Identification and functional characterization of a novel heterozygous missense variant in the LPL associated with recurrent hypertriglyceridemia-induced acute pancreatitis in pregnancy

Abstract

Background: Acute pancreatitis in pregnancy (APIP) is a life-threatening disease for both mother and fetus. To date, only three patients with recurrent hypertriglyceridemia-induced APIP (HTG-APIP) have been reported to carry rare variants in the lipoprotein lipase (LPL) gene, which encodes the key enzyme responsible for triglyceride (TG) metabolism. Coincidently, all three patients harbored LPL variants on both alleles and presented with complete or severe LPL deficiency.

Methods: The entire coding regions and splice junctions of LPL and four other TG metabolism genes (APOC2, APOA5, GPIHBP1, and LMF1) were analyzed by Sanger sequencing in a Han Chinese patient who had experienced two episodes of HTG-APIP. The impact of a novel LPL missense variant on LPL protein expression and activity was analyzed by transient expression in HEK293T cells.

Results: A novel heterozygous LPL missense variant, p.His210Leu (c.629A > T), was identified in our patient. This variant did not affect protein synthesis but significantly impaired LPL secretion and completely abolished the enzymatic activity of the mutant protein.

Conclusion: This report describes the first identification and functional characterization of a heterozygous variant in the LPL that predisposed to recurrent HTG-APIP. Our findings confirm a major genetic contribution to the etiology of individual predisposition to HTG-APIP.

Keywords: HTG-APIP; lipoprotein lipase (LPL) gene; missense variant; recurrent acute pancreatitis in pregnancy.

Figure 1

Timeline of the patient's two episodes of hypertriglyceridemia‐induced acute pancreatitis during pregnancy and her triglyceride (TG) levels. Note that (i) only some of the treatment procedures adopted have been illustrated and (ii) the patient was transferred to the Surgical Intensive Care Unit (SICU) at Nanjing on the 5 July 2017. AP, acute pancreatitis; EN, enteral nutrition; PN, parenteral nutrition

Figure 2

Computer tomography images of the patient taken during her second episode of hypertriglyceridemia‐induced acute pancreatitis during pregnancy. (a) Image taken upon the patient's admission to our service. Arrows indicate walled‐off pancreatic necrosis. (b) Image showing puncture and drainage of accumulated fluid in the affected pancreas under computer tomography guidance. Arrow indicates the puncture needle. (c) Image taken at discharge from our hospital. Peripancreatic fluid collection and necrosis were greatly reduced (arrows)

Figure 3

The novel LPL missense variant found in the patient. (a) Sanger sequencing electropherogram showing the heterozygous A > T substitution at position c.629 of the LPL (indicated by arrow) that would be predicted to change the CAC codon for histidine at position p.210 (underlined) to a CTC codon specifying leucine (i.e., p.His210Leu). Upper panel, patient. Lower panel, a healthy control. (b) Alignment of LPL amino acid sequences from a range of vertebrates illustrating the strict evolutionary conservation of histidine at residue 210

Figure 4

Western blot analysis of LPL expression in cell lysates (a) and media (b) of transfected human embryonic kidney (HEK293T) cells treated with heparin, whose role was to release LPL into the cell medium. In each panel, a representative blot is shown on the left while the LPL expression level in the p.His201Leu mutant vector‐transfected cells relative to that in the wild‐type vector‐transfected cells is shown on the right. Results were the average taken from three independent experiments. EV, empty vector; mut, mutant; wt, wild‐type. GPDAH was used as a loading control. *p < .05; **p < .01

Figure 5

Western blot analysis of LPL expression in cell lysates of transfected HEK293T cells without heparin treatment. A representative blot is shown on the left. The LPL expression level in the p.His201Leu mutant vector‐transfected cells relative to that in the wild‐type vector‐transfected cells is shown on the right. Results were the average taken from three independent experiments. EV, empty vector; mut, mutant; ns, not significant; wt, wild‐type. GPDAH was used as a loading control