Pathophysiology and treatment of IgA nephropathy in children

Transcription

1 Pediatr Nephrol (2001) 16: IPNA 2001 INVITED REVIEW Norishige Yoshikawa Ryojiro Tanaka Kazumoto Iijima Pathophysiology and treatment of IgA nephropathy in children Received: 19 September 2000 / Revised: 18 January 2001 / Accepted: 20 January 2001 Abstract IgA nephropathy is the most-common primary glomerulonephritis worldwide, and about 20% 50% of patients develop progressive renal failure. The pathogenesis is still unknown and treatment has not yet been established. Knowledge concerning childhood IgA nephropathy has expanded greatly in the last 10 years, and its importance as the major form of glomerulonephritis and major contributor to end-stage renal disease is also becoming apparent in children. This review focuses on the pathophysiology and treatment of IgA nephropathy in children. Keywords Pathogenesis Treatment IgA nephropathy Genetic factors Introduction IgA nephropathy is the commonest variety of primary glomerulonephritis in the world today. IgA nephropathy was initially considered a benign disease with a favorable prognosis; however as data from long-term followup studies became available, progression of the disease to renal failure in 20% 50% of adult patients was recognized. In children, a more-benign prognosis has been reported; however, recent studies do not support the prevailing belief that IgA nephropathy in children is an entirely benign disease [1, 2, 3, 4, 5, 6]. The pathogenesis of IgA nephropathy is still unknown and treatment for children with IgA nephropathy has not yet been established. However, knowledge concerning childhood IgA nephropathy has expanded greatly over the last 10 years. This review will therefore focus on the pathophysiology and treatment of IgA nephropathy in children. N. Yoshikawa ( ) Department of Pediatrics, Wakayama Medical University, Kimiidera, Wakayama City, Japan nori@wakayama-med.ac.jp Tel.: , Fax: R. Tanaka K. Iijima Department of Pediatrics, Kobe University School of Medicine, Kobe, Japan Epidemiology IgA nephropathy has been diagnosed all over the world, but its prevalence varies widely from one country to another. In Japan, France, Italy, and Australia it accounts for between 18% and 40% of all primary glomerular diseases, whereas in the United States, the United Kingdom, and Canada it is responsible for only 2% 10%. The explanation for this apparent variability in incidence is uncertain, but it may be due to a racial difference in the basic underlying pathology of IgA nephropathy or to racial differences in patterns of referral and biopsy selection practices [7]. In Australia [8], where the population is heterogeneous and includes many immigrants from Third World countries, all racial groups seem to be affected equally. The high incidence of IgA nephropathy in certain countries may reflect the practice of routine urinalysis. In Japan, all children between the ages of 6 and 18 years are screened annually and those found to have urinary abnormalities are referred for further investigation. Thus, IgA nephropathy is the commonest primary glomerulopathy in children seen in Kobe University Hospital, detected in about 30% of biopsy specimens obtained since This periodic screening of urine of healthy populations and subsequent investigation of those found to have abnormalities is also an accepted routine amongst adults in Japan. Genetic factors and environmental influences could also contribute to geographic differences in prevalence. A lower prevalence among blacks than whites has been reported in the United States. However, in American children, similar incidences of IgA nephropathy in Caucasian and African-American children from Shelby County, Tennessee have been reported [9]. Genetic factors Predisposing genetic factors have been suggested as important in the development of IgA nephropathy. Moreover, it has been suggested that genetic factors may not

2 only determine susceptibility to glomerulonephritis, but also influence the pathological severity and natural course of IgA nephropathy [10, 11]. Familial clustering Evidence for genetic factors being important in IgA nephropathy is provided by family studies [10, 11, 12, 13, 14]. Rambausek et al. [10] discovered that 9.6% of patients with mesangial IgA nephropathy in Germany had one or more siblings with glomerulonephritis. Julian et al. [12] described a kindred from eastern Kentucky in which six patients with IgA nephropathy descended from one ancestor, eight other patients belonged to potentially related pedigrees. Moreover, they indicated that at least 48 (60%) of 80 IgA nephropathy patients who were born in the same region were related to at least one other patient [13]. Recently Scolari et al. [14] reported that 26 (14%) of 185 patients with IgA nephropathy investigated in Italy were related to at least one other patient with the disease. These family studies suggest that familial predisposition is a very common finding and genetic factors influence the pathogenesis of IgA nephropathy. Human leukocyte antigen genes Most efforts to study the genetics of IgA nephropathy have focused on the huma leukocyte antigen (HLA) system. Significant associations between the incidence of IgA nephropathy and some class I (HLA-B12, Bw35, B37) and II (HLA-DR1, DR4) major histocompatibility phenotypes have been reported. Moreover, the recent application of HLA polymorphisms has focused on three class II products, DP, DQ, and DR, has shown the association between the susceptibility to IgA nephropathy and DQB1, DQw7, DQβ3b (DQ7), DQB (DQw4/8/9), and D-DR4. However, none of these associations has been consistently confirmed. Further investigations on a large number of informative families are needed before firm conclusions can be drawn. IgA immune system 447 Several findings, such as high serum levels of IgA, high levels of IgA-bearing cells, and an increased in vitro production of IgA by peripheral blood mononuclear cells are