Mutant gene now linked to Parkinson’s

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A recently discovered mutant gene causes nearly 20 per cent of Parkinson’s cases in Ashkenazi Jews and 30 per cent in North African Arabs—a surprising finding as genetics had been thought to play a small role in the disorder. The discovery will allow genetic counselling and early diagnosis in the affected groups, said Dr Susan B Bressman, a neurologist at the Albert Einstein College of Medicine and the leader of one of two studies published in the New England Journal of Medicine.

Although there is no way to prevent development of the disease, early diagnosis would allow expanded use of newer drugs to delay onset. The fact that the gene plays such a large role in these two groups suggests that other altered genes—perhaps even different variants of this—cause it in other ethnic groups. The mutant form,LRRK2, was linked to Parkinson’s in late 2004 by two groups, a US-Spanish team and one at the University of Tubingen in Germany. It was identified in members of a large family in the Basque region of Spain and the protein it produces was named dardarin, Basque for ‘‘tremor.’’ It was the third gene linked to the disorder. The two other genes produce unusual forms of Parkinson’s disease that have an earlier onset and a more aggressive course.

Bressman and her colleagues studied DNA from 120 Ashkenazi Jews with Parkinson’s disease and 317 healthy Jews. Ashkenazim, who account for an estimated 80 per cent of all Jews worldwide, are of recent Eastern European descent. They found that 18 per cent of the Jews with Parkinson’s carried the specific mutation, compared to only about 1 per cent of the Jewish population at large —meaning that the presence of the gene increased risk of developing Parkinson’s 15 to 20 times. Among patients with a family history of the disorder, 30 per cent carried the mutant gene. In a similar study led by Dr Alexa Brice and geneticist Suzanne Lesarge of the French research institute INSERM, about 30 per cent of North Africans with Parkinson’s were found to carry the specific mutation, compared with 3 per cent of the healthy subjects. Among North African Arabs, the incidence of the gene rose to 37 per cent. ‘‘The importance of genetics (in Parkinson’s disease) has been disputed for years and years,’’ Bressman said.

Most people thought it was primarily environmental in origin, perhaps from pesticides or some other toxin. Now, in at least two ethnic groups, genetics ‘‘is very important,’’ she said. Dr Neil Risch of the University of California, San Francisco, who participated in the Bressman study, said the mutation probably arose in a common ancestor of the Jews and Arabs several thousand years ago.

(Los Angeles Times)

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