Regulators in the United States are considering whether to permit trials of a controversial assisted-reproduction technique intended to help women to avoid passing certain genetic defects on to their children. On 22 October, the US Food and Drug Administration (FDA) is scheduled to meet in Silver Spring, Maryland, to discuss a method that could prevent transmission of defects in mitochondria - cellular components that contain a small amount of DNA - from mother to child. The defects, which can cause fatal developmental conditions, affect as many as 4,000 US births a year. The technique places nuclear DNA from the egg of a woman with a mitochondrial defect into a donated egg that has had its nuclear DNA removed, but contains healthy mitochondrial DNA. Once the egg is fertilized, the resulting embryo would, in a sense, have three parents, because the donor mitochondrial DNA is passed down along with the mother and fathers nuclear DNA.
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