Fast and Easy Nanopore Sequencing Workflow for Rapid Genetic Testing of Familial Hypercholesterolemia.

Familial hypercholesterolemia (FH) is an autosomal dominant lipid metabolism disorder characterized by severely elevated plasma low-density lipoprotein cholesterol levels. The disease is caused by mutations in 3 genes (LDLR, APOB and PCSK9) while over 90% of the mutations are located within the LDLR gene. Thus, genetic analysis of the LDLR gene is the first step in the genetic diagnosis of FH. However, conventional methods like Sanger and NextGen sequencing are still costly and time-consuming. In contrast, Oxford Nanopore technology sequencing is an emerging third-generation sequencing technology featured by easy operability, low cost, small size and the capability of parallel sample sequencing. Here, we present an easy Nanopore-sequencing-based workflow for the rapid genetic testing of FH taking only 3 days and costing less than $50 per sample without the requirement for deep bioinformatic knowledge. Using our workflow, we were able to identify the underlying pathogenic variants of 10 FH patients including one novel, not yet recorded pathogenic variants. Our workflow allows the rapid evaluation of the pathogenic variants by utilizing detailed variant information from Ensembl. Additionally, our workflow is not restricted to sequencing the LDLR gene alone but can be easily adapted to the other FH-causing genes and more importantly, to any desired gene contributing to any hereditary disease. Therefore, our workflow is an attractive opportunity for every diagnostic laboratory to offer fast and easy in-house genetic diagnostics.

Increased KCNJ18 promoter activity as a mechanism in atypical normokalemic periodic paralysis.

OBJECTIVE: To identify the genetic basis of a patient with symptoms of normokalemic sporadic periodic paralysis (PP) and to study the effect of KCNJ18 mutations. METHODS: A candidate gene approach was used to identify causative gene mutations, using Sanger sequencing. KCNJ18 promoter activity was analyzed in transfected HEK293 cells with a luciferase assay, and functional analysis of Kir2.6 channels was performed with the two-electrode voltage-clamp technique. RESULTS: Although we did not identify harmful mutations in SCN4A, CACNA1S, KCNJ2 and KCNE3, we detected a monoallelic four-fold variant in KCNJ18 (R39Q/R40H/A56E/I249V), together with a variant in the respective promoter of this channel (c.-542T/A). The exonic variants in Kir2.6 did not alter the channel function; however, luciferase assays revealed a 10-fold higher promoter activity of the c.-542A promoter construct, which is likely to cause a gain-of-function by increased expression of Kir2.6. We found that reducing extracellular K+ levels causes a paradoxical reduction in outward currents, similar to that described for other inward rectifying K+ channels. Thus, reducing the extracellular K+ levels might be a therapeutic strategy to antagonize the transcriptionally increased KCNJ18 currents. Consistently, treatment of the patient with K+ reducing drugs dramatically improved the health situation and prevented PP attacks. CONCLUSIONS: We show that a promoter defect in the KCNJ18 gene is likely to cause periodic paralysis, as the observed transcriptional upregulation will be linked to increased Kir2.6 function. This concept is further supported by our observation that most of the PP attacks in our patient disappeared on medical treatment with K+ reducing drugs.

Oncological and surgical outcome of total laryngectomy in combination with neck dissection in the elderly.

There are controversial data on oncological and surgical outcome after major head and neck cancer surgery in the elderly. The aim of this study was to evaluate the outcome of elderly cancer patients after total laryngectomy in combination with neck dissection. A total of 58 patients separated into two age groups (28 < 65 vs. 30 ≥ 65 years) with hypopharyngeal and laryngeal cancer who underwent total laryngectomy and neck dissection were enrolled. Comorbidities of both age groups using the Charlson comorbidity index, hospitalization days as well as surgical complications evaluated by the Clavien-Dindo classification were examined. Overall and disease-free survivals of all patients were analyzed. The average follow-up was 2.9 years. Surgical complication rate was significantly increased in elderly (p = 0.04). However, complications could be treated without surgical intervention in most cases without significant extension of hospitalization. Locoregional and distant control did not significantly differ in both age groups. Disease-free and overall survival showed no significant differences for the two age groups by the Kaplan-Meier analysis (p = 0.66 and 0.08, respectively). Total laryngectomy in combination with neck dissection can be considered in elderly patients with satisfactory oncological and surgical outcome.

