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

Association of lipoprotein lipase (LPL) gene variants with hyperlipidemic acute pancreatitis in southeastern Chinese population

Objective

The study aims to explore the relationship between lipoprotein lipase (LPL) variants and hyperlipidemic acute pancreatitis (HLAP) in the southeastern Chinese population.

Subjects and methods

In total, 80 participants were involved in this study (54 patients with HLAP and 26 controls). All coding regions and intron-exon boundaries of the LPL gene were sequenced. The correlations between variants and phenotypes were also analysed.

Results

The rate of rare LPL variants in the HLAP group is 14.81% (8 of 54), higher than in controls. Among the detected four variants (rs3735959, rs371282890, rs761886494 and rs761265900), the most common variant was rs371282890. Further analysis demonstrated that subjects with rs371282890 "GC" genotype had a 2.843-fold higher risk for HLAP (odds ratio [OR]: 2.843, 95% confidence interval [CI]: 1.119-7.225, p = 0.028) than subjects with the "CC" genotype. After adjusting for sex, the association remained significant (adjusted OR: 3.083, 95% CI: 1.208-7.869, p = 0.018). Subjects with rs371282890 "GC" genotype also exhibited significantly elevated total cholesterol, triglyceride and non-high-density lipoprotein cholesterol levels in all the participants and the HLAP group (p < 0.05).

Conclusion

Detecting rare variants in LPL might be valuable for identifying higher-risk patients with HLAP and guiding future individualised therapeutic strategies.

Approach to the Management of Hypertriglyceridemia Complicated With Acute Pancreatitis in Pregnancy: A Case Report

This is a case of a 32-year-old woman, Gravida 3 para 2, previous two cesarean sections, who presented to our emergency department at 24+3 weeks of gestation complaining of severe epigastric pain radiating to the back. She was diagnosed with severe hypertriglyceridemia complicated with acute pancreatitis and was managed by a multi-disciplinary team, which included obstetrics, gastroenterology, endocrinology, hematology, nutrition, and ICU team. Initially, conservative treatment was employed for her management. She was placed on nil per oral status and initiated on a normal saline infusion at a rate of 150 ml/hour, along with insulin infusion at 0.1 unit/kg/hour and dextrose (D5) at 80 ml/hour. Additionally, she received omeprazole, meropenem, clexane (40 mg once daily subcutaneous injection), iron, vitamin supplements, and analgesics as required. Subsequently, due to the failure of the initial conservative medical management, the patient was admitted to the ICU. Plasmapheresis was performed after the insertion of a vascath, using 3000 ml of albumin 5% as replacement fluid and oral calcium. Following this, she was prescribed Omacor (Omega 3) at a dosage of 2 grams orally twice daily, along with a low carbohydrate and fat diet, to manage her triglyceride levels. After the removal of the central line, her triglycerides increased to 14.3 mmol/L, leading to the initiation of fenofibrate at a daily dose of one tablet. With persistent elevation to 16.4 mmol/L, Lipitor at 40 mg once daily was introduced. Following this intervention, her triglyceride levels stabilized, and her overall condition improved. She was discharged at 25+1 weeks with a prescribed regimen, and scheduled follow-ups were arranged in the endocrine and obstetrics clinics. At 36 weeks of gestation, she presented to the emergency room with abdominal, back, and leg pain. Fetal distress, indicated by fetal tachycardia (170-180 bpm) on cardiotocography, prompted an urgent category 1 cesarean section, which proceeded without complications.

Loss-of-Function Homozygous Variant in LPL Causes Type I Hyperlipoproteinemia and Renal Lipidosis

Introduction

Lipoprotein lipase (LPL) is an important enzyme in lipid metabolism, individuals with LPL gene variants could present type I hyperlipoproteinemia, lipemia retinalis, hepatosplenomegaly, and pancreatitis. To date, there are no reports of renal lipidosis induced by type I hyperlipoproteinemia due to LPL mutation.

Methods

Renal biopsy was conducted to confirm the etiological factor of nephrotic syndrome in a 44-year-old Chinese man. Lipoprotein electrophoresis, apoE genotype detection, and whole-exome sequencing were performed to confirm the dyslipidemia type and genetic factor. Analysis of the 3-dimensional protein structure and in vitro functional study were conducted to verify variant pathogenicity.

