A molecular genetic service for diagnosing individuals with familial hypercholesterolaemia (FH) in the United Kingdom

Assessing the genetic burden of familial hypercholesterolemia in a large middle eastern biobank

BACKGROUND

The genetic architecture underlying Familial Hypercholesterolemia (FH) in Middle Eastern Arabs is yet to be fully described, and approaches to assess this from population-wide biobanks are important for public health planning and personalized medicine.

METHODS

We evaluate the pilot phase cohort (n = 6,140 adults) of the Qatar Biobank (QBB) for FH using the Dutch Lipid Clinic Network (DLCN) criteria, followed by an in-depth characterization of all genetic alleles in known dominant (LDLR, APOB, and PCSK9) and recessive (LDLRAP1, ABCG5, ABCG8, and LIPA) FH-causing genes derived from whole-genome sequencing (WGS). We also investigate the utility of a globally established 12-SNP polygenic risk score to predict FH individuals in this cohort with Arab ancestry.

RESULTS

Using DLCN criteria, we identify eight (0.1%) 'definite', 41 (0.7%) 'probable' and 334 (5.4%) 'possible' FH individuals, estimating a prevalence of 'definite or probable' FH in the Qatari cohort of ~ 1:125. We identify ten previously known pathogenic single-nucleotide variants (SNVs) and 14 putatively novel SNVs, as well as one novel copy number variant in PCSK9. Further, despite the modest sample size, we identify one homozygote for a known pathogenic variant (ABCG8, p. Gly574Arg, global MAF = 4.49E-05) associated with Sitosterolemia 2. Finally, calculation of polygenic risk scores found that individuals with 'definite or probable' FH have a significantly higher LDL-C SNP score than 'unlikely' individuals (p = 0.0003), demonstrating its utility in Arab populations.

CONCLUSION

We design and implement a standardized approach to phenotyping a population biobank for FH risk followed by systematically identifying known variants and assessing putative novel variants contributing to FH burden in Qatar. Our results motivate similar studies in population-level biobanks - especially those with globally under-represented ancestries - and highlight the importance of genetic screening programs for early detection and management of individuals with high FH risk in health systems.

Genetic testing for familial hypercholesterolemia-past, present, and future

In the early 1980s, the Nobel Prize winning cellular and molecular work of Mike Brown and Joe Goldstein led to the identification of the LDL receptor gene as the first gene where mutations cause the familial hypercholesterolemia (FH) phenotype. We now know that autosomal dominant monogenic FH can be caused by pathogenic variants of three additional genes (APOB/PCSK9/APOE) and that the plasma LDL-C concentration and risk of premature coronary heart disease differs according to the specific locus and associated molecular cause. It is now possible to use next-generation sequencing to sequence all exons of all four genes, processing 96 patient samples in one sequencing run, increasing the speed of test results, and reducing costs. This has resulted in the identification of not only many novel FH-causing variants but also some variants of unknown significance, which require further evidence to classify as pathogenic or benign. The identification of the FH-causing variant in an index case can be used as an unambiguous and rapid test for other family members. An FH-causing variant can be found in 20-40% of patients with the FH phenotype, and we now appreciate that in the majority of patients without a monogenic cause, a polygenic etiology for their phenotype is highly likely. Compared with those with a monogenic cause, these patients have significantly lower risk of future coronary heart disease. The use of these molecular genetic diagnostic methods in the characterization of FH is a prime example of the utility of precision or personalized medicine.

Mutational Spectrum of LDLR and PCSK9 Genes Identified in Iranian Patients With Premature Coronary Artery Disease and Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is a common, yet underdiagnosed, genetic disorder characterized by lifelong elevated low-density lipoprotein cholesterol levels, which can increase the risk of early-onset coronary artery disease (CAD). In the present study, we screened the nucleotide variations of the LDLR and PCSK9 genes, as well as a part of the APOB gene, in Iranian patients with FH and premature CAD to find the genetic cause of the disorder. Fifteen unrelated individuals with a clinical diagnosis of FH and premature CAD were recruited. Direct DNA sequencing was applied to screen the whole coding exons and exon-intron boundaries of the LDLR and PCSK9 genes and the main parts of their introns, together with exon 26 of the APOB gene. The pathogenicity of the identified mutations was investigated via either segregation analyses in the family or in silico predictive software. Six different point mutations (p.Cys148Tyr, p.Cys216Tyr, p.Cys302Trp, p.Cys338Trp, p.Leu479Gln, and p.G593Afs∗72) in LDLR and a double mutation (p.Asp172His and p.Ala53Val) in both LDLR and PCSK9 genes were identified in seven families with clinically diagnosed FH (43%), whereas no pathogenic mutations were found in eight families with clinically diagnosed FH. This study is the first to identify 1 pathogenic mutation in the LDLR gene (c.1014C > G [p.Cys338Trp]) and to cosegregate it from the affected individual in the family. No mutations were found in the APOB gene, whereas several silent mutations/polymorphisms were identified in the LDLR and PCSK9 genes. Genetic testing and reports on nucleotide alterations in the Iranian population are still limited. Our findings not only further confirm the significant role of FH in the incidence of premature CAD but also enlarge the spectrum of LDLR and PCSK9 variations and exhibit the heterogeneity of FH in Iranians. In patients with no mutation in the examined genes, the disease could be begotten either by a polygenic cause or by gene defects occurring in other related genes and regions not targeted in this study.

Higher Responsiveness to Rosuvastatin in Polygenic versus Monogenic Hypercholesterolaemia: A Propensity Score Analysis

Background: The monogenic defect in familial hypercholesterolemia (FH) is detected in ∼40% of cases. The majority of mutation-negative patients have a polygenic cause of high LDL-cholesterol (LDL-C). We sought to investigate whether the underlying monogenic or polygenic defect is associated with the response to rosuvastatin.

METHODS

FH Individuals were tested for mutations in LDLR and APOB genes. A previously established LDL-C-specific polygenic risk score (PRS) was used to examine the possibility of polygenic hypercholesterolemia in mutation-negative patients. All of the patients received rosuvastatin and they were followed for 8 ± 2 months. A propensity score analysis was performed to evaluate the variables associated with the response to treatment.

RESULTS

Monogenic subjects had higher mean (±SD) baseline LDL-C when compared to polygenic (7.6 ± 1.5 mmol/L vs. 6.2 ± 1.2 mmol/L; p < 0.001). Adjusted model showed a lower percentage of change in LDL-C after rosuvastatin treatment in monogenic patients vs. polygenic subjects (45.9% vs. 55.4%, p < 0.001). The probability of achieving LDL-C targets in monogenic FH was lower than in polygenic subjects (0.075 vs. 0.245, p = 0.004). Polygenic patients were more likely to achieve LDL-C goals, as compared to those monogenic (OR 3.28; 95% CI: 1.23-8.72).

CONCLUSION

Our findings indicate an essentially higher responsiveness to rosuvastatin in FH patients with a polygenic cause, as compared to those carrying monogenic mutations.

