Relationship between physical and psychological functioning and health-related quality of life in congenital Aniridia

PURPOSE

Congenital aniridia is a serious eye disease characterized by absence of iris to various degrees. The aims of this study were to investigate health-related quality of life (HRQoL) in adults with aniridia and assess the relationships between HRQoL, psychological status, ocular health and obesity.

METHODS

Twenty-nine adults with congenital aniridia (48% male, aged 18-79 years) participated. HRQoL was measured with SF-36 and the EQ visual analogue scale (VAS). The physical (PCS) and mental (MCS) component summaries of the SF-36 were calculated with higher scores indicating better HRQoL. Symptoms of anxiety and depression were measured using the Hospital Anxiety and Depression Scale (HADS). Obesity was assessed with the Patient-Reported Outcomes in Obesity (PROS). Sociodemographic characteristics, genetic variants and ocular and medical health variables were also analysed.

RESULTS

The participants scored significantly lower in the general health domain of the SF-36 than the general population (65.2 vs. 75.3, p = 0.017). The EQ VAS score was also lower in the aniridia group (64.9 vs. 77.9, p = 0.021). Low PCS score was correlated with presence of ocular pain (p = 0.019), high HADS score (p = 0.017) and high PROS score (p = 0.009). Low MCS score was related to higher educational level (p = 0.038) and high HADS score (p < 0.001). High HADS and PROS scores were both related to low EQ VAS scores.

CONCLUSION

Adults with congenital aniridia scored worse on certain measures of HRQoL than the general population. Poorer HRQoL was associated with increased symptoms of anxiety, depression and obesity and with presence of ocular pain.

Lamin A/C cardiomyopathy: young onset, high penetrance, and frequent need for heart transplantation

Aims

Lamin A/C (LMNA) mutations cause familial dilated cardiomyopathy (DCM) with frequent conduction blocks and arrhythmias. We explored the prevalence, cardiac penetrance, and expressivity of LMNA mutations among familial DCM in Norway. Furthermore, we explored the risk factors and the outcomes in LMNA patients.

Methods and results

During 2003–15, genetic testing was performed in patients referred for familial DCM. LMNA genotype-positive subjects were examined by electrocardiography, Holter monitoring, cardiac magnetic resonance imaging, and echocardiography. A positive cardiac phenotype was defined as the presence of atrioventricular (AV) block, atrial fibrillation/flutter (AF), ventricular tachycardia (VT), and/or echocardiographic DCM. Heart transplantation was recorded and compared with non-ischaemic DCM of other origin. Of 561 unrelated familial DCM probands, 35 (6.2%) had an LMNA mutation. Family screening diagnosed an additional 93 LMNA genotype-positive family members. We clinically followed up 79 LMNA genotype-positive [age 42 ± 16 years, ejection fraction (EF) 45 ± 13%], including 44 (56%) with VT. Asymptomatic LMNA genotype-positive family members (age 31 ± 15 years) had a 9% annual incidence of a newly documented cardiac phenotype and 61% (19/31) of cardiac penetrance during 4.4 ± 2.9 years of follow-up. Ten (32%) had AV block, 7 (23%) AF, and 12 (39%) non-sustained VT. Heart transplantation was performed in 15 of 79 (19%) LMNA patients during 7.8 ± 6.3 years of follow-up.

Conclusion

LMNA mutation prevalence was 6.2% of familial DCM in Norway. Cardiac penetrance was high in young asymptomatic LMNA genotype-positive family members with frequent AV block and VT, highlighting the importance of early family screening and cardiological follow-up. Nearly 20% of the LMNA patients required heart transplantation.

Data on exercise and cardiac imaging in a patient cohort with hypertrophic cardiomyopathy

Data presented in this paper are supplementary material to our study "Vigorous exercise in patients with hypertrophic cardiomyopathy" [1]. The current article presents supplementary data on collection and analyses of exercise parameters and genetic data in the original research article.

The systolic paradox in hypertrophic cardiomyopathy

Objective

We explored cardiac volumes and the effects on systolic function in hypertrophic cardiomyopathy (HCM) patients with left ventricular hypertrophy (HCM LVH+) and genotype-positive patients without left ventricular hypertrophy (HCM LVH−).

Methods

We included 180 HCM LVH+, 100 HCM LVH− patients and 80 healthy individuals. End-Diastolic Volume Index (EDVI), End-Systolic Volume Index (ESVI) and ejection fraction (EF) were assessed by echocardiography. Left ventricular (LV) global longitudinal strain (GLS) was measured by speckle tracking echocardiography.

Results

EDVI and ESVI were significantly smaller in HCM LVH+ compared with HCM LVH− patients (41±14 mL/m² vs 49±13 mL/m² and 16±7 mL/m² vs 19±6 mL/m², respectively, both p<0.001) and in healthy individuals (41±14 mL/m² vs 57±14 mL/m² and 16±7 mL/m² vs 23±9 mL/m², respectively, both p<0.001). HCM LVH− patients had significantly lower EDVI and ESVI compared with healthy individuals (49±13 mL/m² vs 57±14 mL/m² and 19±6 mL/m² vs 23±9 mL/m², both p<0.001). EF was similar (61%±7% vs 60%±8% vs 61%±6%, p=0.43) in the HCM LVH+, HCM LVH– and healthy individuals, despite significantly worse GLS in the HCM LVH+ (−16.4%±3.7% vs −21.3%±2.4% vs −22.3%±3.7%, p<0.001). GLS was worse in the HCM LVH− compared with healthy individuals in pairwise comparison (p=0.001). Decrease in ESVI was closely related to EF in HCM LVH+ and HCM LVH− (R=0.45, p<0.001 and R=0.43, p<0.001) as expected, but there was no relationship with GLS (R=0.02, p=0.77 and R=0.11, p=0.31). Increased maximal wall thickness (MWT) correlated significantly with worse GLS (R=0.58, p<0.001), but not with EF (R=0.018, p=0.30) in the HCM LVH+ patients.

Conclusion

HCM LVH+ had smaller cardiac volumes that could explain the preserved EF, despite worse GLS that was closely related to MWT. HCM LVH− had reduced cardiac volumes and subtle changes in GLS compared with healthy individuals, indicating a continuum of both volumetric and systolic changes present before increased MWT.

Novel mutation in the SLC12A3 gene in a Sri Lankan family with Gitelman syndrome & coexistent diabetes: a case report

Background

Gitelman syndrome (GS) is a rare autosomal recessively inherited salt-wasting tubulopathy associated with mutations in the SLC12A3 gene, which encodes for NaCl cotransporter (NCC) in the kidney.

Case presentation

In this report, we describe two siblings from a Sri Lankan non-consanguineous family presenting with hypokalaemia associated with renal potassium wasting, hypomagnesemia, hypocalciuria and hypereninemic hyperaldosteronism with normal blood pressure. Genetic testing showed that both were homozygotes for a novel missense mutation in exon 10 of the SLC12A3 gene [NM_000339.2, c.1276A > T; p.N426Y], which has not previously been reported in the literature in association with GS. Their mother was a heterozygous carrier for the same mutation. The father was not alive at the time of testing. This novel mutation extends the spectrum of known SLC12A3 gene mutations and further supports the allelic heterogeneity of GS. Interestingly both siblings had young onset Diabetes with strong family history.

