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Background: Glomerulonephritis clusters in families. However, infections are common inducers of glomerulonephritis and may also cluster in families. Studies of adoptees and their biological and adoptive parents may disentangle genetic from environmental causes of familial clustering. This is the first adoption study aimed to estimate the genetic contribution to the familial transmission of glomerulonephritis., Materials and Methods: We performed a family study for Swedish-born adoptees (born 1945-2000) and their biological and adoptive parents. The Swedish Multi-Generation Register was linked to the Hospital Inpatient Register for the period 1964-2012 and the Hospital Outpatient Register for 2001-2012. Odds ratio (OR) for glomerulonephritis was determined for adoptees with a biological parent with glomerulonephritis compared with adoptees without an affected biological parent. Similarly, the OR for glomerulonephritis was also determined in adoptees with an affected adoptive parent compared with adoptees without an affected adoptive parent. Heritability was estimated to be twice the observed tetrachoric correlation among adoptees and biological parents, under the assumption that only additive genetic factors contribute to the similarity between biological parents and adoptees., Results: The OR for glomerulonephritis was 4.08 in adoptees (95% confidence interval [CI] 1.79-9.27, P-value = 0.001) of biological parents diagnosed with glomerulonephritis. The OR for glomerulonephritis was 1.67 in adoptees (95% CI 0.53-5.26, P-value = 0.380) of adoptive parents diagnosed with glomerulonephritis. The heritability was 48%., Conclusion: Family history of glomerulonephritis in a biological parent is a risk factor for glomerulonephritis. The present study indicates that genetic factors play an important role in the aetiology of glomerulonephritis., (© 2019 Stichting European Society for Clinical Investigation Journal Foundation.)