PT - JOURNAL ARTICLE AU - Rasmus Waehrens AU - Bengt Zöller AU - Jan Sundquist AU - Kristina Sundquist AU - MirNabi Pirouzifard TI - A Swedish national adoption study of risk of irritable bowel syndrome (IBS) AID - 10.1136/bmjgast-2017-000156 DP - 2017 Oct 01 TA - BMJ Open Gastroenterology PG - e000156 VI - 4 IP - 1 4099 - http://bmjopengastro.bmj.com//content/4/1/e000156.short 4100 - http://bmjopengastro.bmj.com//content/4/1/e000156.full AB - Objectives Irritable bowel syndrome (IBS) clusters in families, but the familial risk of IBS has not been determined in adoptees. Studying adoptees and their biological and adoptive parents is a strong study design for separating genetic from environmental causes of familial clustering. This nationwide study aimed to separate the biological (genetic) and familial environmental contribution to the familial transmission of IBS.Methods We performed a family study for Swedish-born adoptees born from 1951 until 1995, and their biological and adoptive parents. The Swedish Multigeneration Register was linked to the Hospital Register (inpatients and outpatients) for the period 1964–2012 and the Swedish Outpatient Care Register for 2001–2012, and the Swedish Primary Healthcare register for 1989–2012. ORs for IBS were calculated for adoptees with an affected biological parent with IBS compared with adoptees without a biological parent with IBS. The OR for IBS was also determined in adoptees with an adoptive parent with IBS compared with adoptees without an adoptive parent with IBS. Heritability h 2 (±SE) was also determined.Results The ORs for IBS were 1.67 in adoptees (95% CI 1.06 to 2.62) of biological parents diagnosed with IBS. The ORs for IBS were 0.88 in adoptees (95% CI 0.48 to 1.63) of adoptive parents diagnosed with IBS. The heritability was 19.5%±8.5%.Conclusions The present study indicates that biological (genetic) factors are important for the familial clustering of IBS. The heritability calculated is in the range from twin studies and suggests that heritability may be estimated in adoptees.