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The experimental biotech startup Verve Therapeutics has paused the first phase of a buzzy human gene-editing trial due to strange side effects in a patient, according to a report from Bloomberg.

The trial in question — dubbed the "Heart-1" trial — is the company's attempt to use gene editing to reduce heart-attack-causing cholesterol in patients with familial hypercholesterolemia, a passed-down genetic disorder that causes buildups of LDL cholesterol in individuals. LDL is the bad kind of cholesterol, and familial hypercholesterolemia drastically heightens patients' risk of early heart attack and can lower life expectancy overall. Verve's proposed solution: inject "VERVE-101," a serum designed to lower fatty LDL molecules by genetically altering the cholesterol-managing PCSK9 gene, into trial participants' livers.

While promising tests on monkeys paved the way for Verve's much-anticipated human trial, however, Heart-1 has now hit another speed bump.

Late last year, it was revealed that a patient enrolled in Heart-1 had passed away from a heart attack. A panel of experts concurred that VERVE-101 wasn't responsible — according to Nature, experts concluded that the patient's death was the result of their already-advanced heart disease — but coupled with some gnarly reported side effects, the tragic incident did raise some alarm bells. And now, some particularly bad side effects experienced by another Heart-1 participant have raised enough safety concerns to pause the trial altogether.

Of the first six patients enrolled in the Heart-1 trial, according to Bloomberg, five saw their cholesterol levels decrease. Meanwhile, though, a sixth patient developed "abnormal liver enzymes" as well as thrombocytopenia, which is the medical term for a low blood platelet count in a patient. Thrombocytopenia is a serious condition that, in the worst cases, can lead to deadly internal bleeding.

Thankfully, the patient's troubling symptoms reportedly disappeared after a few days off the drug. And per Bloomberg, Verve says it believes the abnormalities were caused by the fatty lipids found in the serum used to deliver VERVE-101 into patients' livers. So, in other words, the researchers think it's a problem with the delivery method, rather than the gene-editing process itself.

According to Verve's website, 13 patients in total were treated with VERVE-101. But now, due to the abnormal side effects, the biotech startup is turning its focus to VERVE-102, a version of the gene-editing drug suspended in a different lipid serum. Per Verve, this delivery system was "well tolerated" by patients in a third-party clinical trial. This new trial, expectedly dubbed Heart-2, is set to start in the second quarter of this year.

Genetic heart conditions are an elusive and widespread problem, and if Verve can make a successful, one-and-done gene-editing treatment that alleviates some of these ailments, the company could change — and save — a lot of lives. While the Heart-1 trials did show some promise, though, it seems that Verve still has a way to go.

More on Heart-1: Patient Dies after Being Gene-Edited to Have Lower Cholesterol

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