Endoplasmic reticulum quality control of LDLR variants associated with familial hypercholesterolemia

Loss-of-function mutations in the low-density lipoprotein receptor (LDLR) gene can cause familial hypercholesterolemia (FH), but detailed functional evidence for pathogenicity is limited to a few reported mutations. Here, we investigated the cellular pathogenic mechanisms of three mutations in LDLR causing FH, which are structurally identical to pathogenic mutations in the very low-density lipoprotein receptor (VLDLR). Similar to the VLDLR mutants, LDLR mutants D482H and C667F were found to be localized to the ER, while D445E, which is a conserved amino acid change, did not affect the trafficking of the receptor to the plasma membrane, as confirmed by the N-glycosylation profile. Although the ER-retained mutant proteins were soluble, induction of ER stress was observed as indicated by spliced X-box binding protein-1 (XBP-1) mRNA levels. The mutants were found to associate with ER quality control components, and their stability was enhanced by inhibitors of proteasome. Our results contribute to the growing list of transport-deficient class II LDLR variants leading to FH and provide evidence for the involvement of endoplasmic reticulum-associated degradation in their stability.

New Case Detection by Cascade Testing in Familial Hypercholesterolemia: A Systematic Review of the Literature

BACKGROUND

The prevalence of familial hypercholesterolemia is 1 in 250, but <10% of patients are diagnosed. Cascade testing enables early detection of cases through systematic family tracing. Establishment of familial hypercholesterolemia cascade testing programs in the US could be informed by approaches used elsewhere.

METHODS

We conducted a systematic review of published studies in the English language of cascade testing for familial hypercholesterolemia, which reported the number of index cases and number of relatives tested and specified methods of contacting relatives and testing modalities methods utilized. For each study, we calculated yield (proportion of relatives who test positive) and new cases per index case, to facilitate comparison.

RESULTS

We identified 10 studies from the literature that met inclusion criteria; the mean number of probands and relatives per study was 242 and 826, respectively. The average yield was 44.76% with a range of 30% to 60.5%, and the mean new cases per index case was 1.65 with a range of 0.22 to 8.0. New cases per index case tended to be greater in studies that used direct contact versus indirect contact (2.06 versus 0.86), tested beyond first-degree relatives versus only first-degree relatives (3.65 versus 0.80), used active sample collection versus collection at clinic (4.11 versus 1.06), and utilized genetic testing versus biochemical testing (2.47 versus 0.42).

CONCLUSIONS

New case detection in familial hypercholesterolemia cascade testing programs tended to be higher with direct contact of relatives, testing beyond first-degree relatives, in-home-based sample collection, and genetic testing. These findings should be helpful for establishing cascade testing programs in the United States.

Current Genetic Service Delivery Models for the Provision of Genetic Testing in Europe: A Systematic Review of the Literature

Background: The provision of genetic services, along with research in the fields of genomics and genetics, has evolved in recent years to meet the increasing demand of consumers interested in prediction of genetic diseases and various inherited traits. The aim of this study is to evaluate genetic services in order to identify and classify delivery models for the provision of genetic testing in European and in extra-European countries. Methods: A systematic review of the literature was conducted using five electronic resources. Inclusion criteria were that studies be published in English or Italian during the period 2000-2015 and carried out in European or extra-European countries (Canada, USA, Australia, or New Zealand). Results: 148 genetic programs were identified in 117 articles and were delivered mostly in the UK (59, 40%), USA (35, 24%) or Australia (16, 11%). The programs were available nationally (66; 45%), regionally (49; 33%) or in urban areas (21, 14%). Ninety-six (64%) of the programs were integrated into healthcare systems, 48 (32.21%) were pilot programs and five (3%) were direct-to-consumer genetic services. The genetic tests offered were mainly for BRCA1/2 (59, 40%), Lynch syndrome (23, 16%), and newborn screening (18, 12%). Healthcare professionals with different backgrounds are increasingly engaged in the provision of genetic services. Based on which healthcare professionals have prominent roles in the respective patient care pathways, genetic programs were classified into five models: (i) the geneticists model; (ii) the primary care model; (iii) the medical specialist model; (iv) the population screening programs model; and (v) the direct-to-consumer model. Conclusions: New models of genetic service delivery are currently under development worldwide to address the increasing demand for accessible and affordable services. These models require the integration of genetics into all medical specialties, collaboration among different healthcare professionals, and the redistribution of professional roles. An appropriate model for genetic service provision in a specific setting should ideally be defined according to the type of healthcare system, the genetic test provided within a genetic program, and the cost-effectiveness of the intervention. Only applications with proven efficacy and cost-effectiveness should be implemented in healthcare systems and made available to all citizens.

p.(Asp47Asn) and p.(Thr62Met): non deleterious LDL receptor missense variants functionally characterized in vitro

Familial Hypercholesterolemia (FH) is a common genetic disorder caused most often by mutations in the Low Density Lipoprotein Receptor gene (LDLr) leading to high blood cholesterol levels, and ultimately to development of premature coronary heart disease. Genetic analysis and subsequent cascade screening in relatives allow diagnosis of FH at early stage, especially relevant to diagnose children. So far, more than 2300 LDLr variants have been described but only a minority of them have been functionally analysed to evaluate their pathogenicity in FH. Thus, identifying pathogenic mutations in LDLr is a long-standing challenge in the field. In this study, we investigated in vitro the activity p.(Asp47Asn) and p.(Thr62Met) LDLr variants, both in the LR1 region. We used CHO-ldlA7 transfected cells with plasmids carrying p.(Asp47Asn) or p.(Thr62Met) LDLr variants to analyse LDLr expression by FACS and immunoblotting, LDL binding and uptake was determined by FACS and analysis of mutation effects was assessed in silico. The in vitro activity assessment of p.(Asp47Asn) and p.(Thr62Met) LDLr variants shows a fully functional LDL binding and uptake activities. Therefore indicating that the three of them are non-pathogenic LDLr variants. These findings also emphasize the importance of in vitro functional LDLr activity studies to optimize the genetic diagnosis of FH avoiding the report of non-pathogenic variants and possible misdiagnose in relatives if cascade screening is carried out.

Genetic Analysis of Iranian Patients with Familial Hypercholesterolemia

Background:

Familial hypercholesterolemia (FH) is a frequent autosomal dominant disorder of lipoprotein metabolism. This disorder is generally caused by mutations in low-density lipoprotein receptor (LDLR), apolipoprotein B 100 (APOB), and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes. In the present study, we aimed at identifying the common LDLR and APOB gene mutations in an Iranian population.

Methods:

Eighty unrelated Iranian patients with FH entered the study, based on Simon Broome diagnostic criteria. All samples were screened for two common APOB gene mutations, including R3500Q and R3500W, by the means of ARMS-PCR and PCR- RFLP assays, respectively. In addition, exons 3, 4, 9, and 10 of LDLR gene were sequenced in all patients.

Results:

A novel mutation in exon 3 (C95W) and a previously described mutation in exon 4 (D139H) of LDLR gene were found. Three previously reported polymorphisms in LDLR gene as well as three novel polymorphisms were detected in the patients. However, in the studied population, no common mutations were observed in APOB gene.

Conclusion:

The results of our study imply that the genetic basis of FH in Iranian patients is different from other populations.

