Frameshift coding sequence variants in the LPL gene: identification of two novel events and exploration of the genotype-phenotype relationship for variants reported to date.

BACKGROUND: Lipoprotein lipase (LPL) is the rate-limiting enzyme for triglyceride hydrolysis. Homozygous or compound heterozygous LPL variants cause autosomal recessive familial chylomicronemia syndrome (FCS), whereas simple heterozygous LPL variants are associated with hypertriglyceridemia (HTG) and HTG-related disorders. LPL frameshift coding sequence variants usually cause complete functional loss of the affected allele, thereby allowing exploration of the impact of different levels of LPL function in human disease. METHODS: All exons and flanking intronic regions of LPL were Sanger sequenced in patients with HTG-related acute pancreatitis (HTG-AP) or HTG-AP in pregnancy. Previously reported LPL frameshift coding sequence variants were collated from the Human Gene Mutation Database and through PubMed keyword searching. Original reports were manually evaluated for the following information: zygosity status of the variant, plasma LPL activity of the variant carrier, disease referred for genetic analysis, patient's age at genetic analysis, and patient's disease history. SpliceAI was employed to predict the potential impact of collated variants on splicing. RESULTS: Two novel rare variants were identified, and 53 known LPL frameshift coding sequence variants were collated. Of the 51 variants informative for zygosity, 30 were simple heterozygotes, 12 were homozygotes, and 9 were compound heterozygotes. Careful evaluation of the 55 variants with respect to their clinical and genetic data generated several interesting findings. First, we conclude that 6-7% residual LPL function could significantly delay the age of onset of FCS and reduce the prevalence of FCS-associated syndromes. Second, whereas a large majority of LPL frameshift coding sequence variants completely disrupt gene function through their "frameshift" nature, a small fraction of these variants may act wholly or partly as "in-frame" variants, leading to the generation of protein products with some residual LPL function. Third, we identified two candidate LPL frameshift coding sequence variants that may retain residual function based on genotype-phenotype correlation or SpliceAI-predicted data. CONCLUSIONS: This study reported two novel LPL variants and yielded new insights into the genotype-phenotype relationship as it pertains to LPL frameshift coding sequence variants.

Analyses of familial chylomicronemia syndrome in Pereira, Colombia 2010-2020: a cross-sectional study.

BACKGROUND AND AIM: Familial chylomicronemia syndrome (FCS) is a rare autosomal recessive metabolic disorder caused by mutations in genes involved in chylomicron metabolism. On the other hand, multifactorial chylomicronemia syndrome (MCS) is a polygenic disorder and the most frequent cause of chylomicronemia, which results from the presence of multiple genetic variants related to chylomicron metabolism, in addition to secondary factors. Indeed, the genetic determinants that predispose to MCS are the presence of a heterozygous rare variant or an accumulation of several SNPs (oligo/polygenic). However, their clinical, paraclinical, and molecular features are not well established in our country. The objective of this study was to describe the development and results of a screening program for severe hypertriglyceridemia in Colombia. METHODS: A cross-sectional study was performed. All patients aged >18 years with triglyceride levels ≥500 mg/dL from 2010 to 2020 were included. The program was developed in three stages: 1. Review of electronic records and identification of suspected cases based on laboratory findings (triglyceride levels ≥500 mg/dL); 2. Identification of suspected cases based on laboratory findings that also allowed us to exclude secondary factors; 3. Patients with FCS scores <8 were excluded. The remaining patients underwent molecular analysis. RESULTS: In total, we categorized 2415 patients as suspected clinical cases with a mean age of 53 years, of which 68% corresponded to male patients. The mean triglyceride levels were 705.37 mg/dL (standard deviation [SD] 335.9 mg/dL). After applying the FCS score, 2.4% (n = 18) of patients met the probable case definition and underwent a molecular test. Additionally, 7 patients had unique variants in the APOA5 gene (c.694 T > C; p. Ser232Pro) or in the GPIHBP1 gene (c.523G > C; p. Gly175Arg), for an apparent prevalence of familial chylomicronemia in the consulting population of 0.41 per 1.000 patients with severe HTG measurement. No previously reported pathogenic variants were detected. CONCLUSION: This study describes a screening program for the detection of severe hypertriglyceridemia. Although we identified seven patients as carriers of a variant in the APOA5 gene, we diagnosed only one patient with FCS. We believe that more programs of these characteristics should be developed in our region, given the importance of early detection of this metabolic disorder.

