 cases of the major primary glomerulopathies were identified (Table 1); and out of 1082 non-transplant renal biopsies in those aged 20–39 years, 416 cases of the major primary glomerulopathies were identified (Table 1). Among all adults, 435 had FSGS and 313 had IgAN. (IgAN:FSGS ∷ 0.72:1). However, in the young adults (aged 20–39 years), there were 154 instances of IgAN and 143 of FSGS (IgAN:FSGS ∷ 1.08:1). The male to female ratio of IgAN among all adults was 200:113 (1.8:1) and 94:60 (1.6:1) in those aged 20–39 years. The distribution of cases of IgAN and FSGS in adults every half decade from age 20 years onwards is shown in Figure 1. The peak incidence of IgAN was in the third and fourth decades of life with a gradual decline over the remaining years. The peak incidence of FSGS is in the fourth decade, with a secondary peak in the seventh decade of life. IgAN was the most common primary glomerulopathy in the third decade of life (IgAN/FSGS 77/49 1.57:1). In the fourth decade of life, the ratio of IgAN/FSGS was 78/95 (0.82/1.0). IgAN was also slightly more common than FSGS in all young adults aged 20–39 years 154/143 (1.08/1).Table 1Distribution of common primary glomerulopathiesAgeIgANFSGSMNMinimal change diseaseMPGNTotal≥20aExpressed as a percentage of all adult biopsies (n=4504).313 (6.9%)435 (9.6%)310 (6.8%)116 (2.5%)54 (1.2%)122820–39bExpressed as a percentage of biopsies in young adults (n=1082).154 (14.2%)143 (13.2%)70 (6.5%)42 (3.9%)7 (0.6%)416FSGS, focal segmental glomerulosclerosis; IgAN, IgA nephropathy; MN, membranous nephropathy; MPGN, membranoproliferative glomerulonephritis Type I.a Expressed as a percentage of all adult biopsies (n=4504).b Expressed as a percentage of biopsies in young adults (n=1082). Open table in a new tab FSGS, focal segmental glomerulosclerosis; IgAN, IgA nephropathy; MN, membranous nephropathy; MPGN, membranoproliferative glomerulonephritis Type I. Race information was available for 216 patients (72.7%) in the young adult group with either FSGS or IgAN (Tables 2 and 3). In all, 118 patients were Caucasian, 64 African American, 17 Hispanic, 13 Asian, two East Indian, one Native American, and one Filipino/Caucasian (Table 2). IgAN was the most common primary glomerulopathy in Caucasians aged 20–39 years (IgAN/FSGS 80/38 2.1:1) as opposed to African Americans in whom FSGS was more common (FSGS/IgAN 58/6 9.7:1) (Table 2).Table 2Distribution of IgAN/FSGS among races in young adultsAACauHispAsianOtherTotalIgAN6809102107FSGS5838832109Total6411817134216AA, African American; Cau, Caucasian; Hisp, Hispanic; FSGS, focal segmental glomerulosclerosis; IgAN, IgA nephropathy. Open table in a new tab Table 3ESRD in various races among young adultsAACauHispOtherTotalIgAN180110FSGS1221116Total13101226AA, African American; Cau, Caucasian; Hisp, Hispanic; ESRD, end-stage renal disease; FSGS, focal segmental glomerulosclerosis; IgAN, IgA nephropathy.Renal function follow-up data was available on 149 young adults with IgAN/FSGS. Open table in a new tab AA, African American; Cau, Caucasian; Hisp, Hispanic; FSGS, focal segmental glomerulosclerosis; IgAN, IgA nephropathy. AA, African American; Cau, Caucasian; Hisp, Hispanic; ESRD, end-stage renal disease; FSGS, focal segmental glomerulosclerosis; IgAN, IgA nephropathy. Renal function follow-up data was available on 149 young adults with IgAN/FSGS. Follow-up time in this study is very brief and follow-up history was available in 149 (50.1%) of young adult patients with IgAN/FSGS. Yet, 26 patients from this group have progressed to end-stage renal disease (ESRD) (Table 3). Of the 13 African Americans with ESRD, FSGS was the primary diagnosis in 12 and IgAN in one. However, of the 10 Caucasians with ESRD, IgAN was the primary diagnosis in eight and FSGS in two. In the USA, epidemiological studies of the general population pertaining to both IgAN and FSGS are lacking. Reports that show increased incidence of FSGS are mostly from metropolitan hospitals which serve a large African American population.1.D'Agati V. The many masks of focal segmental glomerulosclerosis.Kidney Int. 1994; 46: 1223-1241Abstract Full Text PDF PubMed Scopus (272) Google Scholar, 2.Haas M. Spargo B. Coventry S. Increasing incidence of focal-segmental glomerulosclerosis among adult nephropathies: a 20-year renal biopsy study.Am J Kidney Dis. 1995; 26: 740-750Abstract Full Text PDF PubMed Scopus (188) Google Scholar, 4.Korbet S. Genchi R. Borok R. et al.The racial prevalence of glomerular lesions in nephrotic adults.Am J Kidney Dis. 1996; 27: 647-651Abstract Full Text PDF PubMed Scopus (187) Google Scholar, 5.Dragovic D. Rosenstock J. Wahl S. et al.Increasing incidence of focal segmental glomerulosclerosis and an examination of demographic patterns.Clin Nephrol. 