Genome sequencing and gene-based therapies appear poised to advance the management of rare lipoprotein disorders and associated dyslipidaemias. However, in practice, underdiagnosis and undertreatment of these disorders are common, in large part due to interindividual variability in the genetic causes and phenotypic presentation of these conditions. To address these challenges, the European Atherosclerosis Society formed a task force to provide practical clinical guidance focusing on patients with extreme concentrations (either low or high) of plasma low-density lipoprotein cholesterol, triglycerides, or high-density lipoprotein cholesterol. The task force also recognises the scarcity of quality information regarding the prevalence and outcomes of these conditions. Collaborative registries are needed to improve health policy for the care of patients with rare dyslipidaemias.

Authors: Robert A Hegele, Jan Borén, Henry N Ginsberg, Marcello Arca, Maurizio Averna, Christoph J Binder et al.

Severe hypertriglyceridemia is an endocrine emergency and is associated with acute pancreatitis and hyperviscosity syndrome. We describe an infant with lipoprotein lipase deficiency with severe hypertriglyceridemia who presented with acute pancreatitis. She was managed acutely with fasting and intravenous insulin infusion, followed by low-fat diet with no pharmacological agent. Subsequent follow-up until the age of 5 years showed satisfactory lipid profile and she has normal growth and development.

Authors: Sarah W Y Poon, Karen K Y Leung and Joanna Y L Tung

Familial chylomicronaemia syndrome (FCS) is a rare, inherited disorder characterised by impaired clearance of triglyceride (TG)-rich lipoproteins from plasma, leading to severe hypertriglyceridaemia (HTG) and a markedly increased risk of acute pancreatitis. It is due to the lack of lipoprotein lipase (LPL) function, resulting from recessive loss of function mutations in the genes coding LPL or its modulators. A large overlap in the phenotype between FCS and multifactorial chylomicronaemia syndrome (MCS) contributes to the inconsistency in how patients are diagnosed and managed worldwide, whereas the incidence of acute hypertriglyceridaemic pancreatitis is more frequent in FCS. A panel of European experts provided guidance on the diagnostic strategy surrounding FCS and proposed an algorithm-based diagnosis tool for identification of these patients, which can be readily translated into practice. Features included in this FCS score comprise: severe elevation of plasma TGs (fasting TG levels >10 mmol/L [885 mg/dL] on multiple occasions), refractory to standard TG-lowering therapies, a young age at onset, the lack of secondary factors (except for pregnancy and oral oestrogens) and a history of episodes of acute pancreatitis. Considering 53 FCS patients from three cohorts and 52 MCS patients from three cohorts, the overall sensitivity of the FCS score (≥10) was 88% (95% confidence interval [CI]: 0.76, 0.97) with an overall specificity of 85% (95% CI: 0.75, 0.94). Receiver operating characteristic curve area was 0.91. Pragmatic clinical scoring, by standardising diagnosis, may help differentiate FCS from MCS, may alleviate the need for systematic genotyping in patients with severe HTG and may help identify high-priority candidates for genotyping.

Authors: Philippe Moulin^a  Robert Dufour^b  Maurizio Averna^c Marcello Arca^d Angelo B. Cefalù^c Davide Noto^c  Laura D’Erasmo^d Alessia Di Costanzo^d Christophe Marçais^a Luis Antonio Alvarez-Sala Walther^e  Maciej Banach^f  Jan Borén^g  Robert Cramb^h  Ioanna Gouni-Bertholdⁱ  Elizabeth Hughes^j Colin Johnson^k Xavier Pintó^l  Željko Reiner^m   Jeanine Roeters van Lennepⁿ Handrean Soran^o Claudia Stefanutti^p  Erik Stroes^q  Eric Bruckert^r

The DNA sequences were determined for the lipoprotein lipase (LPL) gene from five unrelated Japanese patients with familial LPL deficiency. The results demonstrated that all five patients are homozygotes for distinct point mutations dispersed throughout the LPL gene. Patient 1 has a G-to-A transition at the first nucleotide of intron 2, which abolishes normal splicing. Patient 2 has a nonsense mutation in exon 3 (Tyr61----Stop) and patient 3 in exon 8 (Trp382----Stop). The latter mutation emphasizes the importance of the carboxy-terminal portion of the enzyme in the expression of LPL activity. Missense mutations were identified in patient 4 (Asp204----Glu) and patient 5 (Arg243----His) in the strictly conserved amino acids. Expression study of both mutant genes in COS-1 cells produced inactive enzymes, establishing the functional significance of the two mis-sense mutations. In these patients, postheparin plasma LPL mass was either virtually absent (patients 1 and 2) or significantly decreased (patients 3-5). To detect these mutations more easily, we developed a rapid diagnostic test for each mutation. We also determined the DNA haplotypes for patients and confirmed the occurrence of multiple mutations on the chromosomes with an identical haplotype. These results demonstrate that familial LPL deficiency is a heterogeneous genetic disease caused by a wide variety of gene mutations.

