Homozygous missense mutation (G56R) in glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPI-HBP1) in two siblings with fasting chylomicronemia (MIM 144650)

<p>Abstract</p> <p>Background</p> <p>Mice with a deleted <it>Gpihbp1 </it>gene encoding glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPI-HBP1) develop severe chylomicronemia. We screened the coding regions of the human homologue – <it>GPIHBP1 </it>– from the genomic DNA of 160 unrelated adults with fasting chylomicronemia and plasma triglycerides >10 mmol/L, each of whom had normal sequence of the <it>LPL </it>and <it>APOC2 </it>genes.</p> <p>Results</p> <p>One patient with severe type 5 hyperlipoproteinemia (MIM 144650), fasting chylomicronemia and relapsing pancreatitis resistant to standard therapy was found to be homozygous for a novel <it>GPIHBP1 </it>missense variant, namely G56R. This mutation was absent from the genomes of 600 control subjects and 610 patients with hyperlipidemia. The <it>GPIHBP1 </it>G56 residue has been conserved throughout evolution and the G56R mutation was predicted to have compromised function. Her homozygous brother also had refractory chylomicronemia and relapsing pancreatitis together with early coronary heart disease. G56R heterozygotes in the family had fasting mild hypertriglyceridemia.</p> <p>Conclusion</p> <p>Thus, a very rare <it>GPIHBP1 </it>missense mutation appears to be associated with severe hypertriglyceridemia and chylomicronemia.</p

Noninvasive Phenotypes of Atherosclerosis: Similar Windows but Different Views

Background and Purpose-Noninvasive measures of atherosclerosis, such as carotid intima-media thickness, total carotid plaque area, and carotid stenosis, probably represent different phenotypes with distinct determinants. For instance, total carotid plaque area may reflect atherosclerotic lesion size more closely than carotid stenosis, which instead may reflect hemodynamic compromise within the arterial lumen. Methods-In 1821 patients from a Premature Atherosclerosis Clinic, we studied determinants of total carotid plaque area and carotid stenosis as measured by ultrasound using multivariate regression analysis with traditional risk factors and some emerging risk factors. Results-Regression modeling showed that (1) traditional atherosclerosis risk factors were more strongly associated with total carotid plaque area than with carotid stenosis (R = 0.53 and 0.13, respectively), and (2) individual risk factors had different relationships with total carotid plaque area and carotid stenosis. For instance, age accounted for 53% and 26% of the explained variance of total carotid plaque area and carotid stenosis, respectively. Female sex was inversely associated with total carotid plaque area but positively associated with carotid stenosis. Nontraditional risk variables such as plasma homocysteine had different associations with the 2 analytes. Conclusions-Total carotid plaque area and carotid stenosis had different associations with specific atherosclerosis risk factors. Thus, for future studies of the determinants of atherosclerosis, it is important to distinguish between different phenotypes and to appreciate that they will not necessarily have the same determinants

Gene-gene and gene-environment interactions: new insights into the prevention, detection and management of coronary artery disease

Despite the recent success of genome-wide association studies (GWASs) in identifying loci consistently associated with coronary artery disease (CAD), a large proportion of the genetic components of CAD and its metabolic risk factors, including plasma lipids, type 2 diabetes and body mass index, remain unattributed. Gene-gene and gene-environment interactions might produce a meaningful improvement in quantification of the genetic determinants of CAD. Testing for gene-gene and gene-environment interactions is thus a new frontier for large-scale GWASs of CAD. There are several anecdotal examples of monogenic susceptibility to CAD in which the phenotype was worsened by an adverse environment. In addition, small-scale candidate gene association studies with functional hypotheses have identified gene-environment interactions. For future evaluation of gene-gene and gene-environment interactions to achieve the same success as the single gene associations reported in recent GWASs, it will be important to pre-specify agreed standards of study design and statistical power, environmental exposure measurement, phenomic characterization and analytical strategies. Here we discuss these issues, particularly in relation to the investigation and potential clinical utility of gene-gene and gene-environment interactions in CAD

Lipoprotein lipase (LPL) gene variation and progression of carotid artery plaque

Background and Purpose - Coding single nucleotide polymorphisms (cSNPs) in the lipoprotein lipase (LPL) gene have been associated with lipoprotein phenotypes and vascular disease risk. We studied the association between LPL cSNPs and a novel noninvasive measure of disease, namely, cross-sectional carotid plaque area (CPA) on B-mode ultrasound. Methods - Four hundred fifty-two patients from an atherosclerosis prevention clinic had determinations of baseline and total CPA. Traditional atherosclerosis risk factors were recorded, and the LPL D9N, N291S, and S447X cSNPs were genotyped. Multiple regression analysis was used to identify determinants of CPA. Results - Minor allele frequencies for LPL D9N, N291S, and S447X were 2.8%, 0.9%, and 4.4%, respectively. There were no significant between-genotype differences in treated fasting lipids. The LPL D9N genotype was a significant predictor of both baseline CPA (P=0.008) and plaque progression from baseline to 1 year later (P=0.001). Heterozygotes for the N9 allele had higher mean baseline CPA and plaque progression than did LPL D9/D9 homozygotes. Conclusions - LPL D9N genotype may be a determinant of atherosclerosis as estimated by static baseline CPA and by progression of CPA

A mechanism-based operational definition and classification of hypercholesterolemia

In contrast to strong evidence-based clinical recommendations for lipid-lowering treatment, there is no analogous definitive diagnostic definition of hypercholesterolemia and its various subtypes. For many clinicians, guideline indications for hypolipidemic treatment can become broadly conflated with hypercholesterolemia in a non-specific sense. In this statement, we propose a unified definition and mechanism-based classification of hypercholesterolemia, which in turn should help to stratify patients and guide efficient diagnosis without interfering with the current strategies of ASCVD risk reduction