described in patients with IgA nephropathy [17]. These abnormalities in the IgA immune system have also been reported in some healthy relatives of patients with IgA nephropathy [12, 18]. These results suggest that genetic background plays a crucial role in the pathogenesis of IgA nephropathy. In an attempt to determine the basic molecular mechanisms of IgA synthesis in IgA nephropathy, polymorphisms of the switch region of immunoglobulin heavy chain gene and Iα1 germ-line transcript regulatory region gene have been reported. Immunoglobulin class switch The switch region of immunoglobulin heavy chain is important in switching from one immunoglobulin class to another class. Polymorphism of the immunoglobulin heavy chain switch region genes is associated with differences in the variable heavy chain region. Alterations in the Sµ and Sα gene regions probably influence the immunoglobulin heavy chain switch region. Demaine et al. [19] reported increases in the frequency of homozygotes with either allele coding for the IgM switch regions (Sµ) in patients with IgA nephropathy. These results suggested that immunoglobulin heavy chain loci might play an important role in the pathogenesis of IgA nephropathy. However, these observations have not been confirmed in other studies [20, 21]. Our recent studies [20] have shown that the genotypic frequency of the Sµ_ and Sα alleles in patients is similar to normal controls. However, there is a decreased frequency of the 2.6/2.1 kb Sµ heterozygosity in patients showing diffuse mesangial proliferation compared with controls or patients showing minimal/focal mesangial proliferation. Our results suggest that immunoglobulin heavy chain switch region genes may not influence susceptibility to IgA nephropathy, but may influence the pathological expression of IgA nephropathy. Complement factors C4 is encoded by two loci (C4A and C4B) within the major histocompatibility complex. Its deficiency may affect the solubilization and/or clearance of immune complexes. McLean et al. [15] reported that the homozygous null C4 phenotype is significantly increased in frequency in IgA nephropathy. C3 plays, together with factor B, a major role in the activation of the alternative pathway. C3 gene is polymorphic with two main alleles: F and S. Rambausek et al. [16] found a significant excess of homozygous phenotype C3FF in IgA nephropathy compared with normal. Iα 1 germ-line transcript regulatory region gene Germ-line transcript, another characteristic molecular event in immunoglobulin class switching, has recently received attention. Yano et al. [22] reported structural and functional changes in the Iα 1 germ-line transcript regulatory region gene in patients with IgA nephropathy and presented the polymorphism of that gene. The polymorphism of the Iα1 germ-line transcript regulatory region gene was observed more frequently in patients with IgA nephropathy than in controls. Patients with the mutations showed higher levels of serum IgA and higher in vitro IgA synthesis. This gene may play an important role as the disease-causing gene in IgA nephropathy.

3 448 IgA1 O-galactosylation The IgA subclass prominent in IgA nephropathy is generally considered to be IgA1. IgA1 is unique among all immunoglobulins in its possession of a hinge region rich in proline, serine, and threonine, and characterized by five O-glycosylation sites. These O-glycosylation sites consist of N-acetylgalactosamine O-linked to the serine residues of the hinge region. Abnormal galactosylated IgA1 has increased affinity for glomerular fibronectin, laminin, and collagen IV [23], and may lead to accumulation of IgA in the mesangium. Preliminary data indicate that deficient galactosylation of hinge region glycans may be detected even in family members of patients with IgA nephropathy [24]. An altered amino acid sequence of the IgA1 hinge region is a possible mechanism to consider for abnormal galactosylation of IgA1. However, the hinge region is a highly conserved region of the IgA1 molecule. There is no evidence for any nucleotide sequence alteration or transcriptional abnormality of the hinge region in IgA nephropathy [25]. It has also been postulated that altered galactosylated IgA1 in IgA nephropathy may be due to a deficiency of structural modification of β 1,3-galactosyltransferase, the enzyme responsible for the terminal galactosylation of GalNAc on O-linked glycans [26]. This structural or functional deficiency may be genetically determined. Understanding the basis of genetic abnormalities in β1,3-galactosyltransferase will improve, since it has been sequenced [27, 28]. Genes of the renin-angiotensin system Recent studies on IgA nephropathy have demonstrated intrarenal angiotensin II hyperreactivity in patients with progressive disease [29], while angiotensin I converting enzyme (ACE) inhibitor has been shown to reduce proteinuria and attenuate the progressive decline in renal function in IgA nephropathy [30]. These studies suggest that activation of the renin-angiotensin system might play an important role in the progression of IgA nephropathy. Moreover, some investigators have reported that genetic variability of the renin-angiotensin system modifies renal progression in IgA nephropathy. Angiotensin I converting enzyme gene An insertion (I)/deletion (D) polymorphism in intron 16 of the ACE gene is associated with variation in circulating levels of ACE [31]. Thus, the II genotype is associated with low levels of serum ACE, whereas the DD genotype is associated with high levels, with ID genotypes having intermediate levels of ACE. Several recent studies have shown a significant association between ACE gene polymorphism and progression to chronic renal failure in IgA nephropathy [32, 33, 34]. While no difference was found in genotype distribution between the patients with IgA nephropathy and the control population, the rate of progression was significantly worse in patients with the DD genotype. Moreover, we investigated