Identification of a recurrent frameshift mutation at the LDLR exon 14 (c.2027delG, p.(G676Afs*33)) causing familial hypercholesterolemia in Saudi Arab homozygous children

Familial hypercholesterolemia (FH) is an autosomal dominant disease, predominantly caused by variants in the low-density lipoprotein (LDL) receptor gene (LDLR). Herein, we describe genetic analysis of severely affected homozygous FH patients who were mostly resistant to statin therapy and were managed on an apheresis program. We identified a recurrent frameshift mutation p.(G676Afs*33) in exon 14 of the LDLR gene in 9 probands and their relatives in an apparently unrelated Saudi families. We also describe a three dimensional homology model of the LDL receptor protein (LDLR) structure and examine the consequence of the frameshift mutation p.(G676Afs*33), as this could affect the LDLR structure in a region involved in dimer formation, and protein stability. This finding of a recurrent mutation causing FH in the Saudi population could serve to develop a rapid genetic screening procedure for FH, and the 3D-structure analysis of the mutant LDLR, may provide tools to develop a mechanistic model of the LDLR function.

Identification of a novel nonsense variant c.1332dup, p.(D445*) in the LDLR gene that causes familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal dominant disease predominantly caused by a mutation in the low-density lipoprotein receptor (LDLR) gene. Here, we describe two severely affected FH patients who were resistant to statin therapy and were managed on an apheresis program. We identified a novel duplication variant c.1332dup, p.(D445*) at exon 9 and a known silent variant c.1413A>G, p.(=), rs5930, NM_001195798.1 at exon 10 of the LDLR gene in both patients.

Refinement of variant selection for the LDL cholesterol genetic risk score in the diagnosis of the polygenic form of clinical familial hypercholesterolemia and replication in samples from 6 countries

BACKGROUND

Familial hypercholesterolemia (FH) is an autosomal-dominant disorder caused by mutations in 1 of 3 genes. In the 60% of patients who are mutation negative, we have recently shown that the clinical phenotype can be associated with an accumulation of common small-effect LDL cholesterol (LDL-C)-raising alleles by use of a 12-single nucleotide polymorphism (12-SNP) score. The aims of the study were to improve the selection of SNPs and replicate the results in additional samples.

METHODS

We used ROC curves to determine the optimum number of LDL-C SNPs. For replication analysis, we genotyped patients with a clinical diagnosis of FH from 6 countries for 6 LDL-C-associated alleles. We compared the weighted SNP score among patients with no confirmed mutation (FH/M-), those with a mutation (FH/M+), and controls from a UK population sample (WHII).

RESULTS

Increasing the number of SNPs to 33 did not improve the ability of the score to discriminate between FH/M- and controls, whereas sequential removal of SNPs with smaller effects/lower frequency showed that a weighted score of 6 SNPs performed as well as the 12-SNP score. Metaanalysis of the weighted 6-SNP score, on the basis of polymorphisms in CELSR2 (cadherin, EGF LAG 7-pass G-type receptor 2), APOB (apolipoprotein B), ABCG5/8 [ATP-binding cassette, sub-family G (WHITE), member 5/8], LDLR (low density lipoprotein receptor), and APOE (apolipoprotein E) loci, in the independent FH/M- cohorts showed a consistently higher score in comparison to the WHII population (P < 2.2 × 10(-16)). Modeling in individuals with a 6-SNP score in the top three-fourths of the score distribution indicated a >95% likelihood of a polygenic explanation of their increased LDL-C.

CONCLUSIONS

A 6-SNP LDL-C score consistently distinguishes FH/M- patients from healthy individuals. The hypercholesterolemia in 88% of mutation-negative patients is likely to have a polygenic basis.

Impaired trafficking of the very low density lipoprotein receptor caused by missense mutations associated with dysequilibrium syndrome

Dysequilibrium syndrome (DES, OMIM 224050) is a genetically heterogeneous condition that combines autosomal recessive non-progressive cerebellar ataxia with mental retardation. The subclass dysequilibrium syndrome type 1 (CAMRQ1) has been attributed to mutations in the VLDLR gene encoding the very low density lipoprotein receptor (VLDLR). This receptor is involved in the Reelin signaling pathway that guides neuronal migration in the cerebral cortex and cerebellum. Three missense mutations (c.1459G>T; p.D487Y, c.1561G>C; p.D521H and c.2117G>T; p.C706F) have been previously identified in VLDLR gene in patients with DES. However, the functional implications of those mutations are not known and therefore we undertook detailed functional analysis to elucidate the cellular mechanisms underlying their pathogenicity. The mutations have been generated by site-directed mutagenesis and then expressed in cultured cell lines. Confocal microscopy and biochemical analysis have been employed to examine the subcellular localization and functional activities of the mutated proteins relative to wild type. Our results indicate that the three missense mutations lead to defective intracellular trafficking and ER retention of the mutant VLDLR protein. This trafficking impairment prevents the mutants from reaching the plasma membrane and binding exogenous Reelin, the initiating event in Reelin signaling. Collectively, our results provide evidence that ER quality control is involved in the functional inactivation and underlying pathogenicity of these DES-associated mutations in the VLDLR.

Genetics of coronary heart disease with reference to ApoAI-CIII-AIV gene region

Cardiovascular diseases are affected by multiple factors like genetic as well as environmental hence they reveal factorial nature. The evidences that genetic factors are susceptible for developing cardiovascular diseases come from twin studies and familial aggregation. Different ethnic populations reveal differences in the prevalence coronary artery disease (CAD) pointing towards the genetic susceptibility. With progression in molecular techniques different developments have been made to comprehend the disease physiology. Molecular markers have also assisted to recognize genes that may provide evidences to evaluate the role of genetic factors in causation of susceptibility towards CAD. Numerous studies suggest the contribution of specific “candidate genes”, which correlate with various roles/pathways that are involved in the coronary heart disease. Different studies have revealed that there are large numbers of genes which are involved towards the predisposition of CAD. However, these reports are not consistent. One of the reasons could be weak contribution of genetic susceptibility of these genes. Genome wide associations show different chromosomal locations which dock, earlier unknown, genes which may attribute to CAD. In the present review different ApoAI-CIII-AIV gene clusters have been discussed.

The reduced cost of providing a nationally recognised service for familial hypercholesterolaemia

OBJECTIVE

Familial hypercholesterolaemia (FH) affects 1 in 500 people in the UK population and is associated with premature morbidity and mortality from coronary heart disease. In 2008, National Institute for Health and Care Excellence (NICE) recommended genetic testing of potential FH index cases and cascade testing of their relatives. Commissioners have been slow to respond although there is strong evidence of cost and clinical effectiveness. Our study quantifies the recent reduced cost of providing a FH service using generic atorvastatin and compares NICE costing estimates with three suggested alternative models of care (a specialist-led service, a dual model service where general practitioners (GPs) can access specialist advice, and a GP-led service).

METHODS

Revision of existing 3 year costing template provided by NICE for FH services, and prediction of costs for running a programme over 10 years. Costs were modelled for the first population-based FH service in England which covers Southampton, Hampshire, Isle of Wight and Portsmouth (SHIP). Population 1.95 million.

