Pediatric IgA nephropathy: clinical features at presentation and outcome for African-Americans and Caucasians

Epidemiology of IgA Nephropathy: A Global Perspective

IgA nephropathy (IgAN), or Berger's disease, is the most common primary glomerular disease worldwide, but varies largely in its geographic distribution. A systematic review of 1,619 publications from the five continental regions of the world was performed to assess the prevalence of IgAN in different worldwide regions and analyze factors responsible for geographic differences. All observational studies that described the prevalence and incidence data on glomerulonephritis were considered. IgAN is more frequent in Asian populations (45 cases per million population/y in Japan) than in Caucasians (31 cases per million population/y in France). These differences are owing to some relevant aspects: (1) systematic mass screening of urine in populations, as occurring in some Asian countries (Hong Kong, Japan, Korea, and Singapore), is not common in Western countries; (2) general practitioners and health care professionals in Western countries underestimate persistent microscopic hematuria and/or mild proteinuria in apparently healthy individuals causing late referral to a nephrologist; and (3) nephrologists adopt different indications for kidney biopsy in individuals with persistent urinary abnormalities. In addition, differences also are owing to the source of data, because the frequency of IgAN observed in a nephrology center with a high incidence of kidney biopsies is higher than in a regional renal biopsy registry that receives data from many centers. In conclusion, greater efforts should be made to diagnose IgAN earlier in individuals who manifest persistent microhematuria and/or mild proteinuria and to introduce less stringent indications for kidney biopsies. This preventive approach, followed by early therapy, may reduce the global burden of end-stage kidney disease caused by IgAN.

The genetics and immunobiology of IgA nephropathy

IgA nephropathy (IgAN) represents the leading cause of kidney failure among East Asian populations and the most frequent form of primary glomerulonephritis among Europeans. Patients with IgAN develop characteristic IgA1-containing immune complexes that deposit in the glomerular mesangium, producing progressive kidney injury. Recent studies define IgAN as an autoimmune trait of complex architecture with a strong genetic determination. This Review summarizes new insights into the role of the O-glycosylation pathway, anti-glycan immune response, mucosal immunity, antigen processing and presentation, and the alternative complement pathway in the pathogenesis of IgAN.

IgA nephropathy and Henoch-Schönlein purpura nephritis

PURPOSE OF REVIEW

IgA nephropathy and Henoch-Schönlein purpura nephritis are common glomerular disorders in pediatrics that can potentially progress to end-stage renal disease in some patients. This review summarizes our current understanding of the pathogenesis of these closely related conditions and discusses the rationale for development of diagnostic tests and prognostic markers. The review also presents the best data for long-term outcome, clinical markers of prognosis, and the results of randomized controlled trials.

RECENT FINDINGS

Our understanding of the defective galactosylation of O-linked glycans in the hinge region of human IgA1 and its role in the pathogenesis of IgA nephropathy and Henoch-Schönlein purpura nephritis has evolved over the past decade. This review discusses studies that suggest that demonstration of galactose-deficient IgA1 in the serum may become an important diagnostic tool for these conditions. Proteomic techniques for development of biomarkers for diagnosis and prognosis show promise. Although data from randomized controlled trials have failed to support the use of immunosuppressive agents in pediatric IgA nephropathy and Henoch-Schönlein purpura nephritis, recent data indicate that angiotensin converting enzyme inhibitor therapy is indicated for reduction of proteinuria.

SUMMARY

Childhood IgA nephropathy and Henoch-Schönlein purpura nephritis have the potential for serious morbidity, either during childhood or later in adulthood. In the future clinical tests will be used for noninvasive diagnosis and as markers for judging response to treatment, particularly in those individuals at highest risk for eventual progression to end-stage renal disease.

C1q nephropathy: features at presentation and outcome

The study population comprised all 20 patients followed since 1990 through December 2004 at the Le Bonheur Children's Medical Center with diagnosis of C1q nephropathy (55% boys; 60% African Americans). All were aged under 18 years at biopsy (mean 11.2 years, 65% aged 11 or over); the youngest presented at age 10 months and progressed to end-stage renal disease at 14 months. None had clinical or laboratory features of systemic lupus erythematosis or membranoproliferative glomerulonephritis. Clinical features assessed at diagnosis were age, gender, blood pressure, history of macroscopic hematuria, urinary protein to creatinine ratio, serum creatinine, estimated glomerular filtration rate, renal histology, and pattern for immunofluorescent reactants. At the time of biopsy 40% had nephrotic syndrome and 30% nephrotic range proteinuria without nephrotic syndrome. Three patients with nephrotic syndrome also had chronic renal insufficiency at diagnosis. The most common histological feature was focal segmental glomerulosclerosis in 40%, but 30% had minimal change lesion. Four patients, all with nephrotic syndrome at diagnosis, progressed to end-stage renal disease. Of the 12 patients not presenting with nephrotic syndrome, none had chronic renal insufficiency at last follow-up. Kidney survival was 94% and 78% at 1 and 5 years, respectively, in all patients and 88% and 49% in those presenting with nephrotic syndrome.