In a Prediabetic Model, Empagliflozin Improves Hepatic Lipid Metabolism Independently of Obesity and before Onset of Hyperglycemia.

Recent studies suggest that treatment with SGLT-2 inhibitors can reduce hepatic lipid storage and ameliorate non-alcoholic fatty liver disease (NAFLD) development beyond their glycemic benefits. However, the exact mechanism involved is still unclear. We investigated the hepatic metabolic effect of empagliflozin (10 mg/kg/day for eight weeks) on the development of NAFLD and its complications using HHTg rats as a non-obese prediabetic rat model. Empagliflozin treatment reduced neutral triacylglycerols and lipotoxic diacylglycerols in the liver and was accompanied by significant changes in relative mRNA expression of lipogenic enzymes (Scd-1, Fas) and transcription factors (Srebp1, Pparγ). In addition, alterations in the gene expression of cytochrome P450 proteins, particularly Cyp2e1 and Cyp4a, together with increased Nrf2, contributed to the improvement of hepatic lipid metabolism after empagliflozin administration. Decreased circulating levels of fetuin-A improved lipid metabolism and attenuated insulin resistance in the liver and in peripheral tissues. Our results highlight the beneficial effect of empagliflozin on hepatic lipid metabolism and lipid accumulation independent of obesity, with the mechanisms understood to involve decreased lipogenesis, alterations in cytochrome P450 proteins, and decreased fetuin-A. These changes help to alleviate NAFLD symptoms in the early phase of the disease and before the onset of diabetes.

Metformin Affects Cardiac Arachidonic Acid Metabolism and Cardiac Lipid Metabolite Storage in a Prediabetic Rat Model.

Metformin can reduce cardiovascular risk independent of glycemic control. The mechanisms behind its non-glycemic benefits, which include decreased energy intake, lower blood pressure and improved lipid and fatty acid metabolism, are not fully understood. In our study, metformin treatment reduced myocardial accumulation of neutral lipids-triglycerides, cholesteryl esters and the lipotoxic intermediates-diacylglycerols and lysophosphatidylcholines in a prediabetic rat model (p < 0.001). We observed an association between decreased gene expression and SCD-1 activity (p < 0.05). In addition, metformin markedly improved phospholipid fatty acid composition in the myocardium, represented by decreased SFA profiles and increased n3-PUFA profiles. Known for its cardioprotective and anti-inflammatory properties, metformin also had positive effects on arachidonic acid metabolism and CYP-derived arachidonic acid metabolites. We also found an association between increased gene expression of the cardiac isoform CYP2c with increased 14,15-EET (p < 0.05) and markedly reduced 20-HETE (p < 0.001) in the myocardium. Based on these results, we conclude that metformin treatment reduces the lipogenic enzyme SCD-1 and the accumulation of the lipotoxic intermediates diacylglycerols and lysophosphatidylcholine. Increased CYP2c gene expression and beneficial effects on CYP-derived arachidonic acid metabolites in the myocardium can also be involved in cardioprotective effect of metformin.

Familial hypertriglyceridemia/polygenic hypertrigliceridemia. / Quilomicronemia familiar/quilomicronemia poligénica.

For decades, familial hypertriglyceridemia (HTG) has been considered a specific entity characterized by an increase in VLDL particles and an autosomal dominant inheritance pattern. In the genomics era, it has been proven that familial HTG, although it could be grouped in families, had a polygenic inheritance in which the phenotype would be determined by concomitant environmental factors. Hence its inclusion in the group of polygenic HTGs. Clinically, they are characterized by moderate HTG, with the consequent increase in cardiovascular risk, and in rare cases, by severe HTG with risk of acute pancreatitis. Treatment will be based on controlling environmental factors, implementing hygienic-dietetic measures and sometimes drugs, to reduce cardiovascular risk in moderate HTGs and acute pancreatitis risk in severe HTGs.

Management strategy and novel ophthalmological findings in neonatal severe hypertriglyceridemia: a case report and literature review.

