Obesity, POMC, and POMC-processing Enzymes: Surprising Results From Animal Models.

Peptides derived from proopiomelanocortin (POMC) are well-established neuropeptides and peptide hormones that perform multiple functions, including regulation of body weight. In humans and some animals, these peptides include α- and ß-melanocyte-stimulating hormone (MSH). In certain rodent species, no ß-MSH is produced from POMC because of a change in the cleavage site. Enzymes that convert POMC into MSH include prohormone convertases (PCs), carboxypeptidases (CPs), and peptidyl-α-amidating monooxygenase (PAM). Humans and mice with inactivating mutations in either PC1/3 or carboxypeptidase E (CPE) are obese, which was assumed to result from defective processing of POMC into MSH. However, recent studies have shown that selective loss of either PC1/3 or CPE in POMC-expressing cells does not cause obesity. These findings suggest that defects in POMC processing cannot alone account for the obesity observed in global PC1/3 or CPE mutants. We propose that obesity in animals lacking PC1/3 or CPE activity depends, at least in part, on deficient processing of peptides in non-POMC-expressing cells either in the brain and/or the periphery. Genetic background may also contribute to the manifestation of obesity.

ER Stress Drives Lipogenesis and Steatohepatitis via Caspase-2 Activation of S1P.

Nonalcoholic fatty liver disease (NAFLD) progresses to nonalcoholic steatohepatitis (NASH) in response to elevated endoplasmic reticulum (ER) stress. Whereas the onset of simple steatosis requires elevated de novo lipogenesis, progression to NASH is triggered by accumulation of hepatocyte-free cholesterol. We now show that caspase-2, whose expression is ER-stress inducible and elevated in human and mouse NASH, controls the buildup of hepatic-free cholesterol and triglycerides by activating sterol regulatory element-binding proteins (SREBP) in a manner refractory to feedback inhibition. Caspase-2 colocalizes with site 1 protease (S1P) and cleaves it to generate a soluble active fragment that initiates SCAP-independent SREBP1/2 activation in the ER. Caspase-2 ablation or pharmacological inhibition prevents diet-induced steatosis and NASH progression in ER-stress-prone mice. Caspase-2 inhibition offers a specific and effective strategy for preventing or treating stress-driven fatty liver diseases, whereas caspase-2-generated S1P proteolytic fragments, which enter the secretory pathway, are potential NASH biomarkers.

(Pro)renin receptor mediates albumin-induced cellular responses: role of site-1 protease-derived soluble (pro)renin receptor in renal epithelial cells.

Proteinuria is a characteristic of chronic kidney disease and also a causative factor that promotes the disease progression, in part, via activation of the intrarenal renin-angiotensin system (RAS). (Pro)renin receptor (PRR), a newly discovered component of the RAS, binds renin and (pro)renin to promote angiotensin I generation. The present study was performed to test the role of soluble PRR (sPRR) in albumin overload-induced responses in cultured human renal proximal tubular cell line human kidney 2 (HK-2) cells. Bovine serum albmuin (BSA) treatment for 24 h at 20 mg/ml induced renin activity and inflammation, both of which were attenuated by a PRR decoy inhibitor PRO20. BSA treatment induced a more than fivefold increase in medium sPRR due to enhanced cleavage of PRR. Surprisingly, this cleavage event was unaffected by inhibition of furin or a disintegrin and metalloproteinase 19. Screening for a novel cleavage enzyme led to the identification of site-1 protease (S1P). Inhibition of S1P with PF-429242 or siRNA remarkably suppressed BSA-induced sPRR production, renin activity, and inflammatory response. Administration of a recombinant sPRR, termed sPRR-His, reversed the effects of S1P inhibition. In HK-2 cells overexpressing PRR, mutagenesis of the S1P, but not furin cleavage site, reduced sPRR levels. Together, these results suggest that PRR mediates albumin-induced cellular responses through S1P-derived sPRR.

Glia initiate brain assembly through noncanonical Chimaerin-Furin axon guidance in C. elegans.

