Scientists have identified more than 100 cases of "extreme inbreeding" in the UK as a result of a large genetic study looking into the health impacts of incest.

A study led by the University of Queensland of nearly half a million people in the UK found there were 125 people whose DNA suggested their parents were first-degree and second-degree relatives, which has been defined as "extreme inbreeding".

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Based on the data, the researchers estimate one in every 3652 people born in Britain with a European ancestry are inbred.

The study, published in journal Nature Communications, also found that in this cohort, extreme inbreeding was linked to a host of negative health outcomes.

They include reduced lung function, fertility, cognitive function and a general higher risk of disease.

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Dr Loic Yengo from UQ's Institute for Molecular Bioscience led the research and estimated the prevalence of extreme inbreeding using anonymous data from 456,414 individuals in the UK Biobank.

It looked for an unusually high amount of homozygosity, where a person's genome possesses two identical forms of a particular gene.

If this is significantly higher than normal, it can indicate a person's parents are closely related.

The American College of Medical Genetics says extreme inbreeding can be suspected if over 10 per cent of the DNA sequence in an individual has runs of homozygosity.

Health outcomes

"This is the first time that 10 per cent or more homozygosity in the genome has been quantified in a sample of nearly half a million people," said Dr Yengo.

Dr Yengo and colleagues confirmed previous findings suggesting that inbreeding leads to reduced stature, cognitive ability, lung function and fertility.

The participants with more than 10 per cent of their genome homozygous were approximately at 44 per cent higher risk of diagnosis of any kind of disease, compared to the rest of the sample.

“Our study reinforces that inbreeding has negative consequences on health and implies that the overall burden of disease in populations can be reduced by policies that minimise it," Dr Yengo said.