2005; 63: 1-7Crossref PubMed Scopus (82) Google Scholar, 6.Pontier P. Patel T. Racial differences in the prevalence and presentation of glomerular disease in adults.Clin Nephrol. 1994; 42: 79-84PubMed Google Scholar Some of these studies do not provide information on IgAN and some deal primarily with diseases causing nephrotic syndrome rather than primary glomerulopathy and exclude IgAN. The largest epidemiological study available is from the United States Renal Data System (USRDS) databank.25.US Renal Data System USRDS 2004 Annual Data Report. Atlas of End-Stage Renal Disease in the United States, National Institutes of Health. National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD2004Google Scholar However, this databank only includes ESRD patients. While USRDS data may give a broad idea of incidence and prevalence of the two diseases, an accurate assessment of incidence and prevalence may not be possible as the progression to ESRD differs between patients with FSGS and IgAN. Awareness that IgAN is more common in the USA than previously reported is slowly emerging. Only one epidemiological survey of a localized area in the USA is available for IgAN but not for FSGS and other primary glomerulopathies. This study of Central and Eastern Kentucky indeed shows that the incidence of ESRD due to IgAN nephropathy has increased from 5.4 to 12.4 patients per million population over a period of 20 years from 1975–1994.26.Wyatt R. Julian B. Baehler R. et al.Epidemiology of IgA nephropathy in central and eastern Kentucky for the period 1975 through 1994. Central Kentucky Region of the Southeastern United States IgA Nephropathy DATABANK Project.J Am Soc Nephrol. 1998; 9: 853-858PubMed Google Scholar According to USRDS (The data reported here has been supplied by the USRDS. The interpretation and reporting of these data are the responsibility of the author(s) and in no way should be seen as an official policy or interpretation of the US government) data, the incidence of ESRD due to IgAN has increased 45-fold from 0.16 to 3% over a period of 20 years.3.Kitiyakara C. Eggers P. Kopp J. Twenty-one-year trend in ESRD due to focal segmental glomerulosclerosis in the United States.Am J Kidney Dis. 2004; 44: 815-825Abstract Full Text Full Text PDF PubMed Scopus (212) Google Scholar A small biopsy series from a military hospital shows that IgAN is far more common in young white individuals than FSGS (40 IgAN ∷ 8 FSGS), while the reverse was true in black indivisuals (0 IgAN ∷ 66 FSGS).6.Pontier P. Patel T. Racial differences in the prevalence and presentation of glomerular disease in adults.Clin Nephrol. 1994; 42: 79-84PubMed Google Scholar Another small biopsy series from a community hospital has shown IgAN to be the cause of 51% of primary glomerulopathies in young Caucasian adults.5.Dragovic D. Rosenstock J. Wahl S. et al.Increasing incidence of focal segmental glomerulosclerosis and an examination of demographic patterns.Clin Nephrol. 2005; 63: 1-7Crossref PubMed Scopus (82) Google Scholar The current study is the largest and only biopsy series which specifically addresses the frequency of IgAN in biopsies of adults across various age groups in the USA. Our data show that IgAN is as common as FSGS in young adults when all races were considered. In African Americans, FSGS remains the most common primary glomerulopathy. However in Caucasians, who constitute 67.4% of the US population,27.US Census Bureau Table 4. Annual estimates of the population by race alone and Hispanic or Latino origin for the United States – July 1. 2004www.census.govGoogle Scholar IgAN is the most common primary glomerulopathy. In countries where systematic screening for urinary abnormalities is done, IgAN is by far the most frequent primary glomerulopathy.28.Levy M. Berger J. Worldwide perspective of IgA nephropathy.Am J Kidney Dis. 1988; 12: 340-347Abstract Full Text PDF PubMed Scopus (200) Google Scholar Since the early studies were primarily out of Asia, the high frequency of IgAN was at first thought to be limited to those of Asian origin. However, reports documenting that IgAN is the most common primary glomerulopathy in Finland, France, Italy, the UK, Germany, Australia, etc. suggest otherwise.9.Ballardie F.W. O'Donnaghue D.J. Peehally J. Increasing frequency of adult IgA nephropathy in the UK?.Lancet. 