Brain assembly is hypothesized to begin when pioneer axons extend over non-neuronal cells, forming tracts guiding follower axons. Yet pioneer-neuron identities, their guidance substrates, and their interactions are not well understood. Here, using time-lapse embryonic imaging, genetics, protein-interaction, and functional studies, we uncover the early events of C. elegans brain assembly. We demonstrate that C. elegans glia are key for assembly initiation, guiding pioneer and follower axons using distinct signals. Pioneer sublateral neurons, with unique growth properties, anatomy, and innervation, cooperate with glia to mediate follower-axon guidance. We further identify a Chimaerin (CHIN-1)- Furin (KPC-1) double-mutant that severely disrupts assembly. CHIN-1 and KPC-1 function noncanonically, in glia and pioneer neurons, for guidance-cue trafficking. We exploit this bottleneck to define roles for glial Netrin and Semaphorin in pioneer- and follower-axon guidance, respectively, and for glial and pioneer-neuron Flamingo (CELSR) in follower-axon navigation. Taken together, our studies reveal previously undescribed glial roles in pioneer-axon guidance, suggesting conserved principles of brain assembly.

PCSK9 inhibitors: an overview on a new promising lipid-lowering therapy.

Atherosclerosis is characterized by cholesterol deposition in the arterial intima, with subsequent plaque formation and arterial disease. Low-density lipoprotein cholesterol (LDL-C) plays the most important role in the atherogenesis process, which is the substrate of cardiovascular disease and is the leading cause of death worldwide. Several studies show that a strict control of risk factors, particularly the reduction of LDL-C levels, is a cornerstone in primary and secondary prevention of coronary heart disease. Statins are currently the most effective drugs for lowering LDL-C, but the discovery of proprotein convertase subtilisin kexin 9 (PCSK9) has opened up new therapeutic options in lipid management. PCSK9 reduces LDL-receptors' recycling resulting in a decrease of LDL-C receptors on the surface of hepatocytes and an increase of LDL-C levels in plasma. Obviously, inhibition of PCSK9 has been associated with an increase of LDL-C receptors with subsequent lowering of plasma levels of LDL-C. The clinical development of monoclonal antibodies against PCSK9 has been achieved through phase I and II studies, and nowadays there are many ongoing phase III trials with promising preliminary results. The aim of this review is to update the evidence for PCSK9 monoclonal antibodies, such as evolocumab, alirocumab and bococizumab, in LDL-C management and to discuss their therapeutic perspectives based on the most recent clinical studies, with attention to side-effects.

[Proprotein convertases - family of serine proteases with a broad spectrum of physiological functions]. / Konwertazy probialkowe - rodzina proteaz serynowych o szerokim spektrum funkcji fizjologicznych.

A large group of secretory proteins involved in proper functioning of living organisms, is synthesized as inactive precursor molecules. Their biologically active forms are obtained as a result of numerous post-translational modifications. Some of these processes occur irreversibly, permanently changing the initial compound structure. An example of such modifications is catalytic treatment of proteins performed by proteolytic enzymes. Among five separate classes of these enzymes, the most numerous are serine proteases. Mammalian proprotein convertases (PCs), which include: furin, PC1/3, PC2, PACE4, PC4, PC5/6, PC7, PCSK9, SKI-1, represent serine endoproteases family. PCs play a key role in the activation of a number of precursor proteins causing formation of biologically active forms of enzymes, hormones, signaling molecules, transcription and growth factors. This article summarizes current state of knowledge on biosynthesis, structure and substrate specificity of PCs, identifies the relationship between location and intracellular activity of these enzymes, and their physiological functions in mammals.

Mechanism of Folding and Activation of Subtilisin Kexin Isozyme-1 (SKI-1)/Site-1 Protease (S1P).

The proprotein convertase subtilisin kexin isozyme-1 (SKI-1)/site-1 protease (S1P) is implicated in lipid homeostasis, the unfolded protein response, and lysosome biogenesis. The protease is further hijacked by highly pathogenic emerging viruses for the processing of their envelope glycoproteins. Zymogen activation of SKI-1/S1P requires removal of an N-terminal prodomain, by a multistep process, generating the mature enzyme. Here, we uncover a modular structure of the human SKI-1/S1P prodomain and define its function in folding and activation. We provide evidence that the N-terminal AB fragment of the prodomain represents an autonomous structural and functional unit that is necessary and sufficient for folding and partial activation. In contrast, the C-terminal BC fragment lacks a defined structure but is crucial for autoprocessing and full catalytic activity. Phylogenetic analysis revealed that the sequence of the AB domain is highly conserved, whereas the BC fragment shows considerable variation and seems even absent in some species. Notably, SKI-1/S1P of arthropods, like the fruit fly Drosophila melanogaster, contains a shorter prodomain comprised of full-length AB and truncated BC regions. Swapping the prodomain fragments between fly and human resulted in a fully mature and active SKI-1/S1P chimera. Our study suggests that primordial SKI-1/S1P likely contained a simpler prodomain consisting of the highly conserved AB fragment that represents an independent folding unit. The BC region appears as a later evolutionary acquisition, possibly allowing more subtle fine-tuning of the maturation process.

