Gene-editing first for US doctors

Doctors have edited a patient’s genes in a world-first attempt to alter DNA from within the human body.

The doctors in California administered the experimental intravenous treatment, which provides the body with instructions to change DNA, on Brian Madeux, who suffers from Hunter’s syndrome.

People with Hunter’s syndrome are unable to break down long, sugary molecules called mucopolysaccharides. This leads to the molecules building up and causing brain and organ damage, and in severe cases it can be fatal. Sufferers require regular enzyme replacement therapy.

Madeux said he opted to take part in a trial as he was “in pain every second of the day”. The 44-year-old from Arizona underwent the treatment at UCSF Benioff Children’s Hospital in Oakland on Monday. It is too soon to know whether the pioneering procedure has worked, but if successful his DNA will now have the instructions for making the enzyme.

Madeux intravenously received billions of copies of a corrective gene and genetic tools to cut his DNA in a precise spot. They travel to the liver, where cells use the instructions to make molecular scissors and prepare the corrective gene. The DNA is cut, allowing the new gene to slip in. The new gene then directs the cell to make the enzyme the patient lacked.

“We cut your DNA, open it up, insert a gene, stitch it back up. Invisible mending,” said Dr Sandy Macrae, president of Sangamo Therapeutics, the Californian company testing this for two metabolic diseases and haemophilia. “It becomes part of your DNA and is there for the rest of your life.”

The technique has been carried out before but previous procedures have involved cells being taken out of the body to be edited before being returned. However this is impossible to do with cells within organs like the liver, heart or brain.

In this attempt, the genetic therapy has been designed so it becomes active only once it enters Madeux’s liver cells.