1987; 2: 1205Abstract PubMed Scopus (16) Google Scholar, 10.Briganti E. Dowling J. Finlay M. et al.The incidence of biopsy-proven glomerulonephritis in Australia.Nephrol Dial Transplant. 2001; 16: 1364-1367Crossref PubMed Scopus (168) Google Scholar, 14.Pettersson E. von Bonsdorff M. Tornroth T. et al.Nephritis among young Finnish men.Clin Nephrol. 1984; 22: 217-222PubMed Google Scholar, 15.Rivera F. Lopez-Gomez J. Perez-Garcia R. Frequency of renal pathology in Spain, 1994–1999.Nephrol Dial Transplant. 2002; 17: 1594-1602Crossref PubMed Scopus (152) Google Scholar, 16.Schena F. Survey of Italian Registry of renal biopsies. Frequency of renal diseases for 7 consecutive years.Nephrol Dial Transplant. 1997; 12: 418-426Crossref PubMed Scopus (191) Google Scholar, 20.Stratta P. Segoloni G. Canavese C. et al.Incidence of biopsy-proven primary glomerulonephritis in an Italian province.Am J Kidney Dis. 1996; 27: 631-639Abstract Full Text PDF PubMed Scopus (71) Google Scholar, 28.Levy M. Berger J. Worldwide perspective of IgA nephropathy.Am J Kidney Dis. 1988; 12: 340-347Abstract Full Text PDF PubMed Scopus (200) Google Scholar Thus, it would seem that IgAN is not actually less common in the USA, but less commonly diagnosed. The criteria for biopsying patients with hematuria varies among nephrologists and most do not do a renal biopsy unless, in addition to hematuria, there is nephrotic range proteinuria and/or evidence of renal dysfunction.28.Levy M. Berger J. Worldwide perspective of IgA nephropathy.Am J Kidney Dis. 1988; 12: 340-347Abstract Full Text PDF PubMed Scopus (200) Google Scholar, 29.Geddes C. Rauta V. Gronhagen-Riska C. et al.A tricontinental view of IgA nephropathy.Nephrol Dial Transplant. 2003; 18: 1541-1548Crossref PubMed Scopus (146) Google Scholar This would result in detection of the disease only in those already at a more advanced stage, underestimating the total population of patients with IgAN and selecting for those with potentially a much poorer outcome.11.Floege J. Grone H. IgA nephropathy: frequent, but rarely diagnosed.Internist (Berlin). 2003; 44: 1131-1139Crossref PubMed Scopus (3) Google Scholar, 28.Levy M. Berger J. Worldwide perspective of IgA nephropathy.Am J Kidney Dis. 1988; 12: 340-347Abstract Full Text PDF PubMed Scopus (200) Google Scholar In addition, the number of IgAN cases may be underestimated because some renal pathologists in the USA use the criteria of more than 1+ staining intensity to render a definitive diagnosis of IgAN.30.Jennette J. The immunohistology of IgA nephropathy.Am J Kidney Dis. 1988; 12: 348-352Abstract Full Text PDF PubMed Scopus (105) Google Scholar However, it is very possible that 'early', 'quiescent', or 'burned-out' IgAN would have trace to 1+ amounts of IgA staining which would then be ignored or reported as a non-specific finding. Given the variable light microscopy changes seen in IgAN, some of these cases could actually end up being called FSGS further tilting the data. Imprecision of diagnostic criteria for FSGS may also falsely inflate the number of patients in that category leading to an inappropriately higher incidence of FSGS in comparison to the more strictly defined IgAN. For example, in the USRDS databank, the category focal glomerulosclerosis/focal glomerulonephritis includes not only typical FSGS but also other entities such as focal global glomerulosclerosis or focal glomerulonephritis of an inflammatory type. Finally, the difficulty in distinguishing between primary and secondary FSGS is well known.31.Cameron J. Focal segmental glomerulosclerosis in adults.Nephrol Dial Transplant. 2003; 18: Svi45-Svi51Google Scholar Recent reports document that IgAN is the most common primary glomerulopathy in Hispanics and that the frequency of ESRD due to IgAN has dramatically increased in this ethnic group.3.Kitiyakara C. Eggers P. Kopp J. Twenty-one-year trend in ESRD due to focal segmental glomerulosclerosis in the United States.Am J Kidney Dis. 2004; 44: 815-825Abstract Full Text Full Text PDF PubMed Scopus (212) Google Scholar, 7.Braden G. Mulhern J. O'Shea M. et al.Changing incidence of glomerular diseases in adults.Am J Kidney Dis. 2000; 35: 878-883Abstract Full Text Full Text PDF PubMed Scopus (194) Google Scholar Specific data from Hispanic patients in our study is too limited to draw conclusions. However, the Hispanic population is projected to double to 24.4% nationwide by 2050 emphasizing the importance of monitoring this group for primary glomerular disease, particular IgAN. An increase in the incidence