BACKGROUND: Neonatal severe hypertriglyceridemia is rarely reported in the literature and there is no consensus for hypertriglyceridemia management at this age group. METHODS: The index case is a 4-week-old male infant with severe hypertriglyceridemia accidentally discovered during a circumcision surgery. His clinical and genetic characteristics and his successful management strategy are described. Furthermore, a detailed ophthalmological examination of the proband was conducted at 3 and 6 months of age using Fourier-domain-optical coherence tomography. RESULTS: Triglycerides level at presentation was extremely high 33,727 mg/dL (380.8 mmol/L). Two sessions of exchange blood transfusion on two consecutive days successfully reduced triglycerides to 382 mg/dL (4.3 mmol/L) with no adverse effects. The infant was discharged 3 days later. At discharge, the mother was advised to continue breastfeeding together with a medium-chain triglycerides formula. Satisfactory growth parameters and lipid profile values were obtained for a follow-up duration of 5 months with no reported attacks of acute pancreatitis. Lipoprotein lipase deficiency was confirmed by the detection of the LPL homozygous pathogenic variant c.805G > A; p.(Glu269Lys). Early corneal and macular lesions were detected and persisted on follow-up despite relatively good lipemic control. CONCLUSION: This case highlights the importance of the early discovery of severe hypertriglyceridemia during the neonatal period, which is needed for prompt management and prevention of severe complications. Rationalized breastfeeding can be tolerated within the diet plan of the disease with satisfactory outcomes. To our knowledge, it is the first study reporting early corneal and macular affection by severe hypertriglyceridemia in a neonate. Prolonged follow-up is needed to determine the extent of ophthalmological lesions.

Familial hypertriglyceridemia: an entity with distinguishable features from other causes of hypertriglyceridemia.

BACKGROUND: Familial hypertriglyceridemia (FHTG) is a partially characterized primary dyslipidemia which is frequently confused with other forms hypertriglyceridemia. The aim of this work is to search for specific features that can help physicians recognize this disease. METHODS: This study included 84 FHTG cases, 728 subjects with common mild-to-moderate hypertriglyceridemia (CHTG) and 609 normotriglyceridemic controls. All subjects underwent genetic, clinical and biochemical assessments. A set of 53 single nucleotide polymorphisms (SNPs) previously associated with triglycerides levels, as well as 37 rare variants within the five main genes associated with hypertriglyceridemia (i.e. LPL, APOC2, APOA5, LMF1 and GPIHBP1) were analyzed. A panel of endocrine regulatory proteins associated with triglycerides homeostasis were compared between the FHTG and CHTG groups. RESULTS: Apolipoprotein B, fibroblast growth factor 21(FGF-21), angiopoietin-like proteins 3 (ANGPTL3) and apolipoprotein A-II concentrations, were independent components of a model to detect FHTG compared with CHTG (AUC 0.948, 95%CI 0.901-0.970, 98.5% sensitivity, 92.2% specificity, P < 0.001). The polygenic set of SNPs, accounted for 1.78% of the variance in triglyceride levels in FHTG and 6.73% in CHTG. CONCLUSIONS: The clinical and genetic differences observed between FHTG and CHTG supports the notion that FHTG is a unique entity, distinguishable from other causes of hypertriglyceridemia by the higher concentrations of insulin, FGF-21, ANGPTL3, apo A-II and lower levels of apo B. We propose the inclusion of these parameters as useful markers for differentiating FHTG from other causes of hypertriglyceridemia.

Generation of a gene-corrected isogenic iPSC line (AHQUi001-A-1) from a patient with familial hypertriglyceridemia (FHTG) carrying a heterozygous p.C310R (c.928 T > C) mutation in LPL gene using CRISPR/Cas9.

Mutations in the LPL gene lead to familial hypertriglyceridemia (FHTG) . We have previously generated an iPSC line (AHQUi001-A) from a FHTG patient with a heterozygous p.C310R (c.928 T > C) mutation in the LPL gene. Here we genetically corrected the C310R mutation in the LPL gene using CRISPR/Cas9 technology to generate AHQUi001-A-1, which demonstrates normal karyotype, morphology, pluripotency, and potential to differentiate towards three germ layers.

Generation of the induced pluripotent stem cell(iPSC) line (AHQUi001-A) from a patient with familial hypertriglyceridemia (FHTG) carrying a heterozygous p.C310R (c.928 T > C) mutation in LPL gene.

Familial hypertriglyceridemia (FHTG) is an autosomal dominant disorder of lipoprotein metabolism, partly caused by mutations in the LPL gene, which encodes for the lipoprotein lipase. LPL deficiency can impair triglyceride hydrolysis which causes elevated plasma triglyceride levels. An induced pluripotent stem cell (iPSC) line was generated from peripheral blood mononuclear cells (PBMCs) of a 53 years-old male patient with FHTG who had a heterozygous p.C310R (c.928 T > C) mutation in the LPL gene based on the sendai virus delivery system. The cellular model will offer a powerful tool to investigate pathogenic mechanisms in FHTG and to develop a treatment for FHTG.