whether there was any association between ACE gene polymorphism and clinicopathological findings in IgA nephropathy. Our study of 97 Japanese children with IgA nephropathy showed that although ACE gene polymorphism might not influence the extent of mesangial proliferation and crescents that are acute lesions, the ID/DD genotypes are associated with chronic lesions, such as capsular adhesions or glomerulosclerosis and urinary protein excretion [35]. Thus, this gene polymorphism may not determine susceptibility to IgA nephropathy, but may influence the pathological severity and natural course of childhood IgA nephropathy. Angiotensinogen gene The M235T polymorphism of the angiotensinogen gene has been demonstrated in essential hypertension [36]. Recently, Pei et al. [37] have reported that 168 Caucasian patients with IgA nephropathy and one or both copies of the angiotensinogen T235 allele had a faster rate of decline in their renal function than patients homozygous for the M235 allele. However, this association could not be consistently demonstrated in IgA nephropathy. Angiotensin II type I receptor gene The A1166C polymorphism of the angiotensin II type I receptor gene has been associated with essential hypertension [38], and thus has been examined in IgA nephropathy. However, in two studies of Yoshida et al. [33] and Hunley et al. [34], the frequency distribution of genotype was not significantly different between those with and those without progression. Platelet-activating factor acetylhydrolase gene Platelet-activating factor (PAF) is a potent mediator of inflammatory injury in renal diseases. PAF is degraded to inactive products by PAF acetylhydrolase. Recently a point mutation (G to T transversion) of the PAF acetylhydrolase gene was observed at position 994, and this mutation was found to contribute to the variability in plasma PAF levels, with undetectable plasma PAF acetylhydrolase activity occurring in homozygous patients (TT genotype) and reduced levels of activity in heterozygous patients (GT genotype) [39]. We investigated the effect of the PAF acetylhydrolase gene mutation on the pathogenesis and progression of IgA nephropathy [40]. Genomic DNA was obtained from 89 children with IgA nephropathy and 100 controls. There was no significant difference in genotypic frequency between patients and controls. However, urinary protein excretion at the time of biopsy was significantly higher in patients with the GT/TT geno-

4 types than in those with the GG genotype. The percentage of glomeruli with mesangial cell proliferation was significantly higher in patients with the GT/TT genotypes than in those with the GG genotype. These results indicate that the PAF acetylhydrolase gene mutation may influence the degree of proteinuria and the extent of mesangial proliferation in the early stage of childhood IgA nephropathy. Other genes Neuropeptide Y Y1 receptor gene The neuropeptide Y Y1 receptor (NPYY1R) gene is found predominantly at the sympathetic postjunctional site in blood vessels, especially arterioles; it is considered to be related to vascular smooth muscle cell constriction and increased blood pressure. Recently, Herzog et al. [41] cloned a 14-kb pair region of genomic DNA encoding the NPYY1R gene. They also reported a single point mutation in the first intron of the NPYY1R gene [42]. Ito et al. [43] reported that the distribution of the NPYY1R genotypes, which were defined as YY, Yy, and yy genotypes, did not differ between 68 patients with IgA nephropathy and 60 normal control subjects. However, in patients with IgA nephropathy, the rate of urinary protein excretion was higher in the non-yy genotype than in the YY genotype group. The reciprocal of the serum creatinine level was lower in the non-yy genotype than in the YY genotype group. They proposed that the NPYY1R gene polymorphism might be a novel prognostic predictor in patients with IgA nephropathy. T-cell receptor constant alpha chain gene The changes of T-cell receptor (TCR) constant alpha chain might alter the interaction with CD3 and/or the function of the TCR-CD3 complex and could evoke immunological abnormality that leads to the progression of IgA nephropathy. Deenitchina et al. [44] reported that the genotype distributions of the TCR constant alpha chain gene polymorphism did not differ between 213 Japanese patients with IgA nephropathy and 73 normal control subjects. However, the T allele was associated with a poor renal prognosis in patients with IgA nephropathy. A TCR constant alpha chain gene polymorphism was associated with development of IgA nephropathy among Chinese patients [45]. However, there was no link with the progression of disease. Some of the discrepancies between the two reports may be due to the different sample size and different geographical regions of the studies. These findings need confirmation in the future. Etiology and pathogenesis Although the etiology and pathogenesis of IgA nephropathy remain uncertain, there is substantial evidence that it is an immune complex disease [46, 47]. Granular electron-dense deposits are observed in the glomerular mesangial areas by electron microscopy, and confirmed as containing IgA and C3 by immunofluorescence microscopy. Circulating IgA immune complexes have been detected by several different specific assays, often associated with IgG immune complexes. Many immunological abnormalities that may lead to the formation of IgA immune complexes have been reported in patients with IgA nephropathy. Recurrences of IgA nephropathy are observed frequently in allografted kidneys, and the rapid disappearance of glomerular IgA deposits is observed when kidneys with mesangial IgA deposits are transplanted into patients without IgA nephropathy. Although much of this work was performed in adults, there is no evidence to suggest that the findings cannot be extrapolated to children. Moreover, glomerular IgA deposits associated with histological lesions similar to those of