Identification of compound heterozygous mutations (G188E/W382X) of lipoprotein lipase gene in a Japanese infant with hyperchylomicronemia: the G188E mutation was newly identified in Japanese

A case of eruptive xanthomas associated with pregnancy unmasking a G188E heterozygous mutation of the lipoprotein lipase gene: A case report

A case of eruptive xanthomas with exceptionally high levels of blood triglycerides without any complication during pregnancy is reported. Eruptive xanthomas may develop in the setting of severe hypertriglyceridemia. Clinically, patients present with small and smooth papules with a characteristic yellow hue. The condition can also be associated with morbid systemic complications. Estrogen replacement therapy is a known cause of secondary hypertriglyceridemia. Estrogen increase in pregnancy is associated with a physiologic elevation of blood triglycerides in order to provide sufficient nutrition for the fetus. However, in the setting of primary dyslipidemia, severe hypertriglyceridemia can occur. The case presented here was explained by a partial primary lipoprotein lipase deficiency with a heterozygous G188E mutation of the LPL gene. The delivery by induced labor and the introduction of fenofibrate led to a rapid decrease of triglycerides and a resolution of cutaneous lesions without any complication for the patient or her baby.

Identification of a novel LPL nonsense variant and further insights into the complex etiology and expression of hypertriglyceridemia-induced acute pancreatitis

Background

Hypertriglyceridemia (HTG) is a leading cause of acute pancreatitis. HTG can be caused by either primary (genetic) or secondary etiological factors, and there is increasing appreciation of the interplay between the two kinds of factors in causing severe HTG.

Objectives

The main aim of this study was to identify the genetic basis of hypertriglyceridemia-induced acute pancreatitis (HTG-AP) in a Chinese family with three affected members (the proband, his mother and older sister).

Methods

The entire coding and flanking sequences of LPL, APOC2, APOA5, GPIHBP1 and LMF1 genes were analyzed by Sanger sequencing. The newly identified LPL nonsense variant was subjected to functional analysis by means of transfection into HEK-293 T cells followed by Western blot and activity assays. Previously reported pathogenic LPL nonsense variants were collated and compared with respect to genotype and phenotype relationship.

Results

We identified a novel nonsense variant, p.Gln118* (c.351C > T), in the LPL gene, which co-segregated with HTG-AP in the Chinese family. We provided in vitro evidence that this variant resulted in a complete functional loss of the affected LPL allele. We highlighted a role of alcohol abuse in modifying the clinical expression of the disease in the proband. Additionally, our survey of 12 previously reported pathogenic LPL nonsense variants (in 20 carriers) revealed that neither serum triglyceride levels nor occurrence of HTG-AP was distinguishable among the three carrier groups, namely, simple homozygotes, compound heterozygotes and simple heterozygotes.

Conclusions

Our findings, taken together, generated new insights into the complex etiology and expression of HTG-AP.

Lipoprotein Lipase Deficiency Arising in Type V Dyslipidemia

A 40-year-old Japanese man presented with child-onset hypertriglyceridemia recently complicated by diabetes mellitus. The patient's diabetes mellitus was maintained, but he had persistent insulin resistance. The patient also had persistent severe hypertriglyceridemia (1,224-4,104 mg/dL), despite the administration of bezafibrate and ezetimibe. Type V dyslipidemia was revealed by agarose gel electrophoresis and the refrigerator test, and a significantly reduced post-heparin lipoprotein lipase mass of 26 ng/mL was confirmed. Genetic testing confirmed two heterozygous LPL variants, p.Tyr88X and p.Gly215Glu in trans; thus, the patient was diagnosed with lipoprotein lipase deficiency. Lipoprotein lipase deficiency typically arises in type I dyslipidemia, but is latent in type V dyslipidemia.

