Some people are born lucky. A rare few carry two broken copies of a gene called ANGPTL3, and the consequence is unusually low cholesterol and triglycerides for life, along with a reduced risk of the artery disease that causes most heart attacks. They do not seem to pay a price for it. That natural experiment has made ANGPTL3 one of the most tempting targets in cardiology. What if you could give everyone else the same broken gene?
A phase 1 trial published in the New England Journal of Medicine tried exactly that, and it did the editing inside living people. Fifteen adults with stubbornly high cholesterol or triglycerides, all already on the strongest lipid-lowering drugs they could tolerate, each received a single intravenous dose of a therapy called CTX310. The drug is a lipid nanoparticle carrying CRISPR-Cas9 machinery: messenger RNA coding for the Cas9 cutting enzyme, plus a guide RNA that steers it to ANGPTL3 in liver cells. Once inside the hepatocytes, the system cuts the gene and lets the cell's own repair errors disable it. The change is meant to be permanent.
The dose is where the story lives
The trial climbed through five dose levels, from 0.1 up to 0.8 milligrams per kilogram of body weight. The low doses did almost nothing. At 0.1 and 0.3 mg/kg, the average ANGPTL3 protein level actually drifted slightly upward, by around 9 percent, with wide swings between individuals. Then the curve broke. At 0.6 mg/kg the mean ANGPTL3 level fell by roughly a third. At 0.7 mg/kg it dropped 79.7 percent, and at 0.8 mg/kg it fell 73.2 percent. That is the signature of a therapy that needs to reach a threshold before enough liver cells are edited to matter.
These are protein numbers, not heart-attack numbers. The trial measured how much ANGPTL3 disappeared from the blood, which is a marker that the edit worked, not proof that anyone will live longer. ANGPTL3 normally blocks two enzymes that clear fat from the bloodstream, so knocking it out should let the body strip out more cholesterol and triglycerides. Whether that translates into fewer clogged arteries is a question for much larger and longer trials.
What a first-in-human safety read looks like
The main job of a phase 1 trial is not to prove the drug works. It is to find out whether it hurts people. On that front the results were mostly reassuring, with one hard caveat. No dose-limiting toxic effects tied to CTX310 showed up. Three participants had infusion-related reactions. One person, who already had elevated liver enzymes going in, saw those enzymes spike transiently to three to five times baseline around day 4, then settle back to normal by day 14. That kind of temporary liver bump is a familiar feature of nanoparticle drugs aimed at the liver.
Two serious adverse events occurred. One was a herniated spinal disk, which is hard to pin on a gene therapy. The other was a death. A participant who had received the lowest 0.1 mg/kg dose died suddenly 179 days after treatment. At that dose the ANGPTL3 level had barely moved, which argues against a direct effect of the editing, but a single death in a 15-person trial is exactly the kind of signal that gets watched closely as more people are enrolled.
Editing once, forever
What separates this from the cholesterol drugs already on pharmacy shelves is permanence. Statins, injectable antibodies and the newer RNA-based lipid drugs all work by being present in the body. Stop taking them and the effect fades. An edited gene does not wash out. That is the appeal for a lifelong condition where adherence is a constant problem, and it is also the reason for caution. A cut you cannot take back demands that the guide RNA hits ANGPTL3 and nothing else, and that the off-target editing checks hold up across many more patients than fifteen.
A few things worth keeping in mind. This was a small, open trial run mainly to gauge safety, so the efficacy figures come with large error bars and no control group. Follow-up was short, at least 60 days for everyone, which cannot capture the durability or the rare late risks that only show up in thousands of patients. And the study was funded by CRISPR Therapeutics, the company developing the drug. The concept has cleared a real bar here: you can dose an intravenous CRISPR therapy, edit a target gene in the human liver, and drive a large drop in a disease-linked protein. Turning that into a treatment is the harder decade of work that follows.
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