Improving the cost effectiveness equation of cascade testing for Familial Hypercholesterolaemia (FH)

Purpose of Review : Many International recommendations for the management of Familial Hypercholesterolaemia (FH) propose the use of Cascade Testing (CT) using the family mutation to unambiguously identify affected relatives. In the current economic climate DNA information is often regarded as too expensive. Here we review the literature and suggest strategies to improve cost effectiveness of CT. Recent findings : Advances in next generation sequencing have both speeded up the time taken for a genetic diagnosis and reduced costs. Also, it is now clear that, in the majority of patients with a clinical diagnosis of FH where no mutation can be found, the most likely cause of their elevated LDL-cholesterol (LDL-C) is because they have inherited a greater number than average of common LDL-C raising variants in many different genes. The major cost driver for CT is not DNA testing but of treatment over the remaining lifetime of the identified relative. With potent statins now off-patent, the overall cost has reduced considerably, and combining these three factors, a FH service based around DNA-CT is now less than 25% of that estimated by NICE in 2009. Summary : While all patients with a clinical diagnosis of FH need to have their LDL-C lowered, CT should be focused on those with the monogenic form and not the polygenic form

Variants within TSC2 exons 25 and 31 are very unlikely to cause clinically diagnosable tuberous sclerosis

Inactivating mutations in TSC1 and TSC2 cause tuberous sclerosis complex (TSC). The 2012 international consensus meeting on TSC diagnosis and management agreed that the identification of a pathogenic TSC1 or TSC2 variant establishes a diagnosis of TSC, even in the absence of clinical signs. However, exons 25 and 31 of TSC2 are subject to alternative splicing. No variants causing clinically diagnosed TSC have been reported in these exons raising the possibility that such variants would not cause TSC. We present truncating and in-frame variants in exons 25 and 31 in three individuals unlikely to fulfil TSC diagnostic criteria and examine the importance of these exons in TSC using different approaches. Amino acid conservation analysis suggests significantly less conservation in these exons compared to the majority of TSC2 exons, and TSC2 expression data demonstrates that the majority of TSC2 transcripts lack exons 25 and/or 31 in many human adult tissues. In vitro assay of both exons shows that neither exon is essential for TSC complex function. Our evidence suggests that variants in TSC2 exons 25 or 31 are very unlikely to cause classical TSC, although a role for these exons in tissue/stage specific development cannot be excluded

The Genetic Architecture of Familial Hypercholesterolaemia

Familial Hypercholesterolaemia (FH) is a common autosomal dominant disorder of the defective plasma clearance of LDL-cholesterol. Mutations in three genes, LDLR/APOB/PCSK9, can be detected in 60-90% of definite FH patients. DNA-based testing for FH mutations has important clinical utility and is recommended by the UK and European guidelines to identify affected relatives. This thesis aimed to determine the frequency and spectrum of FH mutations in two independent cohorts of FH patients (from one Oxford lipid clinic, and of Indian background). The FH mutation spectrum was shown to be highly heterogeneous and the mutation detection rate was significantly dependent on the pre-treatment total cholesterol and triglyceride levels. This project also validated the findings that a proportion of clinically diagnosed FH patients have a polygenic cause of hypercholesterolaemia due to an accumulation of common mild LDL-C-raising alleles by analysing LDL-C gene score in 88 mutation negative and 21 mutation positive FH patients, and by replicating the results in further 231 FH patients. A high-throughput DNA sequencing method was assessed as a novel diagnostic tool for detection of FH mutations, and compared it with the currently used methods. This highlighted the need for updating the current FH mutation screening methods as well as the need for more efficient bioinformatics for the next generation sequencing data analysis. Lastly, whole exome sequencing of 125 definite FH patients with no mutations detected in known genes was performed to identify novel monogenic causes of FH. Variants in two genes, CH25H and INSIG2, were identified as potential novel FH mutations. Overall, the results of this thesis demonstrate the heterogeneous FH aetiology and help to understand the genetic architecture of the disease

Genetic testing for Familial Hypercholesterolaemia - 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 Low Density Lipoprotein Receptor (LDLR) gene as the first gene where mutations cause the Familial Hypercholesterolaemia (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 (CHD) differs according to the specific locus and associated molecular cause. It is now possible to use Next Generation Sequencing (NGS) 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 many novel FH-causing variants, but also some "Variants of Unknown Significance (VUSs)" 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 aetiology for their phenotype is highly likely. Compared to those with a monogenic cause, these patients have significantly lower risk of future CHD. The use of these molecular genetic diagnostic methods in the characterization of FH is a prime example of the utility of precision or personalised medicine

Filamin C variants are associated with a distinctive clinical and immunohistochemical arrhythmogenic cardiomyopathy phenotype.

BACKGROUND: Pathogenic variants in the filamin C (FLNC) gene are associated with inherited cardiomyopathies including dilated cardiomyopathy with an arrhythmogenic phenotype. We evaluated FLNC variants in arrhythmogenic cardiomyopathy (ACM) and investigated the disease mechanism at a molecular level. METHODS: 120 gene-elusive ACM patients who fulfilled diagnostic criteria for arrhythmogenic right ventricular cardiomyopathy (ARVC) were screened by whole exome sequencing. Fixed cardiac tissue from FLNC variant carriers who had died suddenly was investigated by histology and immunohistochemistry. RESULTS: Novel or rare FLNC variants, four null and five variants of unknown significance, were identified in nine ACM probands (7.5%). In FLNC null variant carriers (including family members, n = 16) Task Force diagnostic electrocardiogram repolarization/depolarization abnormalities were uncommon (19%), echocardiography was normal in 69%, while 56% had >500 ventricular ectopics/24 h or ventricular tachycardia on Holter and 67% had late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging (CMRI). Ten gene positive individuals (63%) had abnormalities on ECG or CMRI that are not included in the current diagnostic criteria for ARVC. Immunohistochemistry showed altered key protein distribution, distinctive from that observed in ARVC, predominantly in the left ventricle. CONCLUSIONS: ACM associated with FLNC variants presents with a distinctive phenotype characterized by Holter arrhythmia and LGE on CMRI with unremarkable ECG and echocardiographic findings. Clinical presentation in asymptomatic mutation carriers at risk of sudden death may include abnormalities which are currently non-diagnostic for ARVC. At the molecular level, the pathogenic mechanism related to FLNC appears different to classic forms of ARVC caused by desmosomal mutations