Conclusion

These findings have implications in providing appropriate genetic counseling to the family with regard to the risk associated with inbreeding, the detection of carrier/presymptomatic relatives. It further expands the known spectrum of genotypic and phenotypic characteristics of Gitelman syndrome.

Variable phenotypic expression of nonsense mutation p.Thr5* in the APOE gene

Subjects with hypercholesterolemia who do not carry a mutation in the low density lipoprotein receptor gene, in the apolipoprotein B gene or in the proprotein convertase subtilisin/kexin type 9 gene, could possible carry a mutation in the apolipoprotein E (APOE) gene. DNA from 844 unrelated hypercholesterolemic subjects who did not carry a mutation in any of the three above mentioned genes, was subjected to DNA sequencing of the APOE gene. Two subjects were found to be heterozygous for mutation p.Thr5*. This mutation which generates a stop codon in the signal peptide, is assumed to prevent the synthesis of APOE. Family studies revealed that the mutation was carried on an APOE4 allele in both families. In one of the families only those who had an APOE2 allele as the second allele, had hypercholesterolemia. These were functionally hemizygous for APOE2 and presented with a Type III hyperlipoproteinemia phenotype. However, in the second family, hypercholesterolemia was observed in the index patient who had APOE3 as the second allele, but not in four heterozygous family members who also had APOE3 as the second allele. These findings underscore that the phenotypic expression of mutations in the APOE gene is variable and that the trait exhibits reduced penetrance.

Identification and characterization of two novel mutations in the LPL gene causing type I hyperlipoproteinemia

BACKGROUND

Type 1 hyperlipoproteinemia is a rare autosomal recessive disorder most often caused by mutations in the lipoprotein lipase (LPL) gene resulting in severe hypertriglyceridemia and pancreatitis.

OBJECTIVES

The aim of this study was to identify novel mutations in the LPL gene causing type 1 hyperlipoproteinemia and to understand the molecular mechanisms underlying the severe hypertriglyceridemia.

METHODS

Three patients presenting classical features of type 1 hyperlipoproteinemia were recruited for DNA sequencing of the LPL gene. Pre-heparin and post-heparin plasma of patients were used for protein detection analysis and functional test. Furthermore, in vitro experiments were performed in HEK293 cells. Protein synthesis and secretion were analyzed in lysate and medium fraction, respectively, whereas medium fraction was used for functional assay.

RESULTS

We identified two novel mutations in the LPL gene causing type 1 hyperlipoproteinemia: a two base pair deletion (c.765_766delAG) resulting in a frameshift at position 256 of the protein (p.G256TfsX26) and a nucleotide substitution (c.1211 T > G) resulting in a methionine to arginine substitution (p.M404 R). LPL protein and activity were not detected in pre-heparin or post-heparin plasma of the patient with p.G256TfsX26 mutation or in the medium of HEK293 cells over-expressing recombinant p.G256TfsX26 LPL. A relatively small amount of LPL p.M404 R was detected in both pre-heparin and post-heparin plasma and in the medium of the cells, whereas no LPL activity was detected.

CONCLUSIONS

We conclude that these two novel mutations cause type 1 hyperlipoproteinemia by inducing a loss or reduction in LPL secretion accompanied by a loss of LPL enzymatic activity.

Genetics of hypertrophic cardiomyopathy in Norway

Genetic testing for hypertrophic cardiomyopathy (HCM) became available in Norway in 2003. Here, we describe the results of this testing in probands with HCM referred until the end of 2012. The translated exons of MYBPC3, MYH7, TNNI3, TNNT2, MYL2 and MYL3 were analyzed in two groups of probands. In Group 1, comprising 696 probands above 1 year of age, a mutation was found in 203 patients (29.2%). Of those, 5.9% were carriers of two mutations. Mean age in double mutation carriers, single mutation carriers and mutation negative probands was 44 years (± 19 years), 50 years (± 5 years) and 55 years (± 6 years), respectively. In Group 2, comprising 26 infants below the age of 1, a mutation was found in 15.4%. A total of 120 different mutations were found of which 51 (42.5%) were novel.

PCSK9-mediated degradation of the LDL receptor generates a 17 kDa C-terminal LDL receptor fragment

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the LDL receptor (LDLR) at the cell surface and reroutes the internalized LDLR to intracellular degradation. In this study, we have shown that PCSK9-mediated degradation of the full-length 160 kDa LDLR generates a 17 kDa C-terminal LDLR fragment. This fragment was not generated from mutant LDLRs resistant to PCSK9-mediated degradation or when degradation was prevented by chemicals such as ammonium chloride or the cysteine cathepsin inhibitor E64d. The observation that the 17 kDa fragment was only detected when the cells were cultured in the presence of the γ-secretase inhibitor DAPT indicates that this 17 kDa fragment undergoes γ-secretase cleavage within the transmembrane domain. The failure to detect the complementary 143 kDa ectodomain fragment is likely to be due to its rapid degradation in the endosomal lumen. The 17 kDa C-terminal LDLR fragment was also generated from a Class 5 mutant LDLR undergoing intracellular degradation. Thus, one may speculate that an LDLR with bound PCSK9 and a Class 5 LDLR with bound LDL are degraded by a similar mechanism that could involve ectodomain cleavage in the endosome.

Mutations in the SORT1 gene are unlikely to cause autosomal dominant hypercholesterolemia

OBJECTIVE

To study whether mutations in the SORT1 gene could be a cause of autosomal dominant hypercholesterolemia and to study the effect of sortilin on the binding and internalization of low density lipoprotein (LDL).

METHODS

842 unrelated hypercholesterolemic subjects without mutations in genes known to cause autosomal dominant hypercholesterolemia, were screened for mutations in the SORT1 gene by DNA sequencing. Transfections of wild-type or mutant SORT1 plasmids in HeLa T-REx cells and the use of siRNA were used to study the effect of sortilin on the number of cell-surface LDL receptors and on the binding and internalization of LDL.

RESULTS

A total of 45 mutations in the SORT1 gene were identified of which 15 were missense mutations. Eight of these were selected for in vitro studies, of which none had a major impact on the amount of LDL bound to the cell surface. There was a positive correlation between the amount of sortilin on the cell surface and the amount of LDL bound. The observation that a mutant sortilin which is predominantly found on the cell surface rather than in post-Golgi compartments, bound very high amounts of LDL, indicates that sortilin does not increase the binding of LDL through an intracellular mechanism. Rather, our data indicate that sortilin binds LDL on the cell surface.

CONCLUSION

Even though sortilin binds and internalizes LDL by receptor-mediated endocytosis, mutations in the SORT1 gene are unlikely to cause autosomal dominant hypercholesterolemia and may only have a marginal effect on plasma LDL cholesterol levels.