Authors: T Gotoda, N Yamada, M Kawamura, K Kozaki, N Mori, S Ishibashi, H Shimano, F Takaku, Y Yazaki and Y Furuichi

There has been great interest over the past two decades in developing gene therapies (GTs) to treat a variety of diseases; however, translating research findings into clinical treatments have proved to be a challenge. A major milestone in the development of GT has been achieved with the approval of alipogene tiparvovec (Glybera(®)) in Europe for the treatment of familial lipoprotein lipase deficiency. At this important stage with the evolution of GT into the clinic, this review will examine the safety aspects GT with adeno-associated virus (AAV) vectors. The topics that will be covered include acute reactions, immunological reactions to the AAV capsid and expressed transgene, viral biodistribution and shedding, DNA integration and carcinogenicity. These safety aspects of GT will be discussed with a focus on alipogene tiparvovec, in addition to other AAV vector GT products currently in clinical development.

Authors: Salmon F, Grosios K and Petry H

The present review summarizes the clinical development of adeno-associated viral vector (AAV)1-lipoprotein lipase (LPL)^S447X gene therapy (alipogene tiparvovec) for lipoprotein lipase deficiency. Lipoprotein lipase deficiency is a rare inherited disease characterized by severe hypertriglyceridaemia, chylomicronaemia and risk of recurrent pancreatitis or other complications. AAV1-LPL^S447X gene therapy is based on the rationale that by adding episomal copies of functional LPL genes into muscle cells lacking active LPL, metabolic function could be improved or restored.

Authors: Daniel Gaudet, Julie Méthot and John Kastelein

Lipoprotein lipase (LPL) deficiency is a monogenetic disorder that underlies persistently elevated triglyceride (TG) levels and consequently predisposes patients to potentially life-threatening pancreatitis.

Authors: Erik S. Stroes, Melchior C. Nierman, Janneke J. Meulenberg, Remco Franssen, Jaap Twisk, C. Pieter Henny, Mario M. Maas, Aeilko H. Zwinderman, Colin Ross, Eleonora Aronica, Katherine A. High, Marcel M. Levi, Michael R. Hayden, John J. Kastelein, and Jan Albert Kuivenhoven

Clinical characteristics.

Familial lipoprotein lipase (LPL) deficiency usually presents in childhood and is characterized by very severe hypertriglyceridemia with episodes of abdominal pain, recurrent acute pancreatitis, eruptive cutaneous xanthomata, and hepatosplenomegaly. Clearance of chylomicrons from the plasma is impaired, causing triglycerides to accumulate in plasma and the plasma to have a milky (lactescent or lipemic) appearance. Symptoms usually resolve with restriction of total dietary fat to ≤20 g/day.

Authors: John R Burnett, MB ChB, MD, PhD, FRCPA, Amanda J Hooper, PhD, and Robert A Hegele, MD, FRCPC, FACP.

Raised plasma triglycerides (TGs) and nonesterified fatty acid (NEFA) concentrations are thought to play a role in the pathogenesis of insulin-resistant diabetes. We report on two sisters with extreme hypertriglyceridemia and overt diabetes, in whom surgical normalization of TGs cured the diabetes. In all of the family members (parents, two affected sisters, ages 18 and 15 years, and an 11-year-old unaffected sister), we measured oral glucose tolerance, insulin sensitivity (by the euglycemic-hyperinsulinemic clamp technique), substrate oxidation (indirect calorimetry), endogenous glucose production (by the [6,6-2H2]glucose technique), and postheparin plasma lipoprotein lipase (LPL) activity. In addition, GC-clamped polymerase chain reaction-amplified DNA from the promoter region and the 10 coding LPL gene exons were screened for nucleotide substitution. Two silent mutations were found in the father's exon 4 (Glu118 Glu) and in the mother's exon 8 (Thr361 Thr), while a nonsense mutation (Ser447 Ter) was detected in the mother's exon 9. Mutations in exons 4 and 8 were inherited by the two affected girls. At 1-2 years after the appearance of hyperchylomicronemia, both sisters developed hyperglycemia with severe insulin resistance. Because medical therapy (including high-dose insulin) failed to reduce plasma TGs or control glycemia, lipid malabsorption was surgically induced by a modified biliopancreatic diversion. Within 3 weeks of surgery, plasma TGs and NEFA and cholesterol levels were drastically lowered. Concurrently, fasting plasma glucose levels fell from 17 to 5 mmol/l (with no therapy), while insulin-stimulated glucose uptake, oxidation, and storage were all markedly improved. Throughout the observation period, plasma TG levels were closely correlated with both plasma glucose and insulin concentrations, as measured during the oral glucose tolerance test. These cases provide evidence that insulin-resistant diabetes can be caused by extremely high levels of TGs.