RESULTS

With expiry of the Lipitor (Pfizer atorvastatin) patent the cost of providing a 10-year FH service in SHIP reduces by 42.5% (£4.88 million on patent vs £2.80 million off patent). Further cost reductions are possible as a result of the reduced cost of DNA testing, more management in general practice, and lower referral rates to specialists. For instance a dual-care model with GP management of patients supported by specialist advice when required, costs £1.89 million.

CONCLUSIONS

The three alternative models of care are now <50% of the cost of the original estimates undertaken by NICE.

LipidSeq: a next-generation clinical resequencing panel for monogenic dyslipidemias

We report the design of a targeted resequencing panel for monogenic dyslipidemias, LipidSeq, for the purpose of replacing Sanger sequencing in the clinical detection of dyslipidemia-causing variants. We also evaluate the performance of the LipidSeq approach versus Sanger sequencing in 84 patients with a range of phenotypes including extreme blood lipid concentrations as well as additional dyslipidemias and related metabolic disorders. The panel performs well, with high concordance (95.2%) in samples with known mutations based on Sanger sequencing and a high detection rate (57.9%) of mutations likely to be causative for disease in samples not previously sequenced. Clinical implementation of LipidSeq has the potential to aid in the molecular diagnosis of patients with monogenic dyslipidemias with a high degree of speed and accuracy and at lower cost than either Sanger sequencing or whole exome sequencing. Furthermore, LipidSeq will help to provide a more focused picture of monogenic and polygenic contributors that underlie dyslipidemia while excluding the discovery of incidental pathogenic clinically actionable variants in nonmetabolism-related genes, such as oncogenes, that would otherwise be identified by a whole exome approach, thus minimizing potential ethical issues.

Analysis of the frequency and spectrum of mutations recognised to cause familial hypercholesterolaemia in routine clinical practice in a UK specialist hospital lipid clinic

Aim

To determine the frequency and spectrum of mutations causing Familial Hypercholesterolaemia (FH) in patients attending a single UK specialist hospital lipid clinic in Oxford and to identify characteristics contributing to a high mutation detection rate.

Methods

289 patients (272 probands) were screened sequentially over a 2-year period for mutations in LDLR, APOB and PCSK9 using standard molecular genetic techniques. The Simon Broome (SB) clinical diagnostic criteria were used to classify patients and a separate cohort of 409 FH patients was used for replication.

Results

An FH-causing mutation was found in 101 unrelated patients (LDLR = 54 different mutations, APOB p.(Arg3527Gln) = 10, PCSK9 p.(Asp374Tyr) = 0). In the 60 SB Definite FH patients the mutation detection rate was 73% while in the 142 with Possible FH the rate was significantly lower (27%, p < 0.0001), but similar (14%, p = 0.06) to the 70 in whom there was insufficient data to make a clinical diagnosis. The mutation detection rate varied significantly (p = 9.83 × 10⁻⁵) by untreated total cholesterol (TC) levels (25% in those <8.1 mmol/l and 74% in those >10.0 mmol/l), and by triglyceride levels (20% in those >2.16 mmol/l and 60% in those <1.0 mmol/l (p = 0.0005)), with both effects confirmed in the replication sample (p for trend = 0.0001 and p = 1.8 × 10⁻⁶ respectively). There was no difference in the specificity or sensitivity of the SB criteria versus the Dutch Lipid Clinic Network score in identifying mutation carriers (A_ROC respectively 0.73 and 0.72, p = 0.68).

Conclusions

In this genetically heterogeneous cohort of FH patients the mutation detection rate was significantly dependent on pre-treatment TC and triglyceride levels.

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54 different LDLR mutations found in a cohort of 272 FH probands.

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The cohort was found to be genetically heterogeneous with no specific FH mutation.

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Mutation detection rate was highly dependent on pre-treatment TC and TG levels.

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No difference in specificity/sensitivity between 2 clinical FH diagnosis approaches.

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Inadequate LDL-C reduction marks the need for more effective lipid-lowering therapy.

Defining the role of lipoprotein apheresis in the management of familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal co-dominant disorder characterized by a marked elevation of serum low-density lipoprotein (LDL) cholesterol (LDL-C) concentration, which in turn is associated with a greatly increased risk of premature cardiovascular disease. International consensus recommends the use of statins as the first line of treatment for patients with this condition. However, homozygote FH patients with persistently elevated LDL-C levels are usually resistant to multiple-drug therapy. Fortunately, LDL apheresis (or simply 'lipoprotein apheresis') provides a treatment option for patients who are refractory or intolerant to lipid-lowering medications, or if there is progressive cardiovascular disease despite maximal drug therapy. Lipoprotein apheresis is an extracorporeal LDL-C-lowering treatment similar in concept to renal dialysis. There are now five main methods for extracorporeal lipoprotein apheresis in use, namely dextran sulfate adsorption (DSA), heparin extracorporeal LDL precipitation (HELP), polyacrylate full blood adsorption (PFBA or DALI® system) using hemoperfusion, immunoadsorption, and filtration plasmapheresis. Lipoprotein apheresis has been shown to be successful in reducing LDL-C levels, as well as levels of lipoprotein(a) [Lp(a)], a prothrombotic proatherogenic lipoprotein. In contrast, however, lipoprotein apheresis seems to have a smaller effect in preventing atherosclerosis progression, thus suggesting that a major component of the reduction in cardiovascular events may be mediated by mitigating Lp(a) levels. Side effects are infrequent and mild, and have mainly consisted of lightheadedness, nausea, vomiting, and hypotension. As these are often bradykinin-mediated and associated with concomitant ACE inhibitor use, angiotensin type 2 receptor antagonists should be used instead of ACE inhibitors with DALI and PFBA. Nevertheless, there is scope for wider application of lipoprotein apheresis. The high cost and invasive nature of lipoprotein apheresis limits uptake; however, it is an important treatment modality that should be considered in carefully selected patients. National and international registries compiling outcome data for lipoprotein apheresis need to be established to help expand the evidence base regarding its effectiveness.

Advances in genetics show the need for extending screening strategies for autosomal dominant hypercholesterolaemia

Aims Autosomal dominant hypercholesterolaemia (ADH) is a major risk factor for coronary artery disease. This disorder is caused by mutations in the genes coding for the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and proprotein convertase subtilisin/kexin 9 (PCSK9). However, in 41% of the cases, we cannot find mutations in these genes. In this study, new genetic approaches were used for the identification and validation of new variants that cause ADH. Methods and results Using exome sequencing, we unexpectedly identified a novel APOB mutation, p.R3059C, in a small-sized ADH family. Since this mutation was located outside the regularly screened APOB region, we extended our routine sequencing strategy and identified another novel APOB mutation (p.K3394N) in a second family. In vitro analyses show that both mutations attenuate binding to the LDLR significantly. Despite this, both mutations were not always associated with ADH in both families, which prompted us to validate causality through using a novel genetic approach. Conclusion This study shows that advances in genetics help increasing our understanding of the causes of ADH. We identified two novel functional APOB mutations located outside the routinely analysed APOB region, suggesting that screening for mutations causing ADH should encompass the entire APOB coding sequence involved in LDL binding to help identifying and treating patients at increased cardiovascular risk.