Proprotein convertase subtilisin/kexin type 9 inhibition: a new therapeutic mechanism for reducing cardiovascular disease risk.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in the regulation of cholesterol homeostasis. By binding to hepatic low-density lipoprotein (LDL) receptors and promoting their lysosomal degradation, PCSK9 reduces LDL uptake, leading to an increase in LDL cholesterol concentrations. Gain-of-function mutations in PCSK9 associated with high LDL cholesterol and premature cardiovascular disease have been causally implicated in the pathophysiology of autosomal-dominant familial hypercholesterolemia. In contrast, the more commonly expressed loss-of-function mutations in PCSK9 are associated with reduced LDL cholesterol and cardiovascular disease risk. The development of therapeutic approaches that inhibit PCSK9 function has therefore attracted considerable attention from clinicians and the pharmaceutical industry for the management of hypercholesterolemia and its associated cardiovascular disease risk. This review summarizes the effects of PCSK9 on hepatic and intestinal lipid metabolism and the more recently explored functions of PCSK9 in extrahepatic tissues. Therapeutic approaches that prevent interaction of PCSK9 with hepatic LDL receptors (monoclonal antibodies, mimetic peptides), inhibit PCSK9 synthesis in the endoplasmic reticulum (antisense oligonucleotides, siRNAs), and interfere with PCSK9 function (small molecules) are also described. Finally, clinical trials testing the safety and efficacy of monoclonal antibodies to PCSK9 are reviewed. These have shown dose-dependent decreases in LDL cholesterol (44%-65%), apolipoprotein B (48%-59%), and lipoprotein(a) (27%-50%) without major adverse effects in various high-risk patient categories, including those with statin intolerance. Initial reports from 2 of these trials have indicated the expected reduction in cardiovascular events. Hence, inhibition of PCSK9 holds considerable promise as a therapeutic option for decreasing cardiovascular disease risk.

PCSK6-mediated corin activation is essential for normal blood pressure.

Hypertension is the most common cardiovascular disease, afflicting >30% of adults. The cause of hypertension in most individuals remains unknown, suggesting that additional contributing factors have yet to be discovered. Corin is a serine protease that activates the natriuretic peptides, thereby regulating blood pressure. It is synthesized as a zymogen that is activated by proteolytic cleavage. CORIN variants and mutations impairing corin activation have been identified in people with hypertension and pre-eclampsia. To date, however, the identity of the protease that activates corin remains elusive. Here we show that proprotein convertase subtilisin/kexin-6 (PCSK6, also named PACE4; ref. 10) cleaves and activates corin. In cultured cells, we found that corin activation was inhibited by inhibitors of PCSK family proteases and by small interfering RNAs blocking PCSK6 expression. Conversely, PCSK6 overexpression enhanced corin activation. In addition, purified PCSK6 cleaved wild-type corin but not the R801A variant that lacks the conserved activation site. Pcsk6-knockout mice developed salt-sensitive hypertension, and corin activation and pro-atrial natriuretic peptide processing activity were undetectable in these mice. Moreover, we found that CORIN variants in individuals with hypertension and pre-eclampsia were defective in PCSK6-mediated activation. We also identified a PCSK6 mutation that impaired corin activation activity in a hypertensive patient. Our results indicate that PCSK6 is the long-sought corin activator and is important for sodium homeostasis and normal blood pressure.

[PERSONALIZED APPROACH TO LIPID-LOWERING THERAPY]. / APPROCHE PERSONNALISÉE DU TRAITEMENT DES DYSLIPIDÉMIES.