Results

Renal biopsy revealed numerous CD68 positive foam cells infiltrated in the glomeruli; immunoglobulin and complement staining were negative; and electron microscopy revealed numerous lipid droplets and cholesterol clefts in the cytoplasm of foam cells. Lipoprotein electrophoresis revealed that the patient fulfilled the diagnostic criteria of type I hyperlipoproteinemia. The apoE genotype of the patient was the ε3/ε3 genotype. Whole-exome sequencing revealed an LPL (c.292G > A, p.A98T) homozygous variant with α-helix instability and reduced post-heparin LPL activity but normal lipid uptake capability compared to the wild-type variant.

Conclusion

LPL (c.292G > A, p.A98T) is a pathogenic variant that causes renal lipidosis associated with type I hyperlipoproteinemia. This study provides adequate evidence of the causal relationship between dyslipidemia and renal lesions. However, further research is needed to better understand the pathogenetic mechanism of LPL variant-related renal lesions.

The East Asian-specific LPL p.Ala288Thr (c.862G > A) missense variant exerts a mild effect on protein function

BACKGROUND

Lipoprotein lipase (LPL) is the key enzyme responsible for the hydrolysis of triglycerides. Loss-of-function variants in the LPL gene are associated with hypertriglyceridemia (HTG) and HTG-related diseases. Unlike nonsense, frameshift and canonical GT-AG splice site variants, a pathogenic role for clinically identified LPL missense variants should generally be confirmed by functional analysis. Herein, we describe the clinical and functional analysis of a rare LPL missense variant.

METHODS

Chinese patients with HTG-associated acute pancreatitis (HTG-AP) were screened for rare nonsense, frameshift, missense or canonical GT-AG splice site variants in LPL and four other lipid metabolism-related genes (APOC2, APOA5, GPIHBP1 and LMF1) by Sanger sequencing. The functional consequences of the LPL missense variant of interest were characterized by in vitro expression in HEK-293T and COS-7 cells followed by Western blot and LPL activity assays.

RESULTS

Five unrelated HTG-AP patients were found to be heterozygous for a rare East Asian-specific LPL missense variant, c.862G > A (p.Ala288Thr). All five patients were adult males, and all were overweight and had a long history of alcohol consumption. Transfection of LPL wild-type and c.862G > A expression vectors into two cell lines followed by Western blot analysis served to exclude the possibility that the p.Ala288Thr missense variant either impaired protein synthesis or increased protein degradation. Contrary to a previous functional study that claimed that p.Ala288Thr had a severe impact on LPL function (reportedly having 36% normal activity), our experiments consistently demonstrated that the variant had a comparatively mild effect on LPL functional activity, which was mediated through its impact upon LPL protein secretion (~ 20% reduced secretion compared to wild-type).

CONCLUSIONS

In this study, we identified the East Asian-specific LPL c.862G > A (p.Ala288Thr) missense variant in five unrelated HTG-AP patients. We demonstrated that this variant exerted only a relatively mild effect on LPL function in two cell lines. Heterozygosity for this LPL variant may have combined with alcohol consumption to trigger HTG-AP in these patients.

Digenic Inheritance and Gene-Environment Interaction in a Patient With Hypertriglyceridemia and Acute Pancreatitis

The etiology of hypertriglyceridemia (HTG) and acute pancreatitis (AP) is complex. Herein, we dissected the underlying etiology in a patient with HTG and AP. The patient had a 20-year history of heavy alcohol consumption and an 8-year history of mild HTG. He was hospitalized for alcohol-triggered AP, with a plasma triglyceride (TG) level up to 21.4 mmol/L. A temporary rise in post-heparin LPL concentration (1.5–2.5 times of controls) was noted during the early days of AP whilst LPL activity was consistently low (50∼70% of controls). His TG level rapidly decreased to normal in response to treatment, and remained normal to borderline high during a ∼3-year follow-up period during which he had abstained completely from alcohol. Sequencing of the five primary HTG genes (i.e., LPL, APOC2, APOA5, GPIHBP1 and LMF1) identified two heterozygous variants. One was the common APOA5 c.553G > T (p.Gly185Cys) variant, which has been previously associated with altered TG levels as well as HTG-induced acute pancreatitis (HTG-AP). The other was a rare variant in the LPL gene, c.756T > G (p.Ile252Met), which was predicted to be likely pathogenic and found experimentally to cause a 40% loss of LPL activity without affecting either protein synthesis or secretion. We provide evidence that both a gene-gene interaction (between the common APOA5 variant and the rare LPL variant) and a gene-environment interaction (between alcohol and digenic inheritance) might have contributed to the development of mild HTG and alcohol-triggered AP in the patient, thereby improving our understanding of the complex etiology of HTG and HTG-AP.

