Familial defective apolipoprotein B-100: A review

Familial defective apolipoprotein B-100 (FDB) is an autosomal dominant genetic disorder of lipid metabolism associated with hyperlipidemia and elevated risk for atherosclerosis. FDB is caused by mutations in APOB reducing the binding affinity between apolipoprotein B-100 and the low-density lipoprotein receptor. Population studies suggest that approximately 0.1% of Northern Europeans and US Caucasians carries the R3500Q variant in APOB most commonly associated with FDB; in addition, the APOB R3500 W variant is known to make a significant contribution to familial hypercholesterolemia (FH) among East Asians. However, the elevation of plasma low-density lipoprotein cholesterol observed in FDB is frequently milder than that of FH due to mutations in LDLR, and FDB is subsequently underdiagnosed according to standard FH diagnostic criteria.     

Genetic causes of monogenic familial hypercholesterolemia in the Greek population: Lessons,mistakes, and the way forward

Familial hypercholesterolemia (FH) is a leading cause of premature atherosclerosis. Genetic defects in the LDLR, APOB and PCSK9 genes cause FH, and confirmation of a gene defect is essential for an indisputable diagnosis of the disease. FH is underdiagnosed and we aimed to revise the genetic defects that have been characterized in FH patients of Greek origin and define an effective, future strategy for genetic studies. A literature search was performed in MEDLINE and EMBASE on genetic studies with FH patients of Greek origin. To date, no APOB and PCSK9 mutations have been found in the Greek population. It must be noted however, that only a small number of patients has been screened for PCSK9 mutations. In total, 41 LDLR defects have been characterized, with 6 common mutations c.1646G>A (p.Gly546Asp), c.858C>A (p.Ser286Arg), c.81C>G (p.Cys27Trp), c.1285G>A (p.Val429Met), c.517T>C (p.Cys173Arg), and c.1775G>A (p.Gly592Glu) that account for >80% of all mutations. Due to geographic isolation, ​founder mutations exist in a subpopulation in North West Greece and the Greek Cypriot population but not in the general population. Genetic testing should focus primarily on LDLR, and subsequently on PCSK9 and APOB. The Greek population is genetically homogeneous, which allows for a quick molecular diagnosis of the disease. Cascade screening is feasible and will certainly facilitate the identification of additional patients.     

Characterization of low density lipoprotein receptor (LDLR) gene mutations in Albania

Introduction

Familial hypercholesterolaemia (FH) is a clinical syndrome characterised by elevated serum total cholesterol (TCHOL) levels due to an increase in low-density lipoprotein (LDL) cholesterol, by tendon xanthomata and clinical manifestations of ischaemic heart disease in early life. Typically, it results from mutations in the low-density lipoprotein receptor (LDLR) gene. So far, more than 800 mutations have been reported for the LDLR gene and account for FH. The nature of LDLR gene mutations varies among different ethnicities. Until now no mutations of LDLR have been reported in the Albanian population.

Material and methods

We assessed the contribution of the LDLR gene mutations as causes of FH in an Albanian population. Fifty probands with a clinical diagnosis of FH were included. We analysed all the exons and the promoter of the LDLR gene by using restriction isotyping or direct sequencing.

Results

Twenty-one patients were heterozygous for the 1646G>A mutation (FH Genoa) in exon 11 and 9 patients were heterozygous for the 81T>C mutation in exon 2 of the LDLR gene.

Conclusions

This report describes two LDLR gene mutations accounting for FH in Albania (1646G>A, 81T>C).     

