Scientists Found 125 Cases of Extreme Inbreeding in the U.K.'s Biobank—and Studied the Associated Health Impacts

Researchers have identified 125 cases of extreme inbreeding in the U.K. Biobank—a huge genetic study including data from half a million people—allowing them to look at the health impacts of incest.

The team defined extreme inbreeding as the result of offspring produced by first or second degree relatives. This would include siblings, grandparents, aunts and uncles. It would not include the offspring of first cousins.

The negative health effects of inbreeding are well documented. Numerous studies in human, animal and plants have shown it increases the risk of mutations that can impact reproductive fitness. However, most human-based studies are confined to less extreme cases of inbreeding—for example, where first cousins have a child. This is because many countries allow this, meaning the representative sample is larger. Instances of extreme inbreeding are far lower—and the social stigma attached also means fewer people are likely to want to be involved in research about it.

By looking at data already in the biobank, researchers were able to get an insight into extreme inbreeding with limited bias. The team looked at data on 456,414 individuals from the biobank. These were people aged between 40-69 years when they submitted their genetic information between 2006 and 2010.

To find instances of extreme inbreeding, the researchers, led by Loic Yengo from The University of Queensland, looked for people who had more than 10 percent of the same DNA from both mother and father. This is based on runs of homozygosity, where stretches of the genome came from both parents. If a person has over 10 percent of homozygosity in their genome, extreme inbreeding can be suspected.

In doing this, the team found 125 cases of extreme inbreeding. From this, the team looked at the health impacts inbreeding may have had. Their findings are published in the journal Nature Communications.

The team found people there were a host of negative health effects associated with extreme inbreeding. They had a shorter stature, reduced cognitive ability and lower fertility. They also had reduced lung function and, overall, appeared to have a 44 percent increased risk of disease of any kind, in comparison to the general population.

Researchers said there are a number of limitations to their study. Generally, people who submitted their genetic information to the biobank were healthier than average and have a higher level of education: "Highly inbred individuals who suffer severe health consequences may be less likely to participate in a study such as the U.K. Biobank," the authors said in a statement. "Therefore, our estimate of the prevalence might be too low."

They found the prevalence of extreme inbreeding was one in 3,652 participants. Estimates for extreme inbreeding in England and Wales—gathered through police reports of incest offences—is one in 5,247.

"Our study reinforces that inbreeding has negative consequences on health-related outcomes and implies that the overall burden of disease in populations can be reduced by policies that minimize it," the researchers said.

Representative image showing DNA. Researchers have looked at extreme inbreeding within the U.K.'s Biobank and looked at the associated health impacts. iStock