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A NEW way in which hereditary human disease can strike has been found. A snippet of mitochondrial DNA can invade a cell’s nucleus, lodging itself in a gene vital to development. Leslie Biesecker of the National Human Genome Research Institute in Bethesda, Maryland, and his team found that this caused Pallister-Hall syndrome in one patient. They suspect that the mutation occurred in the father’s sperm or immediately after the patient was conceived in Ukraine, shortly after the Chernobyl accident (Human Genetics, vol 112, p 303). Radiation could have damaged the cell’s mitochondria.