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© Kyle & Kelly Adams
By the middle of 2014, the prospect of altering DNA to produce a genetically-modified human could move from science fiction to science reality. At some point between now and July, the UK parliament is likely to vote on whether a new form of in vitro fertilization (IVF) - involving DNA from three parents - becomes legally available to couples. If it passes, the law would be the first to allow pre-birth human-DNA modification, and another door to the future will open.

The procedure involves replacing mitochondrial DNA (mtDNA) to avoid destructive cell mutations. Mitochondria are the power plants of human cells that convert energy from food into what our cells need to function, and they carry their own DNA apart from the nuclear DNA in our chromosomes where most of our genetic information is stored. Only the mother passes on mtDNA to the child, and it occasionally contains mutations that can lead to serious problems.

According to the journal Nature, an estimated 1 in 5,000-10,000 people carry mtDNA with mutations leading to blindness, diabetes, dementia, epilepsy and several other impairments (the equivalent of 1,000 - 4,000 children born each year in the U.S.). Some of the mutations lead to fatal diseases, like Leigh Syndrome, a rare neurological disorder that emerges in infancy and progressively destroys the ability to think and move.

By combining normal mitochondrial DNA from a donor with the nucleus from a prospective mother's egg, the newborn is theoretically free from mutations that would eventually lead to one or more of these disorders. While never tried in humans (human cell research on mtDNA has so far been confined to the lab), researchers have successfully tested the procedure in rhesus monkeys.

Last March, the UK Human Fertilization and Embryology Authority wrapped up a lengthy study of safety and ethical considerations and advised parliament to approve the procedure in humans. According to New Scientist magazine, parliament is likely to vote on the procedure by July of this year. If the procedure overcomes that hurdle, it will still take several months to pass into law, but the initial vote will allow researchers to begin recruiting couples for the first human mtDNA replacement trials.

The U.S. is not nearly as close to approving mtDNA replacement as the UK seems poised to do; the U.S. Food and Drug Administration will start reviewing the data in earnest in February. Among the concerns on the table is whether the mtDNA donor mother could be considered a true "co-parent" of the child, and if so, can she claim parental rights?

Even though the donor would be contributing just 0.1 percent of the child's total DNA (according to the New Scientist report), we don't as yet have a DNA benchmark to judge the issue. Who is to say what percentage of a person's DNA must come from another human to constitute biological parenthood?

Other scientists have raised concerns about the compatibility of donor mtDNA with the host nucleus and believe the push to legalize human trials is premature. By artificially separating mtDNA from the nucleus, these researchers argue, we may be short-circuiting levels of genetic communication that we're only beginning to fully understand.

These are but two of many issues that this procedure will surface in the coming months. One thing is certain: we're rapidly moving into new and deeper waters, and chances are we're going to need a bigger boat.