Individualized therapeutic strategy of dyslipidemias, classically relies upon a phenotypic approach. The pattern of lipid profile allows the choice of the best pharmacological option (statin, fibrate) and the patient's clinical risk profile allows the definition of therapeutic goals, especially LDL cholesterol target levels. Dyslipidemias have a major genetic component, which is best illustrated by familial hypercholesterolemia, with its two heterozygous and homozygous forms. There is a huge between-subject variability in the response to lipid-lowering therapies (especially to statins) and ongoing pharmacogenetic and pharmacogenomic studies should help to better understand this inter-individual heterogeneity. The recent discovery of mutations in the PCSK9 rene opened new perspectives regarding the understanding of some forms of familial hypercholesterolemia and led to the development of monoclonal antibodies that selectively inhibit PCSK9. These PCSK9 inhibitors allow, when combined to a statin, drastic reductions in LDL cholesterol concentrations, even when familial hypercholesterolemia is present. They are currently tested in large prospective controlled trials aiming to demonstrate a significant reduction in the residual cardiovascular risk in statin-treated patients.

Role of PCSK9 beyond liver involvement.

PURPOSE OF REVIEW: Proprotein convertase subtilisin kexin type 9 (PCSK9) acts as an endogenous natural inhibitor of the LDL receptor pathway, by targeting the receptor to lysosomes for degradation. Beside the liver, PCSK9 is also expressed at significant levels in other tissues, where its function remains unclear. The current review focuses on the extrahepatic actions of PCSK9. RECENT FINDINGS: The generation of liver-specific PCSK9 knockout mice has clearly indicated that PCSK9 affects cholesterol homeostasis via its action on extrahepatic organs. PCSK9 is highly expressed in the intestine, where it controls the production of triglyceride-rich lipoproteins and the transintestinal cholesterol excretion. The role of PCSK9 in the endocrine pancreas and glucose homeostasis remains unclear because conflicting data exist concerning the metabolic phenotype of PCSK9-deficient mice. Sparse data suggest that PCSK9 might also play a role in kidneys, vascular smooth muscle cells, and neurons. SUMMARY: Based on the virtuous combination of genetic and pharmacological approaches, the major function of PCSK9 as a key regulator of hepatic LDL receptor metabolism had quickly emerged. Accumulating evidence indicates that intestinal PCSK9 is also involved in the modulation of lipid homeostasis. Additional studies are warranted to decipher the physiological function of PCSK9 in other extrahepatic tissues and thus to better assess the safety of PCSK9 inhibitors.

MMP-2 inhibits PCSK9-induced degradation of the LDL receptor in Hepa1-c1c7 cells.

Low-density lipoprotein receptor (LDLR) catalyzes the uptake of LDL-cholesterol by liver and peripheral organs. The function of the LDLR is antagonized by pro-protein convertase subtilisin/kexin type 9 (PCSK9), which binds to LDLR at the plasma membrane inducing LDLR degradation. Here, we report that matrix metalloproteinase-2 (MMP-2) interacts with and cleaves PCSK9, as evidenced by proteomic, chemical cross-linkage, blue native-PAGE and domain-specific antibodies Western blot analyses. Furthermore, MMP-2 overexpression renders Hepa1-c1c7 cells resistant to PCSK9-induced LDLR degradation. The data suggest that pathological MMP-2 overexpression may protect the LDLR from PCSK-9-induced degradation.

Molecular and cellular function of the proprotein convertase subtilisin/kexin type 9 (PCSK9).

The proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a promising treatment target to lower serum cholesterol, a major risk factor of cardiovascular diseases. Gain-of-function mutations of PCSK9 are associated with hypercholesterolemia and increased risk of cardiovascular events. Conversely, loss-of-function mutations cause low-plasma LDL-C levels and a reduction of cardiovascular risk without known unwanted effects on individual health. Experimental studies have revealed that PCSK9 reduces the hepatic uptake of LDL-C by increasing the endosomal and lysosomal degradation of LDL receptors (LDLR). A number of clinical studies have demonstrated that inhibition of PCSK9 alone and in addition to statins potently reduces serum LDL-C concentrations. This review summarizes the current data on the regulation of PCSK9, its molecular function in lipid homeostasis and the emerging evidence on the extra-hepatic effects of PCSK9.