Lipoprotein(a)-clinical aspects and future challenges.

Lipoprotein(a) (Lp(a)) was first described by K. Berg and is known for more than 50 years. It is an interesting particle and combines the atherogenic properties of low-density lipoprotein (LDL)-cholesterol as well as the thrombogenic properties of plasminogen inactivation. However, due to technical problems and publication of negative trials the potential role of Lp(a) in atherosclerosis was severely underestimated. In recent years our understanding of the function and importance of Lp(a) improved. Interventional trials with niacin failed to demonstrate any benefit of lowering Lp(a); however, several studies confirmed the residual cardiovascular disease (CVD) risk of elevated Lp(a). LDL/Lp(a) apheresis is able to lower Lp(a) and some new drugs under development should help us to lower Lp(a) in the near future. It will be important to follow this with hard endpoint trials. Until then most clinicians recommend the use of an aggressive LDL-lowering approach in patients with high Lp(a). Since most of these patients with high Lp(a) might have manifested atherosclerosis anyway, we would also consider the use of acetylsalicylic acid.

Mutation screening of the APOA5 gene in subjects with coronary artery disease.

OBJECTIVE: Hyperlipidemia is a risk factor for coronary artery disease (CAD). Apolipoprotein A5 (APOA5) is a member of the apolipoprotein APOA1/C3/A4/A5 gene cluster and a major determinant of plasma triglyceride levels in the population. Various studies have identified a number of common (APOA5 c.56C>G; p.S19W; rs 3135506 ) and rare variants in the APOA5 gene in individuals with hypertriglyceridemia. However, little is known on the impact of rare APOA5 mutations for the risk of coronary artery disease; therefore, we screened the APOA5 gene in subjects with CAD. METHODS: The coding region of the APOA5 gene was screened in 501 subjects (334 with CAD and 167 CAD-free) undergoing diagnostic coronary angiography by denaturing gradient gel electrophoresis. RESULTS: APOA5 p.S19W variant c.56 C>G was found in a total of 61 subjects, five of them homozygous. Beside this well-known mutation, the denaturing gradient gel electrophoresis screening identified only one subject with a synonymous APOA5 mutation, c.70C>A; p.R24R. APOA5 p.S19W was more frequent in patients with CAD (CAD, 14.4%; no CAD, 7.8%; P = 0.021); and in addition, all homozygous subjects (n = 5) for APOA5 p.S19W had CAD. Furthermore, carriers of the p.19W allele had significantly higher triglyceride levels (240 ± 149 vs 185 ± 118 mg/dL; P < 0.01). CONCLUSIONS: From these data, we conclude that (1) APOA5 p.S19W is a common variant, with very few additional APOA5 gene mutations; (2) APOA5 p.S19W plays a major role in triglyceride metabolism; and (3) APOA5 p.S19W is a CAD risk factor.

Pharmacogenetic aspects in familial hypercholesterolemia with the special focus on FHMarburg (FH p.W556R).

OBJECTIVE: Familial hypercholesterolemia (FH) is an autosomal dominant inherited disorder caused by mutations in the low density lipoprotein receptor (LDLR) gene. FH is characterized by elevated plasma LDL cholesterol, premature atherosclerosis, and a high risk of premature myocardial infarction. In general, mutations within LDLR gene can cause five different classes of defects, namely: class I defect: no LDLR synthesis; class II defect: no LDLR transport; class III defect: no low density lipoprotein (LDL) to LDLR binding; class IV defect: no LDLR/LDL internalization; and class V defect: no LDLR recycling. One might expect that both the class of LDLR defect as well as the precise mutation influences the severity of hypercholesterolemia on one hand and the response on drug treatment on the other. To clarify this question we studied the effect of the LDLR mutation p.W556R in two heterozygote subjects. RESULTS: We found that two heterozygote FH patients with the LDLR mutation p.W556R causing a class II LDLR defect (transport defective LDLR) respond exceedingly well to the treatment with simvastatin 40 mg/ezetimibe 10 mg. There was a LDL cholesterol decrease of 55 and 64%, respectively. In contrast, two affected homozygote p.W556R FH patients, in the mean time undergoing LDL apheresis, had no response to statin but a 15% LDL cholesterol decrease on ezetimibe monotherapy. CONCLUSIONS: The LDLR mutation p.W556R is a frequent and severe class II defect for FH. The affected homozygote FH patients have a total loss of the functional LDLR and-as expected-do not respond on statin therapy and require LDL apheresis. In contrast, heterozygote FH patients with the same LDLR defect respond exceedingly well to standard lipid-lowering therapy, illustrating that the knowledge of the primary LDLR defect enables us to foresee the expected drug effects.