human IgA nephropathy can be induced in laboratory animals by passive administration of preformed IgA immune complex or by active immunization [48, 49, 50]. Nature of IgA deposits 449 IgA is the second most-common immunoglobulin and contributes to immunity at the level of the external secretory system. IgA exists in monomeric and polymeric forms. Monomeric IgA represents approximately 90% of the serum IgA, and is produced mainly by the circulating lymphocytes and plasma cells in the spleen and bone marrow. Polymeric IgA is produced mostly by lymphocytes and plasma cells in the gastrointestinal and respiratory tracts, where it is synthesized as monomers and then secreted as dimers linked by the J-chain, which is also produced within the plasma cells. During the passage of dimeric IgA molecules through the mucosal epithelium toward the external lumen, the secretory component is attached through specific noncovalent interactions; this component appears to protect the dimeric IgA from the proteolytic enzymes present in the external secretions. IgA has two subclasses, IgA1 and IgA2. About 90% of serum is composed of IgA1, whereas IgA2 is mostly derived from the local mucosa of the gastrointestinal and respiratory tracts. Both IgA1 and IgA2 are produced in the mucosa. The most-prominent finding in the glomeruli of renal biopsy specimens from patients with IgA nephropathy is mesangial IgA deposition. The majority of investigators have indicated that IgA1 is the predominant subclass present in the glomeruli [51]. J-chain, independent of IgM, has also been identified in the mesangium in patients with IgA nephropathy [52]. Secretory component is not present in the mesangial deposits, but immunofluorescence studies of renal biopsy sections from patients with IgA nephropathy have indicated that it binds to the mesangial areas in vitro [53]. These observations suggest that the mesangial IgA deposits are polymeric, a hypothesis further supported by the immunochemical character-

5 450 ization of IgA eluted from renal biopsy sections [54]. Assessment of polymeric IgA1 production by in situ hybridization for J chain mrna in IgA plasma cells shows downregulation in the mucosa [55] and upregulation in the bone marrow [56]. Impaired mucosal IgA responses allowing enhanced antigen challenge to the marrow (shown by de Fijter et al. [57]) could be the primary abnormality in IgA nephropathy, although this remains unproven [58]. A number of studies have suggested that the alternative complement pathway has a pathogenetic role in IgA nephropathy. This hypothesis is consistent with the typical immunohistological demonstration of C3 and properdin in a pattern and distribution similar to that of IgA in the glomeruli, often in the absence of C1q and C4. The detection of the membrane attack complex of complement further supports the pathogenetic role of complement activation in this disease [59]. Certain types of IgA aggregates or IgA myeloma complexes have been shown to activate complement in vitro [60], but there is no direct evidence that the activation is mediated by IgA deposits in the glomeruli. Activation of C3 is observed in the majority of adult and pediatric patients with IgA nephropathy, but the mediator as well as the pathophysiological significance of this complement activation remains to be determined. Because IgA is the main immunoglobulin directed against antigens (viral and bacterial) in the exocrine system, and because of the frequent association between upper respiratory tract or gastrointestinal infection, the onset of macroscopic hematuria, and the clinical development of IgA nephropathy, it has been suggested that certain viral or bacterial infections may lead to IgA nephropathy and that IgA may act as the antibody to viral or bacterial antigens. Considerable effort has been directed towards the search for antigens and for the antibody specificity of the mesangial IgA, but with limited success. Many antigens, including herpes simplex virus, cytomegalovirus, Epstein-Barr virus nuclear antigen, adenovirus, and milk antigen, have been identified. The observation of numerous antigenic substances in the glomeruli indicates that the antigenic materials in IgA nephropathy may be heterogeneous. The presence of Hemophilus parainfluenza antigens in a diffuse and global distribution in the glomerular mesangium and the presence of IgA antibody against H. parainfluenza in the sera of Japanese patients with IgA nephropathy have been demonstrated [61, 62]. With regard to antibody specificity, IgA eluted from cryostat sections of IgA nephropathy biopsies has been reported to react with the mesangial areas of their own and other IgA nephropathy patients biopsies [63]. Such eluates have also been shown to contain antibodies that react with tonsillar cells and cultured fibroblasts obtained from patients with IgA nephropathy [64]. IgA glycosylation has received recent attention as a putative nonimmune feature of IgA that may explain the abnormal behavior and glomerular deposition in IgA nephropathy [65]. Circulating IgA1 has reduced terminal galactose on O-linked hinge-region sugars in IgA nephropathy [66], apparently because of a B-cell defect in β1,3-galactosyltransferase, the enzyme responsible for placing terminal galactose on O-linked sugars [67]. The IgA1 O-glycan chains are truncated in IgA nephropathy [68]. As yet there is no proof that this abnormality directly promotes mesangial IgA1 deposition. In summary, the immunochemical nature of the mesangial deposits in IgA nephropathy is consistent with antigen-polymeric IgA complexes predominantly of A1 subclass, and perhaps multispecific for ubiquitous mucosally derived antigens. IgA immune system There is now general agreement that serum levels of IgA are increased in 50% 70% of patients with IgA nephropathy, with elevations in both monomeric and polymeric IgA. The proportion of IgA-λ in serum IgA is also increased. Serum IgA is more anionic, owing to the increased