Spectrum of LDLR gene mutations, including a novel mutation causing familial hypercholesterolaemia, in North-western Greece

BACKGROUND

Familial Hypercholesterolaemia (FH) is a clinical syndrome characterised by elevated serum low-density lipoprotein (LDL) cholesterol, by tendon xanthomata and clinical manifestations of ischaemic heart disease in early life. Typically, it results from mutations in the low-density lipoprotein receptor (LDLR) gene. Furthermore, there are 3 additional genetic disorders that cause clinical syndromes that mimic FH. These are: 1) familial ligand-defective apolipoprotein (apo)-B (FLDH), 2) familial hypercholesterolaemia type 3 (FH3) and 3) autosomal recessive hypercholesterolaemia (ARH). The aim of this study was to elaborate the impact of the above genetic disorders in Greek patients with a clinical diagnosis of FH.

METHODS

In this study, we assessed the contribution of the LDLR, Apo B, ARH and PCSK9 genes in the expression of FH in North-western Greece. Two hundred and fifty-four (254) probands with a clinical diagnosis of FH were included in the study.

RESULTS

One hundred and sixty-nine (169) patients had one of the following LDLR gene mutations: 81T>G, 1775G>A, 517T>C, 858C>A, 1352T>C, 1285G>A, 761A>C, 1195G>A, 1646G>A and a deletion mutation g.387-410del24 in exon 4. We sequenced the Apo B, ARH and PCSK9 genes in 40, randomly selected patients, from the 85 patients with no identified LDLR gene defects. In these 40, randomly selected patients, with the exception of benign single nucleotide polymorphisms, no functional mutations were identified for all the above mentioned sequenced genes.

CONCLUSION

Our results reveal substantial genetic heterogeneity for FH in North-western Greece with at least ten LDLR gene mutations present in the study population. One of these mutations although quite rare is reported here for the first time in the scientific literature. The detection of these mutations is important as they may be used to design multiplex detection assays for large scale population screening programmes to facilitate primary and secondary prevention of cardiovascular disease in the region. Finally, ARH, Apo B and PCSK9 gene defects were excluded from causing FH in a subgroup of the study population indicating that other yet unrecognized genes may be involved in causing the clinical feature of FH, and/or that large scale deletions/duplications evaded the applied mutation detection techniques of this study.

A double heterozygote for familial hypercholesterolaemia and familial defective apolipoprotein B-100

Autosomal dominant hypercholesterolaemia is genetically heterogeneous, but most commonly (approximately 93%) caused by mutations in low-density lipoprotein receptor (LDLR), where the disease is known as familial hypercholesterolaemia (FH), or apolipoprotein B-100 (APOB) (approximately 5.5%), where the disease is known as familial defective APOB (FDB), while in approximately 2% of patients the mutation is in the proprotein convertase subtilisin/kexin type 9 gene. Homozygous FH having inheritance of two LDLR mutations is a rare but recognized syndrome associated with an extreme hypercholesterolaemia and early-onset coronary artery disease. We present a 15-year-old girl with untreated total cholesterol levels of 8.8 mmol/L who was heterozygous for both the LDLR p.Leu479Pro and APOB p.Arg3527Gln mutation. Cascade testing confirmed the paternal origin of the LDLR mutation and revealed a maternal diagnosis of FDB. This case provides further evidence that the combined effect of an LDLR and an APOB mutation give rise to a phenotype more severe than either mutation alone and is more severe than homozygous FDB, but less severe than homozygous FH. It also highlights the need to consider the presence of additional mutations in families where relatives have varying phenotypes.

Mutation detection rate and spectrum in familial hypercholesterolaemia patients in the UK pilot cascade project

Cascade testing using DNA-mutation information is now recommended in the UK for patients with familial hypercholesterolaemia (FH). We compared the detection rate and mutation spectrum in FH patients with a clinical diagnosis of definite (DFH) and possible (PFH) FH. Six hundred and thirty-five probands from six UK centres were tested for 18 low-density lipoprotein receptor gene (LDLR) mutations, APOB p.Arg3527Gln and PCSK9 p.Asp374Tyr using a commercial amplification refractory mutation system (ARMS) kit. Samples with no mutation detected were screened in all exons by single strand conformation polymorphism analysis (SSCP)/denaturing high performance liquid chromatography electrophoresis (dHPLC)/direct-sequencing, followed by multiplex ligation-dependent probe amplification (MLPA) to detect deletions and duplications in LDLR.The detection rate was significantly higher in the 190 DFH patients compared to the 394 PFH patients (56.3% and 28.4%, p > 0.00001). Fifty-one patients had inadequate information to determine PFH/DFH status, and in this group the detection rate was similar to the PFH group (25.5%, p = 0.63 vs PFH). Overall, 232 patients had detected mutations (107 different; 6.9% not previously reported). The ARMS kit detected 100 (44%) and the MLPA kit 11 (4.7%). Twenty-eight (12%) of the patients had the APOB p.Arg3527Gln and four (1.7%) had the PCSK9 p.Asp374Tyr mutation. Of the 296 relatives tested from 100 families, a mutation was identified in 56.1%. In 31 patients of Indian/Asian origin 10 mutations (two previously unreported) were identified. The utility of the ARMS kit was confirmed, but sequencing is still required in a comprehensive diagnostic service for FH. Even in subjects with a low clinical suspicion of FH, and in those of Indian origin, mutation testing has an acceptable detection rate.

Development of a high-resolution melting method for mutation detection in familial hypercholesterolaemia patients

Aims

Current screening methods, such as single strand conformational polymorphism (SSCP) and denaturing high performance liquid chromatography (dHPLC) that are used for detecting mutations in familial hypercholesterolaemia (FH) subjects are time consuming, costly and only 80–90% sensitive. Here we have tested high-resolution melt (HRM) analysis for mutation detection using the Rotor-Gene6000 realtime rotary analyser.

Methods and subjects

Polymerase chain reaction and melt conditions (HRM) for 23 fragments of the LDL-receptor gene, a region of exon 26 in the APOB gene (including p.R3527Q) and exon 7 of the PCSK9 gene (including p.D374Y) were optimized. Two double stranded DNA saturating dyes, LC-Green and Syto9, were compared for sensitivity. Eighty-two samples with known mutations were used as positive controls. Twenty-eight Greek FH heterozygous patients and two homozygous patients from the UK and Croatia were screened.

Results

HRM was able to identify all the positive control mutations tested, with similar results with either dye. Eight different variations were found in 17 of the 28 Greek FH patients for an overall detection rate of 61%: c.41delT (1), p.W165X (1), p.C173R (3), p.S286R (2), p.V429M (4), p.G549D (4), p.V613I (1), and a previously unreported mutation p.F694V (1) which is predicted to be FH-causing by functional algorithms. Mutations were found in both the homozygous patients; p.Q92X (Croatia) and p.Y489C (UK); both patients were homozygous for their respective mutations.

Conclusions

HRM is a sensitive, robust technique that could significantly reduce the time and cost of screening for mutations in a clinical setting.