The impact of severe LDL receptor mutations on SREBP-pathway regulation in homozygous familial hypercholesterolemia (FH).

Familial hypercholesterolemia (FH), Niemann-Pick disease type C (NPC) and Tangier disease (TD) are genetic inherited disorders with impaired processing of cholesterol, caused by mutations in genes that regulate cellular uptake, intracellular movement and transport of cholesterol. Various studies have shown a crucial regulatory role of the SREBP-pathway for cellular cholesterol homeostasis in these diseases. Since cholesterol is an essential structural component of cells, we assessed the impact of a severe FH causing LDLR mutation (FH p.W556R) on the SREBP pathway in primary FH fibroblasts. Primary FH fibroblasts derived from patients with the LDL receptor mutation p.W556R were used for gene expression experiments. Gene expression studies revealed increased expressions of SREBP regulated genes HMGCR, LDLR, SREBP-2, SREBP-1, SR-BI, INSIG-1, but interestingly not SCAP. In contrast expression of ABCA1, was strongly decreased in homozygous, but not in heterozygous p.W556R fibroblasts. Gene expression experiments with LDL receptor lacking primary FH fibroblasts, revealed that SR-BI and ABCA1 are important regulators for cholesterol acquisition in FH cells, consistent with findings in cells from NPC and TD patients.

Genetics and kinetics of familial hypercholesterolemia, with the special focus on FH-(Marburg) p.W556R.

OBJECTIVE: Familial hypercholesterolemia (FH) is an autosomal dominant inherited disorder, caused by mutations in the low density lipoprotein receptor (LDLR) gene. FH is characterized by elevated plasma LDL cholesterol, premature atherosclerosis and high risk of premature myocardial infarction. Extended work has been done to understand both, the primary genetic defect as well as the in vivo kinetic consequences of this disease. Both approaches, genetics and kinetics, are challenging but also fruitful approaches for a better understanding of this devastating disease. For this we reviewed the recent literature and used our in vitro and in vivo data on one of the most frequently occurring types of FH, the FH(Marburg) p.W556R. METHODS: To identify the primary genetic defect of the FH(Marburg) we used denaturing gradient gel electrophoresis (DGGE) mutation analysis. In vivo kinetic studies were performed in a heterozygote FH(Marburg) subject and in 5 healthy control subjects utilizing a stable isotope tracer kinetic approach with 3D-leucine. RESULTS: DGGE screening of the LDLR gene identified a tryptophan (W) to arginine (R) substitution at residue 556 (p.W556R) in the fifth conserved YWTD repeat of the LDLR-beta-propeller in FH(Marburg). In vivo kinetic studies in a heterozygote FH subject for FH(Marburg) and in 5 healthy control subjects demonstrated a severe decrease in LDL FCR and a mild increase of LDL PR in FH compared to healthy controls. CONCLUSIONS: The LDLR mutation p.W556R is a frequent and severe defect for FH. This defect has a major influence on the in vivo lipoprotein kinetics and lipid levels. In a heterozygote FH patient we found a dual defect for the increase in LDL cholesterol, namely a decrease in the fractional catabolic rate (FCR) of LDL but also an increase in LDL production rate (PR). By this a well defined, single genetic defect may have a series of different in vivo metabolic consequences which could be used for potential therapeutic approaches to this disease.