Dyslipidemia in Alagille Syndrome: Preliminary Results from the Multicenter ALPACA Study (Alagille syndrome Lipoprotein Profile And Cholesterol Assessment)."

Background: Alagille syndrome (ALGS) is a rare, autosomal dominant disease characterized by abnormal development of intrahepatic bile ducts, heart, arteries and kidneys due to disrupted Notch signaling. Although hypercholesterolemia is a hallmark feature of ALGS, lipid and lipoprotein profiles have been studied only in small patient cohorts. Aim: to characterize the lipid and lipoprotein profiles in ALGS and explore their relationship to disease phenotype with a particular focus on liver involvement. Secondary aims include assessing the impact of dyslipidemia on renal and cardiovascular outcomes. Methods: ALPACA is an observational, multicenter, cross-sectional study. The study population includes individuals of any age and sex with a diagnosis of ALGS. Clinical assessments, standardized biochemical and instrumental tests - including carotid intima-media thickness (IMT) and pulse wave velocity (PWV) measurements - were collected in a REDCap database. Blood samples from each center were processed for comprehensive lipid and lipoprotein profiling. In vitro assays were conducted to evaluate the effects of plasma lipids and Lipoprotein X (LpX) on a podocyte cell model. Descriptive and exploratory statistical analyses were conducted using IBM SPSS Statistics. Results: 25 subjects affected by ALGS (16 patients from the University of Padova and 9 from ISMETT, Palermo) were enrolled (56% male, 14/25), with a median age of 13 years (IQR: 4.0–16.75). The cohort included 20 patients with native livers and 5 liver transplant recipients. ALGS patients with native liver exhibited a distinctive lipid profile, characterized by high total cholesterol (TC, 42%), elevated free cholesterol (FC, 47.6%) and phospholipids (52%). Most patients also had elevated HDL (81%, median 68 mg/dl [54-115]) and LDL-cholesterol (LDL-C, 33%), though with a low median ApoB/LDL ratio (0.79 [0.64–0.99]). LpX was identified in 62% of the cohort and was absent in patients without cholestasis (p < 0.001). LpX-positive patients exhibited higher LDL-C levels (125.5 mg/dL vs. 68.5 mg/dL, p=0.004), FC/TC ratios (0.29 vs. 0.24, p=0.008), and median HDL (78 mg/dL [55.8–121]). LpX presence was associated with markers of cholestatic liver disease, including elevated conjugated bilirubin (p=0.005), bile salts (p=0.035), GGT (p=0.005), ALT (p=0.005), and APRI index (p=0.005). LCAT activity was generally reduced across the ALGS cohort, with significantly lower levels in LpX-positive patients (median 18 U/L, IQR: 7.5–26.7) compared to the LpX-negative group. A significant negative correlation was observed between LCAT activity and the FC/TC ratio (Pearson’s ρ = −0.636, p < 0.001), indicating a moderately strong inverse relationship. LCAT also showed a moderate negative correlation with bile acids (Pearson’s ρ = −0.50, p = 0.014). ALGS patients had IMT and PWV values exceeding the 95th percentile for age in 60% (9/15) and 38% (5/13) of cases, respectively. IMT and PWV values were not associated with dyslipidemia or LpX. The presence of LpX was not linked to proteinuria or chronic kidney disease. In vitro, plasma from LpX-positive patients induced significant podocyte necrosis (p=0.03). Plasma containing both LDL and LpX, further caused podocyte necrosis (p=0.030) and apoptosis (p=0.050), compared to LDL from LpX-negative patients. Additionally, LpX reduced the expression of NPHS2, encoding podocin (p=0.005). Conclusions. Cholestatic ALGS patients present with a distinctive LpX-driven dyslipidemia, characterized by elevated LDL-c, FC, HDL and phospholipids alongside the presence of LpX. This dyslipidemia reflects altered cholesterol homeostasis, likely due to increased FC release from the cholestatic liver and reduced LpX catabolism due to low LCAT activity. ALGS-associated dyslipidemia does not appear atherogenic. However, in vitro findings indicate a nephrotoxic role for LpX, highlighting its potential contribution to renal complications in ALGS.