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

Identification and functional analysis of novel homozygous LMF1 variants in severe hypertriglyceridemia

BACKGROUND

The genetic basis of hypertriglyceridemia (HTG) is complex and includes variants in lipase maturation factor 1 (LMF1), an endoplasmic reticulum (ER)-chaperone involved in the post-translational activation of lipoprotein lipase (LPL).

OBJECTIVE

The objective of this study was to identify and functionally characterize biallelic LMF1 variants in patients with HTG.

METHODS

Genomic DNA sequencing was used to identify biallelic LMF1 variants in HTG patients without deleterious variants in LPL, apolipoprotein C-II (APOC2), glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) or apolipoprotein A-V (APOA5). LMF1 variants were functionally evaluated by in silico analyses and assessing their impact on LPL activity, LMF1 protein expression, and specific activity in transiently transfected HEK293 cells.

RESULTS

We identified four homozygous LMF1 variants in patients with severe HTG: two novel rare variants (p.Asn147Lys and p.Pro246Arg) and two low-frequency variants (p.Arg354Trp and p.Arg364Gln) previously reported at heterozygosity. We demonstrate that all four variants reduce the secretion of enzymatically active LPL by impairing the specific activity of LMF1, whereas p.Asn147Lys also diminishes LMF1 protein expression.

CONCLUSION

This study extends the role of LMF1 as a genetic determinant in severe HTG and demonstrates that rare and low-frequency LMF1 variants can underlie this condition through distinct molecular mechanisms. The clinical phenotype of patients affected by partial loss of LMF1 function is consistent with multifactorial chylomicronemia syndrome (MCS) and suggests that secondary factors and additional genetic determinants contribute to HTG in these subjects.

Comprehensive analysis of Chinese patients with non-LPL familial chylomicronemia syndrome: Genetic variants, dietary interventions, and clinical insights

BACKGROUND

Familial chylomicronemia syndrome (FCS) comprises a group of ultrarare disorders caused by biallelic variants in LPL or, less frequently, by GPIHBP1, APOC2, APOA5, or LMF1.

OBJECTIVES

To evaluate the phenotypes and management of eight non-lipoprotein lipase (LPL)-FCS patients.

METHODS

Seven pediatric and one adult patients with non-LPL-FCS were enrolled. Clinical features, treatment outcomes, and genetic profiles were assessed.

RESULTS

Among the 33 patients with FCS, 25 (76%) had LPL-FCS and eight (24%) had non-LPL-FCS; five had variants in GPIHBP1, one each in the LMF1, APOC2, and one with composite heterozygous variants in APOA5 and LPL. Twelve non-LPL variants were identified, five of which were novel variants in GPIHBP1 and two in LMF1. In silico predictions indicated that all novel variants might impact protein function. Elevated baseline triglyceride (TG) levels [22.9 (17.4-30.8) mmol/L, 2026.7 (1540.0-2728.5) mg/dL] were observed in all patients. Among the pediatric patients (7/7), chylomicronemia was the most common onset symptom. Acute pancreatitis was observed in only one patient with LMF1-FCS during pregnancy. The frequency of symptoms and lipid levels in the non-LPL-FCS group were slightly lower than those in the LPL-FCS group (P > 0.05). Dietary fat restriction reduced TG levels by 84.0% to 4.21 mmol/L (372.6 mg/dL, P < 0.01). Compared with other non-LPL-FCS patients, GPIHBP1-FCS patients experienced greater challenges in managing TG levels (P < 0.05).

CONCLUSION

This study unveiled the genetic profile of the Chinese FCS cohort and enriched the mutation spectrum of non-LPL-FCS. The clinical characteristics and treatment outcomes of patients with non-LPL-FCS were delineated.

The role of lipase maturation factor 1 in hypertriglyceridaemia and atherosclerosis: An update

Lipase maturation factor 1 is an endoplasmic reticulum-resident transmembrane protein, which acts as a critical chaperone necessary for the folding, dimerisation, and secretion of lipases. In this review, we summarise data about the recently revealed role of lipase maturation factor 1 in endoplasmic reticulum redox homeostasis, its novel interaction partners among oxidoreductases and lectin chaperones, and the identification of fibronectin and the low-density lipoprotein receptor as novel non-lipase client proteins of lipase maturation factor 1. Additionally, the role of lipase maturation factor 1-derived circular RNA in atherosclerosis progression via the miR-125a-3p/vascular endothelial growth factor A\Fibroblast Growth Factor 1 axis is discussed. Finally, we focus on the causative role of lipase maturation factor 1 variants in the development of hypertriglyceridaemia - a type of dyslipidaemia that significantly contributes to the development of atherosclerosis and other cardiovascular diseases via different mechanisms.

