Having high levels of high-density lipoprotein (HDL), the so-called “good” cholesterol, has been thought of as a good thing.

However, researchers have found a gene mutation in a small percentage of people with elevated levels of HDL that actually increases the risk of heart disease.

The findings from scientists at Perelman School of Medicine at the University of Pennsylvania were published today in the journal Science.

The mutation is found in only about six of every 10,000 people in the general population. It also appears to be specific to people of Ashkenazi Jewish descent.

However, Dr. Daniel J. Rader, the study’s senior author and chair of the school’s department of genetics, told Healthline that this is the first time research has shown a genetic mutation linked to high levels of HDL.

He added the study could eventually lead to the discovery of other mutations involving cholesterol and better treatments for certain conditions.

“It helps us understand the very complex relationship between elevated HDL and heart disease,” Rader said.

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What the Researchers Found

The Penn researchers studied lipid-modifying regions of the genomes of 328 people with noticeably elevated HDL.

They also compared these patients to a control group of people with lower HDL levels.

Rader said one person in the high HDL group had two copies of the gene mutation. Another 15 people had one copy.

One of the genes the researchers focused on was SCARB1, which encodes for Scavenger Receptor B1 (SR-B1), the major receptor for HDL on the surface of cells.

The ways all of these components function and interact is rather technical, so Rader offered a simple analogy to explain the importance.

HDL basically acts like dump trucks within your blood system. They drive around picking up plaque left along your artery walls by lower-density lipoproteins (LDL).

If too much plaque builds up, it can clog arteries and lead to heart attacks or other problems.

The HDL dump trucks transport the plaque to the liver, where it is deposited and eventually eliminated.

However, the gene mutation blocks the trucks from dumping their loads. That means full HDL trucks continue to drive around the blood system but can’t pick up any more LDL waste.

“They can’t do their job,” Rader said.

That means plaque can build up. The end result is the same as somebody who has low HDL and high LDL.

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What It Means

Rader said the research dispels the notion that simply raising a person’s HDL automatically lowers their risk of heart disease.

That may be true for most people but not for everybody.

For patients with the gene mutation, it might be more important for them to lower their LDL even more instead of raising their HDL, which isn’t functioning as it should.

Rader said the researchers want to continue to study the gene mutation so they can better understand how it works.

They also want to see if there are other gene mutations in high HDL, or if they can find mutations in people who have low HDL.

“If we are better able to tell people more about their HDL, I think that would be important,” he said.

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