Description of a large family with autosomal dominant hypercholesterolemia associated with the APOE p.Leu167del mutation

Apolipoprotein (apo) E mutants are associated with type III hyperlipoproteinemia characterized by high cholesterol and triglycerides levels. Autosomal dominant hypercholesterolemia (ADH), due to the mutations in the LDLR, APOB, or PCSK9 genes, is characterized by an isolated elevation of cholesterol due to the high levels of low-density lipoproteins (LDLs). We now report an exceptionally large family including 14 members with ADH. Through genome-wide mapping, analysis of regional/functional candidate genes, and whole exome sequencing, we identified a mutation in the APOE gene, c.500_502delTCC/p.Leu167del, previously reported associated with sea-blue histiocytosis and familial combined hyperlipidemia. We confirmed the involvement of the APOE p.Leu167del in ADH, with (1) a predicted destabilization of an alpha-helix in the binding domain, (2) a decreased apo E level in LDLs, and (3) a decreased catabolism of LDLs. Our results show that mutations in the APOE gene can be associated with bona fide ADH.

The prevalence of mutations in KCNQ1, KCNH2, and SCN5A in an unselected national cohort of young sudden unexplained death cases

INTRODUCTION

Sudden unexplained death account for one-third of all sudden natural deaths in the young (1-35 years). Hitherto, the prevalence of genopositive cases has primarily been based on deceased persons referred for postmortem genetic testing. These deaths potentially may represent the worst of cases, thus possibly overestimating the prevalence of potentially disease causing mutations in the 3 major long-QT syndrome (LQTS) genes in the general population. We therefore wanted to investigate the prevalence of mutations in an unselected population of sudden unexplained deaths in a nationwide setting.

METHODS

DNA for genetic testing was available for 44 cases of sudden unexplained death in Denmark in the period 2000-2006 (equaling 33% of all cases of sudden unexplained death in the age group). KCNQ1, KCNH2, and SCN5A were sequenced and in vitro electrophysiological studies were performed on novel mutations.

RESULTS

In total, 5 of 44 cases (11%) carried a mutation in 1 of the 3 genes corresponding to 11% of all investigated cases (R190W KCNQ1, F29L KCNH2 (2 cases), P297S KCNH2 and P1177L SCN5A). P1177L SCN5A has not been reported before. In vitro electrophysiological studies of P1177L SCN5A revealed an increased sustained current suggesting a LQTS phenotype.

CONCLUSION

In a nationwide setting, the genetic investigation of an unselected population of sudden unexplained death cases aged 1-35 years finds a lower than expected number of mutations compared to referred populations previously reported. We therefore conclude that the prevalence of mutations in the 3 major LQTS associated genes may not be as abundant as previously estimated.

Characterization of a naturally occurring degradation product of the LDL receptor

In this study we have characterized a naturally occurring truncated form of the low density lipoprotein receptor (LDLR). Western blot analysis of transfected cells indicated that the truncated form (∆N-LDLR) is a degradation product of the full-length LDLR generated by cleavage in the linker region between ligand-binding repeats 4 and 5 of the ligand-binding domain. The cleavage of the linker was not caused by components of the culture media, as heat inactivation of the media did not prevent cleavage. Rather, it is assumed that cleavage was caused by an enzyme secreted from the cells. Biotinylation experiments showed that ∆N-LDLR is located on the cell surface and is detectable approximately 5 h after synthesis of the full-length LDLR. Flow cytometric analysis showed that ∆N-LDLR was not able to bind and internalize low density lipoprotein (LDL). ∆N-LDLR appeared to be equally stable as the full-length LDLR. Thus, generation of ∆N-LDLR does not appear to be the first signal for degradation of the LDLR. The existence of two functionally different populations of LDLRs on the cell surface, of which ∆N-LDLR constitutes 28%, must be taken into account when interpreting results of experiments to study LDLRs on the cell surface. Furthermore, if the cleavage of the linker between ligand-binding repeats 4 and 5 could be prevented by an enzyme inhibitor, this could represent a novel therapeutic strategy to increase the number of functioning LDLRs and thereby decrease the levels of plasma LDL cholesterol.

Interaction between the ligand-binding domain of the LDL receptor and the C-terminal domain of PCSK9 is required for PCSK9 to remain bound to the LDL receptor during endosomal acidification

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the epidermal growth factor homology domain repeat A of the low-density lipoprotein receptor (LDLR) at the cell surface and disrupts recycling of the internalized LDLR. As a consequence, the LDLR is rerouted to the lysosomes for degradation. Although PCSK9 may bind to an LDLR lacking the ligand-binding domain, at least three ligand-binding repeats of the ligand-binding domain are required for PCSK9 to reroute the LDLR to the lysosomes. In this study, we have studied the binding of PCSK9 to an LDLR with or without the ligand-binding domain at increasingly acidic conditions in order to mimic the milieu of the LDLR:PCSK9 complex as it translocates from the cell membrane to the sorting endosomes. These studies have shown that PCSK9 is rapidly released from an LDLR lacking the ligand-binding domain at pH in the range of 6.9-6.1. A similar pattern of release at acidic pH was also observed for the binding to the normal LDLR of mutant PCSK9 lacking the C-terminal domain. Together these data indicate that an interaction between the negatively charged ligand-binding domain of the LDLR and the positively charged C-terminal domain of PCSK9 is required for PCSK9 to remain bound to the LDLR during the early phase of endosomal acidification as the LDLR translocates from the cell membrane to the sorting endosome.

Role of the C-terminal domain of PCSK9 in degradation of the LDL receptors

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low density lipoprotein receptor (LDLR) at the cell surface and disrupts the normal recycling of the LDLR. In this study, we investigated the role of the C-terminal domain for the activity of PCSK9. Experiments in which conserved residues and histidines on the surface of the C-terminal domain were mutated indicated that no specific residues of the C-terminal domain, apart from those responsible for maintaining the overall structure, are required for the activity of PCSK9. Rather, the net charge of the C-terminal domain is important. The more positively charged the C-terminal domain, the higher the activity toward the LDLR. Moreover, replacement of the C-terminal domain with an unrelated protein of comparable size led to significant activity of the chimeric protein. We conclude that the role of the evolutionary, poorly conserved C-terminal domain for the activity of PCSK9 reflects its overall positive charge and size and not the presence of specific residues involved in protein-protein interactions.

Subjects with molecularly defined familial hypercholesterolemia or familial defective apoB-100 are not being adequately treated

OBJECTIVES

To study whether subjects with a molecular genetic diagnosis of familial hypercholesterolemia (FH) or familial defective apoB-100 (FDB) are being adequately treated.

DESIGN

A questionnaire regarding medical history was sent to 2611 subjects who had been provided with a molecular genetic diagnosis of FH or FDB, and a blood sample was obtained for lipid measurements.

