A genetic ‘bad’ cholesterol protein has been flagged as a hidden problem in coronary heart disease (CHD), with current medication that treats low-density lipoproteins (LDL) having little effect on this particular variant.
In an observational study of 607 adults aged 60 and over, across 16 years, levels of lipoprotein(a) – known as Lp(a) – were both higher and more prevalent in those who had experienced a recurrent CHD event. While this doesn’t go as far as proving direct causation, it does highlight a link and shines a light on the need for Lp(a)-targeted therapies.
“This finding adds to growing evidence of a relationship between increased Lp(a) and the risk of recurrent CHD,” said lead author Leon Simons, associate professor at the School of Clinical Medicine, at the University of New South Wales Sydney. “It is well-established that people who have already experienced CHD are at very high risk of another event.
“Our new results indicate that new therapeutics in development that aim to reduce elevated Lp(a) might help prevent recurrent disease,” added Simons, who has been working on resolving the mysteries of this macromolecular complex for decades.
Lipoproteins, which also includes high-density lipoprotein (HDL), are the mechanisms by which cholesterol is moved around the bloodstream. HDL is generally considered the good, because it takes its piggybacked cholesterol to the liver, where it can be removed from the body.
LDLs, on the other hand, are responsible for cholesterol build-ups on artery walls. Lp(a), also found in human plasma, is assembled from LDL and a large hydrophilic glycoprotein called apolipoprotein(a). And it has structural elements from the lipoprotein and blood clotting systems linked to premature CHD and stroke. Earlier research has highlighted its role in heart attack and stroke.
Lp(a) levels are 75-95% heritable, and an estimated one in five people are born with the genetic coding for it. But while most adults in the US will be screened for cholesterol, a common blood test won’t check for Lp(a) levels; fewer than 1% will be screened for this variant to the LPA gene. (On the plus side, because it’s genetic, levels remain consistent throughout life so frequent testing isn’t required.)
It’s also particularly insidious, as high levels of Lp(a) are unlikely to present with any noticeable physical symptoms. For some, the first evidence of their elevated risk is a heart attack.
This study also revealed that adults with prior CHD, elevated Lp(a) levels of more than 355mg/L presented a 53% risk of recurrent heart attacks, when compared to those in the study with the lowest levels (below 50mg/L) during the 16-year period.
“Elevated Lp(a) is an important predictor of recurrent CHD in older people,” said Simons. “Upper reference Lp(a) levels of 500 mg/L or 300 mg/L both appear to be appropriate for identifying those at higher risk who may benefit from more intensive risk reduction interventions.”
Lp(a) levels may not yet be the target of medical intervention, but risk can be mitigated diet and exercise, which is recommended for anyone with all ‘bad’ cholesterol readings. Researchers hope more understanding into the role Lp(a) plays in cardiovascular disease will lead to medical intervention that can better target it.
“While current medications, such as statins, are often prescribed to lower ‘bad cholesterol’ in patients at higher risk of cardiovascular disease, these do not have any major or proven impact on elevated Lp(a),” Simons said. “But there is hope for the future – as some novel therapeutics that are designed to lower the levels of Lp(a) are currently in the advanced stages of clinical development.”
The research was published in the journal Current Medical Research & Opinion.