A 30-year-old woman was diagnosed with primary sclerosing cholangitis (PSC) during pregnancy at age 25 years. She was normocholesterolemic prior to the diagnosis of PSC (total cholesterol [TC], 188 mg/dL [to convert to millimoles per liter, multiply by 0.0259]). Following the diagnosis of PSC, she developed moderate hypercholesterolemia (representative TC, 256 mg/dL). She first noted the appearance of periorbital xanthelasmata 2 years after PSC diagnosis (Figure 1A). Approximately 6 months prior to referral, she developed marked worsening of biliary obstruction, deterioration of liver function, and clinical jaundice (aspartate aminotransferase, 145 U/L; alanine aminotransferase, 111 U/L; alkaline phosphatase, 726 U/L; and bilirubin, 6.7mg/dL), and she noted palmar xanthomata in the creases of her palms and fingers (Figure 1B).At the time of referral, she had severe hypercholesterolemia (TC, 832 mg/dL; triglycerides, 114 mg/dL [to convert to millimoles per liter, multiply by 0.0113]; and high-density lipoprotein cholesterol, 18 mg/dL; low-density lipoprotein cholesterol was not calculated). Medications at the time of referral were 1000 mg per day of ursodeoxycholic acid and 2 g of colestipol twice daily for symptomatic relief of pruritus. The majority of TC (719 mg/dL) consisted of free cholesterol (518 mg/dL) instead of the usual esterified cholesterol. Serum phospholipids levels were high (1186 mg/dL), while triglycerides were normal (97 mg/dL). Fast protein liquid chromatography analysis of serum lipoproteins, after ultracentrifugation to remove very-low-density lipoprotein, indicated the unique composition and distribution of lipid classes in a special form of dyslipidemia known as lipoprotein X (LpX), ie, high unesterified cholesterol and phospholipids in large lipid-containing particles. Based on results of analysis of genomic DNA in a custom targeted lipid gene resequencing panel, she had no rare mutations in 25 genes known to be associated with abnormal lipid traits (including LDLR, APOB, PSCK9, LDLRAP1, APOE, ABCG5, ABCG8, LIPA, and STAP1) and had APOE E3/E3 genotype. 1