IgA nephropathy has a clear genetic component, but it is not a simple inherited disease caused by a single gene. Most cases arise from a combination of multiple genetic risk factors and environmental triggers. Between 2% and 17% of people with IgA nephropathy have a positive family history of kidney disease, meaning the vast majority of cases appear sporadically, without an obvious pattern of inheritance in the family.
How Strong Is the Genetic Influence?
The best evidence for a genetic role comes from twin studies. Researchers found that the heritability of galactose-deficient IgA1, the abnormal protein at the center of the disease, is around 80%. That number is strikingly high. In identical twins, the correlation in levels of this protein was 0.84, compared to 0.46 in fraternal twins. This gap is a classic signal that genetics, rather than shared environment, is the main driver of how much of this protein your body produces.
However, having high levels of this abnormal protein is not the same as having the disease. Plenty of people produce galactose-deficient IgA1 and never develop kidney problems. The disease itself requires additional steps, including an immune response to the abnormal protein and the resulting inflammation in the kidneys. Those additional steps involve their own mix of genetic and non-genetic factors.
The Genes Involved
More than 20 distinct regions of the genome have been linked to IgA nephropathy through large-scale genetic studies. Together, these known regions account for only about 6% to 8% of overall disease risk, which means many contributing genetic factors remain undiscovered. No single gene causes the disease on its own. Instead, each variant nudges risk up by a small amount, and their effects accumulate.
The strongest genetic signals sit in the HLA region, a stretch of DNA that governs how your immune system recognizes threats. Four independent signals within HLA have been confirmed, all involving genes that shape the immune response. Outside the HLA region, risk genes cluster around a few key biological themes:
- Complement regulation. A common deletion affecting two complement factor H-related genes on chromosome 1 alters how your body clears immune complexes from the blood.
- Mucosal defense. Variants near the alpha-defensin gene cluster on chromosome 8 affect antimicrobial proteins produced in the gut lining.
- Immune cell signaling. Genes involved in how white blood cells communicate and activate, including those at the ITGAM-ITGAX and CARD9 loci, have been linked to disease susceptibility.
Two genes deserve special attention because they directly explain the abnormal IgA1 protein. C1GALT1 and its partner C1GALT1C1 encode the molecular machinery that attaches galactose molecules to IgA1. When variants at these loci reduce expression of either gene, cells produce 30% to 50% more galactose-deficient IgA1. These two genetic signals alone explain about 7% of the variation in abnormal IgA1 levels.
Why Ethnicity Matters
IgA nephropathy is far more common in people of East Asian descent than in those of European ancestry, and rarest in people of African descent. In a Southern California study, the incidence among Asian patients was 2.75 per 100,000, compared to 0.7 per 100,000 overall and just 0.1 per 100,000 among Black patients. That is a nearly 28-fold difference between the highest and lowest groups.
This pattern maps onto the distribution of risk alleles, which follow an East-to-West and South-to-North gradient. Asian populations carry more of the known risk variants than European populations, which in turn carry more than populations of African ancestry. Part of the geographic difference in diagnosis rates also reflects screening practices. In Japan, for instance, routine urinalysis catches more cases early, leading to higher biopsy rates. But the genetic data confirm that true biological risk differs by ancestry, not just detection.
Genes and Environment Work Together
One of the more striking findings is that IgA nephropathy risk alleles correlate strongly with local pathogen diversity. Regions of the world with greater exposure to viruses, bacteria, protozoa, and helminths tend to have populations carrying more of the risk variants. The leading explanation is that these gene variants were historically beneficial because they enhanced mucosal immune defenses against intestinal pathogens. The trade-off is an overactive IgA response that, in some people, leads to kidney damage.
This gene-environment interaction plays out at the individual level too. Many of the susceptibility genes overlap with those involved in inflammatory bowel diseases, reinforcing the idea that gut barrier integrity and the mucosal immune response are central to whether someone with genetic predisposition actually develops IgA nephropathy. The host’s reaction to common bacteria, rather than exposure to any specific microbe, appears to be what tips the balance. Variations in immune receptors that recognize bacterial DNA have been correlated with more severe kidney damage in patients who do develop the disease, and genetic risk alleles significantly influence the age at which symptoms first appear.
What Family History Means for Risk
If you have a first-degree relative with IgA nephropathy, your risk is higher than the general population’s, but the absolute risk remains low. Studies consistently find that 2% to 17% of IgA nephropathy patients report a family history of kidney disease. One large single-center study put the figure at about 12%. Notably, patients with a positive family history tended to have worse kidney outcomes than those without, suggesting that familial cases may carry a heavier burden of risk variants.
Despite this, there is no routine genetic test recommended for family members of IgA nephropathy patients. The disease involves dozens of small-effect genetic variants rather than a single mutation that can be screened for, which makes panel-based genetic testing of limited practical value for predicting IgA nephropathy specifically. Genetic testing in kidney disease is most useful for conditions caused by single-gene mutations, such as polycystic kidney disease. For IgA nephropathy, the most practical step for family members is periodic urine testing to check for blood or protein, which can catch early signs of kidney involvement regardless of the underlying genetic architecture.