Inter-relationships between proprotein convertase subtilisin/kexin type 9, apolipoprotein C-III and plasma apolipoprotein B-48 transport in obese subjects: a stable isotope study in the postprandial state.

Postprandial lipaemia, due to elevated plasma apolipoprotein (apo) B-48 concentrations, contributes to increased cardiovascular (CV) risk in obesity. Proprotein convertase subtilisin/kexin type 9 (PCSK9) and apoC-III may play a role in regulating triacylglycerol-rich lipoprotein (TRL)-apoB-48 metabolism. We investigated the associations between plasma PCSK9 and apoC-III concentrations and the kinetics of apoB-48 in obese subjects. Seventeen obese subjects were given an oral fat load. ApoB-48 tracer/tracee ratios were measured after an intravenous 2H3-leucine administration using GC-MS. Kinetic parameters, including secretion and fractional catabolic rates (FCRs), were derived using a multi-compartmental model. Plasma PCSK9 and apoC-III concentrations were significantly and positively (P<0.05 in all) associated with the total area-under-curve (AUC) and incremental AUC for apoB-48 and inversely with TRL-apoB-48 FCR. Plasma PCSK9 and apoC-III concentrations were not correlated (P>0.05 in all) with basal secretion or the number of TRL-apoB-48 secreted over the postprandial period. In the stepwise regression analysis, plasma PCSK9 was the best predictor of the total and incremental AUCs for plasma apoB-48 and the FCR of TRL-apoB-48. The association between plasma PCSK9 and apoC-III and TRL-apoB-48 FCR remained significant (P<0.05 in all) after adjusting for age, homoeostasis model assessment (HOMA) score, hepatic lipase or lipoprotein lipase (LPL). In a multiple regression model, 31% of variance in TRL-apoB-48 FCR was accounted for by plasma PCSK9 and apoC-III concentrations (adjusted R2=0.306, P<0.05). However, their associations with TRL-apoB-48 FCR were not independent of each other. Our results suggest that the catabolism of TRL-apoB-48 in the postprandial state may be co-ordinated by PCSK9 and apoC-III in obese individuals.

PCSK9: A key factor modulating atherosclerosis.

Coronary artery disease (CAD) due to obstructive atherosclerosis is a leading cause of death and has been recognized as a worldwide health threat. Measures to decrease low-density lipoprotein cholesterol (LDL-C) levels are the cornerstone in the management of patients with atherosclerotic cardiovascular disease, particularly those with CAD, for over two decades. Proprotein convertase subtilisin/kexin type 9 (PCSK9), a newly recognized protein, plays a key role in cholesterol homeostasis by enhancing degradation of hepatic LDL receptor (LDLR). Interestingly, PCSK9 is also involved in the inflammatory process. Plasma PCSK9 and lipid or nonlipid cardiovascular risk factors are correlated, and the associations between PCSK9 with cardiovascular health and disease make this protein worthy of attention for the treatment of hyperlipidemia and atherosclerosis. Here, we provide an overview of the physiological role of PCSK9, which contributes to atherosclerosis, and provide data on PCSK9 as a novel pharmacological target. Clinical evidence shows that PCSK9 inhibition is as promising as statins as a target to treat CAD. The efficacy of these drugs may potentially enable effective CAD prophylaxis for more patients.

Variable effects of gender and Western diet on lipid and glucose homeostasis in aged PCSK9-deficient C57BL/6 mice CSK9PC57BL/6.