Identification of a Compound Heterozygous LMF1 Variants in a Patient with Severe Hypertriglyceridemia - Case Report and Literature Review

Familial chylomicronemia syndrome (FCS) and multifactorial chylomicronemia (MCM), characterized by highly variable triglyceride levels with acute episodes of severe hypertriglyceridemia (HTG), are caused by rare variants in genes associated with the catabolism of circulating lipoprotein triglycerides, mainly including LPL, APOC2, APOA5, GPIHBP1, and LMF1. Among them, the LMF1 gene only accounts for 1%. This study described a Chinese patient with severe HTG carrying compound heterozygous variants of a rare nonsense variant p.W168X in exon 3 and a missense variant p.R416Q in exon 9 in the LMF1 gene. These heterozygous variants account for his family's decreased lipase activity and mass, which caused the FCS phenotype.

Biochemical, Clinical, and Genetic Characteristics of Mexican Patients with Primary Hypertriglyceridemia, Including the First Case of Hyperchylomicronemia Syndrome Due to GPIHBP1 Deficiency

Primary hypertriglyceridemia (PHTG) is characterized by a high concentration of triglycerides (TG); it is divided between familial hyperchylomicronemia syndrome and multifactorial chylomicronemia syndrome. In Mexico, hypertriglyceridemia constitutes a health problem in which the genetic bases have been scarcely explored; therefore, our objective was to describe biochemical-clinical characteristics and variants in the APOA5, GPIHBP1, LMF1, and LPL genes in patients with primary hypertriglyceridemia. Thirty DNA fragments were analyzed using PCR and Sanger sequencing in 58 unrelated patients. The patients' main clinical-biochemical features were hypoalphalipoproteinemia (77.6%), pancreatitis (18.1%), and a TG median value of 773.9 mg/dL. A total of 74 variants were found (10 in APOA5, 16 in GPIHBP1, 34 in LMF1, and 14 in LPL), of which 15 could be involved in the development of PHTG: 3 common variants with significative odds and 12 heterozygous rare pathogenic variants distributed in 12 patients. We report on the first Mexican patient with hyperchylomicronemia syndrome due to GPIHBP1 deficiency caused by three variants: p.R145*, p.A154_G155insK, and p.A154Rfs*152. Moreover, eleven patients were heterozygous for the rare variants described as causing PHTG and also presented common variants of risk, which could partially explain their phenotype. In terms of findings, two novel genetic variants, c.-40_-22del LMF1 and p.G242Dfs*10 LPL, were identified.

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.

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.

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.

Involvement of a homozygous exon 6 deletion of LMF1 gene in intermittent severe hypertriglyceridemia

Severe hypertriglyceridemia (HTG), characterized by triglycerides (TG) permanently over 10 mmol/L, may correspond to familial chylomicronemia syndrome (FCS), a rare disorder. However, hypertriglyceridemic patients more often present multifactorial chylomicronemia syndrome (MCS), characterized by highly variable TG. A few nonsense variants of LMF1 gene were reported in literature in FCS patients. In this study, we described a woman with an intermittent severe HTG. NGS analysis and the sequencing of a long range PCR product revealed a homozygous deletion of 6507 base pairs in LMF1 gene, c.730-1528_898-3417del, removing exon 6, predicted to create an in-frame deletion of 56 amino acids, p.(Thr244_Gln299del). Despite an exon 6 homozygous deletion of LMF1, the patient's highly variable lipid phenotype was suggestive of MCS diagnosis.

Genetic and functional studies of the LMF1 gene in Thai patients with severe hypertriglyceridemia

