Consanguinity, endogamy and genetic disease profiles in developing countries
Although marriage between close biological relatives is very common in much of Asia and Africa, and to a lesser degree in South America, representative prevalence data are poor or non-existent for almost 70% of the world's population. As a conservative estimate, some 900 million people live in countries where 20-50+% of marriages are contracted between spouses related as second cousins or closer, and a further 3,000 million are resident in regions with 1-10% consanguinity. Despite the many studies of consanguineous marriage that have been conducted, and the thousands of scientific papers that have been written on the subject, much misunderstanding remains and many important aspects of consanguinity have been inadequately investigated. There have been, for example, only limited efforts to determine why consanguineous marriage is widely preferential, or why particular types of consanguineous unions are chosen in different societies. In examining the effect of consanguinity on fertility and birth outcomes, little attempt has been made to adequately control for major non-genetic variables, such as maternal age, birth intervals and parental education, resulting in questionable conclusions. Similarly, the influence of random inbreeding has rarely been considered in medical genetic studies, and a large majority of reports have concentrated on infant and childhood morbidity and mortality, or on generally obscure single gene defects. Given the rapidly increasing life expectancy in most developing countries, there is a particular need to investigate the influence of consanguinity on adult-onset diseases. The purpose of this presentation is to encourage a more representative and balanced approach to the overall topic of consanguineous marriage, with the outcomes incorporated into community-acceptable education and genetic counselling programmes.