BACKGROUND: Proprotein convertase subtilisin/kexin-type 9 (PCSK9) downregulates clearance of plasma cholesterol by liver. Its inactivation increases this clearance, reducing cardiovascular risk. However, a lack of PCSK9 could also lead to cholesterol accumulation in pancreatic islet beta cells, impairing insulin secretion. We reported earlier that 4-month-old male PCSK9-deficient (KO) C57BL/6 mice were hyperglycemic and insulin-insufficient relative to their wild-type (WT) counterparts. Here, we examined how gender and diet affect lipid and glucose homeostasis in these mice at 8 months of age. METHODS: After being fed a normal diet or a Western diet for over 6 months, KO mice were compared with same-gender WT mice for fasting plasma levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), glucose, and insulin; for glucose disposal and glucose-stimulated insulin secretion (GSIS); and for pancreatic islet morphology. RESULTS: A. Females: On normal diet, KO mice showed lower plasma TC, HDL-C, and LDL-C, higher plasma glucose, and normal glucose disposal despite impaired GSIS. On Western diet, they showed comparable plasma TC and HDL-C, but lower LDL-C, higher plasma glucose, and normal glucose disposal despite impaired GSIS. B. Males: On normal and Western diets, KO mice showed lower plasma TC, HDL-C, and LDL-C, similarly elevated plasma glucose, glucose intolerance, and impaired GSIS. C. Both: KO mice on either diet showed pancreatic islet dysmorphism, with larger, possibly immature secretory granules. CONCLUSIONS: Lower LDL-C and impaired GSIS are two major phenotypes in aged PCSK9-deficient C57BL/6 mice. These phenotypes are modulated by gender and diet.

Proprotein convertase subtilisin/kexin 9 inhibitors: an emerging lipid-lowering therapy?

Proprotein convertase subtilisin/kexin 9 (PCSK9) is part of the proteinase K subfamily of subtilases and plays a key role in lipid metabolism. It increases degradation of the low-density lipoprotein receptor (LDL-R), modulates cholesterol metabolism and transport, and contributes to the production of apolipoprotein B (apoB) in intestinal cells. Exogenous PCSK9 modifies the activity of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and acyl coenzyme A:cholesterol acyltransferase and enhances secretion of chylomicrons by modulating production of lipids and apoB-48. Statins increase PCSK9 messenger RNA expression and attenuate the capacity to increase LDL-R levels. Therefore, the inhibition of PCSK9 in combination with statins provides a promising approach for lowering low-density lipoprotein cholesterol (LDL-C) concentrations. This review will address new therapeutic strategies targeting PCSK9, including monoclonal antibodies, antisense oligonucleotides, small interfering RNAs, and other small molecule inhibitors. Further studies are still needed to determine the efficacy and safety of the PCSK9 inhibitors not only to decrease LDL-C but also to investigate the potential underlying mechanisms involved and to test whether these compounds actually reduce cardiovascular end points and mortality.

Genotypic and phenotypic features in homozygous familial hypercholesterolemia caused by proprotein convertase subtilisin/kexin type 9 (PCSK9) gain-of-function mutation.

BACKGROUNDS: Familial hypercholesterolemia (FH) is an autosomal dominant disease characterized by hypercholesterolemia, tendon xanthomas, and premature coronary heart disease. FH is caused by mutations of "FH genes," which include the LDL-receptor (LDLR), apolipoprotein B-100 (APOB) or proprotein convertase subtilisin/kexin type 9 (PCSK9). We evaluated the usefulness of FH gene analysis for diagnosing homozygous FH (homo-FH), particularly in cases caused by gain-of-function (g-o-f) mutations in PCSK9 (PCSK9 E32K). OBJECTIVES: To evaluate the frequency of homo-FH caused by PCSK9 E32K compared with FH due to other genetic causes and to report the phenotypic features of homo-FH caused by PCSK9 E32K. METHODS: Genomic DNA was prepared from white blood cells, and LDLR and PCSK9 mutations were identified using the Invader assay method. RESULTS: Of the 1055 hetero-FH patients, 62 patients (5.9%) carried the PCSK9 E32K mutation, while in the 82 alleles of 41 homo-FH patients, 13 (15.9%) had double mutations of LDLR allele and PCSK9 E32K mutation. Mean plasma total cholesterol (TC) (9.93 ± 2.95 mmol/L, mean ± SD) in true homo-FH cases with PCSK9 E32K or double hetero-FH cases with PCSK9 E32K and LDLR mutations were significantly lower than those in true homo-FH (18.06 ± 4.96 mmol/L) and compound heterozygous cases with LDLR mutations (14.84 ± 1.62 mmol/L). Mean plasma TC concentrations in the 59 hetero-FH cases with PCSK9 E32K (7.21 ± 1.55 mmol/L) were significantly lower than those (8.94 ± 1.53 mmol/L) in the hetero-FH by LDLR mutations. CONCLUSIONS: FH caused by PCSK9 g-o-f mutations is relatively common in Japan and causes a mild type of homo- and hetero-FH compared with FH caused by LDLR mutations.