Homozygous Familial Hypercholesterolemia Phenotype Research Articles

Abstract 18931: A PCSK9 and APOB Double Heterozygote Presenting Phenotypically Similar to Homozygous Familial Hypercholesterolemia

Introduction: Familial hypercholesterolemia (FH) is an inherited disorder associated with mutations in APOB, PCSK9 and LDLR genes. Heterozygous FH (HeFH) generally has one gene mutation. Homozygous FH (HoFH) has two mutations in the same gene and is characterized by vastly elevated plasma LDL-C, accelerated ASCVD and resistance to standard lipid-lowering therapy. Combinations of mutations can present with a phenotype similar to HoFH. We present a double heterozygous patient with unreported mutations in PCSK9 and APOB genes, exhibiting clinical features of HoFH. Hypothesis: Patients with multiple gene mutations for FH can present clinically similar to HoFH and would benefit from novel lipid lowering therapies Methods: 73-year-old female with a history of diabetes and hyperlipidemia presented in 2018 with dyspnea on exertion. Cholesterol (TC) and triglycerides (TG) were 430 and 715 mg/dl respectively, on rosuvastatin 40 mg and omega 3 fatty acids. Physical exam showed arcus senilis. A nuclear stress test showed ST depressions in inferolateral leads but normal scintigraphy. Genetic testing revealed APOB and PCSK9 mutations. She was then treated with rosuvastatin, icosapentyl ethyl, ezetimibe and fenofibrate. TC, LDL, TG and ApoB levels were 463, 236, 747 and >240 mg/dl respectively. Evolocumab was added, with reduction of TC, TG and ApoB levels to 326, 432 and 182mg/dl, despite maximal available therapy. Results: Genetic testing revealed APOB variant NP_000375.2:p.Gln3378His and PCSK9 variant NP_777596.2:pAla544Thr, which were unreported mutations with unknown clinical significance. Genetically, this patient is a double heterozygote but expresses a phenotype similar to HoFH due to a poor response to maximum therapy. Conclusions: Although usually genetically defined, the phenotype of HoFH can present with different genetic variations. Chaudhry et al established genetic diagnosis of HoFH in 0.9% of patients initially diagnosed as HeFH, of which 3 were true homozygotes and 3 were compound heterozygotes. These findings support the idea that various heterozygous combinations of mutations in the genes for LDLR, APOB and PCSK9, may present clinically similar to HoFH. Patients with these mutations could benefit from novel agents such as evinacumab.

Phenotypical, Clinical, and Molecular Aspects of Adults and Children With Homozygous Familial Hypercholesterolemia in Iberoamerica.

Characterize homozygous familial hypercholesterolemia (HoFH) individuals from Iberoamerica. Approach and Results: In a cross-sectional retrospective evaluation 134 individuals with a HoFH phenotype, 71 adults (age 39.3±15.8 years, 38.0% males), and 63 children (age 8.8±4.0 years, 50.8% males) were studied. Genetic characterization was available in 129 (96%). The majority (91%) were true homozygotes (true HoFH, n=79, 43.0% children, 46.8% males) or compound heterozygotes (compound heterozygous familial hypercholesterolemia, n=39, 51.3% children, 46.2% males) with putative pathogenic variants in the LDLR. True HoFH due to LDLR variants had higher total (P=0.015) and LDL (low-density lipoprotein)-cholesterol (P=0.008) compared with compound heterozygous familial hypercholesterolemia. Children with true HoFH (n=34) tended to be diagnosed earlier (P=0.051) and had a greater frequency of xanthomas (P=0.016) than those with compound heterozygous familial hypercholesterolemia (n=20). Previous major cardiovascular events were present in 25 (48%) of 52 children (missing information in 2 cases), and in 43 (67%) of 64 adults with LDLR variants. Children who are true HoFH had higher frequency of major cardiovascular events (P=0.02), coronary heart (P=0.013), and aortic/supra-aortic valve diseases (P=0.022) than compound heterozygous familial hypercholesterolemia. In adults, no differences were observed in major cardiovascular events according to type of LDLR variant. From 118 subjects with LDLR variants, 76 (64%) had 2 likely pathogenic or pathogenic variants. In 89 subjects with 2 LDLR variants, those with at least one null allele were younger (P=0.003) and had a greater frequency of major cardiovascular events (P=0.038) occurring at an earlier age (P=0.001). There was a high frequency of cardiovascular disease even in children. Phenotype and cardiovascular complications were heterogeneous and associated with the type of molecular defect.