Severe hypertriglyceridemia (HTG) due to chylomicronemia is associated with acute pancreatitis and is related to genetic disturbances in several proteins involved in triglyceride (TG) metabolism. Lipase maturation factor 1 (LMF1) is a protein essential for the maturation of lipoprotein lipase (LPL). In this study, we examined the genetic spectrum of the LMF1 gene among subjects with severe HTG and investigated the functional significance of 6 genetic variants in vitro. All 11 exons of the LMF1 gene were sequenced in 101 Thai subjects with severe HTG. For an in vitro study, we performed site-directed mutagenesis, transient expression in cld cells, and measured LPL protein and LPL activity. We identified 2 common variants [p.(Gly36Asp) and p.(Pro562Arg)] and 12 rare variants [p.(Thr143Met), p.(Asn249Ser), p.(Ala287Val), p.(Met346Val), p.(Thr395Ile), p.(Gly410Arg), p.(Asp433Asn), p.(Asp491Asn), p.(Asn501Tyr), p.(Ala504Val), p.(Arg523His), and p.(Leu563Arg)] in 29 patients. In vitro study of the p.(Gly36Asp), p.(Asn249Ser), p.(Ala287Val), p.(Asn501Tyr), p.(Pro562Arg) and p.(Leu563Arg) variants, however, revealed that both LPL mass and LPL activity in each of the transfected cells were not significantly different from those in the wild type LMF1 transfected cells, suggesting that these variants might not play a significant role in severe HTG phenotype in our subjects.

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Among 101 subjects with severe hypertriglyceridemia (HTG), 2 common and 12 rare variants in the LMF1 gene were identified

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None of the 6 missense variants studied were associated with a reduction in lipoprotein mass or activity

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These rare variants in the LMF1 gene may not play an important role in severe HTG phenotypes in the Thai population

Variants of Lipid-Related Genes in Adult Japanese Patients with Severe Hypertriglyceridemia

Aim: Hypertriglyceridemia is a type of dyslipidemia that contributes to atherosclerosis and coronary heart disease. Variants in lipoprotein lipase (LPL), apolipoprotein CII (APOC2), apolipoprotein AV (APOA5), glycosylphosphatidylinositol- anchored high-density lipoprotein-binding protein 1 (GPIHBP1), lipase maturation factor 1 (LMF1), and glucokinase regulator (GCKR) are responsible for hypertriglyceridemia. We investigated the molecular basis of severe hypertriglyceridemia in adult patients referred to the Clinical Laboratory at Fukuoka University Hospital.

Methods: Twenty-three adult patients with severe hypertriglyceridemia (> 1,000 mg/dL, 11.29 mmol/L) were selected. The coding regions of candidate genes were sequenced by next-generation sequencing. Forty-nine genes reportedly associated with hypertriglyceridemia were analyzed.

Results: In the 23 patients, we detected 70 variants: 28 rare and 42 common ones. Among the 28 rare variants with < 1% allele frequency, p.I4533L in APOB, p.M490I in MLXIPL, p.L152M in NCAN, and p.S264T in TIMD4 were novel. We did not observe single gene homozygous or compound heterozygous disease-causing rare variants in any of the 23 hypertriglyceridemia cases. However, in silico algorithms and previous reports indicated that five rare variants, APOA5 (p.T184S), GCKR (c.354 + 1G>A), LMF1 (p.G410R), and LRP1 (p.G813R; p.R2173Q), and seven common variants, APOA5 (pG185C), APOE (p.C130R; p.E262K/p.E263K), GCKR (p.V103M), GPIHBP1 (p.C14F), LRP1 (p.Y4054F), and MLXIPL (p.Q241H), can cause hypertriglyceridemia. However, all five disease-causing rare variants detected in this study were heterozygous.

Conclusions: The prevalence of disease-causing rare variants in candidate genes in severe hypertriglyceridemia patients was low. The major causes of severe hypertriglyceridemia were not single gene abnormalities, but involved multiple gene variations and environmental factors.

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.

Abnormality of hepatic triglyceride metabolism in ApcMin/+ mice with colon cancer cachexia

AIMS

Colorectal cancer syndrome has been one of the greatest concerns in the world. Although several epidemiological studies have shown that hepatic low lipoprotein lipase (LPL) mRNA expression may be associated with dyslipidemia and tumor progression, it is still not known whether the liver plays an essential role in hyperlipidemia of Apc^Min/+ mice.

MAIN METHODS

We measured the expression of metabolic enzymes that involved fatty acid uptake, de novo lipogenesis (DNL), β-oxidation and investigated hepatic triglyceride production in the liver of wild-type and Apc^Min/+ mice.

KEY FINDINGS

We found that hepatic fatty acid uptake and DNL decreased, but there was no significant difference in fatty acid β-oxidation. Interestingly, the production of hepatic very low-density lipoprotein-triglyceride (VLDL-TG) decreased at 20 weeks of age, but marked steatosis was observed in the livers of the Apc^Min/+ mouse. To further explore hypertriglyceridemia, we assessed the function of hepatic glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) for the first time. GPIHBP1 is governed by the transcription factor octamer-binding transcription factor-1 (Oct-1) which are involved in the nuclear factor-κB (NF-κB) signaling pathway in the liver of Apc^Min/+ mice. Importantly, it was also confirmed that sn50 (100 μg/mL, an inhibitor of the NF-κB) reversed the tumor necrosis factor α (TNFα)-induced Oct-1 and GPIHBP1 reduction in HepG2 cells.

