Hyperlipidemias: Graham CA

Wierzbicki AS, Graham CA, Young IS, Nicholls DP. · St. Thomas' Hospital, London SE 1 7EH, UK. · Curr Vasc Pharmacol. · Pubmed #18220935 No free full text.

Abstract: Familial combined hyperlipidaemia (FCH) was identified in early genetic studies of populations as a dominant condition associated with mixed hyperlipidaemia and early onset coronary heart disease. Later studies extended the phenotype and noted that this genetic hyperlipidaemia was sensitive to environmental effects. This article reviews the definitions, animal models and genetics of FCH. In contrast to familial hypercholesterolaemia, which is caused by mutations in a limited number of affected genes, the genetics of FCH have remained obscure and very few definite candidate genes have been identified. A strong role for the apoA-I, A-IV, A-V, C-III cluster on chromosome 11 was identified early on and multiple associations have been found to hyperlipidaemia in this region and more strongly to adjacent sections of the chromosome. More recently quantitative trait mapping has identified a number of candidate genes including upstream transcription factor -1 (USF-1) on 1 q21 and CD-36 on chromosome 4. Of these the strongest evidence, based on 4 analyses, links the lipid components of FCH to intronic variants in the USF-1 gene on chromosome 1q21-23. Unfortunately USF-1 yet fails to show clear associations with diabetes and the metabolic syndrome which co-map to this region and are also associated with mixed hyperlipidaemia. Large scale validation of USF-1 variants in other populations is still awaited. It is likely that FCH is a heterogeneous condition, that is subject to wide-scale environmental confounding from common traits such as obesity and the metabolic syndrome, and that the resolution of its genetics is going to prove a severe challenge.

Wright WT, Heggarty SV, Young IS, Nicholls DP, Whittall R, Humphries SE, Graham CA. · Northern Ireland Regional Genetics Centre, Belfast Health and Social Care Trust, Belfast City Hospital, Belfast, UK. · Clin Genet. · Pubmed #18700895 No free full text.

Abstract: Familial hypercholesterolaemia (FH) is a common single gene disorder, pre-disposing to cardiovascular disease, which is most commonly caused by mutations in the LDL-receptor (LDLR) gene. About 5% of patients carry the p.R3527Q (previously R3500Q) mutation in the apolipoprotein B (APOB) gene and 2% carry the p.D374Y mutation in the PCSK9 gene, but the lack of high-throughput methods make routine genetic diagnosis difficult. In this study, we developed an iPLEX MassARRAY Spectrometry mutation test to identify 56 mutations (54 in the LDLR gene, 1 in the APOB gene and 1 in the PCSK9 gene). The iPLEX test was verified by analysing 150 DNA samples from FH patients with a previously characterized mutation and 96 no-mutation control samples. Mutations were identified in all 150 FH mutation-positive samples using the iPLEX assay, with 96% directly called by the software. The false-positive rate in no-mutation control samples was 0.015%. The overall specific mutation assay failure rate was 2.1%. In the UK, this gives an average detection rate of 75%.The FH iPLEX test is not only designed for large-scale targeted population screening for FH mutations, such as lipid clinic patients, but can also be used for population screening. The assay can easily be developed further to include additional FH-causing mutations, thus increasing the sensitivity of the diagnostic assay.

Nicholls DP, Cather M, Byrne C, Graham CA, Young IS. · Regional Lipid Clinic, Royal Victoria Hospital, Belfast, UK. · Int J Clin Pract. · Pubmed #18492057 No free full text.

Abstract: BACKGROUND: Most children with familial hypercholesterolaemia (FH) are diagnosed by raised blood cholesterol levels, but the test lacks sensitivity and specificity. As such children have evidence of vascular dysfunction at an early age, correct identification of affected individuals is important so that treatment can be started. AIM: To determine levels of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) in children with genetically proven FH and their unaffected siblings, in order to identify a diagnostic cut-off point if possible. DESIGN: Retrospective case-note survey. METHODS: We studied the notes of 115 children aged 3-16 years, 69 proven FH and 46 unaffected sibs, 65 boys and 50 girls, from 31 families and 21 different mutations. Data recorded were age, sex, TC, and (when available) LDL-C. RESULTS: The lowest TC level in an affected individual was 4.7 mmol/l and the highest in normal individual was 6.05 mmol/l. This overlap range included 21 children (18% of the total). The corresponding figures for LDL-C were 3.0 and 3.7 mmol/l, which included eight children (8%). CONCLUSION: TC is not an effective test for differentiating affected and unaffected children with FH. LDL-C is better, but genetic testing remains the method of choice, especially if treatment decisions are to be taken.

