Spectrum of mutations of the LPL gene identified in Italy in patients with severe hypertriglyceridemia

Germline variant analysis from a cohort of patients with severe hypertriglyceridemia in Brazil

Hypertriglyceridemia (HTG) is a common dyslipidemia associated with an increased risk of cardiovascular disease and pancreatitis. It is well stablished that the severe cases of disease often present with an underlying genetic cause. In this study, we determined the frequency and variation spectrum of genes involved in the triglyceride metabolism in a series of Brazilian patients with severe HTG. A total of 212 patients with very high HTG, defined with fasting triglycerides (TG) ≥ 880 mg/ dL, that underwent a multi-gene panel testing were included in this research. Germline deleterious variants (i.e. Pathogenic/Likely Pathogenic (P/LP) variants) were identified in 28 out of 212 patients, reflecting an overall diagnostic yield of 13% in our cohort. Variants of unknown significance (VUS) were identified in 87 patients, and represent 80% of detected variants in this dataset. We confirm the LPL as the most frequently mutated gene in patients with severe HTG, and we had only one suspected case of familial chylomicronemia syndrome, caused by a homozygous variant in LMF1, in our cohort. Notably, we report 16 distinct and novel variants (P/LP and VUS), each of them representing a single case, not previously reported in any public databases or other studies. Our data expand our knowledge of genetic variation spectrum in patients with severe HTG in the Brazilian population, often underrepresented in public genomic databases, being also a valuable clinical resource for genetic counseling and healthcare programs in the country.

Clinical characterization and mutation spectrum of patients with hypertriglyceridemia in a German outpatient clinic

BACKGROUND

Severe hypertriglyceridemia (HTG) has predominantly multifactorial causes (MCS). Yet a small subset of patients have the monogenetic form (FCS). It remains a challenge to distinguish patients clinically, since decompensated MCS might mimic FCS´s severity. Aim of the current study was to determine clinical criteria that could sufficiently distinguish both forms as well as to apply the FCS score proposed by Moulin and colleagues.

METHODS

We retrospectively studied 72 patients who presented with severe HTG in our clinic during a time span of seven years and received genetic testing. We classified genetic variants (ACMG-criteria), followed by genetic categorization into MCS or FCS. Clinical data were gathered from the medical records and the FCS score was calculated for each patient.

RESULTS

Molecular genetic screening revealed eight FCS patients and 64 MCS patients. Altogether, we found 13 pathogenic variants of which four have not been described before. The FCS patients showed a significantly higher median triglyceride level compared to the MCS. The FCS score yielded a sensitivity of 75% and a specificity of 93.7% in our cohort, and significantly differentiated between the FCS and MCS group (p<0.001).

CONCLUSIONS

In our cohort we identified several variables that significantly differentiated FCS from MCS. The FCS score performed similar to the original study by Moulin, thereby further validating the discriminatory power of the FCS score in an independent cohort.

Genetic and clinical characteristics of patients with lipoprotein lipase deficiency from Slovenia and Pakistan: case series and systematic literature review

Introduction

Hypertriglyceridemia (HTG) is a complex disorder caused by genetic and environmental factors that frequently results from loss-of-function variants in the gene encoding lipoprotein lipase (LPL). Heterozygous patients have a range of symptoms, while homozygous LPL deficiency presents with severe symptoms including acute pancreatitis, xanthomas, and lipemia retinalis.

Methods

We described the clinical characteristics of three Slovenian patients (an 8-year-old female, an 18-year-old man, and a 57-year-old female) and one Pakistani patient (a 59-year-old male) with LPL deficiency. We performed next-generation sequencing (NGS) targeting all coding exons and intron-exon boundaries of the LPL gene, and Sanger sequencing for variant confirmation. In addition, we performed a systematic literature review of all cases with three identified variants and described their clinical characteristics.

Results

Two Slovenian patients with a heterozygous pathogenic variant NM_000237.3:c.984G>T (p.Met328Ile) were diagnosed within the first three years of life and had triglyceride (TG) values of 16 and 20 mmol/L. An asymptomatic Pakistani patient with TG values of 36.8 mmol/L until the age of 44 years, was identified as heterozygous for a pathogenic variant NM_000237.3:c.724G>A (p.Asp242Asn). His TG levels dropped to 12.7 mmol/L on dietary modifications and by using fibrates. A Slovenian patient who first suffered from pancreatitis at the age of 18 years with a TG value of 34 mmol/L was found to be homozygous for NM_000237.3:c.337T>C (p.Trp113Arg).

Conclusions

Patients with LPL deficiency had high TG levels at diagnosis. Homozygous patients had worse outcomes. Good diet and medication compliance can reduce severity.

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.

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.

Genotypic and phenotypic features of dyslipidemia in a sample of pediatric patients in China

BACKGROUND

Dyslipidemia, especially hypercholesterolemia is of significant clinical interest. Precise diagnosis is not paid enough attention to about the management of pediatric patients with hypercholesterolemia, which is especially apparent in China. Given this, we designed this study to confirm the specific molecular defects associated with hypercholesterolemia using whole-exome sequencing (WES) to be helpful for precise diagnosis and treatment.

METHODS

Pediatric patients were enrolled using specific criteria and their clinical information were recorded for later evaluation in conjunction with the WES completed for each of these patients.

RESULTS

Our criteria allowed for the initial enrollment of 35 patients, 30 of whom (aged 1.02-12.99 years) underwent successful genetic sequencing and clinical investment. Positive results were obtained in 63.33% (19/30) of these patients. We identified 25 variants in 30 pediatric patients with persistent hypercholesterolemia, seven of them were novel and variants in LDLR and ABCG5/ABCG8 ranks first and second, respectively. Further analysis revealed that the levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), apolipoprotein B (ApoB) and lipoprotein (a) were higher in patients with positive genetic results.

CONCLUSION

Our study enriched the genetic and phenotypic spectra for hypercholesterolemia in young patients. Genetic testing is important for the prognostics and treatment of pediatric patients. Heterozygous ABCG5/8 variants may be underestimated in pediatric patients with hypercholesterolemia.

