Consanguinity and its Medical ConsequencesProject thesis by Zanira Yaqub AnsariSchool of Medicine, University of OsloNovember 2008AbstractBackground: Consanguineous marriage, marriage between close biological relatives, is rare in Western societies. However, it is a common practise in several countries in the Middle East, North Africa and South Asia. Consanguineous marriage is also frequent in minorities in Norway emigrated from these countries. During the last decade, several studies have demonstrated that marriage between close biological relatives, especially first-cousin, increases the risk of various negative medical outcomes in the children.Material and methods: This thesis presents an overview of data from some of the main studies published on consanguineous marriage and its medical consequences, with a special focus on a report from the Norwegian Institute of Public Health in 2007 on consanguineous marriage in Norway – prevalence and medical consequences. The literature was retrieved from a search in Pubmed and Medline and from relevant references found in the articles.Results: Consanguineous marriage has been shown to be associated with increased fertility. However, it also leads to increased risk of stillbirth, infant death, congenital birth defects and mortality after age 1. The risk for all these conditions is almost double (The risk for stillbirth is less than doubled, being doubled for congenital birth defects and more than doubled for infant death) among children of first cousins or closer compared to unrelated parents. Furthermore, there is also an increased risk of recurrence of all the medical consequences mentioned if the first born is affected, compared to the recurrence risk among unrelated parents.Discussion: Consanguineous marriage is uncommon among people of Norwegian descent and is not a significant cause of death and disease in children on a population level. Conversely, among immigrant communities in Norway, originating from countries where consanguineous marriage is common, parental consanguinity is a common cause of death and disease in the children. From a public health perspective, a reduction in the prevalence of consanguineous marriage would most likely reduce the amount of death and disease among children in those communities. Moreover, parental consanguinity is probably an important cause of death and disease globally, and information about the risks and change of marital practice in high frequency countries will have a greater effect on public health.