Clinical Practice Recommendations for Pediatric Dyslipidemia.

The leading cause of mortality in the United States is atherosclerotic cardiovascular disease (ASCVD). Atherosclerotic lesions begin during childhood and can place individuals at greater risk for ASCVD. Providers play an active role in preventing the progression of risk factors and future ASCVD events through appropriate clinical management of genetic and acquired dyslipidemias in the pediatric population. Health care providers need to be aware of current recommendations related to screening for dyslipidemia, lifestyle modification strategies, pharmacologic treatment, and guidelines for ongoing monitoring. Most patients with mild to moderate dyslipidemia can be managed by a primary care provider. It is imperative that providers understand the pathophysiology, screening methods, and available treatment options to effectively manage the condition. Frequent reassessment of family history and adherence to lifestyle modifications and pharmacologic interventions is essential for effective treatment.

Familial hypertriglyceridaemia and type 2 diabetes in pregnancy: prevention of acute pancreatitis with diet control and omega-3 fatty acids.

Acute pancreatitis in pregnancy is rare and can be caused by hypertriglyceridaemia. The management of hypertriglyceridaemia in pregnancy is complex and challenging as many lipid-lowering medications have been found to be unsafe in pregnancy. Patients who present with hypertriglyceridaemia commonly have multiple risk factors such as, diabetes, alcohol excess and hypothyroidism which pose a greater challenge to the management of these patients. We present a case of a 31-year-old woman presenting with familial hypertriglyceridaemia and type 2 diabetes mellitus in her third pregnancy. She had an uneventful pregnancy with the use of omega-3 fatty acids nutritional support, low-fat diet and tight glucose control with insulin and metformin.

FAMILIAL COMBINED HYPERLIPIDEMIA: CURRENT KNOWLEDGE, PERSPECTIVES, AND CONTROVERSIES.

Familial combined hyperlipidemia (FCHL) is the most prevalent primary dyslipidemia; however, it frequently remains undiagnosed and its precise definition is a subject of controversy. FCHL is characterized by fluctuations in serum lipid concentrations and may present as mixed hyperlipidemia, isolated hypercholesterolemia, hypertriglyceridemia, or as a normal serum lipid profile in combination with abnormally elevated levels of apolipoprotein B. FCHL is an oligogenic primary lipid disorder, which can occur due to the interaction of several contributing variants and mutations along with environmental triggers. Controversies surrounding the relevance of identifying FCHL as a cause of isolated hypertriglyceridemia and a differential diagnosis of familial hypertriglyceridemia are offset by the description of associations with USF1 and other genetic traits that are unique for FCHL and that are shared with other conditions with similar pathophysiological mechanisms. Patients with FCHL are at an increased risk of cardiovascular disease and mortality and have a high frequency of comorbidity with other metabolic conditions such as type 2 diabetes, non-alcoholic fatty liver disease, steatohepatitis, and the metabolic syndrome. Management usually requires lipid-lowering therapy directed toward reducing cholesterol and triglyceride concentrations along with cardiovascular risk protection. In recent years, the number of research studies on FCHL has been decreasing, mainly due to a lack of recognition of its impact on disease burden and comorbidity and the complexity in identifying probands for studies. This creates areas of opportunity to develop research for FCHL in epidemiology, genetics, pathophysiology, therapeutics, and cardiovascular risk management, which are discussed in depth in this review. (REV INVEST CLIN. 2018;70:224-36).

Chewing the Fat: A Case Report of Therapeutic Plasma Exchange in Hypertriglyceridemia-Induced Pancreatitis.

Hypertriglyceridemia is the third most common etiology of acute pancreatitis, but lacks a clear, evidence-based treatment approach. We present the case of a 25-year-old man who was admitted eleven times over seven years for hypertriglyceridemia-induced pancreatitis. In his first ten admissions, he received conservative therapy. During his eleventh admission, he underwent therapeutic plasma exchange with lowering of serum triglycerides from 5080 to 332 mg/dL. He was discharged on hospital day five and was noted to have persistently lowered triglyceride levels upon follow up. The case affirms plasma exchange's ability to rapidly lower serum triglyceride levels and provides future research opportunities for examining the long-term effects of this treatment.

Rare genetic variants with large effect on triglycerides in subjects with a clinical diagnosis of familial vs nonfamilial hypertriglyceridemia.