Nutritional Treatment of Hypertriglyceridemia in Childhood: From Healthy-Heart Counselling to Life-Saving Diet

Hypertriglyceridemia is a lipid disorder with a varying prevalence; it is very common if we consider triglyceride plasma values slightly above the threshold, whereas it is extremely rare if only severely elevated triglyceride levels are considered. In most cases, severe forms of hypertriglyceridemia are caused by genetic mutations in the genes that regulate triglyceride metabolism, thus leading to extreme triglyceride plasma values and acute pancreatitis risk. Secondary forms of hypertriglyceridemia are usually less severe and are mainly associated with weight excess, but they can also be linked to liver, kidney, endocrinologic, or autoimmune diseases or to some class of drugs. Nutritional intervention is the milestone treatment for patients with hypertriglyceridemia and it has to be modulated on the underlying cause and on triglyceride plasma levels. In pediatric patients, nutritional intervention must be tailored according to specific age-related energy, growth and neurodevelopment requests. Nutritional intervention is extremely strict in case of severe hypertriglyceridemia, whereas it is similar to good healthy nutritional habits counselling for mild forms, mainly related to wrong habits and lifestyles, and to secondary causes. The aim of this narrative review is to define different nutritional intervention for various forms of hypertriglyceridemia in children and adolescents.

Infertility and treatments used have minimal effects on first-trimester placental DNA methylation and gene expression

OBJECTIVE

To determine whether deoxyribonucleic acid (DNA) methylation alterations exist in the first-trimester human placenta between conceptions using fertility treatments and those that do not and, if so, whether they are the result of underlying infertility or fertility treatments. We also assessed whether significant alterations led to changes in gene expression.

DESIGN

We compared DNA methylation of the first-trimester placenta from singleton pregnancies that resulted in live births from unassisted, in vitro fertilization (IVF), and non-IVF fertility treatment (NIFT) conceptions using the Infinium MethylationEPIC BeadChip array. Significant CpG sites were compared with corresponding ribonucleic acid sequencing analysis in similar cohorts to determine whether methylation alterations lead to differences in gene expression.

SETTING

Academic medical center.

PATIENT(S)

A total of 138 singleton pregnancies undergoing chorionic villus sampling resulting in a live birth were recruited for methylation analysis (56 unassisted, 38 NIFT, and 44 IVF conceptions). Ribonucleic acid-sequencing data consisted of 141 subjects (74 unassisted, 33 NIFT, and 34 IVF conceptions) of which 116 overlapped with the methylation cohort.

INTERVENTION(S)

In vitro fertilization-conceived pregnancy or pregnancy conceived via NIFT, such as ovulation induction and intrauterine insemination.

MAIN OUTCOME MEASURE(S)

Significant methylation changes at CpG sites after adjustment for multiple comparisons. The secondary outcome was gene expression changes of significant CpG sites.

RESULT(S)

Of the 741,145 probes analyzed in the placenta, few were significant at Bonferroni <0.05: 185 CpG sites (0.025%) significant in pregnancies conceived with the fertility treatments (NIFT + IVF) vs. unassisted conceptions; 28 in NIFT vs. unassisted; 195 in IVF vs. unassisted; and only 13 (0.0018%) in IVF vs. NIFT conceptions. Of all significant CpG sites combined, 10% (35) were located in genes with suggestive gene expression changes, but none were significant after adjustment for multiple comparisons (ribonucleic acid sequencing false discovery rate <0.05). None of the 13 differentially methylated probes in the IVF vs. NIFT placenta were located in genes with suggestive IVF vs. NIFT gene expression differences.

CONCLUSION(S)

Underlying infertility is the most significant contributor to the minimal differences in first-trimester placental methylation, and not the specific fertility treatment used, such as IVF.

Plasma exchange therapy for familial chylomicronemia syndrome in infant: A case report

INTRODUCTION

Familial chylomicronemia syndrome (FCS) is a rare genetic disease. FCS usually manifests by the age of 10 years, and 25% of cases of FCS occur during infancy. Here we present a case of FCS in a male infant and summarize our experiences on the diagnosis and therapy of this case.

PATIENT CONCERNS

A male infant aged 1 month and 8 days had recurrent hematochezia and hyperchylomicronemia.

DIAGNOSIS

FCS based on symptoms and genetic test.

INTERVENTIONS

Plasma exchange therapy.

OUTCOMES

His development was normal with a good spirit and satisfactory weight gain, and no hematochezia occurred again.

CONCLUSION

Genetic test is important for accurate diagnosis of FCS, and we identified a new mutation of lipoprotein lipase gene c.88C>A which conformed to autosomal recessive inheritance. Plasma exchange therapy can be applied to infants with FCS with low risk and good outcomes.

Primary hypertriglyceridemia induced pancreatitis in a cohort of Pakistani children

OBJECTIVES

Primary hypertriglyceridemia is a rare condition in children. Hypertriglyceridemia induced pancreatitis is most commonly reported in adults, accounting for third most common cause after gallstones and alcohol consumption. The study aims to highlight the frequency of hypertriglyceridemia induced pancreatitis in a cohort of children presenting in a tertiary care hospital.

METHODS

A retrospective review of paediatric patients with pancreatitis was conducted in Shifa International hospital, Islamabad, from 2013 to 2020. All patients under 18 years of age who fulfilled the inclusion criteria were included. Medical records of patients were checked for symptoms, signs, age, growth parameters and laboratory investigations. Patients who had HTG were reviewed in detail for family history of pancreatitis or dyslipidemias.

RESULTS

We found a cohort of 6 patients with primary hypertriglyceridemia after excluding secondary causes. Out of these 6 patients, 4 (66.6%) were male and 2 (33.3%) were female. Minimum age of our patient was 2 months and maximum was 17 years with a mean age of 6.5 years. Two patients presented less than one year of age. Mean triglyceride levels was 1,599 + 523 mg/dL. Four patients (66.6%) had acute pancreatitis, one each (16.6%) had recurrent and chronic pancreatitis. Family history was positive for hyperlipidaemia in two patients who had positive consanguinity. Patients with positive family history were symptomatic at earlier age.

