Unravelling the links between consanguinity and genetic diseases Premium

Consanguinity is an age-old practice of marrying close relatives, still widely practised worldwide. It has shaped our cultural and genetic destiny, with evidence suggesting ancient civilisations practised it. Scientists use modern tools to quantify relatedness and study its effects on populations, uncovering new genes and genetic correlations. It has been linked to increased mortality and recessive diseases, but also offers a chance to eliminate deleterious alleles. Future research may uncover its role in common diseases and offer innovative solutions to mitigate risks.

In the rich tapestry of human ancestry and history, there is one genomic thread that weaves a particularly complex narrative. It connects our lineage through the many generations across our existence on the earth, and also defines our genetic vulnerabilities. This thread is none other than consanguinity: the practice of marrying close relatives, an age-old tradition that is still practised widely in several human societies worldwide.

According to one estimate, approximately 15-20% of the world’s population practises inbreeding, especially in Asia and West Africa.

Consanguinity has both shaped our cultural landscapes and left an indelible mark on our genetic destiny. It is a social as well as genetic construct. In the social context, it means marriage between individuals related by blood; in the genetic context, it means marriage between genetically related individuals, otherwise called inbreeding.

Using modern genomic tools, scientists can quantify the relatedness between two individuals as a percentage of the genetic material shared between them (identity by state) or by the genetic material in stretches of a chromosome that are identical to each other and are inherited from parents (identity by descent).

There is evidence to suggest that ancient human civilisations, like those of the Egyptians and Incas, among others, could have practised inbreeding or consanguinity. In particular, a body of historical and genetic evidence suggests that King Tutankhamun of Egypt was born to parents who were blood relatives.

We are still understanding the genetic and population effects of these practices. So it isn’t surprising that many key insights that are biomedically relevant – including discovery of new genes and genetic correlates – have been unearthed by looking through the lens of consanguinity. Many genetic concepts were found by studying the intricate tapestry of royal marriages in Europe and the diseases the individuals have. But since the democratisation of genetics and genomics, scientists have been able to study the general population in the same way, on a larger scale.

Scientists have extensively studied the level of inbreeding in various populations around the world. Some of the most well-studied populations in this regard include the Ashkenazi Jews and the Amish. With more than 4,000 endogamous groups – i.e. people marrying within the same caste/tribe or group – India has been a fertile ground for consanguinity.