anionicity of λ-compared with κ-light chain [69]. In addition to the increased levels of serum IgA, various types of autoantibodies of the IgA class have been recognized. These autoantibodies include IgA class rheumatoid factor [70], antinuclear protein IgA antibodies [71], and anticollagen IgA antibody [72]. However, the IgA may be polyspecific, indicating a polyclonal increase in IgA reactivity rather than true antigen-specific autoantibodies [73]. IgA immune complexes are also frequently detected [74]. Many investigators have shown that cultured peripheral blood lymphocytes from patients with the disease produce more IgA than those of normal individuals, either spontaneously or after polyclonal stimulation in vitro. We also demonstrated an increased spontaneous and pokeweed mitogen-stimulated IgA production by peripheral blood lymphocytes in children with IgA nephropathy [75]. This increased IgA production remained stable during the follow-up period in patients with persistent urinary abnormalities, but decreased towards normal in patients with clinical remission. IgA production is highly T-cell dependent, and the increased production in IgA nephropathy indicates altered T-cell function. An increased circulating OKT4/OKT8 cell ratio, due to increased OKT4 helper T-lymphocytes and decreased OKT8 cytotoxic-suppressor T-lymphocytes, has been reported in patients [76]. Increased IgAspecific helper T-cell activity and decreased IgA-specific suppressor T-cell activity have also been reported [77, 78]. Defective clearance of immune complexes from the circulation may also be important [79], but this seems more likely to be a consequence rather than the cause of the increased immune complex load. Clinical features Although the clinical presentation of IgA nephropathy is varied, ranging from asymptomatic urinary abnormalities to acute renal failure, five different clinical syndromes

6 can generally be identified at onset: (1) macroscopic hematuria; (2) asymptomatic microscopic hematuria and/ or proteinuria; (3) an acute nephritic syndrome defined as hematuria associated with hypertension and/or renal insufficiency; (4) a nephrotic syndrome; and (5) a mixed nephritic-nephrotic syndrome. Of our patients, 62% were found to have microscopic hematuria and/or asymptomatic proteinuria; 26% presented with macroscopic hematuria and 12% with an acute nephritic syndrome and/or nephrotic syndrome. Several studies of IgA nephropathy in children from Europe and the United States have shown that more than 80% of all patients have macroscopic hematuria, and recurrent macroscopic hematuria is traditionally regarded as the hallmark of childhood IgA nephropathy [80, 81, 82]. However, it was the initial feature in only 26% of our series, presumably because of the school screening program that detected a high prevalence of asymptomatic urinary abnormalities, rather than regional variation in the expression of IgA nephropathy. During the observation period, 60% of patients had one or more episodes of macroscopic hematuria, but the other 40% remained asymptomatic without macroscopic hematuria. The incidence of macroscopic hematuria is lower in adults than children with IgA nephropathy. Emancipator et al. [83] summarized the previous reports of IgA nephropathy, in which most of the patients were adults, and reported that 43% had macroscopic hematuria. However, in Japan, only 18% 32% of adult patients have been reported to have macroscopic hematuria [84, 85]. The reasons for the agerelated differences in the incidence of macroscopic hematuria have yet to be elucidated. Macroscopic hematuria often occurs in association with upper respiratory tract infections, and less frequently in association with other infections involving the mucosal system, such as diarrhea and sinusitis. Episodes of macroscopic hematuria are sometimes associated with loin pain. Many patients have recurrent episodes of macroscopic hematuria, each often associated with the same type of infection. The number of recurrences and the intervals between different episodes are variable. In asymptomatic patients, microscopic hematuria is almost always present and persistent. Proteinuria is frequently found, but in amounts less than the nephrotic range. The blood pressure and renal function at onset are normal. Patients with a nephritic and/or nephrotic onset have the most-severe glomerular damage. The commonest presenting symptom is macroscopic hematuria. Hypertension is usually mild to moderate and malignant hypertension is not a presenting feature in childhood. Nephrotic edema is reported in about 10% of patients. Acute renal failure is occasionally associated with episodes of macroscopic hematuria and is usually reversible. However, a number of investigators have documented a subset of patients with IgA nephropathy that is characterized by extensive crescents and a rapidly progressive course [86]. A review of published cases of crescentic IgA nephropathy revealed that 41% of patients with this rapidly progressive form of disease were 16 years of age or younger [87]. Serum IgA levels are increased in 30% 50% of adult patients, but in only 8% 16% in children with IgA nephropathy [3, 88]. For this reason it is seldom of diagnostic significance in children. Pathology Immunofluorescence microscopy The diagnostic immunopathological pattern of IgA nephropathy is the presence of IgA in the glomerular mesangium as the sole or predominant immunoglobulin. IgA deposits often extend just beyond the mesangiocapillary junctions into the adjacent capillary walls. There are also deposits of IgG and/or IgM with the same staining pattern as IgA, usually with lesser intensity and frequency. In our series [3], mesangial IgA deposits were associated with IgG in 32% of patients, IgM in 8%, and both IgG and IgM in 11%. C3 was observed in a similar distribution pattern in 64%, although it was usually less intense than IgA. However, the early classical complement components, C4 or C1q, are usually absent. Fibrin(ogen)-related antigens are found in a diffuse mesangial distribution in 25% 70% of patients and are thought to be one of the injurious agents in the glomeruli [89]. Although, in most patients, IgA is present only in the mesangial regions, in about 10% of patients it is also observed in the peripheral capillary walls. Such peripheral capillary wall deposits, whether documented by immunofluoresence or electron microscopy, have been associated with more-severe clinical manifestations and a poor renal outcome [90, 91, 92, 93]. Light microscopy 451 The most-characteristic abnormality is mesangial enlargement, caused by various combinations of hypercellularity and increase in matrix. Three types of mesangial change are identified in children with IgA nephropathy [2]: 1. Mesangial hypercellularity is more prominent than the increase in matrix. 