CONCLUSIONS

This is the first study to highlight primary hypertriglyceridemia presenting as pancreatitis in paediatric population from Pakistan. All patients had triglycerides level of greater than 1000 mg/dL.

A Heterozygous LMF1 Gene Mutation (c.1523C>T), Combined With an LPL Gene Mutation (c.590G>A), Aggravates the Clinical Symptoms in Hypertriglyceridemia

Hypertriglyceridemia is an important contributor to atherosclerotic cardiovascular disease (ASCVD) and acute pancreatitis. Familial hypertriglyceridemia is often caused by mutations in genes involved in triglyceride metabolism. Here, we investigated the disease-causing gene mutations in a Chinese family with hypertriglyceridemia and assessed the functional significance in vitro. Whole-exome sequencing (WES) was performed revealing that the severe hypertriglyceridemic proband carried a missense mutation (c.590G &gt; A) in exon 5 of the LPL gene, as well as a missense mutation (c.1523C &gt; T) in exon 10 of the LMF1 gene. Conservation analysis by Polyphen-2 showed that the 508 locus in the LMF1 protein and 197 locus in the LPL protein were highly conserved between different species. I-TASSER analysis indicated that the LMF1 c.1523C &gt; T mutation and the LPL c.590G &gt; A mutation changed the tertiary structure of the protein. A decrease in mRNA and protein expression was observed in 293T cells transfected with plasmids carrying the LMF1 c.1523C &gt; T mutation. Subcellular localization showed that both wild-type (WT) and mutant LMF1 protein were localized at the cell cytoplasm. In the cell medium and cell lysates, these LMF1 and LPL gene mutations both caused a decreased LPL mass. Moreover, the combination of LMF1 and LPL gene mutations significantly decreased LPL levels compared to their individual effects on the LPL concentration. Both the clinical and in vitro data suggest that severe hypertriglyceridemia was of digenic origin caused by LMF1 and LPL mutation double heterozygosity in this patient.

A very rare case of chylomicronemia revealed by cerebral thrombophlebitis in a 4-month-old infant

Introduction

Case presentation

Discussion

Conclsuion

•

4months year old patient admitted for hypotonia and drowsiness.

•

The diagnosis was a fatty cerebral venous thrombosis that revealed hyperchylomicronemia that was complicated also by pancreatitis.

•

During the hospitalization a cerebral tuberculosis abcess was diagnosed associated with nosocomial klebsiela pneumoniae sepsis and was succesfully treated.

Genetic Lipid Disorders Associated with Atherosclerotic Cardiovascular Disease: Molecular Basis to Clinical Diagnosis and Epidemiologic Burden

Genetic lipid disorders, ranging from common dyslipidemias such as familial hypercholesterolemia, lipoprotein (a), and familial combined hyperlipidemia to rare disorders including familial chylomicronemia syndrome and inherited hypoalphalipoproteinemias (ie, Tangier and fish eye diseases), affect millions of individuals in the United States and tens of millions around the world and are often undiagnosed in the general population. Clinicians should take into consideration the potential of inherited lipid disorders or syndromes when severe derangements in lipid parameters are observed. Patients' combined genotype and phenotype should be evaluated in conjunction with a host of environmental factors impacting their risk of atherosclerotic cardiovascular disease.

Rare novel LPL mutations are associated with neonatal onset lipoprotein lipase (LPL) deficiency in two cases

Background

Lipoprotein lipase (LPL) deficiency is a monogenic lipid metabolism disorder biochemically characterized by hypertriglyceridemia (HTG) inherited in an autosomal recessive manner. Neonatal onset LPL deficiency is rare. The purpose of this study was to clarify the clinical features of neonatal LPL deficiency and to analyze the genetic characteristics of LPL gene.

Methods

In order to reach a definite molecular diagnose, metabolic diseases-related genes were sequenced through gene capture and next generation sequencing. Meanwhile, the clinical characteristics and follow-up results of the two newborns were collected and analyzed.

Results

Three different mutations in the LPL gene were identified in the two newborns including a novel compound heterozygous mutation (c.347G > C and c.472 T > G) and a reported homozygous mutation (c.836 T > G) was identified. Interestingly, both the two neonatal onset LPL deficiency patients presented with suffered recurrent infection in the hyperlipidemia stage, which was not usually found in childhood or adulthood onset LPL deficiency patients.

Conclusion

The two novel mutaitons, c.347G > C and c.472 T > G, identified in this study were novel, which expanded the LPL gene mutation spectrum. In addition, suffered recurrent infection in the hyperlipidemia stage implied a certain correlation between immune deficiency and lipid metabolism abnormality. This observation further supplemented and expanded the clinical manifestations of LPL deficiency.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-021-02875-x.

Current Diagnosis and Management of Primary Chylomicronemia

Primary chylomicronemia (PCM) is a rare and intractable disease characterized by marked accumulation of chylomicrons in plasma. The levels of plasma triglycerides (TGs) typically range from 1,000 - 15,000 mg/dL or higher.

PCM is caused by defects in the lipoprotein lipase (LPL) pathway due to genetic mutations, autoantibodies, or unidentified causes. The monogenic type is typically inherited as an autosomal recessive trait with loss-of-function mutations in LPL pathway genes ( LPL , LMF1 , GPIHBP1 , APOC2 , and APOA5 ). Secondary/environmental factors (diabetes, alcohol intake, pregnancy, etc.) often exacerbate hypertriglyceridemia (HTG).

The signs, symptoms, and complications of chylomicronemia include eruptive xanthomas, lipemia retinalis, hepatosplenomegaly, and acute pancreatitis with onset as early as in infancy. Acute pancreatitis can be fatal and recurrent episodes of abdominal pain may lead to dietary fat intolerance and failure to thrive.

The main goal of treatment is to prevent acute pancreatitis by reducing plasma TG levels to at least less than 500-1,000 mg/dL. However, current TG-lowering medications are generally ineffective for PCM. The only other treatment options are modulation of secondary/environmental factors. Most patients need strict dietary fat restriction, which is often difficult to maintain and likely affects their quality of life.