RESULTS

956 (36.6%) of the 2611 subjects participated. The mean age for starting lipid-lowering therapy was 33.4 (±12.1) years. Among those below 18 years of age, only 20.4% were on lipid-lowering drugs, whereas 89.1% of those aged 18 and above were on lipid-lowering drugs. The mean levels of total serum cholesterol and LDL-cholesterol were 5.7 (±1.5) mmol/l and 3.9 (±1.3) mmol/l, respectively. Among those who were on lipid-lowering drugs, 29.0% and 12.2% had levels of LDL cholesterol below 3.0 mmol/l and 2.6 mmol/l, respectively. Only 47.3% of the 956 subjects were considered as being adequately treated largely due to a failure to titrate their drug regimens. From the use of cholesterol-years score, lipid-lowering therapy must start before the age of 20 in order to prevent the subjects from contracting premature coronary heart disease.

CONCLUSION

The majority of FH/FDB subjects are being diagnosed late in life and are not being adequately treated. In order to prevent them from contracting premature coronary heart disease, it is key that levels of LDL cholesterol are normalized from a young age and that sufficient doses of lipid-lowering drugs are being used.

Removal of acidic residues of the prodomain of PCSK9 increases its activity towards the LDL receptor

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the low density lipoprotein receptor (LDLR) at the cell surface and mediates intracellular degradation of the LDLR. The amino-terminus of mature PCSK9, residues 31-53 of the prodomain, has an inhibitory effect on this function of PCSK9, but the underlying mechanism is not fully understood. In this study, we have identified two highly conserved negatively charged segments (residues 32-40 and 48-50, respectively) within this part of the prodomain and performed deletions and substitutions to study their importance for degradation of the LDLRs. Deletion of the acidic residues of the longest negatively charged segment increased PCSK9's ability to degrade the LDLR by 31%, whereas a modest 8% increase was observed when these residues were mutated to uncharged amino acids. Thus, both the length and the charge of this part of the prodomain were important for its inhibitory effect. Deletion of the residues of the shorter second negatively charged segment only increased PCSK9's activity by 8%. Substitution of the amino acids of both charged segments to uncharged residues increased PCSK9's activity by 36%. These findings indicate that the inhibitory effect of residues 31-53 of the prodomain is due to the negative charge of this segment. The underlying mechanism could involve the binding of this peptide segment to positively charged structures which are important for PCSK9's activity. One possible candidate could be the histidine-rich C-terminal domain of PCSK9.

Transmural differences in myocardial contraction in long-QT syndrome: mechanical consequences of ion channel dysfunction

BACKGROUND

Long-QT syndrome (LQTS) is characterized by prolonged myocardial action potential duration. The longest action potential duration is reported in the endomyocardium and midmyocardium. Prolonged action potential duration in LQTS may cause prolonged cardiac contraction, which can be assessed by strain echocardiography. We hypothesized that myocardial contraction is most prolonged in subendocardial myofibers in LQTS patients and that inhomogeneous transmural contraction is related to the risk of spontaneous arrhythmia.

METHODS AND RESULTS

We included 101 genotyped LQTS mutation carriers and 35 healthy individuals. A history of cardiac arrhythmias was present in 48 mutations carriers, and 53 were asymptomatic. Myocardial contraction duration was assessed by strain echocardiography as time from the ECG Q wave to peak strain in 16 LV segments. Strain was assessed along the longitudinal axis, predominantly representing subendocardial fibers, and along the circumferential axis, representing midmyocardial fibers. Mean contraction duration was longer in LQTS mutation carriers compared with healthy individuals (445 ± 45 versus 390 ± 40 milliseconds; P<0.001) and longer in symptomatic compared with asymptomatic LQTS mutation carriers (460 ± 40 versus 425 ± 45 milliseconds; P<0.001). Contraction duration by longitudinal strain was longer than by circumferential strain in symptomatic LQTS patients (460 ± 45 versus 445±45 milliseconds; P=0.008) but not in asymptomatic patients and healthy individuals, indicating transmural mechanical dispersion. This time difference was present in a majority of LV segments and was most evident in patients with LQT2 and the Jervell and Lange-Nielsen syndrome.

CONCLUSION

Contraction duration in symptomatic LQTS mutation carriers was longer in the subendocardium than in the midmyocardium, indicating transmural mechanical dispersion, which was not present in asymptomatic and healthy individuals.

Disrupted recycling of the low density lipoprotein receptor by PCSK9 is not mediated by residues of the cytoplasmic domain

Proprotein convertase subtilisin/kexin type 9 (PCSK9) post-translationally regulates the number of cell-surface low density lipoprotein receptors (LDLR). This is accomplished by the ability of PCSK9 to mediate degradation of the LDLR. The underlying mechanism involves binding of secreted PCSK9 to the epidermal growth factor-like repeat A of the extracellular domain of the LDLR at the cell surface, followed by lysosomal degradation of the internalized LDLR:PCSK9 complex. However, the mechanism by which the normal recycling of the LDLR is disrupted by PCSK9, remains to be determined. In this study we have investigated the role of the cytoplasmic domain of the LDLR for this process. This has been done by studying the ability of a mutant LDLR (K811X-LDLR) which lacks the cytoplasmic domain, to be degraded by PCSK9. We show that this mutant receptor is degraded by PCSK9. Thus, the machinery which directs the LDLR:PCSK9 complex to the lysosomes for degradation, does not interact with the cytoplasmic domain of the LDLR.

Mutations in APOA-I and ABCA1 in Norwegians with low levels of HDL cholesterol

BACKGROUND

Epidemiological studies have shown that low levels of plasma high density lipoprotein (HDL) cholesterol are associated with increased risk of ischemic heart disease (IHD), but it appears that genetic forms of low HDL cholesterol levels, as opposed to lifestyle-induced low levels of HDL cholesterol, do not result in increased risk of IHD. Therefore, the etiology of reduced levels of plasma HDL cholesterol may represent a factor that should be considered in risk stratification with respect to primary prevention. Genes encoding proteins involved in HDL metabolism, such as the ATP-binding cassette transporter A1 (ABCA1) and apolipoprotein (apo) A-I genes, are candidate genes for harboring mutations that lead to low HDL cholesterol levels.

METHODS

The ABCA1 and apoA-I genes in 56 Norwegian patients, with a mean HDL cholesterol level of 0.53 (±0.15) mmol/l, were subjected to DNA sequencing.

RESULTS

Several mutations were identified in the ABCA1 gene, and two mutations were identified in the apoA-I gene. A total of 18 patients (32%) were carriers of mutations considered to be pathogenic. Their mean HDL cholesterol level was 0.45 (±0.15) mmol/l compared to 0.57 (±0.14) mmol/l in noncarriers (p<0.005).

CONCLUSION

Mutations in the genes encoding ABCA1 and apoA-I are common in Norwegians, with a markedly decreased HDL cholesterol level.