2. The degrees of mesangial hypercellularity and matrix increase are similar. 3. The increase in matrix is more prominent than the mesangial cellularity. The first type of lesion is seen in biopsies in which the interval between onset of disease and biopsy is short. Serial pathological observations reveal that prominent mesangial hypercellularity is almost exclusively seen in initial biopsies and disappears in follow-up biopsies. These observations suggest that predominant mesangial hypercellularity is characteristic of the early lesion of childhood IgA nephropathy and may disappear within a

7 452 matter of months. An increase in mesangial cells, although sometimes present, is seldom striking in adult patients. In contrast, biopsies with a predominant matrix increase show a long interval between onset of disease and biopsy, and a high percentage of glomerular sclerosis. Serial pathological observations reveal that this type of change is usually seen in follow-up biopsies. An increase in the amount of mesangial matrix with duration of the disease has also been noted in adult patients. These findings suggest that progression of IgA nephropathy may lead to gradual resolution of mesangial hypercellularity and an increase of matrix, associated with the development of sclerosis [94]. Recent studies on children with IgA nephropathy suggest that mesangial proliferation partly result from the local production of cytokines: interleukin (IL)-1, IL-6, tumor necrosis factor, platelet-derived growth factor, transforming growth factor-β, and vascular permeability factor/endothelial growth factor [95, 96, 97, 98]. The severity of tubulointerstitial changes usually reflects the severity of glomerular damage. Vascular lesions such as arterial or arteriolar sclerosis are reported to be common in adults, but are very unusual in children with IgA nephropathy. This difference may be related to the age at biopsy and the duration of disease before biopsy. Electron microscopy Electron-microscopic abnormalities are mainly observed in the mesangium, which is variably enlarged by a combination of increased cytoplasm and matrix. Electrondense deposits in the mesangium are the most-constant and prominent feature and are seen in almost all patients. They are granular masses situated immediately beneath the lamina densa in the perimesangial region and expanded mesangium. The size and extent of mesangial deposits varies from patient to patient, and in several they are so large as to produce localized protrusions. Peripheral glomerular capillary wall deposits are also found in the subendothelial and subepithelial regions. Subendothelial deposits occur most frequently in the capillary wall adjacent to the mesangium, although they are also observed in the peripheral part of the loop. Subepithelial deposits are reported to be unusual in adult patients, but are frequently found in children with IgA nephropathy. They are generally small and flat, and localized to a few capillary loops; the humps typical of acute poststreptococcal glomerulonephritis are never observed. Lysis of the glomerular basement membrane is also seen quite frequently in children [99]. In affected areas of the glomerular capillary walls the lamina densa is thin and irregular, and the epithelial aspect of the glomerular basement membrane shows irregular segments of low electron density with an expanded washed out appearance. The epithelial foot processes are generally well-preserved, but diffuse foot process effacement may be seen in patients with the nephrotic syndrome. Repeat renal biopsy A relatively small number of repeat renal biopsies have been reported. Most of these have not shown either histological improvement or definitive morphological evidence of disease progression. We reported serial renal biopsy findings in children with IgA nephropathy [4]. At the time of the second biopsy, 23 patients showed clinical remission, defined as complete disappearance of proteinuria and hematuria with normal renal function, while 38 had persistent urinary abnormalities with normal renal function. There were no differences between the two groups with regard to the initial clinical findings and the pathological findings in the initial biopsy. The second biopsy of patients who were in clinical remission showed improvement of the glomerular changes on light microscopy, disappearance or diminution of mesangial IgA deposits, and decreased of electron-dense deposits, whereas that obtained from patients with persistent urinary abnormalities showed progression of light microscopy changes and persistence of both mesangial IgA deposits and electron-dense deposits. Clinical remission may occur in adults with IgA nephropathy, but without histological improvement [100]. Natural history and prognosis The overall prognosis of patients with IgA nephropathy remains to be determined. Most adult patients continue to have hematuria and/or proteinuria. In adult series, the incidence of renal insufficiency varies from less than 10% to as high as 45% in patients followed up for more than 1 year. In long-term follow-up of adult