Wright WT, Young IS, Nicholls DP, Graham CA. · Northern Ireland Regional Genetics Centre, Belfast Health and Social Care Trust, Belfast City Hospital, Lisburn Road, Belfast BT9 7AB, Northern Ireland, UK. · Atherosclerosis. · Pubmed #18068174 No free full text.

Abstract: Serum triglyceride (TG) level is an important independent risk factor for coronary heart disease, with the lipoprotein lipase (LPL) enzyme playing the major role in regulating the catabolism of TG rich lipoproteins. The complete sequence analysis of the LPL gene was carried out on 19 individuals with extreme hypertriglyceridaemia (HTG; TG>14 mmol/l) with a total of 42 sequence variants being identified, a number of which are novel to this study. A total of eight patients were shown to have functional variants (p.D36N, p.R197H, p.N318S, p.V340I) that alter amino acids at 11 of the 16 LPL alleles. Multiplex ligation-dependent probe amplification (MLPA) analysis showed no exonic deletion or duplications in this population. Further analysis of the p.N318S (also called N291S) variant identified in the sequencing screen, in larger case and control populations, identified this mutation to be strongly associated with HTG. This study has produced a more comprehensive SNP map of LPL and its surrounding area and identified p.N318S as a major predisposing factor to HTG in the Northern Irish population.

Graham CA, McIlhatton BP, Kirk CW, Beattie ED, Lyttle K, Hart P, Neely RD, Young IS, Nicholls DP. · Regional Genetics Centre, Belfast City Hospital, Belfast BT9 7AB, Northern Ireland, UK. · Atherosclerosis. · Pubmed #16159606 No free full text.

Abstract: Familial hypercholesterolemia (FH) is a common single gene disorder, which predisposes to coronary artery disease. In a previous study, we have shown that in patients with definite FH around 20% had no identifiable gene defect after screening the entire exon coding area of the low density lipoprotein receptor (LDLR) and testing for the common Apolipoprotein B (ApoB) R3500Q mutation. In this study, we have extended the screen to additional families and have included the non-coding intron splice regions of the gene. In families with definite FH (tendon xanthoma present, n=68) the improved genetic screening protocol increased the detection rate of mutations to 87%. This high detection rate greatly enhances the potential value of this test as part of a clinical screening program for FH. In contrast, the use of a limited screen in patients with possible FH (n=130) resulted in a detection rate of 26%, but this is still of significant benefit in diagnosis of this genetic condition. We have also shown that 14% of LDLR defects are due to splice site mutations and that the most frequent splice mutation in our series (c.1845+11 c>g) is expressed at the RNA level. In addition, DNA samples from the patients in whom no LDLR or ApoB gene mutations were found, were sequenced for the NARC-1 gene. No mutations were identified which suggests that the role of NARC-1 in causing FH is minor. In a small proportion of families (<10%) the genetic cause of the high cholesterol remains unknown, and other genes are still to be identified that could cause the clinical phenotype FH.

Wright WT, Young IS, Nicholls DP, Patterson C, Lyttle K, Graham CA. · Centre for Clinical and Population Science, Queen's University, Belfast BT9 7AB, UK. · Atherosclerosis. · Pubmed #16125709 No free full text.

Abstract: Serum triglyceride levels (TG) are important independent risk factors for coronary heart disease. The apolipoproteins C-III (apoCIII) and A-V (apoAV) are central to normal TG metabolism and the complete sequence analysis of these genes was carried out in severe cases (TG > 9 mmol/l) and controls (TG < 2 mmol/l). A total of 53 SNPs were identified in these genes with 17 being novel to this study. Further analysis defined four APOC3 SNPs and three APOA5 SNPs showing strong association with TG levels. Analysis of the two major SNPs from APOA5 [c.56C > G, c.-3A > G] and from APOC3 [c.102C > T, c.340C > G] using THESIAS has identified two major haplotypes relative to the most common CACC haplotype showing very strong association with hypertriglyceridaemia, CGTG and GATC (odds ratio 7.45 and 5.26). Logistic regression analysis of these four SNPs revealed that, carriage of the APOA5 c.56 G allele (odd ratios 4.49) and the APOA5 c.-3 G allele (odds ratio 3.23) were strong independent predictors of hypertriglyceridaemia (P < 0.001), whereas in contrast, carriage of the APOC3 c102 T allele (odds ratio 1.35) and the APOC3 c.340 G allele (odds ratio 1.37), did not show any significant effects that were independent of APOA5.