Timely diagnosis is critical for the best prognosis with currently available management, but PCM is often misdiagnosed and undertreated. The aim of this review is firstly to summarize the pathogenesis, signs, symptoms, diagnosis, and management of PCM, and secondly to propose simple diagnostic criteria that can be readily translated into general clinical practice to improve the diagnostic rate of PCM. In fact, these criteria are currently used to define eligibility to receive social support from the Japanese government for PCM as a rare and intractable disease.

Nevertheless, further research to unravel the molecular pathogenesis and develop effective therapeutic modalities is warranted. Nationwide registry research on PCM is currently ongoing in Japan with the aim of better understanding the disease burden as well as the unmet needs of this life-threatening disease with poor therapeutic options.

Food Chemistry of Selenium and Controversial Roles of Selenium in Affecting Blood Cholesterol Concentrations

Hypercholesterolemia, one of the major risk factors of cardiovascular diseases, is a worldwide public health problem. Nutraceuticals and phytochemicals are attracting attention as a result of their cholesterol-lowering ability and minimal side effects. Among them, selenium (Se) is on the list. The amount of Se in foods varies by region. Se-enriched fertilizers and feeds can raise the Se content in plants and animals, while some processing methods decrease food Se content. This review summarizes recent studies on (1) the content distribution of Se in foods and factors influencing Se-enriched foods, (2) the bioavailability and metabolism of Se, and (3) the role of Se in affecting blood cholesterol and cholesterol metabolism. Although the hypocholesterolemic effect of Se is equivocal, its cholesterol-lowering activity may be more remarkable when the Se supplementation is 200 μg/day or the baseline blood total cholesterol is above 200 mg/dL in humans with low Se status.

Effectiveness and safety of lomitapide in a patient with familial chylomicronemia syndrome

BACKGROUND

Familial chylomicronemia syndrome (FCS) is characterized by severe fasting hypertriglyceridemia, abdominal pain, and recurrent acute pancreatitis. Available triglyceride-lowering drugs are insufficient to avoid pancreatitis. Therefore, there is a significant unmet medical need for effective triglyceride-lowering drugs for patients with FCS.

CASE REPORT

We report the second case of a patient with FCS and recurrent pancreatitis treated with lomitapide. Lomitapide treatment resulted in a reduction of fasting TG levels from 2897 mg/dL (32.71 mmol/L) to an average of 954 mg/dL (10.77 mmol/L) on the 30 mg lomitapide equating to a 67% reduction from baseline. After 26 months of lomitapide treatment, histological activity score for hepatic fibrosis was stable although liver biopsy showed a marked increase of liver steatosis and mild perivenular and perisinusoidal fibrosis.

CONCLUSIONS

Lomitapide is effective in reducing triglycerides in FCS and preventing the recurrence of acute pancreatitis. A longer follow-up is necessary to evaluate long-term risk of progression toward severe stages of liver fibrosis. A prospective clinical trial may identify which subgroup of FCS patients would benefit from lomitapide treatment in the absence of significant liver adverse effects.

Whole exome sequencing for non-selective pediatric patients with hyperlipidemia

BACKGROUND

Hyperlipidemia is a group of conditions with abnormally elevated levels of any or all lipids or lipoproteins in the blood. It is highly heterogeneous both genetically and clinically, which contributes to diagnostic challenges and results in many patients to be underdiagnosed and undertreated in China. Precise diagnosis and early management are critical to reduce the incidence of potential coronary artery disease and cardiovascular disease.

RESULTS

We performed a single center study to demonstrate the clinical utility of the genome-first approach by whole exome sequencing (WES) for 12 pediatric patients with abnormal lipids or lipoproteins levels. In vitro experiments were performed in COS-7 cells to further evaluate the biological function of the novel variants. We identified ten pathogenic and likely pathogenic variants and three of them were novel. Molecular cause was uncovered in five (41.7%) patients including three lipoprotein lipase deficiency patients, one hypercholesterolemia patient and one sitosterolemia patient. We also found three patients with rare variants of uncertain significance. Copy number variant (CNV) analysis with WES data did not reveal any potential hyperlipidemia related CNVs in all patients.

CONCLUSION

We expanded the mutation and phenotype spectra of familial hyperlipidemia. Our study demonstrated the effectiveness of genome-first approach for evaluation pediatric hyperlipidemia patients and showed that WES can be used as the first-tier test for patients with suspected Mendelian hyperlipidemia disorder.

Practical definitions of severe versus familial hypercholesterolaemia and hypertriglyceridaemia for adult clinical practice

Diagnostic scoring systems for familial hypercholesterolaemia and familial chylomicronaemia syndrome often cannot differentiate between adults who have extreme dyslipidaemia based on a simple monogenic cause versus people with a more complex cause involving polygenic factors and an environmental component. This more complex group of patients carries a substantial risk of atherosclerotic cardiovascular disease in the case of marked hypercholesterolaemia and pancreatitis in the case of marked hypertriglyceridaemia. Complications are mainly a function of the degree of disturbance in lipid metabolism resulting in elevated lipid levels, so the added value of knowing the precise genetic cause in clinical decision making is unclear and does not lead to clinically meaningful benefit. We propose that for severe elevations of plasma low density lipoprotein cholesterol or triglyceride, the primary factor driving intervention should be the biochemical perturbation rather than the clinical risk score. This underscores the importance of expanding the definition of severe dyslipidaemias and to not rely solely on clinical scoring systems to identify individuals who would benefit from appropriate treatment approaches. We advocate for the use of simple, practical, clinical, and largely biochemically based definitions for severe hypercholesterolaemia (eg, LDL cholesterol >5 mmol/L) and severe hypertriglyceridaemia (triglyceride >10 mmol/L), which complement current definitions of familial hypercholesterolaemia and familial chylomicronaemia syndrome. Irrespective of the precise genetic cause, individuals diagnosed with severe hypercholesterolaemia and severe hypertriglyceridaemia require intensive therapy, including special consideration for new effective but more expensive therapies.

