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Brian Madeux, 44, from Arizona, USA has been dealing with Hunter syndrome his entire life. He never expected to live past his early 20s and although he has surpassed his life expectancy, he experiences pain every second of the day.

A team of pioneering doctors in California proposed that Brian partake in an experimental trial that could change medical history forever. Brian was recently infused with the first gene-editing therapy directly in his bloodstream at Oakland’s UCSF Benioff Children’s Hospital.

The Mayo Clinic classifies Hunter syndrome as “a very rare, inherited genetic disorder caused by a missing or malfunctioning enzyme. Because the body doesn’t have enough of the enzyme to break down certain complex molecules, the molecules build up in harmful amounts. In Hunter syndrome, the buildup of massive amounts of these harmful substances eventually causes permanent, progressive damage affecting appearance, mental development, organ function and physical abilities.”

Brian’s condition was gravely affecting his quality of life and for some patients, Hunter syndrome can be fatal. Patients normally partake in enzyme replacement therapy to control the condition, but Mr. Madeux’s team of treating doctors took his case one step further and carried out a breakthrough experiment to rewrite Brian’s DNA and alter them with instructions to start correctly producing the enzyme his body needs.

While it is too early to confirm if the gene-editing has been successful, the experiment conducted on Brian marks a medical innovation that could pave the way for many conditions caused by issues found in human DNA in the future.

The therapy Brian’s doctors have attempted to conduct contains two molecular scissors, called zinc finger nucleases that especially cut the DNA at a precise spot creating an opening for a new piece of DNA, containing the desired instructions, to be inserted into the patient’s genetic code.

The genetic therapy is so cleverly designed that it will only become active when it gets inside Brian’s liver cells. Gene editing has never been done in this manner before. Previous attempts required that the cells be removed from the body, modified and then placed back in. Brian’s experimental therapy will take action within the body.

The BBC interviewed Dr Chester Whitley, one of the doctors working on the trial: “If works as well as it does in mice, this has huge ramifications. I’m very optimistic we have a both safe and efficacious way of providing gene therapy.”

He explained to the BBC that his long-term hope is to perform gene-editing shortly after birth, because an “untreated baby with Hunter’s syndrome loses 20 IQ points per year”.

Dr Sandy Macrae, from Sangamo Therapeutics, which designed the therapy also told the BBC that “for the first time, a patient has received a therapy intended to precisely edit the DNA of cells directly inside the body. We are at the start of a new frontier of genomic medicine.”

Brian Madeux remains hopeful and hopes that his experiment “will prolong my life and help scientists find cures for humankind”.