McDonnell MG, Young IS, Nicholls DP, Archbold GP, Graham CA. · Department of Clinical Chemistry, Belfast City Hospital Trust, Belfast BT9 7AB, Northern Ireland, UK. · Br J Biomed Sci. · Pubmed #12866915 No free full text.

Abstract: The aim of this study is to assess whether genetic variation at the lipoprotein lipase (LPL) gene is related to fasting triglyceride levels or to the presence of vascular disease. Hypertriglyceridaemic patients are genotyped for the N291S, G188E, and P207L variants and the HindIII and PvuII restriction fragment length polymorphisms of the LPL gene. Sequence analysis is carried out on exons 1-9 of the LPL gene for patients with severe hypertriglyceridaemia, to search for new gene variants. No differences were found between the patient and control group for the N291S, G188E and P207L variants. The HindIII and PvuII allelic frequencies were found to be similar for patients and controls; however, the frequency of the PvuII P2 allele was higher in patients with vascular disease (allele frequency: 0.56) than patients with no vascular disease (allele frequency, 0.42) (P=0.03). Sequence analysis revealed no exon sequence variants in the LPL gene but two intron sequence variants were found in intron 5 in two patients.

McClean E, Graham CA, Ward AJ, Young IS, Martin S, Nicholls DP. · Clinical Chemistry Department, Belfast City Hospital, Northern Ireland, UK. · Br J Biomed Sci. · Pubmed #10795369 No free full text.

Abstract: Familial defective apolipoprotein B-100 (FDB) R3500Q is an autosomal co-dominant disorder caused by the substitution of glutamine for arginine at amino acid residue 3500 of the apolipoprotein B-100 gene. It is associated with hypercholesterolaemia of varying severity, and with coronary artery disease. Hypercholesterolaemic patients (n = 158) from Northern Ireland were screened for the defect by polymerase chain reaction-mediated, site-directed mutagenesis. Clinical presentation ranged from moderate hypercholesterolaemia with a family history of hypercholesterolaemia or heart disease (n = 104) to those classified as definitely having familial hypercholesterolaemia (FH) (n = 54). Eight (5.1%) unrelated individuals were found to be heterozygous for the FDB R3500Q mutation, including two (3.7%) of those 54 classified clinically as having FH. Treatment with HMG-CoA-reductase-inhibiting drugs (statins) decreased total cholesterol by 22-44% and low-density lipoprotein cholesterol by 34-46% in all but one FDB heterozygote.

Graham CA, McClean E, Ward AJ, Beattie ED, Martin S, O'Kane M, Young IS, Nicholls DP. · Northern Ireland Genetics Centre, Belfast City Hospital Trust, Lisburn Road, Belfast, BT9 7AB, UK. · Atherosclerosis. · Pubmed #10559517 No free full text.

Abstract: The aim of this study was to develop a mutation screening protocol for familial hypercholesterolaemia (FH) patients and to assess genotype/phenotype effects in terms of pre-treatment lipid profiles and presentation of tendon xanthomata (TX). A total of 158 families with clinical definitions of possible (120) or definite (38) FH were studied using a tiered screening protocol. Mutations were identified in 52 families, 44 families showing 23 different LDLR gene defects and eight families showing the common Apo B100 gene defect R3500Q. LDLR defects were detected in various regions of the gene with 56% in the LDL binding domain (exons 2-6) and 37% in the EGF precursor homology domain (exons 7-14). The most common mutations were D461N(7), C210X(5), 932delA(5), and C163Y(4). Frameshift mutations accounted for 20% with nonsense 13%, mis-sense 35%, splice 3%, Apo B 13% and 2% large deletion, 13% of clinically definite FH remained undefined. In conclusion, DNA based diagnosis is possible in 79% (30/38) of clinically definite FH families and of the 120 possible FH families at the start of the screening program, 18% (22/120) now have defined mutations. Overall 60 families from the original 158 meet the clinical and/or genetic criteria for definite FH. Tendon xanthomata were present in only 58% (30/52) of genetically defined FH families, thus limiting its use as a strict diagnostic criteria. Families with low density lipoprotein receptor (LDLR) defects present with higher total and LDL cholesterol levels and a higher incidence of TX than do those with the common Apo B variant, and frameshift mutations appear to have the most severe presentation.

Graham CA, Wright WT, McIlhatton BP, Young IS, Nicholls DP. · No affiliation provided · Atherosclerosis. · Pubmed #16735037 No free full text.

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