There are a few genes in which rare variants have been noted to dramatically lower blood cholesterol and other lipids, thus significantly reducing the progression of atherosclerosis with age. ANGPTL4 is one of them, and based on the work here, so is ANGPTL3. Atherosclerosis is caused by inappropriate reactions to forms of damaged lipids, leading to the formation of plaques that weaken and narrow blood vessels. Lowering overall lipid levels doesn't address these consequences, but it does reduce the input of damaged lipids to the disease process, hence the major industry associated with statin drugs and other methods of reducing lipids in the bloodstream.
In the near future, it seems likely that statins will be replaced by more effective and narrowly targeted genetic means of reducing cholesterol. This has started with therapies in development based on manipulation of PCSK9, producing larger effects than statins. Of interest, studies in recent years have suggested that blood lipids can be reduced to an extremely low level, a tenth of normal amounts or less, with no harm resulting to patients. This may well be a useful general enhancement that everyone undergoes once permanent genetic alteration of adults is a going concern.
People with naturally occurring mutations that cause a loss of function in the gene for ANGPTL3 have reduced blood triglycerides, LDL cholesterol, and risk of coronary heart disease, with no apparent detrimental consequences to their health. This makes the ANGPTL3 protein an attractive target for new heart disease drugs. Earlier studies found that single copies of inactivating mutations in ANGPTL3 are found in about one in every 250 people of European heritage; however, people with mutations in both copies of the gene are more rare.
Researchers assessed in a mouse model whether base editing - a variation of CRISPR genome editing that does not require breaks in the double-strand of DNA - might be used in humans one day to introduce mutations into ANGPTL3 to reduce blood lipid levels. The study took a three-part approach. First, the team injected normal mice with the base-editing treatment for the ANGPTL3 gene. After a week, sequencing of the ANGPTL3 target site in liver samples from the mice revealed a median 35 percent editing rate in the target gene and no off-target mutations. In addition, the mean levels of blood lipids were significantly lower in the treated mice by up to 30 percent compared to untreated mice.
Second, the researchers compared mice with the modified ANGPTL3 gene to those injected with a base-editing treatment for another liver gene, PCSK9, for plasma cholesterol and triglycerides. After a week, ANGPTL3 targeting caused a similar reduction in cholesterol but a much greater decline in triglycerides compared to targeting PCSK9. The PCSK9 protein is the target of currently available medications, including evinacumab, which has been shown to reduce cholesterol (but not triglycerides) as well as the risk of heart attack and stroke.
Third, they looked at how base editing of the ANGPTL3 gene performed in a mouse model of homozygous familial hypercholesterolemia (in which knocking out PCSK9 had little effect). After two weeks, the treated mice showed substantially reduced triglycerides (56 percent) and cholesterol (51 percent) compared to untreated mice. The researchers are now preparing to test CRISPR-based treatments against the human ANGPTL3 gene in human liver cells transplanted into mice. This will provide important information on efficacy and safety that will be needed before human trials can move forward.