A chimeric LDL receptor containing the cytoplasmic domain of the transferrin receptor is degraded by PCSK9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to the extracellular domain of the low density lipoprotein receptor (LDLR) at the cell surface, and disrupts the normal recycling of the LDLR. However, the exact mechanism by which the LDLR is re-routed for lysosomal degradation remains to be determined. To clarify the role of the cytoplasmic domain of the LDLR for re-routing to the lysosomes, we have studied the ability of PCSK9 to degrade a chimeric receptor which contains the extracellular and transmembrane domains of the LDLR and the cytoplasmic domain of the transferrin receptor. These studies were performed in CHO T-REx cells stably transfected with a plasmid encoding the chimeric receptor and a novel assay was developed to study the effect of PCSK9 on the LDLR in these cells. Localization, function and stability of the chimeric receptor were similar to that of the wild-type LDLR. The addition of purified gain-of-function mutant D374Y-PCSK9 to the culture medium of stably transfected CHO T-REx cells showed that the chimeric receptor was degraded, albeit to a lower extent than the wild-type LDLR. In addition, a mutant LDLR, which has the three lysines in the intracellular domain substituted with arginines, was also degraded by D374Y-PCSK9. Thus, the mechanism for the PCSK9-mediated degradation of the LDLR does not appear to involve an interaction between the endosomal sorting machinery and LDLR-specific motifs in the cytoplasmic domain. Moreover, ubiquitination of lysines in the cytoplasmic domain does not appear to play a critical role in the PCSK9-mediated degradation of the LDLR.

[Catecholaminergic polymorphic ventricular tachycardia]

BACKGROUND

CPVT (catecholaminergic polymorphic ventricular tachycardia) is a condition characterized by syncopes and cardiac arrest that was first described in 1975. CPVT has later been classified as a genetic disease with a great risk for life-threatening arrhythmias that are mainly caused by mutations in the ryanodine receptor 2 gene. Starting with a case report, we present an overview of CPVT.

MATERIAL AND METHODS

The literature reviewed was identified through a non-systematic search in PubMed.

RESULTS

Diagnosing CPVT may be difficult, as resting ECG is normal and the syncopes may be misdiagnosed as epilepsy. Information about syncopes related to physical or emotional stress and occurrence of unexplained syncopes or cardiac arrest among family members, is important in the diagnostic evaluation. An exercise stress test often reveals the classical pattern of ventricular arrhythmias at heart rates above 100 beats/min. The diagnosis can be confirmed by genetic testing. By beta-blocker treatment and, if necessary, an ICD (implantable cardioverter defibrillator) the prognosis can be improved.

INTERPRETATION

CPVT is a serious disease with a poor prognosis when left untreated. It is a rare but important differential diagnosis in young individuals with syncopes or cardiac arrest. Genetic screening of relatives has made it possible to identify mutation carriers in affected families in order to provide them with preventive therapy.

High prevalence of exercise-induced arrhythmias in catecholaminergic polymorphic ventricular tachycardia mutation-positive family members diagnosed by cascade genetic screening

AIM

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited cardiac disease predisposing to life-threatening arrhythmias. We aimed to determine the prevalence of arrhythmias and efficacy of beta-blocker treatment in mutation-positive family members diagnosed by cascade genetic screening.

METHODS AND RESULTS

Relatives of six unrelated CPVT patients were tested for the relevant mutation in the ryanodine receptor-2 gene. Mutation carriers underwent an exercise test at inclusion time and 3 months after the initiation of beta-blocker therapy in the highest tolerable dose. The occurrence of ventricular premature beats, couplets, and non-sustained ventricular arrhythmias (nsVT) were recorded in addition to the heart rate at which they occurred. Thirty family members were mutation carriers and were followed for 22 (13-288) months. Previous undiagnosed CPVT-related symptoms were reported by eight subjects. Exercise test induced ventricular arrhythmias in 23 of the 30 mutation carriers. On beta-blocker treatment, exercise-induced arrhythmias occurred at a lower heart rate (117 +/- 17 vs. 135 +/- 34 beats/min, P = 0.02) but at similar workload (P = 0.78). Beta-blocker treatment suppressed the occurrence of exercise-induced nsVT in three of the four patients, while less severe arrhythmias were unchanged. One patient died during follow-up.

CONCLUSION

Exercise test revealed a high prevalence of arrhythmias in CPVT mutation carriers diagnosed by cascade genetic screening. beta-Blocker therapy appeared to suppress the most severe exercise-induced arrhythmias, while less severe arrhythmias occurred at a lower heart rate.

The unique role of proprotein convertase subtilisin/kexin 9 in cholesterol homeostasis

The LDL receptor (LDLR) plays an essential role in the regulation of plasma (LDL) cholesterol concentrations by virtue of its ability to clear plasma LDL. Down-regulation of the LDLR by proprotein convertase subtilisin/kexin 9 (PCSK9) has recently emerged as a regulatory mechanism that controls plasma LDL cholesterol concentrations. Studies in which PCSK9 is over-expressed in mice, have demonstrated that PCSK9, by enhancing hepatic LDLR degradation, decreases the availability of the LDLR for LDL uptake, resulting in increased plasma LDL cholesterol levels. However, PCSK9 has also recently been shown to mediate down-regulation of surface receptors other than the LDLR, suggesting that it may have much broader roles than initially thought.

Tangier disease caused by compound heterozygosity for ABCA1 mutations R282X and Y1532C

BACKGROUND

Inherited low levels of high density lipoprotein (HDL) cholesterol may be due to mutations in the genes encoding the ATP-binding cassette transporter A1 (ABCA1), apolipoprotein (apo) A-I or lecithin:cholesterol acyltransferase (LCAT).

METHODS

The ABCA1, apoA-I and LCAT genes of a 40-year-old male subject with serum HDL cholesterol of 0.06mmol/l were subjected to DNA sequencing. The proband's family was examined for co-segregation between mutations and levels of HDL cholesterol. Cholesterol efflux in fibroblasts from the proband and a normocholesterolemic subject was compared. The effects of an ABCA1 mutation on cholesterol efflux and membrane localization of ABCA1 were studied in transfected HEK293 and HeLa cells, respectively.

RESULTS

The proband was a compound heterozygote for ABCA1 mutations R282X (c.844 C>T) and Y1532C (c.4595 A>G). Relatives who were heterozygous for one of these mutations, had about half-normal HDL cholesterol levels. Cholesterol efflux was reduced in fibroblasts from the proband, as was cholesterol efflux from HEK293 cells transfected with an human (h) ABCA1 expression plasmid harboring the Y1532C mutation. Confocal microscopy of HeLa cells transfected with the Y1532C-hABCA1 plasmid revealed that the Y1532C mutation inhibits ABCA1 from reaching the cellular membrane.

CONCLUSION

Compound heterozygosity for the nonsense mutation R282X and the missense mutation Y1532C in the ABCA1 gene causes Tangier disease. R282X has a detrimental effect on the function of ABCA1 since a premature stop codon is introduced. Mutation Y1532C disrupts the normal function of ABCA1 as determined by in vitro analyses.