patients, 20% 30% have been found to develop progressive renal insufficiency 20 years after the initial discovery of disease [46, 101]. It can be estimated that 1% 2% of adult patients will enter end-stage renal failure each year from time of diagnosis [102]. The long-term prognosis of 241 of our Japanese children indicates that 5% of the patients had developed chronic renal failure by 5 years from onset of the disease, 6% by 10 years, and 11% by 15 years. Because of the variable rate of progression to chronic renal failure, there have been attempts to identify features present at the time of diagnosis that would predict the ultimate outcome. The following clinical findings are regarded as poor prognostic indicators in adult patients [46]: an older age at the onset of the disease, the absence of macroscopic hematuria, persistent hypertension, persistent heavy proteinuria, and reduced glomerular filtration rate at presentation. The majority of investigators agree that renal function in older patients deteriorates more frequently and adult patients with recurrent episodes of macroscopic hematuria have a more-favorable prognosis than those who have never experienced such episodes. The disease also follows a significantly morebenign course in children with younger onset than in those with older onset, and in children with macroscopic hematuria than in those without macroscopic hematuria

8 [1, 103]. In adults, many investigators have shown that heavy proteinuria carries a poor prognosis in IgA nephropathy, and some emphasize the predictive value of urinary protein excretion rate early in the course of the disease [104, 105, 106]. In children, several studies have shown that the degree of proteinuria correlates with the severity of morphological glomerular lesion [81, 82, 92], and heavy proteinuria at the time of biopsy predicts a poor outcome [107]. In contrast, slight proteinuria or its absence at the time of biopsy predicts a favorable outcome. There is general agreement that hypertension and low glomerular filtration rate at presentation are significant factors in determining the outcome of adult patients with IgA nephropathy. However, hypertension and acute renal failure at onset are usually reversible in children [92]. Among the pathological features analyzed in our children with IgA nephropathy, diffuse mesangial proliferation, a high proportion of glomeruli showing sclerosis, crescents or capsular adhesions, the presence of moderate or severe tubulointerstitial changes, and the presence of subepithelial electron-dense deposits and lysis of the glomerular basement membrane by electron microscopy were associated with a poor outcome [107]. Patients with diffuse mesangial proliferation have been reported to have a significantly worse prognosis than those with focal proliferation or with minimal lesions by light microscopy [91]. In many adult studies [108, 109], glomerular sclerosis and crescents have also been associated with poor renal outcome. Levy et al. [81] found that mesangial proliferative glomerulonephritis with crescents was associated with poor prognosis in children. Since the severity of the tubulointerstitial changes usually corresponds with the severity of the glomerular changes, tubulointerstitial changes in IgA nephropathy are thought to be secondary to the glomerular injury. Vascular lesions such as arterial or arteriolar sclerosis have been reported to play an important role in the progression of IgA nephropathy in adults. However, vascular changes are very unusual in children [2, 82]. This difference may be related to the age at biopsy and the duration of disease before biopsy. Treatment IgA nephropathy is a leading cause of chronic renal disease and end-stage renal disease in adult patients, and recent long-term studies assessing the prognosis in children have challenged earlier views that the condition represents a benign disorder. Thus IgA nephropathy presents a therapeutic challenge in both adults and children. Because of the variable rate of progression to renal failure, and because of the probable multifactorial pathogenesis of the disease, the effectiveness of any treatment can only be properly evaluated by means of a controlled trial. When considering treatment protocols, an issue of great importance is the selection of appropriate patients in whom the treatment is to be evaluated. Patients with most-severe glomerular lesions on renal biopsy appear to be at greatest risk of progressive renal deterioration and, therefore, the most-appropriate candidates for specific therapeutic interventions. Patients with long-standing disease and extensive, irreversible glomerular damage are unsuitable for such treatments. The most-appropriate treatment for patients with IgA nephropathy is controversial. These include: (1) prophylactic administration of antibiotics or tonsillectomy to prevent potential entry of microbial antigens, (2) glucocorticoids, immunosuppressive drugs, phenytoin, or danazol to manipulate the abnormal immune response, and (3) plasma exchange to remove circulating IgA immune complexes. Although prophylactic antibiotics [110] and tonsillectomy [111] may reduce the frequency of episodes of macroscopic hematuria, a beneficial effect on the progression to renal failure remains controversial. Glucocorticoids are beneficial in the few patients with a nephrotic syndrome and minimal mesangial lesions. Accumulated experience indicates that long-term glucocorticoid and/or immunosuppressive treatment during the insidiously progressive stage of the disease do not confer any benefit in adult patients [46]. Phenytoin was reported to decrease serum IgA levels and reduce the number of episodes of macroscopic hematuria, but no significant influence on the clinical or histological course was found [112]. In an attempt to improve complement-mediated solubilization of immune complexes, danazol has been tried, but no clear-cut beneficial effects were found [113]. Plasma exchange