Lipoprotein X in autoimmune liver disease causing interference in routine and specialist biochemical investigations

ABSTRACT Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are chronic, immune-mediated diseases which may be associated with the presence of lipoprotein X (LpX). This is an abnormal lipoprotein resulting in marked elevation of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) concentration. LpX is rich in free cholesterol (FC) and phospholipids (PL) and low in esterified cholesterol (CE). We describe two cases with florid lipid stigmata and presence of LpX. A patient with PBC presented with itching and palmar xanthomata. TC = 55.5 mmol/L, direct LDL-C = 14.9 mmol/L, high-density lipoprotein cholesterol (HDL-C) = 0.5 mmol and triglycerides (TG) = 11.3 mmol/L. Lipoprotein electrophoresis (LPE) showed the presence of LpX. An apolipoprotein E (Apo E) phenotype and genotype reported E2E3 and E3E3 isoforms, respectively. A patient with PSC presented with itchy eruptive xanthomata. TC = 22.8 mmol/L, calculated LDL-C = 21.7 mmol/L, HDL-C = 0.2 mmol/L and TG = 1.6 mmol/L. LPE was normal. Both Apo E phenotype and genotype showed E2E3 isoforms. Both patients were treated with statins and showed resolution of lipid stigmata and improvement of lipid parameters, including PL, FC and LpX. In the first case, Apo E phenotype showed an E3E3 phenotype like the genotype following the decrease in LpX. LpX can interfere with other routine biochemical measurements, falsely increase TC and LDL-C levels and in our patient with PBC, we believe that LpX interfered with Apo E phenotype analysis. This has not been previously described.