Severe hypertriglyceridemia due to two novel loss-of-function lipoprotein lipase gene mutations (C310R/E396V) in a Chinese family associated with recurrent acute pancreatitis

Lipoprotein lipase (LPL) is widely expressed in skeletal muscles, cardiac muscles as well as adipose tissue and involved in the catabolism of triglyceride. Herein we have systematically characterized two novel loss-of-function mutations in LPL from a Chinese family in which afflicted members were manifested by severe hypertriglyceridemia and recurrent pancreatitis. DNA sequencing revealed that the proband was a heterozygote carrying a novel c.T928C (p.C310R) mutation in exon 6 of the LPL gene. Another member of the family was detected to be a compound heterozygote who along with the c.T928C mutation also carried a novel missense mutation c.A1187T (p.E396V) in exon 8 of the LPL gene. Furthermore, COS-1 cells were transfected with lentiviruses containing the mutant LPL genes. While C310R markedly reduced the overall LPL protein level, COS-1 cells carrying E396V or double mutations contained similar overall LPL protein levels to the wild-type. The specific activity of the LPL mutants remained at comparable magnitude to the wild-type. However, few LPL were detected in the culture medium for the mutants, suggesting that both mutations caused aberrant triglyceride catabolism. More specifically, E396V and double mutations dampened the transport of LPL to the cell surface, while for the C310R mutation, reducing LPL protein level might be involved. By characterizing these two novel LPL mutations, this study has expanded our understanding on the pathogenesis of familial hypertriglyceridemia (FHTG).

A 60-y-old chylomicronemia patient homozygous for missense mutation (G188E) in the lipoprotein lipase gene showed no accelerated atherosclerosis

BACKGROUND

Familial lipoprotein lipase (LPL) deficiency is a rare autosomal recessive disorder caused by mutations in the LPL gene. Patients with LPL deficiency have chylomicronemia; however, whether they develop accelerated atherosclerosis remains unclear.

METHODS

We investigated clinical and mutational characteristics of a 60-y-old Japanese patient with chylomicronemia.

RESULTS

The patient's fasting plasma triglyceride levels were >9.0 mmol/l. In postheparin plasma, one fifth of the normal LPL protein mass was present; however, LPL activity was undetectable. Molecular analysis of the LPL gene showed the patient to be a homozygote of missense mutation replacing glycine with glutamine at codon 188 (G188E), which had been known to produce mutant LPL protein lacking lipolytic activity. Ultrasonographic examination of the patient's carotid and femoral arteries showed no accelerated atherosclerosis. Moreover, 64-slice mechanical multidetector-row computer tomography (MDCT) angiography did not detect any accelerated atherosclerotic lesions in the patient's coronary arteries. The patient had none of the risk factors such as smoking, hypertension, and diabetes.

CONCLUSIONS

Our case suggests that accelerated atherosclerosis may not develop in patients with LPL deficiency, when they have no risk factors.

Preparation of carbodiimide-terminated dithiolane self-assembly monolayers as a new DNA-immobilization method

A carbodiimide derivative having a dithiolane part at its terminus was designed and synthesized for use to construct carbodiimide-coated self-assembly monolayers (SAMs) on a gold surface with 6-mercaptohexanol (6MH). When treated with poly(dT), poly(dA), or poly(dA)poly(dT), only poly(dT) was immobilized on the surface of the SAMs through a specific reaction of the free imino moiety of thymine (T) with the carbodiimide moiety. The carbodiimide-covered SAM treated with probe DNA was tested in hybridization with sample DNA. Its hybridization efficiency was estimated by ferrocenylnaphthalene diimide (FND), described previously and the result revealed that the carbodiimide-covered SAM electrode can immobilize a DNA probe through the thymine moiety not involved in base pairing. The resulting electrode was capable of hybridizing with the target DNA, as proven by an increased current response of FND.

Reactivity of Ferrocenylcarbodiimide with DNA Duplex Containing Single-mismatched Base Pairs

Ferrocenylcarbodiimide (1), which is known to react with a guanine (G) or thymine (T) base of single stranded DNA, was allowed to react with DNA duplex having a single mismatched base pair of G-T, T-T, or T-cytosine (C). Electrophoreograms of the reaction mixture showed that 1 could react with G or T base of the mismatched sites on the DNA duplex. However, 1 also reacted with the G base of the terminal site on the DNA duplex. This showed that 1 can react with an unpaired base or unstable base pair such as a terminal or mismatched base on the DNA duplex. Electrochemical mismatch detection could be achieved after hybridization of the ferrocenylated mismatched DNA duplex with a selected DNA probe-immobilized electrode. These results revealed that 1 has a potentiality of serving as a labeling reagent of mismatched bases on the DNA duplex, which is important in the search for heterozygous single nucleotide polymorphisms (SNPs).