Genetic variants in the LPL and GPIHBP1 genes, in patients with severe hypertriglyceridaemia, detected with high resolution melting analysis

INTRODUCTION

Pathogenic variants in lipoprotein lipase (LPL) and glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) have been described in patients with severe hypertriglyceridaemia. We aimed to optimise high resolution melting (HRM) assays to detect the presence of functional variants in these genes.

METHODS

One hundred and sixteen patients with severe hypertriglyceridaemia were studied. HRM assays were optimised to scan exons and splice junctions in LPL and GPIHBP1. Sanger sequencing was the reference method. Next-generation-sequencing (NGS) was performed in five patients, including one with Familial Chylomicronemia syndrome (FCS).

RESULTS

We identified 15 different variants in LPL and 6 in GPIHBP1. The variants revealed with NGS were also detected with HRM, including a rare premature stop codon in LPL (p.Trp421*) and two LPL pathogenic variants in the patient with FCS (p.His80Arg + p.Gly215Glu). Having multiple functional variant alleles was associated with pancreatitis onset at younger ages and higher baseline triglycerides.

CONCLUSIONS

Our HRM assays detected the presence of functional gene variants that were confirmed with Sanger and NGS sequencing. The presence of multiple functional variant alleles was associated with differences in the clinical profile. Therefore, these assays represent a reliable, cost-effective tool that can be used to complement the NGS approach for gene scanning.

Spectrum of Mutations and Long-Term Clinical Outcomes in Genetic Chylomicronemia Syndromes

OBJECTIVE

Familial chylomicronemia syndrome (FCS) and multifactorial chylomicronemia syndrome (MCS) are the prototypes of monogenic and polygenic conditions underlying genetically based severe hypertriglyceridemia. These conditions have been only partially investigated so that a systematic comparison of their characteristics remains incomplete. We aim to compare genetic profiles and clinical outcomes in FCS and MCS. Approach and Results: Thirty-two patients with severe hypertriglyceridemia (triglyceride >1000 mg/dL despite lipid-lowering treatments with or without history of acute pancreatitis) were enrolled. Rare and common variants were screened using a panel of 18 triglyceride-raising genes, including the canonical LPL, APOC2, APOA5, GP1HBP1, and LMF1. Clinical information was collected retrospectively for a median period of 44 months. Across the study population, 37.5% were classified as FCS due to the presence of biallelic, rare mutations and 59.4% as MCS due to homozygosity for nonpathogenic or heterozygosity for pathogenic variants in canonical genes, as well as for rare and low frequency variants in noncanonical genes. As compared with MCS, FCS patients showed a lower age of hypertriglyceridemia onset, higher levels of on-treatment triglycerides, and 3-fold higher incidence rate of acute pancreatitis.

CONCLUSIONS

Our data indicate that the genetic architecture and natural history of FCS and MCS are different. FCS expressed the most severe clinical phenotype as determined by resistance to triglyceride-lowering medications and higher incidence of acute pancreatitis episodes. The most common genetic abnormality underlying FCS was represented by biallelic mutations in LPL while APOA5 variants, in combination with high rare polygenic burden, were the most frequent genotype of MCS.

Differentiating Familial Chylomicronemia Syndrome From Multifactorial Severe Hypertriglyceridemia by Clinical Profiles

Context

Differentiation between familial chylomicronemia syndrome (FCS, type 1 hyperlipoproteinemia), a rare metabolic disorder, and the more common multifactorial severe hypertriglyceridemia (sHTG, type 5 hyperlipoproteinemia) is challenging because of their overlapping symptoms but important in patient management.

Objective

To assess whether readily obtainable clinical information beyond triglycerides can effectively diagnose and differentiate patients with FCS from those with sHTG, based on well-curated data from two intervention studies of these conditions.

Methods

The analysis included 154 patients from two phase 3 clinical trials of patients with sHTG, one cohort with genetically confirmed FCS (n = 49) and one with multifactorial sHTG (n = 105). Logistic regression analyses were performed to determine the ability of variables (patient demographics, medical history, and baseline lipids, individually or in sets) to differentiate the patient populations. Receiver operating characteristics were used to determine the variable sets with the highest accuracy (percentage of times actual values matched predicted) and optimal sensitivity and specificity.

Results

The primary model diagnosed 45 of 49 patients with FCS and 99 of 105 patients with sHTG correctly. Optimal sensitivity for all available parameters (n = 17) was 91.8%, optimal specificity was 94.3%, and accuracy was 93.5%. Fasting low-density lipoprotein cholesterol (LDL-C) provided the highest individual predictability. However, a three-variable set of ultracentrifugally measured LDL-C, body mass index, and pancreatitis history differentiated the diseases with a near similar accuracy of 91.0%, and adding high-density lipoprotein cholesterol and very low-density lipoprotein cholesterol for a five-variable set provided a small incremental increase in accuracy (92.2%).

Conclusions

In the absence of genetic testing, hypertriglyceridemic patients with FCS and sHTG can be differentiated with a high degree of accuracy by analyzing readily obtainable clinical information.

Volanesorsen and Triglyceride Levels in Familial Chylomicronemia Syndrome

BACKGROUND

Familial chylomicronemia syndrome is a rare genetic disorder that is caused by loss of lipoprotein lipase activity and characterized by chylomicronemia and recurrent episodes of pancreatitis. There are no effective therapies. In an open-label study of three patients with this syndrome, antisense-mediated inhibition of hepatic APOC3 mRNA with volanesorsen led to decreased plasma apolipoprotein C-III and triglyceride levels.

METHODS

We conducted a phase 3, double-blind, randomized 52-week trial to evaluate the safety and effectiveness of volanesorsen in 66 patients with familial chylomicronemia syndrome. Patients were randomly assigned, in a 1:1 ratio, to receive volanesorsen or placebo. The primary end point was the percentage change in fasting triglyceride levels from baseline to 3 months.