Genetic Determinants of the Familial Hypercholesterolaemia Phenotype

Individuals with familial hypercholesterolaemia (FH) have severely elevated plasma concentrations of low‐density lipoprotein cholesterol (LDL‐C) from birth and as a consequence have an elevated morbidity and mortality due to the development of coronary heart disease (CHD). Monogenic FH can be caused by carrying a single copy of a pathogenic variant in any of four genes (LDLR/APOB/PCSK9/APOE), which are all involved in the clearance of LDL‐C from the blood by the liver. FH is one of the most common inherited disorders, with an estimated prevalence of carriers of around 1/280 individuals in most populations and ancestry groups. However, such variants can be found usually only in 20%–30% of clinically FH subjects, and in the majority of the no‐variant individuals, the phenotype is most likely explained by the inheritance of a greater‐than‐average number of common variants of small effect, with such individuals better given the diagnosis of ‘polygenic hypercholesterolaemia’. Also, in a proportion of no‐variant subjects who meet the clinical criteria, the most likely explanation is due to overproduction of Lp(a) which is an LDL‐C particle with a bound copy of the ‘little‐a’ protein. Here, we review the research that has elucidated the genetic architecture of the FH phenotype and discuss recent studies and future prospects of finding additional genes where variants can cause FH

Prevalence of FH-Causing Variants and Impact on LDL-C Concentration in European, South Asian, and African Ancestry Groups of the UK Biobank

Background: Familial hypercholesterolemia (FH) is a monogenic disease that causes high low-density lipoprotein cholesterol (LDL-C) and higher risk of premature coronary heart disease. The prevalence of FH-causing variants and their association with LDL-C in non-European populations remains largely unknown. Using DNA diagnosis in a population-based cohort, we aimed to estimate the prevalence of FH across 3 major ancestry groups in the United Kingdom. Methods: Principal component analysis was used to distinguish genetic ancestry in UK Biobank participants. Whole exome sequencing data were analyzed to provide a genetic diagnosis of FH. LDL-C concentrations were adjusted for statin use. Results: Principal component analysis distinguished 140 439 European, 4067 South Asian, and 3906 African participants with lipid and whole exome sequencing data. There were significant differences between the 3 groups, including total and LDL-C concentrations, and prevalence and incidence of coronary heart disease. We identified 488, 18, and 15 participants of European, South Asian, and African ancestry carrying a likely pathogenic or pathogenic FH-variant. No statistical difference in the prevalence of an FH-causing variant was observed: 1 out of 288 (95% CI, 1/316–1/264) in European, 1 out of 260 (95% CI, 1/526–1/173) in African, and 1 out of 226 (95% CI, 1/419–1/155) in South Asian. Carriers of an FH-causing variant had significantly higher LDL-C concentration than noncarriers in every ancestry group. There was no difference in mean (statin-use adjusted) LDL-C concentration in FH-variant carriers depending on their ancestry background. Self-reported statin use was nonsignificantly highest in FH-variant carriers of South Asian ancestry (55.6%), followed by African (40.0%) and European (33.8%; P=0.15). Conclusions: The prevalence of FH-causing variants in the UK Biobank is similar across the ancestry groups analyzed. Despite overall differences in lipid concentrations, FH-variant carriers across the 3 ancestry groups had similar LDL-C levels. In all ancestry groups, the proportion of FH-variant carriers treated with lipid-lowering therapy should be improved to reduce future risk of premature coronary heart disease

The familial hypercholesterolaemia phenotype: Monogenic familial hypercholesterolaemia, polygenic hypercholesterolaemia and other causes

Familial Hypercholesterolaemia (FH) is a monogenic disorder characterised by high LDL-C concentrations and increased cardiovascular risk. However, in clinically defined FH cohorts worldwide, an FH-causing variant is only found in 40-50% of the cases. The aim of this work was to characterise the genetic cause of the FH phenotype in Portuguese clinical FH patients. Methods and Results Between 1999 and 2017, 731 index patients (311 children and 420 adults) who met the Simon Broome diagnostic criteria had been referred to our laboratory. LDLR, APOB, PCSK9, APOE, LIPA, LDLRAP1, ABCG5/8 genes were analysed by PCR amplification and Sanger sequencing. The 6-SNP LDL-C genetic risk score (GRS) for polygenic hypercholesterolaemia was validated in the Portuguese population and cases with a GRS over the 25th percentile were considered to have a high likelihood of polygenic hypercholesterolaemia. An FH-causing mutation was found in 39% of patients (94% in LDLR, 5% APOB and 1% PCSK9), while at least 29% have polygenic hypercholesterolaemia and 1% have other lipid disorders. A genetic cause for the FH phenotype was found in 503 patients (69%). All known causes of the FH phenotype should be investigated in FH cohorts to ensure accurate diagnosis and appropriate management. This article is protected by copyright. All rights reserved