of IgAN can be expected over the coming decades due to changes in awareness and biopsy practices, and evolving population demographics. This suggests the need for a comprehensive epidemiological investigation into the prevalence and incidence of IgAN in the US population. Is ESRD due to IgAN more common than recognized, especially in young adults? If so, is a screening program for IgAN justifiable in the USA as in some other countries such as Japan and Singapore where systematic screening reveals an incidence of IgAN as high as 50% of all primary glomerulopathies?28.Levy M. Berger J. Worldwide perspective of IgA nephropathy.Am J Kidney Dis. 1988; 12: 340-347Abstract Full Text PDF PubMed Scopus (200) Google Scholar Also, in some studies, younger age at presentation is associated with a more rapid progression to ESRD.29.Geddes C. Rauta V. Gronhagen-Riska C. et al.A tricontinental view of IgA nephropathy.Nephrol Dial Transplant. 2003; 18: 1541-1548Crossref PubMed Scopus (146) Google Scholar, 32.Radford Jr, M.G. Donadio Jr, J.V. Bergstrahl E.J. et al.Predicting renal outcome in IgA nephropathy.J Am Soc Nephrol. 1997; 8: 199-207PubMed Google Scholar All this has special significance as disease-modifying agents are available for IgAN especially if detected early in the course of the disease.33.Harmankaya O. Ozturk Y. Basturk T. et al.Efficacy of immunosuppressive therapy in IgA nephropathy presenting with isolated hematuria.Int Urol Nephrol. 2002; 33: 167-171Crossref PubMed Scopus (27) Google Scholar, 34.Ibels L. Gyory A. Caterson R. et al.Recognition and management of IgA nephropathy.Drugs. 1998; 55: 73-83Crossref PubMed Scopus (18) Google Scholar The current study provides data to support the impression that IgAN is under-recognized in the USA. This is the largest biopsy series comparing the incidence of IgAN and FSGS in young adults. It is also the first study to show that IgAN is as common as FSGS in young adults, and that IgAN is the most common primary glomerulopathy in young adult Caucasians. In addition, this study suggests that IgAN may be the most common primary glomerulopathy causing ESRD in young adult Caucasians. All kidney biopsies received at Nephropathology Associates over a 4-year period from March 1, 2001 to February 28, 2005 were reviewed. The biopsies were from 24 states of the USA predominantly from the South and the Mid-West regions. Patients were classified by age into two categories: all adults – those 20 years and older and young adults – those 20–39 years of age. The age group 20–39 years was chosen for specific emphasis for the following reasons:(1) 19 years to eliminate pediatric FSGS which is considered by many to be different from adult FSGS and because children with isolated microscopic hematuria are typically not biopsied in the USA, likely leading to underestimation of IgAN in this age group. All cases of IgAN with a secondary cause such as liver disease, autoimmune disorders, and systemic conditions such as Henoch–Schonlein nephritis and other vasculitides were eliminated. All cases of FSGS in which a secondary cause was identified were eliminated. These included diabetes mellitus, HIV, chronic hypertension, immune complex-mediated glomerulonephritis, solitary kidney, obesity, and others. Secondary forms of other primary glomerulopathies were also excluded from analysis. All cases of MN secondary to autoimmune disorders such as systemic lupus erythematosus and rheumatoid arthritis were eliminated. Minimal change disease due to secondary causes such as malignancy and those with associated positive anti-nuclear antibody were excluded. MPGN cases associated with lupus nephritis were excluded. Finally, in the rare instances where repeat biopsies were present, only the first biopsy was included in the study. For the histopathological diagnosis of IgAN, a staining intensity of 2–3+ (out of a maximum of three) in mesangial areas was used. Biopsies with staining intensity of 1 or less were not classified as IgAN. Clinical data were gathered from the biopsy request forms. In addition, a questionnaire was sent to the referring physicians asking for race information and renal function data on all patients aged 20–39 years with a diagnosis of either FSGS or IgAN. Data for IgAN were compared against that for FSGS (the most commonly reported primary glomerulopathy) to assess incidence of disease, ESRD, and race in young adults. Many thanks to Mike Wilson for help during compiling the follow-up data. Support: None.
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