Lipoprotein X: A Cause for Misleading Levels of Low-Density Lipoprotein

Cholesterol metabolism plays a central role in the genesis of cardiovascular disease. Thus, it is critical that we understand the array of disorders that lead to its elevation.

Most commonly, high levels of low-density lipoprotein cholesterol (LDL-C) are a consequence of polygenic variants often in association with lifestyle contributions. There are other less-common causes for elevated LDL-C which must also be considered such as heterozygous and homozygous familial hypercholesterolemia (heterozygous familial hypercholesterolemia and homozygous familial hypercholesterolemia, respectively), as well as sitosterolemia. The management of these disorders varies depending on etiology. Lipoprotein X (LpX) is an ultra-rare etiology of elevated LDL-C that can be seen in patients with significant liver disease and cholestasis. LpX occurs when an abnormal lipoprotein accumulates in patients with liver dysfunction and both intrahepatic and extrahepatic cholestasis. Lipoprotein X disrupts the feedback loop to trigger cholesterol synthesis inhibition leading to LDL-C levels that can exceed 1,000 g/dL.

In this case study, we discuss a patient with LpX and consider the less-common causes of LDL-C elevation and how to manage them.