RESULTS

Patients receiving volanesorsen had a decrease in mean plasma apolipoprotein C-III levels from baseline of 25.7 mg per deciliter, corresponding to an 84% decrease at 3 months, whereas patients receiving placebo had an increase in mean plasma apolipoprotein C-III levels from baseline of 1.9 mg per deciliter, corresponding to a 6.1% increase (P<0.001). Patients receiving volanesorsen had a 77% decrease in mean triglyceride levels, corresponding to a mean decrease of 1712 mg per deciliter (19.3 mmol per liter) (95% confidence interval [CI], 1330 to 2094 mg per deciliter [15.0 to 23.6 mmol per liter]), whereas patients receiving placebo had an 18% increase in mean triglyceride levels, corresponding to an increase of 92.0 mg per deciliter (1.0 mmol per liter) (95% CI, -301.0 to 486 mg per deciliter [-3.4 to 5.5 mmol per liter]) (P<0.001). At 3 months, 77% of the patients in the volanesorsen group, as compared with 10% of patients in the placebo group, had triglyceride levels of less than 750 mg per deciliter (8.5 mmol per liter). A total of 20 of 33 patients who received volanesorsen had injection-site reactions, whereas none of the patients who received placebo had such reactions. No patients in the placebo group had platelet counts below 100,000 per microliter, whereas 15 of 33 patients in the volanesorsen group had such levels, including 2 who had levels below 25,000 per microliter. No patient had platelet counts below 50,000 per microliter after enhanced platelet-monitoring began.

CONCLUSIONS

Volanesorsen lowered triglyceride levels to less than 750 mg per deciliter in 77% of patients with familial chylomicronemia syndrome. Thrombocytopenia and injection-site reactions were common adverse events. (Funded by Ionis Pharmaceuticals and Akcea Therapeutics; APPROACH Clinical Trials.gov number, NCT02211209.).

Genetic association of LPL rs1121923 and rs258 with plasma TG and VLDL levels

Lipoprotein lipase (LPL) is a rate-limiting enzyme for the hydrolysis of triglycerides (TG). Hundreds of genetic variants including single nucleotide polymorphisms have been identified across the 30Kb gene locus on chromosome 8q22. Several of these variants have been demonstrated to have genetic association with lipid level variation but many remain unresolved. Controversial reports on the genetic association of variants among different populations pose a challenge to which variants are informative. This study aimed to investigate "common" LPL variants (rs1121923, rs258, rs328, rs13702) and their possible role in plasma lipid level. Genotyping was performed using Realtime PCR. Based on the observed genotypes, the minor allele frequencies were A: 0.065 for rs1121923; C: 0.379 for rs258; G: 0.087 for rs328 and C: 0.337 for rs13702. Using linear regression, a lowering effect of rs1121923 (p = 0.024) on TG levels (-0.14 B coefficient: CI: -0.27--0.019) and rs258 (p = 0.013) on VLDL levels (B: -0.046; CI: -0.082--0.009) was observed indicating a "protective" role for the two variants. Moreover, the findings indicate the potential for including rs1121923 and rs258 in diagnostic panels for use as an estimator of "risk" scores for dyslipidemia.

Clinical and functional studies of two novel variants in the LPL gene in subjects with severe hypertriglyceridemia

BACKGROUND

Two novel variants (p.Arg270Gly and p.Asp308Glyfs*3) in the LPL gene have recently been identified in subjects with hypertriglyceridemia (HTG). In this study, we investigated clinical and genetic features of their families and examined the functional significance of these two variants in vitro.

METHODS

Clinical and genetic data were collected. Site-directed mutagenesis and transient expression in cld cells were performed. Lipoprotein lipase (LPL) mass and activity were measured.

RESULTS

In vitro studies showed that LPL mass and activity in the media of cells transfected with the p.Arg270Gly variant were significantly reduced. In the cell lysates, however, LPL mass was preserved but LPL activity was reduced, suggesting that the LPL defect was in the secretion and activity. For the p.Asp308Glyfs*3 variant, LPL mass in the cell lysate was relatively preserved compared to that of the wild-type, while LPL mass in the media was decreased albeit not significantly. LPL activities in the cell lysate and in the media of cells transfected with this variant were significantly reduced, suggesting that the p.Asp308Glyfs*3 variant might affect the activity, and possibly, secretion of LPL.

CONCLUSIONS

These novel variants in the LPL gene were likely pathogenic with the defect in secretion and/or activity.

Disappearance of recurrent pancreatitis after splenectomy in familial chylomicronemia syndrome

BACKGROUND AND AIMS

Recurrent pancreatitis is a severe complication of familial chylomicronemia syndrome (FCS) mainly secondary to lipoprotein lipase deficiency. The mechanism and interindividual variability of pancreatitis in FCS are not fully understood, but abnormalities in the drainage system of pancreatic veins could be involved.

METHODS AND RESULTS

Two cases of typical FCS are described with a past history of recurrent pancreatitis that dramatically improved after splenectomy performed in both cases for reasons non-related to FCS.

CONCLUSIONS

These are the first reports of the disappearance of pancreatitis after splenectomy in FCS and they should be considered of anecdotal nature at this time. The disappearance of pancreatitis following splenectomy could be in part due to subsequent improvements in pancreatic drainage. Extrahepatic portal hypertension induced by hypertriglyceridemic splenomegaly leading to pancreatic congestion could also be a contributing factor.

Characterizing familial chylomicronemia syndrome: Baseline data of the APPROACH study

BACKGROUND

Familial chylomicronemia syndrome (FCS) is a rare metabolic disorder caused by mutations in lipoprotein lipase (LPL) or genes required for LPL functionality and is characterized by hyperchylomicronemia that results in recurrent episodes of acute pancreatitis. Owing to the rarity of FCS, there are few case series describing the phenotypic variability in FCS patients in detail.

OBJECTIVE

To provide baseline characteristics in the largest study population to date of patients with FCS.

METHODS

We analyzed baseline demographic and clinical characteristics of adult FCS patients in the phase 3 APPROACH study of volanesorsen sodium (antisense inhibitor of apolipoprotein C-III).

RESULTS

Sixty-six patients were included in the analysis. Mean (SD) age was 46 (13) years; and mean body mass index was 24.9 (5.7) kg/m². We identified causal mutations in 79% (52) of patients, with LPL mutations accounting for 62% (41) of cases. Median age at diagnosis was 24 years, 54% were females, and 81% were Caucasian. All patients followed a low-fat diet, 43% received fibrates, 27% fish oils, and 21% statins. Median fasting triglyceride levels (P25, P75) were 1985 (1179, 3047 mg/dL). Overall, 76% of patients reported ≥1 lifetime episode of acute pancreatitis; 23 patients reported a total of 53 pancreatitis events in the 5 years before enrollment.