P5365Microsomal triglyceride transfer protein inhibitor (lomitapide) efficacy in the treatment of patients with homozygous familial hypercholesterolemia phenotype

Abstract Introduction The majority of patients with homozygous familial hypercholesterolemia (HoFH) phenotype are treated additionally to lipid lowering (LL) drugs (statin + ezetimibe ± colesevelam) with lipoprotein apheresis (LA) sessions. The aim of this study was to evaluate the effect of microsomal triglyceride transfer protein inhibitor (lomitapide) in HoFH patients. Patients and methods In 12 HoFH patients treated with LL drugs ± biweekly LA sessions (9 patients) the 5–40 mg daily of lomitapide was added. Lipid profile [total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), triglycerides (TG) and high density lipoprotein cholesterol (HDL-C)] before (LL drugs ± LA) and after lomitapide treatment were evaluated. Results The follow-up period of lomitapide treatment for 12 patients was 3–24 months (13.8±7.9). The median baseline LDL-C levels was 1000 mg/dL (339–1150). During LL drug therapy, patients showed a median LDL-C level of 383.5 mg/dL (Range: 214–866 mg/dL) and with LL drugs + Time-averaged levels (CAVG) the median was 288.1 mg/dL (Range: 183.69–716.65 mg/dL). The addition of lomitapide at the average dosage of 21.4 mg/day lowered LDL-C levels by 56.8% comparing to LL drugs alone therapy [mean reduction 262.12, 95% CI (105.53, 418.71), p=0.005] and by 54% [mean reduction −182.89, 95% CI (−342.35, −23.43), p=0.031] comparing to LL drugs + LA (CAVG). The CAVG of LDL-C in LL drugs + LA patients compared with LL drugs + lomitapide was 54% in favour of lomitapide (p=0.031). After lomitapide administration to LL drugs + LA treatment, 78% patients discontinued LA and 2 patients reduced their LA frequency by 50%. During follow-up, 2 patients (16.6%) reported side effects (transient diarrhea, 1 patient had liver transaminase >5× ULN and had to decrease dose of lomitapide). Two patients stopped lomitapide due to diet and alcohol restrictions. Median and ranges of lipid and lipoprotein values before any intervention, after LL drugs, LL drugs plus LA, LL drugs plus LA (CAVG) and LL drugs plus lomitapide Total Cholesterol LDL-C HDL-C Triglycerides Before any intervention 1000 (339–1150) 900 (245–1070) 34.5 (25–50) 125 (87–314) After LL drugs 434 (278–915) 383.5 (214–866) 36 (27–51) 113 (62–198) LL drugs + LA (CAVG) 336.13 (248.57–784.16) 288.07 (183.69–716.65) 42.81 (25.84–46.68) 105.09 (55.79–166.68) LL drugs + Lomitapide 228.5 (118–554) 173.5 (74–515) 37.5 (29–50) 83.5 (23–316) LDL graph Conclusions Treatment with lomitapide in HoFH patients has beneficial effect with constant decrease of LDL-C by 57% compared with classical LL therapy and by 54% compared with classical LL therapy and CAVG and seems to be with good safety profile. Although, in some cases the hybrid (all availably drug treatment and LA) therapy may be needed.

Genetic analysis in a compound heterozygote family with familial hypercholesterolemia.

Homozygous familial hypercholesterolemia (FH) is rare, with an incidence of ~one in a million and commonly presents with a genetic mutation. The genetic variations of families with FH were clinically analyzed to investigate the association between the phenotype and genotype of patients. Direct sequencing was conducted for the proband and her parents to detect mutations in the fragment of 18 exons of the low‑density lipoprotein receptor (LDLR) and apolipoprotein B100 Q3500R in the peripheral blood genomic DNA. The gene sequences were compared with normal ones to find mutations using GenBank. The QX200 Droplet Digital PCR system was used to detect target DNA copy number variations of the proband and her parents. The functional alterations resulting from the novel mutations were verified by quantitative polymerase chain reaction, western blotting and flow cytometric analyses. The lipid levels of the proband and her parents were all elevated. Genetic testing results indicated that the proband and her mother had a novel heterozygous missense mutation (C377G, 28893T>G) in exon 8 of the LDLR gene, whereas the proband and her father had LDLR gene DNA fragment deletions in exon 18. Clinically, the proband was of a compound heterozygous genotype and her parents were of the simple heterozygous genotype. Furthermore, both mutations led to impaired expression and LDL binding and internalization function of LDLR invitro. The proband's genotype was confirmed to be compound heterozygous FH, leading to clinical manifestations in line with the homozygous FH phenotype. The phenotype is highly associated with the genotype in this type of compound heterozygous FH.

