New study sheds light on incidence of IgA nephropathy

A recent Kaiser Permanente study described the incidence of IgA nephropathy, an autoimmune kidney disease, nationally, as well as among people of different race and ethnicities. The study was published in the American Journal of Nephrology in November 2024.

“IgA nephropathy is a rare disease. Attempts to determine its incidence in the United States have relied on fragmented and limited data from small, homogeneous populations in specific geographic areas,” said lead author John J. Sim, MD, a nephrologist at the Kaiser Permanente Los Angeles Medical Center and a clinical researcher at the Kaiser Permanente Southern California Department of Research & Evaluation.  “We live in a large diverse country, so we wanted to use a sample from our racially and ethnically diverse population here at Kaiser Permanente Southern California to estimate the incidence of IgA nephropathy overall, and to determine incidence by specific ethnic and racial groups, including some understudied populations such as people who are Hispanic.”

The researchers assessed all adult Kaiser Permanente Southern California patients who had a kidney biopsy-proven diagnosis of IgA nephropathy between 2010 and 2021. The researchers used 2020 U.S. Census data to estimate a standardized rate of IgA nephropathy. Within the racially diverse population in Southern California, the study found an IgA nephropathy incidence of 1.7 cases per 100,000 person-years*. From that the researchers matched the U.S. population on age, sex, and race to the Southern California population to come up with an estimated incidence overall in the United States of 1.4 cases of IgA nephropathy per 100,000 person years.

The research also showed that Asian/Pacific Islander and Hispanic patients had the highest incidence rates of this disease.

IgA nephropathy, also known as Berger’s disease, is a chronic kidney disease that occurs when the immune system produces abnormally formed antibodies that build up in the kidneys. It can happen at any age, and researchers suspect genetic predispositions, and environmental triggers could be to blame. In the disease, antibodies, called immunoglobulin A (IgA), get trapped in the glomeruli, the kidney’s tiny blood vessels that filter blood. This prevents the glomeruli from filtering waste and excess water from the blood, causing the kidneys to leak blood and protein into the urine.

The study showed that of the 9,392 people who had their kidneys biopsied, 606 were identified with primary IgA nephropathy.

Incidence rates were:

  • Asian/Pacific Islander at 4.5 (per 100,000 person years)
  • Hispanic at 1.7
  • White at 1.2
  • Black at 0.6

“In addition to providing a more solid estimate for the overall incidence of IgA nephropathy and describing the racial/ethnic groups most at risk, our study emphasized the importance of early diagnosis,” Dr. Sim said. “IgA nephropathy is a progressive disease and first manifests with isolated blood in the urine or mild proteinuria. We observed that our IgA nephropathy population was diagnosed at advanced disease as evidenced by their kidney function and the amount of proteinuria at biopsy.   Earlier diagnosis and treatment can alter the course of the disease and delay or prevent kidney failure.”

This is one of several studies Dr. Sim is leading that look at issues related to glomerular diseases such as IgA nephropathy including:

  • Focal segmental glomerulosclerosis (FSGS), a kidney disease that causes scarring in the glomeruli, the kidney’s filtering units
  • Membranous glomerulonephritis (MGN), also known as membranous nephropathy, a kidney disease that causes inflammation and damage to the kidney’s filters
  • And other rare kidney diseases including polycystic kidney disease and APOL1 mediated kidney disease, a genetic condition that occurs when there are changes in the apolipoprotein L1 (APOL1) gene, which is highly prevalent among people of African ancestry

Dr. Sim discusses these findings on a ReachMD podcast. Listen here.

The study was supported by Otsuka Pharmaceutical Development and Commercialization, Inc., Princeton, NJ.

Co-authors on the study included Qiaoling Chen MS, Nancy Cannizzaro PhD, and John Chang MPH, of the Department of Research & Evaluation; Simran K. Bhandari MD, of the Kaiser Permanente Bernard J. Tyson School of Medicine; Ancilla W. Fernandes, PhD, and Cibele Pinto, PhD, of Otsuka Pharmaceutical Development and Commercialization, Inc., Princeton, NJ; and Asher D. Schachter MD, and Mohit Mathur MD, of Visterra, Inc., Waltham, MA. Dr. Sim is also affiliated with the Kaiser Permanente Bernard J. Tyson School of Medicine.

*Incidence is the rate of new cases during a specified period.  “Per 100,000 person years” means that for every 100,000 years of combined observation time across a group of people, a certain number of disease occurrences, such as IgA nephropathy, are happening. This statistic allows researchers to compare disease rates even when people are assessed for different lengths of time.