Effects of intronic mutations in the LDLR gene on pre-mRNA splicing: Comparison of wet-lab and bioinformatics analyses

Screening for mutations in the low density lipoprotein receptor (LDLR) gene has identified more than 1000 mutations as the cause of familial hypercholesterolemia (FH). In addition, numerous intronic mutations with uncertain effects on pre-mRNA splicing have also been identified. In this study, we have selected 18 intronic mutations in the LDLR gene for comprehensive studies of their effects on pre-mRNA splicing. Epstein-Barr virus (EBV) transformed lymphocytes from subjects heterozygous for these mutations were established and mRNA was studied by Northern blot analyses and reverse transcription polymerase chain reactions. Furthermore, functional studies of the LDLRs were performed by flow cytometry. The results of the wet-lab analyses were compared to the predictions obtained from bioinformatics analyses using the programs MaxEntScan, NetGene2 and NNSplice 0.9, which are commonly used software packages for prediction of abnormal splice sites. Thirteen of the 18 intronic mutations were found to affect pre-mRNA splicing in a biologically relevant way as determined by wet-lab analyses. Skipping of one or two exons was observed for eight of the mutations, intron inclusion was observed for four of the mutations and activation of a cryptic splice site was observed for two of the mutations. Transcripts from eight of the mutant alleles were subjected to degradation. The computational analyses of the normal and mutant splice sites, predicted abnormal splicing with a sensitivity of 100% and a specificity of 60%. Thus, bioinformatics analyses are valuable tools as a first screening of the effects of intronic mutations in the LDLR gene on pre-mRNA splicing.

The effect of bafilomycin A1 and protease inhibitors on the degradation and recycling of a Class 5-mutant LDLR

The low-density lipoprotein receptor (LDLR) mediates cholesterol homeostasis through endocytosis of lipoprotein particles, particularly low-density lipoproteins (LDLs). Normally, the lipoprotein particles are released in the endosomes and the receptors recycle to the cell surface. Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by mutations in the gene encoding the LDLR. These mutations are divided into five functional classes where Class 5 mutations encode receptors that suffer from ligand-induced degradation and recycling deficiency. The aim of this study was to investigate whether it is possible to prevent the fast ligand-induced degradation of Class 5-mutant LDLR and to restore its ability to recycle to the cell surface. E387K is a naturally occurring Class 5 mutation found in FH patients, and in the present study, we used Chinese hamster ovary cells transfected with an E387K-mutant LDLR. Abrogation of endosomal acidification by adding bafilomycin A1 or addition of the irreversible serine protease inhibitors, 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF) and 3,4-dichloroisocoumarin (DCI), prevented the degradation of the E387K-mutant LDLR. However, the undegraded receptor did not recycle to the cell surface in the presence of LDL. Unexpectedly, AEBSF caused aggregation of early endosome antigen-1- positive endosomes and the intracellular trapped LDLR co-localized with these aggregated early endosomes.

Mutation S462P in the PCSK9 gene reduces secretion of mutant PCSK9 without affecting the autocatalytic cleavage

OBJECTIVE

The normal function of proprotein convertase subtilisin/kexin type 9 (PCSK9) is to mediate degradation of the low density lipoprotein (LDL) receptors. However, the exact mechanism for this function remains to be determined. Characterization of how the naturally occurring mutations in the PCSK9 gene affect the function of PCSK9, may provide important insight into the mechanism by which PCSK9 degrades the LDL receptors.

METHODS

DNA sequencing of the 12 exons with flanking intron sequences of the PCSK9 gene was performed in 1336 unrelated hypercholesterolemic subjects. In vitro assays and bioinformatics analysis were employed to characterize the functional consequences of a novel mutation. EXPERIMENTAL RESULTS: One subject was heterozygous for the novel mutation S462P in exon 9 of the PCSK9 gene. Based upon Western blot analysis of transiently transfected HepG2 cells, S462P-PCSK9 was almost completely retained in the endoplasmic reticulum (ER) even though it did undergo autocatalytic cleavage. Thus, only trace amounts of S462P-PCSK9 were detected in the culture media of transfected cells. Flow cytometric experiments revealed that the S462P-PCSK9 mutant was unable to degrade the LDL receptors.

DISCUSSION

The markedly reduced secretion of S462P-PCSK9 makes S462P a loss-of-function mutation. Ser462 is one of the few residues in the C-terminal domain which is conserved in all known PCSK9 homologs. A hydrogen bond between the side-chain of Ser462 and the backbone of beta-strand 6 of the C-terminal domain, appears to be essential for the proper folding of the C-terminal domain. The S462P mutation is believed to disrupt the normal folding of the C-terminal domain leading to retention of the mutant protein in the ER.

Genome-wide expression analysis of cells expressing gain of function mutant D374Y-PCSK9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key regulator of serum cholesterol. The possibility that PCSK9 also functions in other pathways needs to be addressed. We have transfected HepG2 cells with mutant D374Y-PCSK9 or control vector. Gene expression signatures were determined using the Affymetrix GeneChip technology, and the expression pattern of selected genes was confirmed by quantitative real-time polymerase chain reaction (qRT-PCR). Data was normalized and analyzed using a model-based background adjustment for oligonucleotide expression arrays, then filtered based upon expression within treatments group, and subjected to moderated t-statistics. Five hundred twenty transcripts had altered expression levels between D374Y-PCSK9 and control vector. Among the 520 probes on our top list, 312 were found to have an assigned Gene Ontology (GO) term, and 96 were found in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Genome-wide expression profiling revealed that "steroid biosynthesis," "sterol metabolism," and "cholesterol biosynthsis" were affected by D374Y-PCSK9. Also, the GO biological process terms "response to stresss," "response to virus," "response to unfolded protein," and "immune response" were influenced by D374Y-PCSK9. Our results suggest that D374Y-PCSK9 results in up-regulation of genes involved in sterol biosynthesis and down-regulation of stress-response genes and specific inflammation pathways.

Identification of mutations in the apolipoprotein B-100 gene and in the PCSK9 gene as the cause of hypocholesterolemia

BACKGROUND

Characterization of the normally occurring mutations as the cause of hypocholesterolemia may increase our understanding of the normal lipid metabolism.

METHODS

DNA from 93 unrelated hypocholesterolemic subjects with a mean (+/-SD) value for total serum cholesterol of 3.3 (+/-0.5) mmol/l) were subjected to DNA sequencing of the individual exons of the apolipoprotein B-100 (apoB-100) gene and of the proprotein convertase subtilisin/kexin 9 (PCSK9) gene. The same analyses were also performed in 23 unrelated subjects with autosomal dominant hypercholesterolemia who had unusually low levels of total serum cholesterol.

RESULTS

Of the 93 hypocholesterolemic subjects, 9 subjects (9.7%) were heterozygous for a truncating mutation in the apoB-100 gene and six subjects (6.5%) were heterozygous for a loss-of-function mutation in the PCSK9 gene. Of the 23 subjects with autosomal dominant hypercholesterolemia, four subjects (17.4%) were heterozygous for mutations in the apoB-100 gene.

CONCLUSION

Truncating mutations in the apoB-100 gene are slightly more common as the cause of hypocholesterolemia compared to loss-of-function mutations in the PCSK9 gene. It appears that mutations in the apoB-100 gene may completely normalize the lipid profile in subjects with autosomal dominant hypercholesterolemia, whereas loss-of-function mutations in the PCSK9 gene do not have a sufficient cholesterol-lowering capacity.

