US doctors first to 'edit' DNA of baby with rare genetic disease

Doctors in the US have become the first to use personalized gene-editing therapy on a child after he was diagnosed with a severe genetic disease that kills about half of those affected in early childhood.

International researchers have hailed the achievement as a major medical milestone, saying it demonstrates the potential to treat a range of devastating genetic diseases by “rewriting” the defective DNA of affected children immediately after birth.

Specialists at the Children's Hospital of Philadelphia and the University of Pennsylvania jumped into action as soon as the little boy was diagnosed and completed the complex development, manufacturing and safety testing of the personalized therapy within six months. The baby received his first dose of the specially formulated drug in February, as an intravenous injection, and two more doses in March and April. Doctors said he is doing well, but he will need close monitoring for the rest of his life.

The baby was born with a severe deficiency of CPS1, which affects only one in 1.3 million people. People with this condition lack a liver enzyme that converts ammonia, which is produced during the body’s natural breakdown of proteins, into urea so that it can be excreted in the urine. This leads to a buildup of ammonia, which can damage the liver and other organs, such as the brain.

While some patients with CPS1 deficiency can receive liver transplants, children with severe disease can suffer long before they are old enough for surgery.

In a paper published in the New England Journal of Medicine, doctors described the detailed process of identifying the specific mutations underlying the little patient’s disorder, developing and treating a gene-editing therapy to correct them, and testing the fatty nanoparticles needed to deliver the virus to the liver.

The therapy uses a powerful procedure called base editing, which enables the DNA code to be “rewritten” one letter at a time.

The little boy spent the first few months of his life in the hospital on a strict diet. But after treatment, doctors were able to increase the amount of protein in his diet and use fewer drugs to remove nitrogen from his body.

The details were presented at the annual meeting of the American Society of Gene & Cell Therapy, in New Orleans. The team of doctors said long-term monitoring is needed to see how well the therapy works, but the early signs are encouraging.

Follow NEWS.am Medicine on Facebook and Twitter