[European Guidelines on Cardiovascular Disease Prevention in Clinical Practice. CEIPC 2008 Spanish Adaptation]

The present CEIPC Spanish adaptation of the European Guidelines on Cardiovascular Disease Prevention in Clinical Practice 2008. This guide recommends the SCORE model for risk evaluation. The aim is to prevent premature mortality and morbidity due to CVD by means of dealing with its related risk factors in clinical practice. The guide focuses on primary prevention and emphasizes the role of the nurses and primary care doctors in promoting a healthy life style, based on increasing physical activity, changing dietary habits, and not smoking. The therapeutic goal is to achieve a Blood Pressure<140/90mmHg, but in patients with diabetes, chronic kidney disease, or definite CVD, the objective is<130/80mmHg. Serum cholesterol should be<200mg/dl and cLDL<130mg/dl, although in patients with CVD or diabetes, the objective is<100mg/dl (80mg/dl if feasible in very high-risk patients). Patients with type 2 diabetes and those with metabolic syndrome must lose weight and increase their physical activity, and drugs must be administered whenever applicable, with the objective guided by body mass index and waist circumference. In diabetic type 2 patients, the objective is glycated haemoglobin<7%. Allowing people to know the guides and developing implementation programs, identifying barriers and seeking solutions for them, are priorities for the CEIPC in order to put the recommendations into practice.

Multiplex ligation-dependent probe amplification analysis to screen for deletions and duplications of the LDLR gene in patients with familial hypercholesterolaemia

The most common genetic defect in patients with autosomal dominant hypercholesterolaemia is a mutation of the low-density lipoprotein receptor (LDLR) gene. An estimate of the frequency of major rearrangements has been limited by the availability of an effective analytical method and testing of large cohorts. We present data from a cohort of 611 patients referred with suspected heterozygous familial hypercholesterolaemia (FH) from five UK lipid clinics, who were initially screened for point mutations in LDLR and the common APOB and PCSK9 mutations. The 377 cases in whom no mutation was found were then screened for large rearrangements by multiplex ligation-dependent probe amplification (MLPA) analysis. A rearrangement was identified in 19 patients. This represents 7.5% of the total detected mutations of the cohort. Of these, the majority of mutations (12/19) were deletions of more than one exon, two were duplications of more than one exon and five were single exon deletions that need interpreting with care. Five rearrangements (26%) are previously unreported. We conclude that MLPA analysis is a simple and rapid method for detecting large rearrangements and should be included in diagnostic genetic testing for FH.

Family tracing to identify patients with familial hypercholesterolaemia: the second audit of the Department of Health Familial Hypercholesterolaemia Cascade Testing Project

BACKGROUND

Family tracing is a method recognized to find new patients with familial hypercholesterolaemia (FH). We have implemented family tracing led by FH Nurses and have determined acceptability to patients, feasibility and costs.

METHODS

Nurses were located at five National Health Service (NHS) Trusts; they identified FH patients and offered them family tracing. Responses and test results were recorded on a database and summarized on a family pedigree.

RESULTS

The majority ( approximately 70%) of index cases participated; the proportion was lower when patients had been discharged from the clinics and in metropolitan areas. On average, 34% (range 13-50%) of relatives lived outside the catchment area of the clinics and could not attend the nurse-led FH clinics. Of the previously untested relatives, 76% who lived in the catchment area of the clinic came forward to be tested. One-third of the relatives who came forward for testing were children <or=16 y of age. The proportion of relatives diagnosed as likely to have FH was lower than would be predicted (30% vs. 50%). This was mainly due to the uncertainty of a diagnosis based on lipid measurements. The average cost to identify and test one relative was approximately pound 500 but was higher in the metropolitan areas.

CONCLUSION

Cascade testing for FH in the UK is feasible, acceptable and likely to be cost-effective if it is a routine aspect of clinical care. However, national implementation would require an integrated infrastructure, so that all individuals have access to testing, and specialist services for the management of young people.

Are patients with familial hypercholesterolaemia well managed in lipid clinics? An audit of eleven clinics from the Department of Health Familial Hypercholesterolaemia Cascade Testing project

Background

Familial hypercholesterolaemia (FH) is an autosomal co-dominant disorder which is relatively common, leads to high levels of LDL-cholesterol and if untreated to early coronary heart disease. An audit of current practice at National Health Service Trusts in England was undertaken to determine whether FH patients meet the diagnostic criteria for FH; are being offered appropriate advice and treatment; and to what extent their families are contacted and offered testing for the disorder.

Methods

Medical records of known FH patients (over 18 years of age and diagnosed before 31 December 2003) were accessed to obtain information on diagnosis, treatment and family tracing.

Results

The records of 733 FH patients were examined, 79% met the UK ‘Simon Broome’ register criteria for the diagnosis of definite or possible FH. Analyses showed that patients were usually offered appropriate advice and treatment, with 89% being on a statin. However, the audit indicated a high variability in family tracing between the sites, with significant differences in the frequency of inclusion of a family pedigree in the notes (range 1–71%, mean 35%); the general practitioner (GP) being advised that first-degree relatives should be tested (range 4–52%, mean 27%); and the proportion of relatives contacted and tested (range 6–50%, mean 32%).

Conclusion

FH patients are well cared for in lipid clinics in England, are being given appropriate lifestyle advice and medication, but an increase in recording of LDL-cholesterol levels may lead to improvements in their management. Practice in family tracing appears to vary widely between clinics.

Development of a universal chemiluminometric genotyping method for high-throughput detection of 7 LDLR gene mutations in Greek population

OBJECTIVES

Familial hypercholesterolemia (FH) is caused by mutations in the LDL receptor (LDLR) gene. We report the application of a universal method with high allele discrimination properties to the simultaneous genotyping of 7 LDLR mutations in Greeks, in dry-reagent format.

DESIGN AND METHODS

We genotyped mutations C858A, C939A, G1285A, T1352C, G1646A, G1775A, C/T81G. Unpurified amplicons from a multiplex PCR that produced fragments encompassing all 7 mutations were subjected to probe extension reactions in the presence of fluorescein-modified dCTP, and a microtiter well-based assay of extension products with a peroxidase-antifluorescein conjugate and a chemiluminogenic substrate. We used lyophilized dry reagents and assigned genotypes by the signal ratio of normal-to-mutant-specific probe.

RESULTS

We standardized the method and optimised all steps for specificity. The method was validated by genotyping blindly 119 (833 genotypings). Results were fully concordant with other methods used as standards.

CONCLUSIONS

This method is accurate, simple, rapid and robust. The microtiter well format allows genotyping of a large number of samples in parallel for several mutations.