No effect of a Taql polymorphism in DNA at the endothelin I (EDN1) locus on normal blood pressure level or variability

Endothelin is a peptide reported to be one of the most potent vasoconstrictors known. Presumably, endothelin could play a role in the physiological regulation of blood pressure in healthy or hypertensive people. We have studied a normal restriction fragment length polymorphism (RFLP) at the endothelin-I (EDN1) locus detected with the restriction enzyme TaqI. In three different series comprising 166, 120 and 207 unrelated individuals, we found no evidence for association between genotype in this polymorphism and level of systolic or diastolic blood pressure. In two series of 156 and 117 monozygotic (MZ) twin pairs, respectively, there was no difference between genotypes in within-pair variation in systolic or diastolic blood pressure. Thus neither "level gene" nor "variability gene" effects of normal genes at the EDN1 locus could be detected with the polymorphism analyzed, in healthy population samples.

Characterization of novel mutations in the catalytic domain of the PCSK9 gene

OBJECTIVES

To expand our understanding of the structure and function of proprotein convertase subtilisin/kexin type 9 (PCSK9) by studying how naturally occurring mutations in PCSK9 disrupt the function of PCSK9.

DESIGN

Mutations in PCSK9 were identified by sequencing of DNA from subjects with hypo- or hypercholesterolemia. The effect of the identified mutations on the autocatalytic cleavage and secretion of PCSK9, as well as the effect on PCSK9-mediated degradation of the low density lipoprotein receptors, were determined in HepG2 or HEK293 cells transiently transfected with mutant PCSK9-containing plasmids. The findings were collated to the clinical characteristics of the subjects possessing these mutations, and the phenotypic effects were analysed in terms of available structural data for PCSK9.

RESULTS

Five novel mutations in PCSK9 were identified. Mutation R215H was a gain-of-function mutation which causes hypercholesterolemia. Mutation G236S and N354I were loss-of-function mutations due to failure to exit the endoplasmic reticulum or failure to undergo autocatalytic cleavage, respectively. Mutations A245T and R272Q were most likely normal genetic variants. By comparing the number of patients with gain-of-function mutations in PCSK9 with the number of familial hypercholesterolemia heterozygotes among subjects with hypercholesterolemia, the prevalence of subjects with gain-of-function mutations in PCSK9 in Norway can be estimated to one in 15,000.

CONCLUSION

This study has provided novel information about the structural requirements for the normal function of PCSK9. However, more studies are needed to determine the mechanisms by which gain-of-function mutations in PCSK9 cause hypercholesterolemia.

Berberine decreases PCSK9 expression in HepG2 cells

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) post-transcriptionally downregulates the low-density lipoprotein receptor (LDLR) by binding to the receptor's epidermal growth factor repeat A on the cell surface and shuttling the LDLR to the lysosomes for degradation. Mutations in the PCSK9 gene have been shown to cause either hypo- or hypercholesterolemia. Here we investigated the effect of berberine, a natural plant extract, on PCSK9 expression in HepG2 cells.

RESULTS

Berberine decreases PCSK9 mRNA and protein levels in a time- and dose-dependent manner. This was not due to increased degradation of PCSK9 mRNA but most likely due to a decreased transcription of the PCSK9 gene. We also show that a combination of berberine and mevastatin increases LDLR mRNA and protein levels, while suppressing the increase in PCSK9 mRNA levels caused by mevastatin alone.

CONCLUSION

Berberine may be a useful supplement to statin treatment due to its effects on PCSK9 mRNA and protein levels.

Diagnosis of familial hypercholesterolemia in general practice using clinical diagnostic criteria or genetic testing as part of cascade genetic screening

BACKGROUND

Too few familial hypercholesterolemia (FH) patients are diagnosed. The most cost-effective strategy to diagnose FH is to examine first-degree relatives of already diagnosed patients. This is referred to as cascade genetic screening.

METHODS AND RESULTS

One thousand eight hundred and five first-degree relatives of index patients with molecularly defined FH consented to cascade genetic screening by the use of molecular genetic testing. Of these, 44.8% were mutation carriers and 55.2% were noncarriers. Only 44.2% of the mutation carriers were on lipid-lowering drugs at the time of genetic testing. Of these, only 9.4% had a value for total serum cholesterol below 5 mM. Among adult mutation carriers who were not on lipid-lowering treatment at the time of genetic testing, reductions in total serum cholesterol and low-density lipoprotein cholesterol of 18.4% (p < 0.0001) and 25.3% (p < 0.0001), respectively, were observed 6 months after genetic testing. It is assumed that this improvement in the lipid profile is due to a definite diagnosis obtained by molecular genetic testing. By using the results of genetic testing as the gold standard for diagnosis of FH, data from a questionnaire filled out by the relatives showed that the use of clinical criteria to diagnose FH in general practice had a sensitivity of 46.2% and a specificity of 88.0%.

CONCLUSIONS

The use of clinical diagnostic criteria to diagnose FH in general practice identifies only approximately 50% of FH patients. Molecular genetic testing as part of cascade genetic screening is an efficient tool to diagnose patients, leading to significant improvement in the lipid profile. It should therefore be implemented in clinical medicine.

Multiple inflammatory-, tissue remodelling- and fibrosis genes are differentially transcribed in the livers of Abcb4 (-/ - ) mice harbouring chronic cholangitis

OBJECTIVE

Abcb4 (-/-) mice secrete phosphatidylcholine-free, cytotoxic bile and develop chronic cholangitis. The aim of this study was to identify differentially transcribed genes whose products contribute to the liver tissue pathology during this disease.

MATERIAL AND METHODS

Hepatic gene transcription was measured in 3-, 6-, 9- and 20-week-old Abcb4 (-/-) mice (FVB.129P2-abcb4(tm1Bor)/J) using cDNA microarrays, with FVB/NJ Abcb4 (+/+) mice serving as controls. Focus was on inflammatory-, remodelling- and fibrosis genes. Marked differential transcription of inflammatory-, tissue remodelling- and fibrosis genes found by cDNA microarrays was verified by real-time polymerase chain reaction (PCR). Liver pathology was quantified by histopathology scoring.

RESULTS

Transcription of clade A3 Serpin genes showed early, marked down-regulation. The chemokine genes Ccl2, Ccl20 and Cxcl10 were markedly up-regulated. Tissue remodelling- and fibrosis genes exhibiting markedly up-regulated transcription included: Ctgf, Elf3, Lgals3, Mmp12, Mmp15, Spp1, Loxl2, Pdgfa, Pdgfrb, Sparc, Tgfb1, Tgfb2, Tgfbi, Tgfbr2 and Col1a1, Col1a2, Col2a1, Col3a1, Col4a1 genes. Microarray-based recordings of differential gene transcription of the majority of these genes harmonized with the liver histopathology score. Thus, cDNA microarray-based analysis showed increasing differential transcription of several inflammatory-, tissue remodelling- and fibrosis genes during the first 9 weeks of disease and a tendency towards differential transcription to stabilize at an elevated level from 9 to 20 weeks of disease.