Screening of LDLR and APOB gene mutations in Mexican patients with homozygous familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal dominant disorder that causes accumulation of serum low-density lipoprotein cholesterol and premature cardiovascular disease. It is mainly related to mutations in the LDLR gene. Homozygous FH (HoFH) patients have the most severe form of the disease accounting for a worldwide prevalence of 1:1,000,000. In Mexico, at least 5 cases of HoFH have been reported. The aim of this study was to describe the clinical, biochemical, and molecular data observed in patients with HoFH phenotype. We included 13 patients, belonging to 11 families, with clinical and biochemical diagnoses suggestive of HoFH. Molecular analyses of the LDLR and APOB genes were performed by means of polymerase chain reaction followed by Sanger sequencing. The causal mutation of HoFH was found in 8 of 11 unrelated patients. Excepting 1, all were true homozygotes. Six different variants in LDLR were identified: c.-139delCTCCCCCTGC, p.Glu140Lys, p.Asp360His, p.Asn405Lys, p.Ala755Glyfs*7, and p.Leu759Serfs*6. Of these, p.Asp360His and p.Asn405Lys were detected for the first time in Mexico; p.Leu759Serfs*6 showed to be the most frequent (43.7% of the alleles 7/16), and c.-139delCTCCCCCTGC is a new variant located in the promoter region. This work increases knowledge of biochemical and genetic features in Mexican patients with HoFH. A novel mutation in the LDLR gene promoter was detected: c.-139delCTCCCCCTGC, which possibly inhibits its expression.

Atypical phenotype of homozygous familial hypercholesterolemia

Atypical phenotype of homozygous familial hypercholesterolemia

Familial hypercholesterolemia in a European Mediterranean population—Prevalence and clinical data from 2.5 million primary care patients

Familial hypercholesterolemia (FH), the most frequent hereditary cause of premature coronary heart disease (CHD), is underdiagnosed and insufficiently treated. The objectives of the study were to estimate the prevalence of the FH phenotype (FH-P) and to describe its clinical characteristics in a Mediterranean population. Data were obtained from the Catalan primary care system's clinical records database (Catalan acronym: SIDIAP). Patients aged >7years with at least 1 low-density lipoprotein cholesterol measurement recorded between 2006 and 2014 (n=2,554,644) were included. Heterozygous FH-P and homozygous FH-P were defined by untreated low-density lipoprotein cholesterol plasma concentrations. The presence of cardiovascular diseases and risk factors was defined by coded medical records from primary care and hospital discharge databases. The age- and sex-standardized prevalence of heterozygous FH-P and homozygous FH-P were 1/192 individuals and 1/425,774 individuals, respectively. In the group aged 8 to 18years, 0.46% (95% confidence interval: 0.41-0.52) had FH-P; overall prevalence was 0.58% (95% confidence interval: 0.58-0.60). Among patients with FH-P aged >18years, cardiovascular disease prevalence was 3.5 times higher than in general population, and CHD prevalence in those aged 35 to 59years was 4.5 times higher than in those without FH-P. Lipid-lowering therapy was lacking in 13.5% of patients with FH-P, and only 31.6% of men and 22.7 of women were receiving high or very high-intensity lipid-lowering therapy. Prevalence of FH-P was higher than expected, but underdiagnosed and suboptimally treated, especially in women. Moreover, treatment started late considering the high CHD incidence associated with this condition.

Update on the use of PCSK9 inhibitors in adults: Recommendations from an Expert Panel of the National Lipid Association

An Expert Panel convened by the National Lipid Association was charged with updating the recommendations on the use of proprotein convertase subtilisin/kexin type 9 (PCSK9) antibody therapy that were provided by the 2015 National Lipid Association Recommendations for the Patient-Centered Management of Dyslipidemia: Part 2. Recent studies have demonstrated the efficacy of these agents in reducing low-density lipoprotein cholesterol and non–high-density lipoprotein cholesterol and have confirmed their excellent safety profile. A cardiovascular outcomes study has shown that these agents reduce incident atherosclerotic cardiovascular disease (ASCVD) events in patents with stable ASCVD and concomitant risk factors. The current update provides the Expert Panel's evidence-based recommendations on the clinical utility of PCSK9 inhibitors in patients with stable ASCVD, progressive ASCVD, LDL-C ≥ 190 mg/dL (including polygenic hypercholesterolemia, heterozygous familial hypercholesterolemia and the homozygous familial hypercholesterolemia phenotype) and very-high-risk patients with statin intolerance.