European guidelines on cardiovascular disease prevention in clinical practice: executive summary. Fourth Joint Task Force of the European Society of Cardiology and other societies on cardiovascular disease prevention in clinical practice (constituted by representatives of nine societies and by invited experts)

Other experts who contributed to parts of the guidelines: Edmond Walma, Schoonhoven (The Netherlands), Tony Fitzgerald, Dublin (Ireland), Marie Therese Cooney, Dublin (Ireland), Alexandra Dudina, Dublin (Ireland) European Society of Cardiology (ESC) Committee for Practice Guidelines (CPG):, Alec Vahanian (Chairperson) (France), John Camm (UK), Raffaele De Caterina (Italy), Veronica Dean (France), Kenneth Dickstein (Norway), Christian Funck-Brentano (France), Gerasimos Filippatos (Greece), Irene Hellemans (The Netherlands), Steen Dalby Kristensen (Denmark), Keith McGregor (France), Udo Sechtem (Germany), Sigmund Silber (Germany), Michal Tendera (Poland), Petr Widimsky (Czech Republic), José Luis Zamorano (Spain)

Document reviewers: Irene Hellemans (CPG Review Coordinator) (The Netherlands), Attila Altiner (Germany), Enzo Bonora (Italy), Paul N. Durrington (UK), Robert Fagard (Belgium), Simona Giampaoli(Italy), Harry Hemingway (UK), Jan Hakansson (Sweden), Sverre Erik Kjeldsen (Norway), Mogens Lytken Larsen (Denmark), Giuseppe Mancia (Italy), Athanasios J. Manolis (Greece), Kristina Orth-Gomer (Sweden), Terje Pedersen (Norway), Mike Rayner (UK), Lars Ryden (Sweden), Mario Sammut (Malta), Neil Schneiderman (USA), Anton F. Stalenhoef (The Netherlands), Lale Tokgözoglu (Turkey), Olov Wiklund (Sweden), Antonis Zampelas (Greece)

The PCSK9 gene R46L variant is associated with lower plasma lipid levels and cardiovascular risk in healthy U.K. men

In the present study, we have determined the relative frequency of the R46L, I474V and E670G variants in the PCSK9 (protein convertase subtilisin/kexin type 9) gene and its association with plasma lipid levels and CHD (coronary heart disease) in healthy U.K. men and patients with clinically defined definite FH (familial hypercholesterolaemia). Genotypes were determined using PCR and restriction enzyme digestion in 2444 healthy middle-aged (50–61 years) men from the prospective NPHSII (Second Northwick Park Heart Study), with 275 CHD events (15 years of follow-up), and in 597 U.K. FH patients from the Simon Broome Register. In the NPHSII healthy men, the R46L genotype distribution was in Hardy–Weinberg equilibrium and the frequency of 46L was 0.010 [95% CI (confidence interval), 0.007–0.013], with one man homozygous for the 46L allele. There was significant association of the 46L allele with lower mean (S.D.) total cholesterol [5.74 (1.01) mmol/l for RR compared with 5.26±1.03 mmol/l for RL; P=0.001], apolipoprotein B [0.87 (0.24) g/l for RR compared with 0.75 (0.26) g/l for RL; P<0.0001] and low-density lipoprotein cholesterol [4.01 (0.95) mmol/l for RR compared with 3.62 (0.97) mmol/l for RL; P=0.02]) levels, after adjustment for age, general medical practice, smoking, body mass index and systolic blood pressure. As expected, 46L carriers had a low risk of definite or possible CHD [hazard ratio, 0.46 (95% CI, 0.11–1.84)], but this was not statistically significant (P=0.27). Two other common PCSK9 variants I474V [V allele frequency, 0.179 (95% CI, 0.17–0.19)] and E670G [G allele frequency, 0.034 (CI, 0.03–0.04)] were not associated with any significant effects on lipid levels or CHD risk. In FH patients, the frequency of 46L was 0.003 (95% CI, 0.00–0.01), which was significantly lower (P=0.037) than the healthy subjects. In the four FH patients carrying 46L, mean untreated total cholesterol levels were not different (P=0.91) in carriers and non-carriers (median, 10.3 mmol/l compared with 10.2 mmol/l respectively, after adjustment for age, gender and mutation type). In conclusion, the PCSK9 46L allele is more frequent in healthy U.K. men than in FH patients and is strongly associated with a protective plasma lipid profile risk for CHD. Its low frequency (approx. 2% carriers) means that it does not make a major contribution to determining population CHD risk in the U.K.

Multiplex ARMS analysis to detect 13 common mutations in familial hypercholesterolaemia

DNA analysis and mutation identification is useful for the diagnosis of familial hypercholesterolaemia (FH), particularly in the young and in other situations where clinical diagnosis may be difficult, and enables unambiguous identification of at-risk relatives. Mutation screening of the whole of the three FH-causing genes is costly and time consuming. We have tested the specificity and sensitivity of a recently developed multiplex amplification refractory mutation system assay of 11 low-density lipoprotein receptor gene (LDLR) mutations, one APOB (p.R3527Q) and one PCSK9 (p.D374Y) mutation in 400 patients attending 10 UK lipid clinics. The kit detected a mutation in 54 (14%) patients, and a complete screen of the LDLR gene using single-stranded conformation polymorphism/denaturing high performance liquid chromatography identified 59 different mutations (11 novel) in an additional 87 patients, for an overall detection rate of 35%. The kit correctly identified 38% of all detected mutations by the full screen, with no false-positive or false-negative results. In the patients with a clinical diagnosis of definite FH, the overall detection rate was higher (54/110 = 49%), with the kit detecting 52% of the full-screen mutations. Results can be obtained within a week of sample receipt, and the high detection rate and good specificity make this a useful initial DNA diagnostic test for UK patients.

A functional mutation in the LDLR promoter (−139C>G) in a patient with familial hypercholesterolemia

A novel sequence change in repeat 3 of the promoter of the low-density lipoprotein receptor (LDLR) gene, -139C>G, has been identified in a patient with familial hypercholesterolemia (FH). LDLR -139G has been passed to one offspring who also shows an FH phenotype. Transient transfection studies using luciferase gene reporter assays revealed a considerable reduction (74+/-1.4% SEM) in reporter gene expression from the -139G variant sequence compared to the wild-type sequence, strongly suggesting that this change is the basis for FH in these patients. Analysis using electrophoretic mobility shift assay demonstrated the loss of Sp1 binding to the variant sequence in vitro, explaining the reduction of transcription.

Familial defective apolipoprotein B-100 in Slovakia: are differences in prevalence of familial defective apolipoprotein B-100 explained by ethnicity?

The objective of this study was to examine frequency of familial defective apo-B-100 (FDB, R3500Q mutation) in probands with the phenotype of familial hypercholesterolemia (FH) and in the general population of 40-year-old subjects in Slovakia and to characterize their lipid and clinical criteria and to compare the frequency of FDB with other populations. We identified 35 patients with FDB among 362 probands with clinical diagnosis of FH and two cases of FDB in the 40-year-old cohort of 2323 subjects from general Slovak population. Probands with FDB differed from those with FH only in plasma triglyceride concentrations (1.84+/-1.4 mmol/l versus 1.45+/-0.98 mmol/l, respectively, p<0.01). Evaluation of personal history of premature atherosclerosis did not show any differences (11.4% in FDB versus 20% in FH, p<0.16). The FDB patients had similar manifestation of xanthomatosis as the FH patients (17.1% versus 8.25%, p<0.25). The frequency of FDB of 9.7% found in the FH patients is among the highest of those reported to date. The frequency of R3500Q mutation of 0.09% found in Slovak 40-year-old subjects did not differ significantly from published population molecular data. Our comparison of estimated FDB frequencies with those which were found by DNA analysis demonstrated that estimated frequencies were not only wider in range, but also significantly higher than those which were assessed by the analysis. The definitive answer to the prevalence of FDB and its biochemical and clinical characteristics requires screening of unbiased samples of the general population from different ethnic groups based on molecular genetic methods.