CONCLUSIONS

Multiple genes regulating inflammation, tissue remodelling and fibrosis not previously linked to Abcb4 (-/-) cholangitis are identified as being differentially transcribed in Abcb4 (-/-) livers, where they contribute to the pathogenesis of liver tissue pathology.

[Lipid profile in children and adolescents with familial hypercholesterolemia]

BACKGROUND

Previous reported serum lipid levels in children and adolescents with familial hypercholesterolemia are uncertain. Reasons are that the diagnosis may have been uncertain and that the reported lipid levels have been mainly from patients treated at tertiary referral centres.

MATERIAL AND METHODS

The serum lipid levels in 434 children and adolescents (2-18 years) who had undergone molecular genetic testing for familial hypercholesterolemia as part of cascade genetic screening, were measured.

RESULTS

196/434 (45.2%) were heterozygous for the mutation in the LDL receptor gene that had been identified in the family, while 238/434 (54.8%) were not heterozygous. Those who were heterozygous had mean total serum cholesterol levels of 7.40 (+/- 1.41) mmol/L and LDL cholesterol of 5.60 (+/- 1.38) mmol/L. These values were 1.70 (p < 0.001) and 2.19 (p < 0.001) times higher than the corresponding values in those who were not heterozygous. A total serum cholesterol level of 5.5 mmol/L had a high sensitivity and specificity for the diagnosis of familial hypercholesterolemia.

INTERPRETATION

Familial hypercholesterolemia should mainly be diagnosed by molecular genetic testing. If the underlying mutation cannot be identified a total serum cholesterol value of 5.5 mmol/L and an LDL cholesterol value of 3.5 mmol/L, should be used to diagnose children and adolescents.

The effect of red wine on plasma leptin levels and vasoactive factors from adipose tissue: A randomized crossover trial

AIMS

It has been reported that alcohol has multiple effects on appetite. To elucidate potential mechanisms we measured the levels of plasma leptin and the vasoactive factors after red wine intake.

METHODS

We conducted a randomized crossover trial to study the effect of red wine on the levels of leptin, TNF-alpha, TGF- beta(1), IL-6, ICAM-1, and VCAM-1 in healthy, non-smoking individuals. The subjects were randomized to drinking one glass of red wine (150 ml, 15 g alcohol) every day ('wine period') or to undergo a period of total abstention from alcohol ('abstention period'). After 3 weeks they switched the intervention group. Eighty-seven volunteers completed the study (mean age 50 years).

RESULTS

After 3 weeks' daily intake of red wine, plasma leptin was significantly increased (from 6308 pg/ml to 7402 pg/ml, P = 0.05). There was a marked gender difference, as leptin levels increased only in females (P = 0.012). When calculated as leptin/body mass index (BMI) ratio, the trend and results were similar. Red wine consumption had no significant effect on other vasoactive factors measured in this study.

CONCLUSION

Red wine increases levels of the appetite-regulating hormone leptin in females, but not in males. Whether red wine has an effect on appetite-regulation in its own right, remains to be solved.

[High-risk hypertrophic cardiomyopathy associated with a novel mutation in cardiac Myosin-binding protein C]

Hypertrophic cardiomyopathy is an autosomal dominant inherited disease characterized by ventricular hypertrophy and myofibril disarray. Mutations responsible for hypertrophic cardiomyopathy have been identified in 11 genes that encode for cardiac sarcomere proteins. Traditionally, hypertrophic cardiomyopathy due to mutation of the myosin-binding protein C gene (MYBPC3) has been thought to follow a benign course. We report a family with several members affected by hypertrophic cardiomyopathy in which there was a high incidence of sudden death. Disease was presumably caused by the substitution of cytosine by guanine at nucleotide 269 of MYBPC3 mRNA. This mutation, which has not previously been described, modifies codon 79, which encodes for the incorporation of a tyrosine, and gives rise to a stop codon. The mutation described here appears to confer a higher risk than that previously associated with hypertrophic cardiomyopathy due to MYBPC3 gene mutation.

Analysis of alternatively spliced isoforms of human LDL receptor mRNA

BACKGROUND

The low density lipoprotein receptor (LDLR) family is a family of structurally related cell surface receptors with conserved exon/intron organization. Several members of this family have been shown to undergo alternative splicing. However, no alternative splicing of the LDLR pre-mRNA has so far been described.

METHODS

In the present study alternative splicing of human LDLR pre-mRNA has been studied in eight different tissues and four different cell lines using reverse transcription (RT) PCR. A quantitative real-time PCR with exon-exon boundary spanning primers was established to measure the relative amount of two novel isoforms.

RESULTS

Several novel isoforms were identified by RT-PCR of which the isoforms lacking exon 4 or 12 were two of the most prominent. Although highly detectable by RT-PCR, the quantification by real-time PCR revealed low levels of these isoforms.

CONCLUSIONS

Novel isoforms of LDLR mRNA are described. Quantification by real-time PCR of two of the alternatively spliced isoforms revealed low amount of these isoforms in the examined tissues and cell lines. Further investigations are needed to evaluate if these isoforms represent functional transcripts of LDLR mRNA.

Low-density lipoprotein receptor activity in Epstein-Barr virus-transformed lymphocytes from heterozygotes for the D374Y mutation in the PCSK9 gene

OBJECTIVE

Missense mutations in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene have been found to cause autosomal dominant hypercholesterolemia. The objective of this study was to investigate possible mechanisms by which mutation D374Y in the PCSK9 gene causes hypercholesterolemia.

MATERIAL AND METHODS

Binding and internalization of low-density lipoprotein LDL in Epstein-Barr virus (EBV)-transformed lymphocytes from D374Y heterozygotes were examined. The autocatalytic activity of the D374Y mutant was studied in transiently transfected HEK293 cells.

RESULTS

As determined by Western blot analysis of transiently transfected HEK293 cells, the autocatalytic activity of the D374Y mutant was approximately 95% of the wild-type. Levels of PCSK9 mRNA in EBV-transformed lymphocytes from D374Y heterozygotes and normal controls were similar and less than 1/1000 of the level in HepG2 cells. The amount of cell surface LDL receptors (LDLRs) in EBV-transformed lymphocytes from five D374Y heterozygotes was non-significantly increased by 17% compared with the amount in normal controls. LDLR-dependent binding and internalization of LDL in EBV-transformed lymphocytes from D374Y heterozygotes were non-significantly reduced by 11% and 12%, respectively, compared to the corresponding values in normal controls.

CONCLUSIONS

LDLR-mediated endocytosis of LDL is not reduced in EBV-transformed lymphocytes from D374Y heterozygotes. Because of the extremely low levels of PCSK9 mRNA in EBV-transformed lymphocytes, it is possible that the LDLR-dependent endocytosis of LDL could be more severely affected in hepatocytes from D374Y heterozygotes than in EBV-transformed lymphocytes.