Heterozygous CAV1 frameshift mutations (MIM 601047) in patients with atypical partial lipodystrophy and hypertriglyceridemia

<p>Abstract</p> <p>Background</p> <p>Mice with a deleted <it>Cav1 </it>gene encoding caveolin-1 develop adipocyte abnormalities and insulin resistance. From genomic DNA of patients with atypical lipodystrophy and hypertriglyceridemia who had no mutations in any known lipodystrophy gene, we used DNA sequence analysis to screen the coding regions of human <it>CAV1 </it>(MIM 601047).</p> <p>Results</p> <p>We found a heterozygous frameshift mutation in <it>CAV1</it>, designated I134fsdelA-X137, in a female patient who had atypical partial lipodystrophy, with subcutaneous fat loss affecting the upper part of her body and face, but sparing her legs, gluteal region and visceral fat stores. She had severe type 5 hyperlipoproteinemia, with recurrent pancreatitis. In addition, she had some atypical features, including congenital cataracts and neurological findings. Her father was also heterozygous for this mutation, and had a similar pattern of fat redistribution, hypertriglyceridemia and congenital cataracts, with milder neurological involvement. An unrelated patient had a different heterozygous frameshift mutation in the <it>CAV1 </it>gene, designated -88delC. He also had a partial lipodystrophy phenotype, with subcutaneous fat loss affecting the arms, legs and gluteal region, but sparing his face, neck and visceral fat stores. He also had severe type 5 hyperlipoproteinemia, with recurrent pancreatitis; however he had no clinically apparent neurological manifestations. The mutations were absent from the genomes of 1063 healthy individuals.</p> <p>Conclusion</p> <p>Thus, very rare <it>CAV1 </it>frameshift mutations appear to be associated with atypical lipodystrophy and hypertriglyceridemia.</p

Peroxisomal proliferator activated receptor-γ deficiency in a Canadian kindred with familial partial lipodystrophy type 3 (FPLD3)

BACKGROUND: Familial partial lipodystrophy (Dunnigan) type 3 (FPLD3, Mendelian Inheritance in Man [MIM] 604367) results from heterozygous mutations in PPARG encoding peroxisomal proliferator-activated receptor-γ. Both dominant-negative and haploinsufficiency mechanisms have been suggested for this condition. METHODS: We present a Canadian FPLD3 kindred with an affected mother who had loss of fat on arms and legs, but no increase in facial, neck, suprascapular or abdominal fat. She had profound insulin resistance, diabetes, severe hypertriglyceridemia and relapsing pancreatitis, while her pre-pubescent daughter had normal fat distribution but elevated plasma triglycerides and C-peptide and depressed high-density lipoprotein cholesterol. RESULTS: The mother and daughter were each heterozygous for PPARG nonsense mutation Y355X, whose protein product in vitro was transcriptionally inactive with no dominant-negative activity against the wild-type receptor. In addition the mutant protein appeared to be markedly unstable. CONCLUSION: Taken together with previous studies of human PPARG mutations, these findings suggest that PPAR-γ deficiency due either to haploinsufficiency or to substantial activity loss due to dominant negative interference of the normal allele product's function can each contribute to the FPLD3 phenotype

Abetalipoproteinemia: two case reports and literature review

Abetalipoproteinemia (ABL, OMIM 200100) is a rare, autosomal recessive disorder, characterized by fat malabsorption, acanthocytosis and hypocholesterolemia in infancy. Later in life, deficiency of fat-soluble vitamins is associated with development of atypical retinitis pigmentosa, coagulopathy, posterior column neuropathy and myopathy. ABL results from mutations in the gene encoding the large subunit of microsomal triglyceride transfer protein (MTP; OMIM 157147). To date at least 33 MTP mutations have been identified in 43 ABL patients. We describe the clinical progress of two patients, both currently in the fifth decade of life, who were diagnosed with ABL as children and were treated with high oral doses of fat soluble vitamins, including vitamin E over the last three decades. Treatment appears to have been associated with arrest of the neuropathy and other complications in both patients. Because pharmacologic inhibition of MTP is being developed as a novel approach to reduce plasma cholesterol for prevention of cardiovascular disease, defining the long-term clinical features of patients with a natural deficiency in MTP might provide some insight into the possible effects of such treatments. We review the range of clinical, biochemical and molecular perturbations in ABL

NPC1L1 haplotype is associated with inter-individual variation in plasma low-density lipoprotein response to ezetimibe

BACKGROUND: NPC1L1 encodes a putative intestinal sterol transporter which is the likely target for ezetimibe, a new type of lipid-lowering medication. We previously reported rare non-synonymous mutations in NPC1L1 in an individual who had no plasma lipoprotein response to ezetimibe. We next hypothesized that common variants in NPC1L1 would underlie less extreme inter-individual variations in the plasma LDL cholesterol response to ezetimibe. RESULTS: In 101 dyslipidemic subjects, we found that NPC1L1 haplotype was significantly associated with inter-individual variation in the response of plasma LDL cholesterol to treatment with ezetimibe for 12 weeks. Specifically, about one subject in eight lacked the common NPC1L1 haplotype 1735C-25342A-27677T and these subjects had a significantly greater reduction in plasma LDL cholesterol with ezetimibe than subjects with at least one copy of this haplotype (-35.9+4.0 versus -23.6+1.6 percent reduction, P = 0.0054). This was paralleled by a similar non-significant trend of between-haplotype difference in reduction of total cholesterol. CONCLUSION: These preliminary pharmacogenetic results suggest that NPC1L1 variation is associated with inter-individual variation in response to ezetimibe treatment