BACKGROUND: Most primary severe hypertriglyceridemias (HTGs) are diagnosed in adults, but their molecular foundations have not been completely elucidated. OBJECTIVE: We aimed to identify rare dysfunctional mutations in genes encoding regulators of lipoprotein lipase (LPL) function in patients with familial and non-familial primary HTG. METHODS: We sequenced promoters, exons, and exon-intron boundaries of LPL, APOA5, LMF1, and GPIHBP1 in 118 patients with severe primary HTG (triglycerides >500 mg/dL) and 53 normolipidemic controls. Variant functionality was analyzed using predictive software and functional assays for mutations in regulatory regions. RESULTS: We identified 29 rare variants, 10 of which had not been previously described: c.(-16A>G), c.(1018+2G>A), and p.(His80Arg) in LPL; p.(Arg143Alafs*57) in APOA5; p.(Val140Ile), p.(Leu235Ile), p.(Lys520*), and p.(Leu552Arg) in LMF1; and c.(-83G>A) and c.(-192A>G) in GPIHBP1. The c.(1018+2G>A) variant led to deletion of exon 6 in LPL cDNA, whereas the c.(-16A>G) analysis showed differences in the affinity for nuclear proteins. Overall, 20 (17.0%) of the patients carried at least one allele with a rare pathogenic variant in LPL, APOA5, LMF1, or GPIHBP1. The presence of a rare pathogenic variant was not associated with lipid values, family history of HTG, clinical diagnosis, or previous pancreatitis. CONCLUSIONS: Less than one in five subjects with triglycerides >500 mg/dL and no major secondary cause for HTG may carry a rare pathogenic mutation in LPL, APOA5, LMF1, or GPIHBP1. The presence of a rare pathogenic variant is not associated with a differential phenotype.

Tamoxifen precipitation of familial hypertriglyceridaemia: a rare cause of acute pancreatitis.

Drug-induced pancreatitis is uncommon, and is estimated to account for between 0.1% and 5% of cases. Tamoxifen is commonly used in the management of oestrogen receptor-positive breast cancer. We present a rare case of tamoxifen-related hyperlipidaemia resulting in repeated episodes of pancreatitis, which, to the best of our knowledge, has only been documented a few times in the literature. A 36-year-old woman with familial hypertriglyceridaemia presented with recurrent episodes of abdominal pain, modest increases in serum amylase levels and normal liver function tests. The patient had recently been diagnosed with breast carcinoma and was managed with wide local excision (WLE), adjuvant radiotherapy and tamoxifen. On each admission, the patient's symptoms were confirmed either biochemically and/or radiologically. Analysis of the case led to a diagnosis of precipitation of familial hypertriglyceridaemia from tamoxifen use resulting in pancreatitis. Management was altered with tamoxifen cessation and initiation of second-line hormonal therapy. Tamoxifen use needs consideration, especially in those with familial hyperlipidaemia.

The Regulatory Role of Nuclear Factor Kappa B in the Heart of Hereditary Hypertriglyceridemic Rat.

Activation of nuclear factor-κB (NF-κB) by increased production of reactive oxygen species (ROS) might induce transcription and expression of different antioxidant enzymes and also of nitric oxide synthase (NOS) isoforms. Thus, we aimed at studying the effect of NF-κB inhibition, caused by JSH-23 (4-methyl-N (1)-(3-phenyl-propyl)-benzene-1,2-diamine) injection, on ROS and NO generation in hereditary hypertriglyceridemic (HTG) rats. 12-week-old, male Wistar and HTG rats were treated with JSH-23 (bolus, 10 µmol, i.v.). After one week, blood pressure (BP), superoxide dismutase (SOD) activity, SOD1, endothelial NOS (eNOS), and NF-κB (p65) protein expressions were higher in the heart of HTG rats compared to control rats. On the other hand, NOS activity was decreased. In HTG rats, JSH-23 treatment increased BP and heart conjugated dienes (CD) concentration (measured as the marker of tissue oxidative damage). Concomitantly, SOD activity together with SOD1 expression was decreased, while NOS activity and eNOS protein expression were increased significantly. In conclusion, NF-κB inhibition in HTG rats led to decreased ROS degradation by SOD followed by increased oxidative damage in the heart and BP elevation. In these conditions, increased NO generation may represent rather a counterregulatory mechanism activated by ROS. Nevertheless, this mechanism was not sufficient enough to compensate BP increase in HTG rats.