SIGNIFICANCE

Altogether, these findings highlighted a novel role of GPIHBP1 that might be responsible for hypertriglyceridemia in Apc^Min/+ mice. Hypertriglyceridemia in these mice may be associated with their hepatic lipid metabolism development.

Dyslipidemias in clinical practice

Most dyslipidemic conditions have been linked to an increased risk of cardiovascular disease. Over the past few years major advances have been made regarding the genetic and metabolic basis of dyslipidemias. Detailed characterization of the genetic basis of familial lipid disorders and knowledge concerning the effects of environmental factors on the expression of dyslipidemias have increased substantially, contributing to a better diagnosis in individual patients. In addition to these developments, therapeutic options to lower cholesterol levels in clinical practice have expanded even further in patients with familial hypercholesterolemia and in subjects with cardiovascular disease. Finally, promising upcoming therapeutic lipid lowering strategies will be reviewed. All these advances will be discussed in relation to current clinical practice with special focus on common lipid disorders including familial dyslipidemias.

Characterization of two novel pathogenic variants at compound heterozygous status in lipase maturation factor 1 gene causing severe hypertriglyceridemia

BACKGROUND

Severe hypertriglyceridemia is a rare disease characterized by triglyceride levels higher than 1000 mg/dL (11.3 mmol/L) and acute pancreatitis. The disease is caused by pathogenic variants in genes encoding lipoprotein lipase (LPL), apolipoprotein A5, apolipoprotein C2, glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1, and lipase maturation factor 1 (LMF1).

OBJECTIVE

We aim to identify the genetic cause of severe hypertriglyceridemia and characterize the new variants in a patient with severe hypertriglyceridemia.

METHODS

The proband was a male showing severe hypertriglyceridemia (triglycerides 1416 mg/dL, 16.0 mmol/L); proband's relatives were also screened. Genetic screening included direct sequencing of the above genes and identification of large rearrangements in the LPL gene. Functional characterization of mutant LMF1 variants was performed by complementing LPL maturation in transfected LMF1-deficient mouse fibroblasts.

RESULTS

The proband and his affected brother were compound heterozygotes for variants in the LMF1 gene never identified as causative of severe hypertriglyceridemia c.[157delC;1351C>T];[410C>T], p.[(Arg53Glyfs*5)];[(Ser137Leu)]. Functional analysis demonstrated that the p.(Arg53Glyfs*5) truncation completely abolished and the p.(Ser137Leu) missense variant dramatically diminished the lipase maturation activity of LMF1.

CONCLUSIONS

In addition to a novel truncating variant, we describe for the first time a missense variant functionally demonstrated affecting the lipase maturation function of LMF1. This is the first case in which compound heterozygous variants in LMF1 were functionally demonstrated as causative of severe hypertriglyceridemia.

New rare genetic variants of LMF1 gene identified in severe hypertriglyceridemia

BACKGROUND

The LMF1 (lipase maturation factor 1) gene encodes a protein involved in lipoprotein lipase and hepatic lipase maturation. Homozygous mutations in LMF1 leading to severe hypertriglyceridemia (SHTG) are rare in the literature. A few additional rare LMF1 variants have been described with poor functional studies.

OBJECTIVE

The aim of this study was to assess the frequency of LMF1 variants in a cohort of 385 patients with SHTG, without homozygous or compound heterozygous deleterious mutations identified in lipoprotein lipase (LPL), apolipoprotein A5 (APOA5), apolipoprotein C2 (APOC2), glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) genes, and to determine their functionality.

METHODS

LMF1 coding variants were screened using denaturing high-performance liquid chromatography followed by direct sequencing. In silico studies of LMF1 variants were performed, followed by in vitro functional studies using human embryonic kidney 293T (HEK-293T) cells cotransfected with vectors encoding human LPL and LMF1 cDNA. LPL activity was measured in cell culture medium after heparin addition using human VLDL-TG as substrate.

