A review of the reproductive consequences of consanguinity.

BACKGROUND: Consanguinity is the close union, sexual relationship or marriage between persons who have common biological ancestors usually up to about 2nd cousins. Contrary to general opinion consanguinity is quite common and is practiced worldwide. It is an important topic as while rates of consanguineous unions in certain society have decreased over time, rates have remained stable or increased in other societies with rates as high as 80.6% in some communities. Our aim was to conduct a review looking at general aspects of consanguinity and any published reproductive outcomes in literature. We also looked at possible future directions that could be relevant in the management of the consanguineous couple to help improve reproductive outcomes.
METHOD: We conducted a PUBMED, CINAHL, Web of Knowledge and Google Scholar search looking at articles on consanguinity. Consanguinity articles related to pregnancy and reproduction were searched using additional filters looking at our specific areas of interest. All relevant publications up to March 2015 were reviewed. Additional search for relevant articles pertaining to pre implantation genetic diagnosis for future directions in the management of the consanguineous couple was done. Most publications were found in books, on line articles and journals. Most were retrospective, population or cohort studies. RESULT: Consanguinity is practiced by up to 10% of the world's population with rates ranging from 80.6% in certain provinces in the Middle East to less than 1% in western societies. It predates Islam and has been practiced since Old Testament times. The most commonly cited reason for consanguinity is sociocultural and socioeconomic although it is also more common in certain religions. In areas where rates of Consanguinity are reducing urban migration and increasing education rates are thought to be contributory. Congenital malformations have long been established to be higher in consanguineous couples above the background rate (4.5% Vs 1%).Due to "Founder effect" or a common ancestor, Consanguinity is most commonly associated with Inborn errors of metabolism most of which are autosomal recessive. Consanguinity increases the incidence of multifactorial disorders such as diabetes, cardiovascular disorders, obesity and certain types of cancers. These may in turn affect reproductive outcomes. It may also affect fertility rates. Pregnancy outcomes like increased pregnancy wastages and preterm labor have been reported with consanguinity. Other studies produced conflicting evidence on its effect regarding outcomes like hypertensive disorders of pregnancy and Intrauterine growth restriction.
CONCLUSION: Consanguinity continues to be practiced worldwide and in some countries rates are increasing. The main reason for the practice appears to be sociocultural and socioeconomic although religious beliefs is a contributory factor. The most significant effects on reproductive outcomes are mostly due to autosomal recessive inherited conditions and inborn errors of metabolism. It also significantly increases the inheritance of certain multifactorial disorders like diabetes which may indirectly affect reproductive outcomes. In the future with the completion of the study of the whole human Genome and current advances in Pre implantation Genetic diagnosis and screening it may be possible to mitigate some of the adverse reproductive outcomes associated with consanguinity.