Dyslipemias and pregnancy, an update

During pregnancy there is a physiological increase in total cholesterol (TC) and triglycerides (TG) plasma concentrations, due to increased insulin resistance, oestrogens, progesterone, and placental lactogen, although their reference values are not exactly known, TG levels can increase up to 300mg/dL, and TC can go as high as 350mg/dL. When the cholesterol concentration exceeds the 95^th percentile (familial hypercholesterolaemia (FH) and transient maternal hypercholesterolaemia), there is a predisposition to oxidative stress in foetal vessels, exposing the newborn to a greater fatty streaks formation and a higher risk of atherosclerosis. However, the current treatment of pregnant women with hyperlipidaemia consists of a diet and suspension of lipid-lowering drugs. The most prevalent maternal hypertriglyceridaemia (HTG) is due to secondary causes, like diabetes, obesity, drugs, etc. The case of severe HTG due to genetic causes is less prevalent, and can be a higher risk of maternal-foetal complications, such as, acute pancreatitis (AP), pre-eclampsia, preterm labour, and gestational diabetes. Severe HTG-AP is a rare but potentially lethal pregnancy complication, for the mother and the foetus, usually occurs during the third trimester or in the immediate postpartum period, and there are no specific protocols for its diagnosis and treatment. In conclusion, it is crucial that dyslipidaemia during pregnancy must be carefully evaluated, not just because of the acute complications, but also because of the future cardiovascular morbidity and mortality of the newborn child. That is why the establishment of consensus protocols or guidelines is essential for its management.

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

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.

A Comprehensive Update on the Chylomicronemia Syndrome

The chylomicronemia syndrome is characterized by severe hypertriglyceridemia and fasting chylomicronemia and predisposes affected individuals to acute pancreatitis. When due to very rare monogenic mutations in the genes encoding the enzyme, lipoprotein lipase, or its regulators, APOC2, APOA5, GPIHBP1, and LMF1, it is referred to as the familial chylomicronemia syndrome. Much more frequently, the chylomicronemia syndrome results from a cluster of minor genetic variants causing polygenic hypertriglyceridemia, which is exacerbated by conditions or medications which increase triglyceride levels beyond the saturation point of triglyceride removal systems. This situation is termed the multifactorial chylomicronemia syndrome. These aggravating factors include common conditions such as uncontrolled diabetes, overweight and obesity, alcohol excess, chronic kidney disease and pregnancy and several medications, including diuretics, non-selective beta blockers, estrogenic compounds, corticosteroids, protease inhibitors, immunosuppressives, antipsychotics, antidepressants, retinoids, L-asparaginase, and propofol. A third uncommon cause of the chylomicronemia syndrome is familial forms of partial lipodystrophy. Development of pancreatitis is the most feared complication of the chylomicronemia syndrome, but the risk of cardiovascular disease as well as non-alcoholic steatohepatitis is also increased. Treatment consists of dietary fat restriction and weight reduction combined with the use of triglyceride lowering medications such as fibrates, omega 3 fatty acids and niacin. Effective management of aggravating factors such as improving diabetes control, discontinuing alcohol and replacing or reducing the dose of medications that raise triglyceride levels is essential. Importantly, many if not most cases of the chylomicronemia syndrome can be prevented by effective identification of polygenic hypertriglyceridemia in people with conditions that increase its likelihood or before starting medications that may increase triglyceride levels. Several new pharmacotherapeutic agents are being tested that are likely to considerably improve treatment of hypertriglyceridemia in people at risk.