combined with glucocorticoids and immunosuppressive drugs is probably of value in those rare patients with rapidly progressive crescentic disease, but full recovery remains unlikely [114]. A recent controlled double-blind trial in adult patients with IgA nephropathy and proteinuria [115, 116] showed that treatment with fish oil for 2 years retarded the rate at which renal function was lost. Recent studies have indicated that ACE inhibition reduces urinary protein excretion and preserves renal function in adult patients with IgA nephropathy [117]. However, at present there is no curative therapy for IgA nephropathy [118]. Controlled trial by The Japanese Pediatric IgA Nephropathy Treatment Study Group 453 Our recent controlled trial by The Japanese Pediatric IgA Nephropathy Treatment Study Group demonstrated that treatment of children with severe IgA nephropathy with prednisolone, azathioprine, heparin-warfarin, and dipyridamole for 2 years early in the course of the disease prevents immunological renal injury and progression of the disease [119]. Seventy-eight children with newly diagnosed IgA nephropathy showing diffuse mesangial proliferation were randomly assigned to receive either the combined therapy of prednisolone, azathioprine, heparin-warfarin, and dipyridamole for 2 years (group 1) or the combination of heparin-warfarin and dipyridamole for 2 years

9 454 (group 2). Urinary protein excretion was significantly reduced in group 1 patients, but remained unchanged in group 2 patients. Serum IgA concentration was also significantly reduced in group 1 patients, but was unchanged in group 2 patients. Blood pressure and creatinine clearance were normal at the end of the trial in all but 1 group 2 patient, who developed chronic renal insufficiency. The percentage of glomeruli showing sclerosis was unchanged in group 1 patients, but significantly increased in group 2 patients. The intensity of mesangial IgA deposits significantly decreased in group 1 patients, but remained unchanged in group 2 patients. The beneficial effects of prednisolone, azathioprine, heparin-warfarin, and dipyridamole treatment were accompanied by relatively few serious side effects specifically attributable to the drugs. Mesangial IgA deposits had completely disappeared by the end of treatment in 7 of the 33 group 1 patients examined, but persisted in all 25 group 2 patients examined. These 7 patients showed clinical remission, defined as complete disappearance of proteinuria and hematuria with normal renal function and serum IgA levels, and marked improvement of the glomerular changes with minimal mesangial proliferation, minimal glomerular sclerosis, and no crescents at the end of treatment. Previous studies demonstrating therapeutic benefit have not described loss of mesangial IgA deposits. However, it is likely that administration of prednisolone, azathioprine, heparin-warfarin, and dipyridamole for 2 years does achieve remission in these patients. A controlled trial is currently in progress to compare the effects of prednisolone, azathioprine, heparin-warfarin, and dipyridamole with those of prednisolone alone in children with severe IgA nephropathy. Corticosteroids, immunosuppressive agents, antiplatelet drugs, and anticoagulation have been used singly or in combination in adult patients. However, clinical trials have not provided convincing data to show a beneficial effect of any drugs [120, 121]. The differences in the effects of combination therapy between our patients and adult patients may be due to differences in duration of the disease before treatment. Progression of IgA nephropathy leads to gradual resolution of mesangial hypercellularity and an increase of matrix, associated with the development of sclerosis [2]. The majority of patients with IgA nephropathy in our series are diagnosed early in the course of the disease, and the asymptomatic period before the discovery of urinary abnormalities is short. Patients with long-standing disease and extensive glomerulosclerosis are unsuitable for treatment. In our controlled trial average interval between onset or discovery of disease and start of treatment was 11 months, and no patient showed predominant matrix increase or extensive glomerulosclerosis. Early diagnosis and early treatment is very important in IgA nephropathy. We believe that treatment of adult patients with IgA nephropathy with prednisolone, azathioprine, heparinwarfarin, and dipyridamole early in the course of disease also prevents progression of the disease. References 1. Yoshikawa N, Ito H, Yoshiara S, Nakahara C, Yoshiya K, Hasegawa O, Matsuo T (1987) Clinical course of IgA nephropathy in children. J Pediatr 110: Yoshikawa N, Iijima K, Maehara K, Yoshiara S, Yoshiya K, Matsuo T, Okada S (1987) Mesangial changes in IgA nephropathy in children. Kidney Int 32: Yoshikawa N, Ito H, Nakamura H (1989) IgA nephropathy in children from Japan. 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Pediatr Nephrol 11: Rambausek MH, Waldherr R, Ritz E (1993) Immunogenetic findings in glomerulonephritis. Kidney Int 43:S3 S8 11. Schmidt S, Ritz E (1999) Genetic factors in IgA nephropathy. Ann Med Interne (Paris) 150: Julian BA, Quiggins PA, Thompson JS, Woodford SY, Gleason K, Wyatt RJ (1985) Familial IgA nephropathy. Evidence for an inherited mechanism of disease. N Engl J Med 312: Wyatt RJ, Rivas ML, Julian BA, Quiggins PA, Woodford SY, McMorrow RG, Baehler RW (1987) Regionalization in hereditary IgA nephropathy. Am J Hum Genet 41: Scolari F, Amoroso A, Savoldi S, Mazzola G, Prati E, Valzorio B, Viola BF, Nicola B, Movilli E, Sandrini M, Campanini M, Maiorca R (1999) Familial clustering of IgA nephropathy: further evidence in an Italian population. Am J Kidney Dis 33: McLean RH, Wyatt RJ, Julian BA (1984) Complement phenotypes in glomerulonephritis. Increased frequency of homozygous null C4 phenotypes in IgA nephropathy and Henoch- Schonlein purpura. 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