LOS ANGELES - In a groundbreaking medical milestone, US researchers have successfully developed and delivered a personalized gene-editing therapy to treat an infant suffering from a rare and life-threatening genetic disorder.

The child, diagnosed shortly after birth with carbamoyl phosphate synthetase 1 (CPS1) deficiency, became the first human to receive a customized CRISPR-based treatment targeting the root cause of the condition, according to a release of the US National Institutes of Health (NIH) on Thursday.

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CPS1 deficiency is characterized by an inability to fully break down byproducts from protein metabolism in the liver, causing ammonia to build up to toxic levels in the body. It can cause severe damage to the brain and liver, according to NIH.

A team of researchers at the Children's Hospital of Philadelphia and the Perelman School of Medicine at the University of Pennsylvania developed the customized therapy using the gene-editing platform CRISPR.

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They corrected a specific gene mutation in the baby's liver cells that led to the disorder. CRISPR is an advanced gene editing technology that enables precise changes to DNA inside living cells.

This is the first known case of a personalized CRISPR-based medicine administered to a single patient and was carefully designed to target non-reproductive cells so changes would only affect the patient, according to NIH.

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The child initially received a very low dose of the therapy at six months of age, then a higher dose later. The research team saw signs that the therapy was effective almost from the start, according to NIH. Their findings were published Thursday in The New England Journal of Medicine.

"As a platform, gene editing -- built on reusable components and rapid customization -- promises a new era of precision medicine for hundreds of rare diseases, bringing life-changing therapies to patients when timing matters most: Early, fast, and tailored to the individual," said Joni L. Rutter, director of NIH's National Center for Advancing Translational Sciences.