Genetic causes of familial hypercholesterolaemia in patients in the UK: relation to plasma lipid levels and coronary heart disease risk

AIMS

To determine the relative frequency of mutations in three different genes (low-density lipoprotein receptor (LDLR), APOB, PCSK9), and to examine their effect in development of coronary heart disease (CHD) in patients with clinically defined definite familial hypercholesterolaemia in UK.

PATIENTS AND METHODS

409 patients with familial hypercholesterolaemia patients (158 with CHD) were studied. The LDLR was partially screened by single-strand conformational polymorphism (SSCP) (exons 3, 4, 6-10 and 14) and by using a commercial kit for gross deletions or rearrangements. APOB (p.R3500Q) and PCSK9 (p.D374Y) were detected by specific assays. Coding exons of PCSK9 were screened by SSCP.

RESULTS

Mutations were detected in 253 (61.9%)

PATIENTS

236 (57.7%) carried LDLR, 10 (2.4%) carried APOB p.Q3500 and 7 (1.7%) PCSK9 p.Y374. No additional mutations were identified in PCSK9. After adjusting for age, sex, smoking and systolic blood pressure, compared to those with no detectable mutation, the odds ratio of having CHD in those with an LDLR mutation was 1.84 (95% CI 1.10 to 3.06), for APOB 3.40 (0.71 to 16.36), and for PCSK9 19.96 (1.88 to 211.5; p = 0.001 overall). The high risk in patients carrying LDLR and PCSK9 p.Y374 was partly explained by their higher pretreatment cholesterol levels (LDLR, PCSK9 and no mutation, 10.29 (1.85), 13.12 and 9.85 (1.90) mmol/l, respectively, p = 0.001). The post-statin treatment lipid profile in PCSK9 p.Y374 carriers was worse than in patients with no identified mutation (LDL-C, 6.77 (1.82) mmol/l v 4.19 (1.26) mmol/l, p = 0.001, HDL-C 1.09 (0.27) mmol/l v 1.36 (0.36) mmol/l, p = 0.03).

CONCLUSIONS

The higher CHD risk in patients carrying PCSK9 p.Y347 or a detected LDLR mutation supports the usefulness of DNA testing in the diagnosis and management of patients with familial hypercholesterolaemia. Mutations in PCSK9 appear uncommon in patients with familial hypercholesterolaemia in UK.

Analysis of LDLR mutations in familial hypercholesterolemia patients in Greece by use of the NanoChip® Microelectronic Array Technology

BACKGROUND

Three mutations in the low density lipoprotein receptor (LDLR) gene account for 49% of familial hypercholesterolemia (FH) cases in Greece.

METHODS

We used the microelectronic array technology of the NanoChip Molecular Biology Workstation to develop a multiplex method to analyze these single-nucleotide polymorphisms (SNPs). Primer pairs amplified the region encompassing each SNP. The biotinylated PCR amplicon was electronically addressed to streptavidin-coated microarray sites. Allele-specific fluorescently labeled oligonucleotide reporters were designed and used for detection of wild-type and SNP sequences. Genotypes were compared to PCR-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

We developed three monoplex assays (1 SNP/site) and an optimized multiplex assay (3SNPs/site). We performed 92 Greece II, 100 Genoa, and 98 Afrikaner-2 NanoChip monoplex assays (addressed to duplicate sites and analyzed separately). Of the 580 monoplex genotypings (290 samples), 579 agreed with RFLP. Duplicate sites of one sample were not in agreement with each other. Of the 580 multiplex genotypings, 576 agreed with the monoplex results. Duplicate sites of three samples were not in agreement with each other, indicating requirement for repetition upon which discrepancies were resolved.

CONCLUSIONS

The multiplex assay detects common LDLR mutations in Greek FH patients and can be extended to accommodate additional mutations.

Identification and characterization of novel low-density lipoprotein receptor mutations of familial hypercholesterolaemia patients in Taiwan

BACKGROUND

Familial hypercholesterolaemia (FH) is an autosomal dominant disease associated with a very high risk of coronary vascular disease. The study objective was to identify patients with FH in Taiwan and characterize novel mutations.

MATERIALS AND METHODS

Fifty-one patients with suspected FH living in Taiwan were screened for mutations in both the low-density lipoprotein (LDL) receptor and the apolipoprotein (apoB) genes using the multiplex polymerase chain reaction and exon-by-exon DNA sequencing technique. Functional consequences on LDL receptor activity were characterized in vitro for novel mutations and family pedigree was also analyzed.

RESULTS

Thirteen different functional mutations in the LDL receptor gene and one mutation in the apoB gene were found in 21 patients. Among the 13 mutations in the LDL receptor gene, 10 were single-point missense mutations, one was a two-point mutation in the same allele, one was a non-sense mutation and one was a frame-shift mutation. There were three novel mutations, including two missense mutations (M510K and W512R) and one frame-shift mutation (1953 delTA mutation). The characterization of missense M510K retained 36.2% of the activity of the normal receptor. Conversely, frame-shift 1953 delTA and missense W512R led to defective proteins, with only 0-6% of normal receptor activity.

CONCLUSIONS

The study identified 13 LDL receptor gene mutations and characterized three novel mutations causing FH in Taiwan. This facilitated a better understanding of FH among the Chinese population and may enable diagnosis of FH at the molecular level at a presymptomatic, early age.

Genetic defects causing familial hypercholesterolaemia: identification of deletions and duplications in the LDL-receptor gene and summary of all mutations found in patients attending the Hammersmith Hospital Lipid Clinic

Familial hypercholesterolaemia (FH) results from defective catabolism of low density lipoproteins (LDL), leading to premature atherosclerosis and early coronary heart disease. It is commonly caused by mutations in LDLR, encoding the LDL receptor that mediates hepatic uptake of LDL, or in APOB, encoding its major ligand. More rarely, dominant mutations in PCSK9 or recessive mutations in LDLRAP1 (ARH) cause FH, gene defects that also affect the LDL-receptor pathway. We have used multiplex ligation-dependent probe amplification (MLPA) to identify deletions and rearrangements in LDLR, some not detectable by Southern blotting, thus completing our screening for mutations causing FH in a group of FH patients referred to a Lipid Clinic in London. To summarise, mutations in LDLR were found in 153 unrelated heterozygous FH patients and 24 homozygotes/compound heterozygotes, and in over 200 relatives of 80 index patients. LDLR mutations included 85 different point mutations (7 not previously described) and 13 different large rearrangements. The APOB R3500Q mutation was present in 14 heterozygous patients and a mutation in PCSK9 in another 4; LDLRAP1 mutations were found in 4 "homozygous" FH patients. Our data confirm that DNA-based diagnosis provides information that is important for management of FH in a considerable number of families.