CONCLUSIONS

Our data emphasize the severe hypertriglyceridemia characteristic of FCS patients despite restrictive low-fat diets and frequent use of existing hypolipemic therapies. Acute pancreatitis and recurrent acute pancreatitis are frequent complications of FCS. Diagnosis at an older age suggests likely underdiagnosis and underappreciation of this rare disorder.

Severe hypertriglyceridemia. Clinical characteristics and therapeutic management

INTRODUCTION

The therapeutic management of severe hypertriglyceridaemia represents a clinical challenge.

OBJECTIVES

The objectives of this study were 1) to identify the clinical characteristics of patients with severe hypertriglyceridaemia, and 2) to analyse the treatment established by the physicians in each case.

METHODS

A cross-sectional study was carried out using the computerised medical records of all patients>18 years of age with a blood triglyceride level≥1,000mg/dL between 1 January 2011 and 31 December 2016. Clinical and laboratory variables were collected. The behaviour of the physicians in the 6 months after the lipid finding was analysed.

RESULTS

A total of 420 patients were included (mean age 49.1±11.4 years, males 78.8%). The median of triglycerides was 1,329mg/dL (interquartile range 1,174-1,658). No secondary causes were found in 34.1% of the patients. The most frequent secondary causes were obesity (38.6%) and diabetes (28.1%). Physical activity was recommended and a nutritionist was referred to in 49.1% and 44.2% of the patients, respectively. Secondary causes were identified and attempts were made to correct them in 40.7% of cases. The most indicated pharmacological treatments were fenofibrate 200mg/day (26.5%) and gemfibrozil 900mg/day (19.3%). Few patients received the indication of omega 3 fatty acids or niacin.

CONCLUSION

This study showed, for the first time in our country, the characteristics of a population with severe hypertriglyceridaemia. The therapeutic measures instituted by the physicians were insufficient. Knowing the characteristics in this particular clinical scenario could improve the current approach of these patients.

A novel LPL intronic variant: g.18704C>A identified by re-sequencing Kuwaiti Arab samples is associated with high-density lipoprotein, very low-density lipoprotein and triglyceride lipid levels

The role interethnic genetic differences play in plasma lipid level variation across populations is a global health concern. Several genes involved in lipid metabolism and transport are strong candidates for the genetic association with lipid level variation especially lipoprotein lipase (LPL). The objective of this study was to re-sequence the full LPL gene in Kuwaiti Arabs, analyse the sequence variation and identify variants that could attribute to variation in plasma lipid levels for further genetic association. Samples (n = 100) of an Arab ethnic group from Kuwait were analysed for sequence variation by Sanger sequencing across the 30 Kb LPL gene and its flanking sequences. A total of 293 variants including 252 single nucleotide polymorphisms (SNPs) and 39 insertions/deletions (InDels) were identified among which 47 variants (32 SNPs and 15 InDels) were novel to Kuwaiti Arabs. This study is the first to report sequence data and analysis of frequencies of variants at the LPL gene locus in an Arab ethnic group with a novel “rare” variant (LPL:g.18704C>A) significantly associated to HDL (B = -0.181; 95% CI (-0.357, -0.006); p = 0.043), TG (B = 0.134; 95% CI (0.004–0.263); p = 0.044) and VLDL (B = 0.131; 95% CI (-0.001–0.263); p = 0.043) levels. Sequence variation in Kuwaiti Arabs was compared to other populations and was found to be similar with regards to the number of SNPs, InDels and distribution of the number of variants across the LPL gene locus and minor allele frequency (MAF). Moreover, comparison of the identified variants and their MAF with other reports provided a list of 46 potential variants across the LPL gene to be considered for future genetic association studies. The findings warrant further investigation into the association of g.18704C>A with lipid levels in other ethnic groups and with clinical manifestations of dyslipidemia.

Variants of Lipolysis-Related Genes in Korean Patients with Very High Triglycerides

We investigated the prevalence and characteristics of variants of five lipolysis-related genes in Korean patients with very high triglycerides (TGs). Twenty-six patients with TG levels >885 mg/dL were selected from 13545 Korean subjects. Five candidate genes, LPL, APOC2, GPIHBP1, APOA5, and LMF1, were sequenced by targeted next-generation sequencing. Predictions of functional effects were performed and matched against public databases of variants. Ten rare variants of three genes were found in nine (34.6%) patients (three in LPL, four in APOA5, and three in LMF1). Five were novel and all variants were suspected of being disease-causing. Nine were heterozygous, and one (3.8%) had a homozygous rare variant of LPL. Six common variants of four genes were observed in 25 (96.2%) patients (one in LPL, one in GPIHBP1, two in APOA5, and two in LMF1). The c.G41T variant of GPIHBP1 and c.G533T variant of APOA5 were most frequent and found in 15 (57.7%) and 14 (53.8%) patients, respectively. Rare homozygous variants of the genes were very uncommon, while diverse rare heterozygous variants were commonly identified. Taken together, most study subjects may be manifesting the combined effects of rare heterozygous variants and common variants.

Microduplication of 10q26.3 in a Chinese hypertriglyceridemia patient

Hypertriglyceridemia (HTG) plays an important role in the development and progression of atherosclerosis. It is inherited in an autosomal dominant pattern with a frequency of approximately 1:1,000,000 worldwide. Previous study has demonstrated that more than six genes underlie this disorder. In addition, copy number variants (CNVs) including disease-causing genes also play a crucial role in it. In this study, we have employed SNP-ARRAY chip technology to detect the pathogenic CNVs in a HTG patient who carried no meaningful mutations in HTG candidate genes. And we identified a de novo CNV interstitial 134.7 kb duplication of chromosome region 10q26.3 containing CYP2E1. And this CNV also has been confirmed by Real-time PCR. CYP2E1 is a member of cytochrome P450 superfamily of enzymes which play an important role in fatty acid metabolism. Our study is consistent with previous research and further claimes that CNVs containing CYP2E1 may be related to HTG and obesity. Our study not only further confirmes the hypothesis that the CYP2E1 is a plausible candidate gene for HTG, but also may contribute to the diagnosis and treatment of these genomic diseases.