Interrogation of selected genes influencing serum LDL-Cholesterol levels in patients with well characterized NAFLD

BackgroundThe clinical significance of rare mutations in LDL metabolism genes on nonalcoholic fatty liver disease (NAFLD) severity is not well understood.ObjectiveTo examine the significance of mutations in LDL metabolism genes including apolipoprotein B (APOB), proprotein convertase subtilisin kexin 9 (PCSK9) and LDL receptor (LDLR) in patients with NAFLD.MethodsPatients with biopsy-confirmed NAFLD from the NASH Clinical Research Network studies were stratified into 3 groups of LDL-C (≤50 mg/dL, 130–150 mg/dL, ≥ 190 mg/dL) and then 120 (40 per group) were randomly selected from the strata. We examined the presence of mutations on LDL genes and analyzed its association with selected NAFLD-related features. Multivariable analyses were adjusted for age, race, gender and use of statins.ResultsAmong 40 patients with LDL-C ≤ 50 mg/dL, 7 (18%) patients had heterozygous variants in APOB and 2 had heterozygous variants in PCSK9 (5%). We also found heterozygous mutations in 3 (8%) patients with LDL-C ≥ 190 mg/dL; 2 and 1 located in LDLR and APOE genes, respectively. Compared to wild-type controls with LDL-C ≤ 50, APOB carriers displayed higher levels of alanine aminotransferase (85.86 ± 35.14 U/L vs 45.61 ± 20.84 U/L, Adj. P = 0.002) and steatosis >66% (57% vs 24%, Adj. P = 0.050). These associations remained statistically significant after excluding statin users. Other histological features of NAFLD severity were not different between wild-type controls and APOB mutation carriers.ConclusionMutations in the APOB gene are common among NAFLD patients with very low LDL-C and may be associated with increased aminotransferase levels and steatosis severity.     

Mutation spectrum and polygenic score in German patients with familial hypercholesterolemia

Autosomal-dominant familial hypercholesterolemia (FH) is characterized by increased plasma concentrations of low-density lipoprotein cholesterol (LDL-C) and a substantial risk to develop cardiovascular disease. Causative mutations in three major genes are known: the LDL receptor gene (LDLR), the apolipoprotein B gene (APOB) and the proprotein convertase subtilisin/kexin 9 gene (PCSK9). We clinically characterized 336 patients suspected to have FH and screened them for disease causing mutations in LDLR, APOB, and PCSK9. We genotyped six single nucleotide polymorphisms (SNPs) to calculate a polygenic risk score for the patients and 1985 controls. The 117 patients had a causative variant in one of the analyzed genes. Most variants were found in the LDLR gene (84.9%) with 11 novel mutations. The mean polygenic risk score was significantly higher in FH mutation negative subjects than in FH mutation positive patients (P < .05) and healthy controls (P < .001), whereas the score of the two latter groups did not differ significantly. However, the score explained only about 3% of the baseline LDL-C variance. We verified the previously described clinical and genetic variability of FH for German hypercholesterolemic patients. Evaluation of a six-SNP polygenic score recently proposed for clinical use suggests that it is not a reliable tool to classify hypercholesterolemic patients.     

Functional analysis of two novel splice site mutations of APOB gene in familial hypobetalipoproteinemia

Familial hypobetalipoproteinemia (FHBL) is a co-dominant disorder characterized by reduced plasma levels of low density lipoprotein cholesterol (LDL-C) and its protein constituent apolipoprotein B (apoB), which may be due to mutations in APOB gene, mostly located in the coding region of this gene. We report two novel APOB gene mutations involving the acceptor splice site of intron 11 (c.1471-1G>A) and of intron 23 (c.3697-1G>C), respectively, which were identified in two patients with heterozygous FHBL associated with severe fatty liver disease. The effects of these mutations on APOB pre-mRNA splicing were assessed in COS-1 cells expressing the mutant APOB minigenes.The c.1471-1G>A APOB minigene generated two abnormal mRNAs. In one mRNA the entire intron 11 was retained; in the other mRNA exon 11 joined to exon 12, in which the first nucleotide was deleted due to the activation of a novel acceptor splice site. The predicted products of these mRNAs are truncated proteins of 546 and 474 amino acids, designated apoB-12.03 and apoB-10.45, respectively. The c.3697-1G>C APOB minigene generated a single abnormal mRNA in which exon 23 joined to exon 25, with the complete skipping of exon 24. This abnormal mRNA is predicted to encode a truncated protein of 1220 amino acids, designated apoB-26.89.These splice site mutations cause the formation of short truncated apoBs, which are not secreted into the plasma as lipoprotein constituents. This secretion defect is the major cause of severe fatty liver observed in carriers of these mutations.     

