Severe hypertriglyceridaemia and pancreatitis in a patient with lipoprotein lipase deficiency based on mutations in lipoprotein lipase (LPL) and apolipoprotein A5 (APOA5) genes

Association of Apolipoprotein A5 Gene Variants with Hyperlipidemic Acute Pancreatitis in Southeastern China

Background: Apolipoprotein A5 (APOA5) is involved in serum triglyceride (TG) regulation. Several studies have reported that the rs651821 locus in the APOA5 gene is associated with serum TG levels in the Chinese population. However, no research has been performed regarding the association between the variants of rs651821 and the risk of hyperlipidemic acute pancreatitis (HLAP). Methods: A case-control study was conducted and is reported following the STROBE guidelines. We enrolled a total of 88 participants in this study (60 HLAP patients and 28 controls). APOA5 was genotyped using PCR and Sanger sequencing. Logistic regression models were conducted to calculate odds ratios and a 95% confidence interval. Results: The genotype distribution of the rs651821 alleles in both groups follow the Hardy-Weinberg distribution. The frequency of the "C" allele in rs651821 was increased in HLAP patients compared to controls. In the recessive model, subjects with the "CC" genotype had an 8.217-fold higher risk for HLAP (OR = 8.217, 95% CI: 1.023-66.01, p = 0.046) than subjects with the "TC+TT" genotypes. After adjusting for sex, the association remained significant (OR = 9.898, 95% CI: 1.176-83.344, p = 0.035). Additionally, the "CC" genotype was related to an increased TG/apolipoprotein B (APOB) ratio and fasting plasma glucose (FPG) levels. Conclusions: Our findings suggest that the C allele of rs651821 in APOA5 increases the risk of HLAP in persons from Southeastern China.

Clinical heterogeneity in monogenic chylomicronaemia

Chylomicronaemia accompanies hypertriglyceridaemia, usually due to a polygenic predisposition in combination with secondary risk factors. Monogenic chylomicronaemia represents a small subgroup of patients with hypertriglyceridaemia. This article describes three patients and illustrates the heterogeneity in the presentation of monogenic chylomicronaemia. The first case is a man with mild hypertriglyceridaemia who is a compound heterozygote for two variants in the LMF1 gene, without relevant medical history. The second case is a woman who is a double heterozygote of variants in the LPL and APOA5 genes. She experienced pancreatitis. The third case is a man, with recurrent pancreatitis attributed to severe hypertriglyceridaemia and homozygous for a variant in the APOC2 gene. This article highlights that in patients with hypertriglyceridaemia, the absence of pancreatitis or the presence of mild hypertriglyceridaemia does not exclude monogenic chylomicronaemia. Genetic screening should be considered in patients with unexplained or severe hypertriglyceridaemia, to determine appropriate treatment and follow-up.

Clinical features and functions of a novel Lpl mutation C.986A>C (p.Y329S) in patient with hypertriglyceridemia

OBJECTIVE

To investigate and assess the clinical features and functions of a new lipoprotein lipase (Lpl) gene mutation c.986A>C (p.Y329S) found in hypertriglyceridemia(HTG) patients from a Chinese family.

METHODS

Five members of a family with the proband were diagnosed with HTG were investigated, and fasting peripheral blood was collected . The plasma was then used to measure triglycerides (TG), total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein cholesterol (HDL-C), free fatty acids (FFA), and glucose tolerance. Following that, genomic deoxyribonucleic acid (DNA) was extracted from whole-blood samples using the QIAamp whole-blood DNA kit, and the coding exon regions and flanking regions of 95 dyslipidemia-related genes were captured using GenCap liquid-phase target gene capture technology. The activity of LPL and its mutation were then determined using cell assays, and the newly discovered LPL mutant was functionally analyzed. The binding site of fenofibrate and LPL, as well as the mutation, were subjected to predictive analysis.

RESULTS

The LPL gene's c.986A>C (p.Y329S) heterozygous mutation was discovered, and patients with the mutation had the typical phenotype of LPL deficiency and weakened LPL activity. Furthermore, this mutant has been treated with fenofibrate, and its triglyceride level is perfectly controlled and stable. The prediction analysis of the fenofibrate and LPL binding sites reveals that the wild-type system, Phe378 contributes most to the binding energy of fenofibrate. In the mutant system, Tyr394, which contributes the most to the binding energy of fenofibrate, the contribution of S329 is greater than that of Y329 (0.9∼0.7 kal/mol) . After Y329 is mutated, the hydrogen bond data of fenofibrate and LPL will also increase to quote H-bond diagrams.

CONCLUSIONS

A heterozygous mutation c.986A>C (p.Y329S) in exon 6 of Lpl gene occurs in the proband with familial HTG. Lpl c.986A>C (p.Y329S) mutation weakens the activity of the LPL, which may be the pathogenic mutation of HTG. In addition, The proband has been treated with fenofibrate and the triglyceride level is ideally controlled and stable. The prediction analysis of the fenofibrate and LPL binding site shows that the wild-type system, Phe378 contributes most to the binding energy of fenofibrate. In the mutant system, Tyr394, which contributes the most to the binding energy of fenofibrate, the contribution of S329 is greater than that of Y329 (0.9∼0.7 kal/mol). After Y329 is mutated, the hydrogen bond data of fenofibrate and LPL will also increase, which may be one of the reasons why the mutation has no effect on the therapeutic effect of fenofibrate.

Simple and rapid real-time monitoring of LPL activity in vitro

Since elevated plasma triglycerides are an independent risk factor for cardiovascular diseases, lipoprotein lipase (LPL) is an interesting target for drug development. However, investigation of LPL remains challenging, as most of the commercially available assays are limited to the determination of LPL activity. Thus, we focused on the evaluation of a simple in vitro real-time fluorescence assay for the measurement of LPL activity that can be combined with additional cell or molecular biological assays in the same cell sample. Our procedure allows for a more comprehensive characterization of potential regulatory compounds targeting the LPL system.

The presented assay procedure provides several advantages over currently available commercial in vitro LPL activity assays:1.

12-well cell culture plate design for the simultaneous investigation of up to three different compounds of interest (including all assay controls).

2.

24 h real-time acquisition of LPL activity for the identification of the optimal time point for further measurements.

3.

Measurement of LPL activity can be supplemented by additional cell or molecular biological assays in the same cell sample.