Mutations in the LDL receptor gene in four Chinese homozygous familial hypercholesterolemia phenotype patients

Background and aims Familial hypercholesterolemia (FH) is an autosomal dominant disorder of lipoprotein metabolism caused by mutations in the low-density lipoprotein receptor (LDL-R) gene, leading to elevated levels of cholesterol and an increased risk of coronary heart disease. In this article, from four homozygous FH phenotype probands we identified disease causing mutations and analyzed the relationship between genotype and phenotype. Methods and results DNA sequencing identified five LDL-R point mutations in four unrelated families. We found a novel homozygous mutation (C210R), a homozygous mutation at W462X, a compound heterozygous mutation of C122Y and T383I, and a G>A intron 3 splice site homozygous mutation. The functional alteration caused by the novel C210R mutation was confirmed by FACS analysis. Four probands have high low-density lipoprotein cholesterol (LDL-C) levels, ranging from 14.65 to 27.66 mmol/L. Their heterozygous parents had relatively low levels. B-mode ultrasound supplemented by Doppler was used to examine aortic/mitral valve structural alterations and carotid intima-media thickness (ITM) in all probands. The ITM values were between 1.2 and 2.3 mm, much higher than the normal value of <0.8 mm. Conclusion Our data demonstrated that all the probands were associated with severe hypercholesterolemia, thick carotid IMT and a low CFVR (coronary flow velocity reserve) value. The novel mutation (C120Y) is a disease causing mutation.

Partial ileal bypass inhibits atherosclerosis in WHHL rabbits

The effectiveness of partial ileal bypass (PIB) as a counter-measure against atherosclerosis was evaluated in WHHL rabbits. The effects of PIB and sham operation, each performed in five animals, on serum lipids, lipoproteins and plaque formation were investigated. PIB resulted in an immediate and sustained decrease of 52% (range 29–67%) in serum cholesterol, while sham operation had no effect. The main reduction was in LDL cholesterol; VLDL-cholesterol was lowered to a lesser extent. PIB also appeared to change the electrophoretic behaviour of total serum, very low density and low density lipoproteins. Plaque formation, measured 30 weeks after operation in various aortic segments and arteries, was significantly reduced after PIB. It is concluded that an induced lowering of serum cholesterol can prevent atherosclerosis in WHHL rabbits. Also, these animals must be considered as a model for the receptor-defective cellular phenotype of homozygous familial hypercholesterolemia, not for the receptor-negative type, which is the only truly genetically homozygous form.

Posttranslational processing of the LDL receptor and its genetic disruption in familial hypercholesterolemia.

Synthesis of the low density lipoprotein (LDL) receptor was studied by incubation of cultured human fibroblasts with 35S-methionine followed by immunoprecipitation with a monoclonal antireceptor antibody. The receptor was synthesized as a precursor with an apparent molecular weight of 120 kilodaltons (kd) that was converted to a mature form of 160 kd. This novel form of processing occurred 15-30 min after synthesis and did not appear to be due to the simple addition of N-linked oligosaccharide chains. Fibroblasts from a child with the phenotype of homozygous familial hypercholesterolemia showed a disruption in receptor processing. This child has two different mutant alleles at the LDL receptor locus. One allele, inherited from his heterozygous mother, produces an abnormal 120 kd protein that cannot be processed to the mature 160 kd form. The other allele, inherited from his heterozygous father, produces a receptor that is synthesized as an elongated 170 kd precursor which undergoes a 40 kd increase in molecular weight to form an abnormally large receptor of 210 kd.

Analysis of a mutant strain of human fibroblasts with a defect in the internalization of receptor-bound low density lipoprotein

A new type of mutation that affects a discrete step in the process of adsorptive endocytosis has been identified in one of 22 strains of fibroblasts derived from subjects with the clinical phenotype of homozygous familial hypercholesterolemia (FH). In this unique mutant strain (derived from subject J.D.), the cell surface receptor for plasma low density lipoprotein (LDL) was able to bind 125I-labeled LDL normally, but internalization of the receptor-bound lipoprotein failed to occur. Thus the defect in this strain differed from the defects found in the fibroblasts from the other 21 FH homozygote strains in which the binding of 125I-LDL to the receptor was either absent (receptor-negative) or markedly reduced (receptor-defective). The LDL receptor in the J.D. cells exhibited first, normal kinetics of high affinity binding at 4°C and 37°C; second, normal specificity (affinity for LDL more than 200 fold greater than for HDL); third, normal susceptibility to feedback suppression by 25-hydroxycholesterol plus cholesterol; and fourth, a normal rate of turnover when the cells were treated with cycloheximide. Despite its normal ability to bind 125I-LDL, the LDL receptor in the J.D. cells failed to transport its LDL into the cell, and degradation of the lipoprotein in cellular lysosomes therefore did not occur. As a result, the lipoprotein did not suppress 3-hydroxy-3-methylglutaryl coenzyme A reductase activity; nor did it activate cholesteryl ester formation. A phenocopy of the internalization defect in the J.D. cells could be created by incubation of normal fibroblasts with N-ethyl maleimide, an agent that did not affect 125I-LDL binding to the receptor but blocked its subsequent internalization by the cell. The current data indicate that at least two gene products are necessary for the adsorptive endocytosis of LDL: one that is required for the binding of the lipoprotein, and one that promotes the internalization of the receptor-bound ligand.