Incidental finding of severe hypertriglyceridemia in children. Role of multiple rare variants in genes affecting plasma triglyceride

BACKGROUND

The incidental finding of severe hypertriglyceridemia (HyperTG) in a child may suggest the diagnosis of familial chylomicronemia syndrome (FCS), a recessive disorder of the intravascular hydrolysis of triglyceride (TG)-rich lipoproteins. FCS may be due to pathogenic variants in lipoprotein lipase (LPL), as well as in other proteins, such as apolipoprotein C-II and apolipoprotein A-V (activators of LPL), GPIHBP1 (the molecular platform required for LPL activity on endothelial surface) and LMF1 (a factor required for intracellular formation of active LPL).

OBJECTIVE

Molecular characterization of 5 subjects in whom HyperTG was an incidental finding during infancy/childhood.

METHODS

We performed the parallel sequencing of 20 plasma TG-related genes.

RESULTS

Three children with severe HyperTG were found to be compound heterozygous for rare pathogenic LPL variants (2 nonsense, 3 missense, and 1 splicing variant). Another child was found to be homozygous for a nonsense variant of APOA5, which was also found in homozygous state in his father with longstanding HyperTG. The fifth patient with a less severe HyperTG was found to be heterozygous for a frameshift variant in LIPC resulting in a truncated Hepatic Lipase. In addition, 1 of the patients with LPL deficiency and the patient with APOA-V deficiency were also heterozygous carriers of a pathogenic variant in LIPC and LPL gene, respectively, whereas the patient with LIPC variant was also a carrier of a rare APOB missense variant.

CONCLUSIONS

Targeted parallel sequencing of TG-related genes is recommended to define the molecular defect in children presenting with an incidental finding of HyperTG.

Identification of a novel LMF1 nonsense mutation responsible for severe hypertriglyceridemia by targeted next-generation sequencing

BACKGROUND

Severe hypertriglyceridemia (HTG) may result from mutations in genes affecting the intravascular lipolysis of triglyceride (TG)-rich lipoproteins.

OBJECTIVE

The aim of this study was to develop a targeted next-generation sequencing panel for the molecular diagnosis of disorders characterized by severe HTG.

METHODS

We developed a targeted customized panel for next-generation sequencing Ion Torrent Personal Genome Machine to capture the coding exons and intron/exon boundaries of 18 genes affecting the main pathways of TG synthesis and metabolism. We sequenced 11 samples of patients with severe HTG (TG>885 mg/dL-10 mmol/L): 4 positive controls in whom pathogenic mutations had previously been identified by Sanger sequencing and 7 patients in whom the molecular defect was still unknown.

RESULTS

The customized panel was accurate, and it allowed to confirm genetic variants previously identified in all positive controls with primary severe HTG. Only 1 patient of 7 with HTG was found to be carrier of a homozygous pathogenic mutation of the third novel mutation of LMF1 gene (c.1380C>G-p.Y460X). The clinical and molecular familial cascade screening allowed the identification of 2 additional affected siblings and 7 heterozygous carriers of the mutation.

CONCLUSIONS

We showed that our targeted resequencing approach for genetic diagnosis of severe HTG appears to be accurate, less time consuming, and more economical compared with traditional Sanger resequencing. The identification of pathogenic mutations in candidate genes remains challenging and clinical resequencing should mainly intended for patients with strong clinical criteria for monogenic severe HTG.

Clinical and genetic features of 3 patients with familial chylomicronemia due to mutations in GPIHBP1 gene

BACKGROUND

Familial chylomicronemia is a recessive disorder that may be due to mutations in lipoprotein lipase (LPL) and in other proteins such as apolipoprotein C-II and apolipoprotein A-V (activators of LPL), GPIHBP1 (the molecular platform required for LPL activity on endothelial surface), and LMF1 (a factor required for intracellular formation of active LPL).

METHODS

We sequenced the familial chylomicronemia candidate genes in 2 adult females presenting long-standing hypertriglyceridemia and a history of acute pancreatitis.

RESULTS

Both probands had plasma triglyceride >10 mmol/L but no mutations in the LPL gene. The sequence of the other candidate genes showed that one patient was homozygous for a novel missense mutation p.(Cys83Arg), and the other was homozygous for a previously reported nonsense mutation p.(Cys 89*), respectively, in GPIHBP1. Family screening showed that the hypertriglyceridemic brother of the p.(Cys83Arg) homozygote was also homozygous for this mutation. He had no history of pancreatitis. The p.(Cys83Arg) heterozygous carriers had normal triglyceride levels. The substitution of a cysteine residue in the Ly6 domain of GPIHBP1 is predicted to abolish one of the disulfide bridges required to maintain the structure of GPIHBP1. The p.(Cys89*) mutation results in a truncated protein devoid of function.

CONCLUSIONS

Both mutant GPIHBP1 proteins are expected to be incapable of transferring LPL from the subendothelial space to the endothelial surface.

Chylomicrons: Advances in biology, pathology, laboratory testing, and therapeutics

The adequate absorption of lipids is essential for all mammalian species due to their inability to synthesize some essential fatty acids and fat-soluble vitamins. Chylomicrons (CMs) are large, triglyceride-rich lipoproteins that are produced in intestinal enterocytes in response to fat ingestion, which function to transport the ingested lipids to different tissues. In addition to the contribution of CMs to postprandial lipemia, their remnants, the degradation products following lipolysis by lipoprotein lipase, are linked to cardiovascular disease. In this review, we will focus on the structure-function and metabolism of CMs. Second, we will analyze the impact of gene defects reported to affect CM metabolism and, also, the role of CMs in other pathologies, such as atherothrombotic cardiovascular disease and diabetes mellitus. Third, we will provide an overview of the laboratory tests currently used to study CM disorders, and, finally, we will highlight current treatments in diseases affecting CMs.