Authors: G Mingrone, F L Henriksen, A V Greco, L N Krogh, E Capristo, A Gastaldelli, M Castagneto, E Ferrannini,  G Gasbarrini and H Beck-Nielsen

To describe the characteristics of lipoprotein lipase (LPL)-deficient patients seen in infancy and to evaluate the safety and efficacy of severe fat restriction. LPL deficiency was demonstrated in 16 infants who presented with irritability (n = 7), lower intestinal bleeding (n = 2), pallor, anemia, or splenomegaly (n = 5), and a family history or fortuitous discovery (n = 2). All plasma samples were lactescent at presentation. Chylomicronemia responded rapidly to dietary fat restriction, and it was possible to maintain satisfactory metabolic control for a prolonged period of time. Only 1 adolescent girl had an episode of pancreatitis associated with the use of oral contraceptives. No persistent adverse effects on growth were seen. We obtained abnormal values for serum iron, alkaline phosphatase, and total calcium.

Authors: Juan Carlos Feoli-Fonseca MD, Emile Lévy PhD, Muriel Godard RD, Marie Lambert MD

We herein report a case of a 40-year-old Japanese woman (patient IT) with a history of recurrent aggravation of hypertriglyceridaemia, pancreatitis and miscarriages in three previous pregnancies. However, strict dietary intervention was applied during a fourth pregnancy. As a result, acute pancreatitis was avoided, and the patient gave birth to a healthy infant. Inpatient IT, the underlying etiology of the recurrent aggravation of hypertriglyceridaemia during pregnancy was a lipoprotein lipase (LPL) gene aberration. She was homozygous for LPL deficiency due to a nonsense mutation (TGG1401 ] TGA/Trp382 ] Stop) in exon 8 of the LPL gene, which resulted in the absence of LPL activity and immunoreactive LPL mass. Our findings indicate that, in LPL deficiency, pregnancy seriously exacerbates hypertriglyceridaemia and increases the risk of acute pancreatitis, which endangers both the mother and fetus. Early diagnosis of LPL deficiency and appropriate management thereof are essential for normal childbirth.

Authors: Shigeki Suga, Naoki Tamasawa, Ichiro Kinpara, Hiroshi Murakami, Nobuhiko Kasai, Tomio Onuma, Yasuyuki Ikeda, Atsuko Takagi, Toshihiro Suda

Patients with lipoprotein lipase deficiency usually present with chylomicronemia in childhood. The syndrome has been considered nonatherogenic primarily because of the low levels of low-density lipoprotein (LDL) cholesterol. We prospectively evaluated patients with lipoprotein lipase deficiency for atherosclerosis.

Authors: Pascale Benlian, M.D., Ph.D., Jean Luc De Gennes, M.D., Luc Foubert, M.D., Hanfang Zhang, Ph.D., S. Eric Gagné, M.Sc., and Michael Hayden, M.B., Ch.B., Ph.D.

We studied the molecular basis of familial Type I hyperlipoproteinemia in two brothers of Turkish descent who had normal plasma apolipoprotein C-II levels and undetectable plasma post-heparin lipoprotein lipase (LPL) activity. We cloned the cDNAs of LPL mRNA from adipose tissue biopsies obtained from these individuals by the polymerase chain reaction and directional cloning into M13 vectors. Direct sequencing of pools of greater than 2000 cDNA clones indicates that their LPL mRNA contains two mutations: a missense mutation changing codon 156 from GAU to GGU predicting an Asp156----Gly substitution and a nonsense mutation changing the codon for Ser447 from UCA to UGA, a stop codon, predicting a truncated LPL protein that contains 446 instead of 448 amino acid residues. Both patients were homozygous for both mutations. Analysis of genomic DNAs of the patients and their family members by the polymerase chain reaction, restriction enzyme digestion (the GAT----GGT mutation abolishes a TaqI restriction site), and allele-specific oligonucleotide hybridization confirms that the patients were homozygous for these mutations at the chromosomal level, and the clinically unaffected parents and sibling were true obligate heterozygotes for both mutations. In order to examine the functional significance of the mutations in this family, we expressed wild type and mutant LPLs in vitro using a eukaryotic expression vector. Five types of LPL proteins were produced in COS cells by transient transfection: (i) wild type LPL, (ii) Asp156----Gly mutant, (iii) Ser447----Ter mutant, (iv) Gly448----Ter mutant, and (v) Asp156----Gly/Ser447----Ter double mutant. Both LPL immunoreactive mass and enzyme activity were determined in the culture media and intracellularly. Immunoreactive LPLs were produced in all cases. The mutant LPLs, Asp156----Gly and Asp156----Gly/Ser447----Ter, were devoid of enzyme activity, indicating that the Asp156----Gly mutation is the underlying defect for the LPL deficiency in the two patients. The two mutant LPLs missing a single residue (Gly448) or a dipeptide (Ser447-Gly448) from its carboxyl terminus had normal enzyme activity. Thus, despite its conservation among all mammalian LPLs examined to date, the carboxyl terminus of LPL is not essential for enzyme activity. We further screened 224 unrelated normal Caucasians for the Ser447----Ter mutation and found 36 individuals who were heterozygous and one individual who was homozygous for this mutation, indicating that it is a sequence polymorphism of no functional significance. Human LPL shows high homology to hepatic triglyceride lipase and pancreatic lipase.

Authors: F Faustinella, A Chang, J P Van Biervliet, M Rosseneu, N Vinaimont, L C Smith, S H Chen and L Chan