Genotyping of the human lipoprotein lipase gene by ferrocenylnaphthalene diimide-based electrochemical hybridization assay

A ferrocenylnaphthalene diimide (FND)-based electrochemical hybridization assay (FND-EHA) was applied to the detection of two mutations in human lipoprotein lipase (LPL) gene, G188E (one base transition) and Arita (one base deletion). A probe oligodeoxyribonucleotide of 13 bases representing the wild type (WT) sequence of LPL was immobilized on a gold electrode, followed by hybridization with a sample PCR product of 350 base pairs under conditions in which both WT and mutated (MT) sequences could form a duplex with the probe. The hybridized electrodes were soaked in an electrolyte containing FND under conditions in which only the mismatched duplex could undergo dissociation. FND was concentrated in proportion to the amount of the duplex remaining on the electrode to give rise to a current signal. Blind tests were run to judge the genotype (WT/WT, WT/MT, or MT/MT) of 10 samples each for the G188E and Arita mutations and then, 8 and 10 of them were judged correctly, respectively.

A novel method of identifying genetic mutations using an electrochemical DNA array

We describe the development of a new type of DNA array chip that utilizes electrochemical reactions and a novel method of simultaneously identifying multiple genetic mutations on an array chip. The electrochemical array (ECA) uses a threading intercalator specific to double-stranded nucleotides, ferrocenylnaphthalene diimide (FND), as the indicator. ECA does not require target labeling, and the equipment is simple, durable and less expensive. The simultaneous multiple mutation detection (SMMD) system using an ECA chip and FND utilizes an enzyme to simultaneously distinguish several genetic mutations such as single nucleotide polymorphism (SNP), insertion, deletion, translocation and short tandem repeat. We examined this SMMD system using an ECA chip, by detecting seven different mutations on the lipoprotein lipase (LPL) gene for 50 patients in a blind test. It turned out that all the results obtained were concordant with the sequencing results, demonstrating that this system is a powerful tool for clinical applications.

A Japanese patient with lipoprotein lipase deficiency homozygous for the Gly188Glu mutation prevalent worldwide

We studied the molecular basis of familial lipoprotein lipase (LPL) deficiency in a new Japanese kindred. The proband was a four-month-old infant with severe hyperchylomicronemia. In postheparin plasma, LPL activity was virtually absent, although LPL mass was detectable. Single strand conformational polymorphism (SSCP) analysis showed an abnormal band with exon 5 of the LPL gene that was amplified by PCR from the proband's genomic DNA. DNA sequence analysis of the amplified fragment demonstrated that the proband was homozygous for a G-to-A change at nucleotide position 818 resulting in the substitution of glutamic acid for glycine at codon 188. Although this is among the first Gly188Glu mutations identified in Japanese, the missense mutation has previously been reported as a prevalent cause of familial LPL deficiency worldwide and has been proposed to have a common origin. However, DNA haplotype analysis with either restriction fragment length polymorphism (RFLP) or microsatellite markers revealed that the DNA haplotype of the proband was not identical to the haplotype previously reported as common to the other patients with the Gly188Glu mutation. These results add the Gly188Glu mutation to the growing list of LPL gene mutations underlying familial LPL deficiency in Japanese and indicate that the origin of the Gly188Glu mutation is not necessarily common but would be multicentric at least in part.

Lipoprotein lipase (LPL) deficiency: a new patient homozygote for the preponderant mutation Gly188Glu in the human LPL gene and review of reported mutations: 75 % are clustered in exons 5 and 6

We have investigated the lipoprotein lipase (LPL) gene of a 2-year-old patient presenting classical features of the familial LPL deficiency including undetectable LPL activity. DNA sequence analysis of exon 5 identified the patient as a homozygote for the Gly188Glu mutation, frequently involved in this disease. A review of cases of LPL deficiency with molecular study of the LPL gene showed a total number of 221 reported mutations involved in this disease. Gly188Glu was involved in 23.5 % of cases and 74.6 % of mutations were clustered in exons 5 and 6. Based on these observations, we propose a method of screening for mutations in this gene.