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Island life is famously idyllic, but it has long been known that islanders experience disproportionately high rates of certain rare genetically transmitted diseases. For example, the Faroe Islanders, who live on an archipelago in the North Atlantic Ocean, have a higher than average incidence of carnitine transporter deficiency (CTD), a condition that prevents the body from using some fat for energy. Is. Meanwhile, residents of Gran Canaria, an island off the northwest coast of Africa, are much more likely than average to have familial hypercholesterolemia, a condition where the liver can’t effectively process cholesterol.
A new paper in Nature Communications provides another such example. Jim Flett Wilson of the University of Edinburgh, who led the study, said people living on the Shetland Islands in northern Scotland have a one in 41 chance of carrying the gene variant that causes Batten disease, a life-threatening disease. There is limited neurodegenerative disease. Dr Wilson says the comparable rate elsewhere in the UK is one in 300.
Such increased risk is likely to be the result of genetic isolation. When members of a small population reproduce excessively with their peers, children become more likely to inherit disease-causing mutations (known as variants) from their parents over time. This, says Dr. Wilson, is due to a process known as random genetic drift, whereby some genetic variants become more common and others disappear. “This effect is magnified in small populations, in which there is little or no influx of new people to replenish the genetic pool,” he says.
Such separation need not be simply a product of encircling water. Dr Wilson’s new study also found “genetic islands” on the British mainland. For example, in Lancashire, researchers found that local people were more likely to have ten disease-causing variants – one of which is linked to Zellweger syndrome, a disease affecting the brain, liver and kidneys that occurs earlier in life. It can be fatal within a year. People in the area were 73 times more likely to have the variant. In south Wales, a variant responsible for a hereditary tendency to develop kidney stones later in life was 44 times more common, while in Nottinghamshire a variant causing a severe blistering skin disorder was 65 times more common than elsewhere .
Dr. Wilson says such genetic islands may arise from geography and culture, including a widely shared preference for individuals to choose spouses from the same community in which they grew up. Some such islands are already monitored by health authorities. For example, the NHS runs a screening program for people of Ashkenazi Jewish descent, because around one in 40 Ashkenazi Jewish people carry harmful variants of the BRCA gene that put them at risk of breast or ovarian cancer. This compares with about one in 260 people in the general British population.
The incidence of Batten-disease carriers among Shetland Islanders is similar to that of the BRCA variant among Jews, says Dr. Wilson, and yet no plans exist for a screening program there. He says reliance on a “cascade” model, whereby people are offered testing only after a family member is diagnosed, is only half as reliable in picking up cases as universal testing on demand. Unless such screening programs are implemented, the risk of islanders becoming isolated will double.
© 2024, The Economist Newspaper Limited. All rights reserved. From The Economist, published under license. Original content can be found at www.economist.com
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