Hypercholesterolemia Due to Lipoprotein X: Case Report and Thematic Review

The liver is a key organ in lipid and lipoprotein metabolism, hence hepatic diseases often manifest as lipid disturbances. Cholestatic liver diseases are frequently associated with an important increase in total cholesterol at the expense of lipoprotein X (LpX), an abnormal lipoprotein isolated and characterized in the 1960s to 1970s in patients with obstructive jaundice. Lipoprotein X is rich in phospholipids, albumin, and free cholesterol, has a density similar to low-density lipoprotein (LDL), and a size similar to very low-density lipoprotein (VLDL), which has hampered its detection through routine laboratory tests. Unlike LDL, LpX has no apoB-100, so it is not removed from circulation via the LDL receptor, and it is not clear whether or not it can be atherogenic. Although LpX was initially described in patients with cholestasis, it has also been found in patients with genetic deficiency of lecithin-cholesterol acyltransferase (LCAT), in patients who receive lipid-rich parenteral nutrition and most recently in patients with graft versus host disease of the liver. In the presence of LpX, plasma total cholesterol can rise up to 1000 mg/dL, which may lead to the development of skin xanthomas and hyperviscosity syndrome. Treatment of LpX-dependent hypercholesterolemia with conventional hypolipidemic drugs is frequently ineffective, and definitive treatment relies on correction of the underlying cause of cholestasis. Here, we present the case of a patient with LpX-dependent hypercholesterolemia in the context of primary biliary cholangitis.