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The risks of marriage between cousins

In Brazil, children born from marriages between cousins are 4.16 times more likely to suffer from a rare genetic disease than children born to nonrelated parents, estimated a study by researchers from the Federal University of Rio Grande do Sul (UFRGS). In northeastern Brazil, the rate of consanguineous marriages was up to 13 times higher than in the South. The highest consanguinity coefficient, used to measure the likelihood of two people sharing variations (alleles) of the same gene, was found in the municipality of Lagoa, Paraíba (0.01182), and the lowest was in Belo Horizonte, Minas Gerais (0.00017). “The Northeast is home to a greater number of geographically and culturally isolated populations, such as riverside communities and quilombos, where marriage between relatives is still relatively common,” explains Luzivan Costa Reis of UFRGS, the lead author of the study. Unions between relatives were associated with a higher occurrence of genetic diseases than in the general population. The survey recorded 15 genetic diseases, of which two presented new mutations that could worsen symptoms: pycnodysostosis, which stunts growth and causes skull deformities; and Raine syndrome, which inflames the brain and damages the liver. To alleviate the problem, Reis says health professionals should improve their knowledge of medical genetics and make sure related couples are aware of the risks of their children being born with genetic diseases, in addition to recommending genetic counseling (International Journal of Medical Reviews, March).