RESULTS

Nineteen nonsynonymous coding LMF1 variants were identified in 65 patients; 10 variants were newly described in SHTG. In vitro, p.Gly172Arg, p.Arg354Trp, p.Arg364Gln, and p.Arg537Trp LMF1 variants decreased LPL activity, and the p.Trp464Ter variant completely abolished LPL activity. We identified a young girl heterozygote for the p.Trp464Ter variant and a homozygote carrier of the p.Gly172Arg variant with a near 50% decreased LPL activity in vitro and in vivo.

CONCLUSION

The study confirms the rarity of LMF1 variants in a large cohort of patients with SHTG. LMF1 variants are likely to be involved in multifactorial hyperchylomicronemia. Partial LMF1 defects could be associated with intermittent phenotype as described for p.Gly172Arg homozygous and p.Trp464Ter heterozygous carriers.

A Compound Heterozygous Mutation of Lipase Maturation Factor 1 is Responsible for Hypertriglyceridemia of a Patient

AIM

Dyslipidemia is the most common lipid metabolism disorder in humans, and its etiology remains elusive. Hypertriglyceridemia (HTG) is a type of dyslipidemia that contributes to atherosclerosis and coronary heart disease. Previous studies have demonstrated that mutations in lipoprotein lipase (LPL), apolipoprotein CII (APOC2), apolipoprotein AV (APOA5), glycosylphosphatidylinositol anchored high-density lipoprotein-binding protein 1 (GPIHBP1), lipase maturation factor 1(LMF1), and glycerol-3 phosphate dehydrogenase 1 (GPD1) are responsible for HTG by using genomic microarrays and next-generation sequencing. The aim of this study was to identify genetic lesions in patients with HTG.

METHOD

Our study included a family of seven members from Jiangsu province across three generations. The proband was diagnosed with severe HTG, with a plasma triglyceride level of 38.70 mmol/L. Polymerase chain reaction (PCR) and Sanger sequencing were performed to explore the possible causative gene mutations for this patient. Furthermore, we measured the post-heparin LPL and hepatic lipase (HL) activities using an antiserum inhibition method.

RESULTS

A compound heterozygous mutation in the LMF1 gene (c.257C＞T/p.P86L and c.1184C＞T/p.T395I) was identified and co-segregated with the affected patient in this family. Both mutations were predicted to be deleterious by three bioinformatics programs (Polymorphism Phenotyping-2, Sorting Intolerant From Tolerant, and MutationTaster). The levels of the plasma post-heparin LPL and HL activities in the proband (57 and 177 mU/mL) were reduced to 24% and 75%, respectively, compared with those assayed in the control subject with normal plasma triglycerides.

CONCLUSION

A compound heterozygous mutation of LMF1 was identified in the presenting patient with severe HTG. These findings expand on the spectrum of LMF1 mutations and contribute to the genetic diagnosis and counseling of families with HTG.

Genetic epidemiology of autosomal recessive hypercholesterolemia in Sicily: Identification by next-generation sequencing of a new kindred

BACKGROUND

Autosomal recessive hypercholesterolemia (ARH) is a rare inherited lipid disorder. In Sardinia, differently from other world regions, the mutated allele frequency is high. It is caused by mutations in the low-density lipoprotein receptor adaptor protein 1 gene. Fourteen different mutations have been reported so far; in Sardinia, 2 alleles (ARH1 and ARH2) explain most of the cases. Four ARH patients, all carriers of the ARH1 mutation, have been identified in mainland Italy and 2 in Sicily.

OBJECTIVE

The objectives of the study were to improve the molecular diagnosis of familial hypercholesterolemia (FH) and to estimate the frequency of the ARH1 allele in 2 free-living Sicilian populations.

METHODS

We sequenced by targeted next-generation sequencing 20 genes related to low-density lipoprotein metabolism in 50 hypercholesterolemic subjects. Subjects from 2 free-living populations from Northern (Ventimiglia Heart Study, 848 individuals) and Southern Sicily (Zabut Zabùt Aging Project, 1717 individuals) were genotyped for ARH1 allele.

RESULTS

We identified 1 homozygous carrier of the ARH1 mutation among the 50 hypercholesterolemic outpatients. Population-based genotyping of ARH1 in 2565 subjects allowed the identification of 1 heterozygous carrier. The overall estimated allele frequency of ARH1 in Sicily was 0.0002 (0.02%).

CONCLUSIONS

The identification of a new case of ARH in Sicily among 50 clinically diagnosed FH highlights the importance of next-generation sequencing analysis as tool to improve the FH diagnosis. Our results also indicate that ARH1 carrier status is present in ∼1:2500 of Sicilian inhabitants, confirming that ARH is extremely rare outside Sardinia.