Novel LDLR Variants in Patients with Familial Hypercholesterolemia: In Silico Analysis as a Tool to Predict Pathogenic Variants in Children and Their Families

Familial hypercholesterolemia (FH) is an autosomal dominant disease with a frequency of 1:500 in its heterozygous form. To date, mutations in the low‐density lipoprotein receptor gene (LDLR) are the only identified causes of FH in the Greek population, causing high levels of low‐density lipoprotein (LDL) and total cholesterol and premature atherosclerosis. The Greek FH population is genetically homogeneous, but most previous studies screened for the most common mutations only. The study aimed to characterize and assess novel LDLR variants. LDLR was examined by whole‐gene DNA sequencing in 561 FH patients from 262 families of Greek origin. Novel LDLR variants were analyzed in silico using various software predicting pathogenicity and changes in protein stability. Twelve novel LDLR variants were identified, six of which are putative disease‐causing variants: c.977C>G in exon 7, c.1124A>C in exon 8, c.1381G>T in exon 10, c.628_643dup{636del}, c.661–673dup in exon 4, and 13 c.1987+1_+33del in intron 13. All six putative variants were confirmed in the hypercholesterolemic members of the family. The results show that in silico analysis is a valuable tool to predict potential pathogenicity of novel variants, especially for populations that have not been extensively studied. The identification of novel pathogenic variants will facilitate the molecular diagnosis of FH from early childhood.     

Functional analysis of new variants at the low‐density lipoprotein receptor associated with familial hypercholesterolemia

Familial hypercholesterolemia is an autosomal dominant disease of lipid metabolism caused by defects in the genes LDLR, APOB, and PCSK9. The prevalence of heterozygous familial hypercholesterolemia (HeFH) is estimated between 1/200 and 1/250. Early detection of patients with FH allows initiation of treatment, thus reducing the risk of coronary heart disease. In this study, we performed in vitro characterization of new LDLR variants found in our patients. Genetic analysis was performed by Next Generation Sequencing using a customized panel of 198 genes in DNA samples of 516 subjects with a clinical diagnosis of probable or definitive FH. All new LDLR variants found in our patients were functionally validated in CHO‐ldlA7 cells. The LDLR activity was measured by flow cytometry and LDLR expression was detected by immunofluorescence. Seven new variants at LDLR were tested: c.518 G>C;p.(Cys173Ser), c.[684 G>T;694 G>T];p.[Glu228Asp;Ala232Ser], c.926C>A;p.(Pro309His), c.1261A>G;p.(Ser421Gly), c.1594T>A;p.(Tyr532Asn), and c.2138delC;p.(Thr713Lysfs*17). We classified all variants as pathogenic except p.(Ser421Gly) and p.(Ala232Ser). The functional in vitro characterization of rare variants at the LDLR is a useful tool to classify the new variants. This approach allows us to confirm the genetic diagnosis of FH, avoiding the classification as “uncertain significant variants”, and therefore, carry out cascade family screening.     

Mutational analysis of a cohort with clinical diagnosis of familial hypercholesterolemia: considerations for genetic diagnosis improvement

PurposeFamilial hypercholesterolemia (FH) is a common autosomal dominant disorder of lipid metabolism caused by mutations in LDLR, APOB, and PCSK9. To fulfill the World Health Organization recommendation, the Portuguese FH Study was established. Here, we report the results of the past 15 years and present practical considerations concerning the genetic diagnosis of FH based on our experience.MethodsOur approach comprises a biochemical and molecular study and is divided into five phases, including the study of whole APOB and functional assays.ResultsA total of 2,122 individuals were enrolled. A putative pathogenic variant was identified in 660 heterozygous patients: LDLR (623), APOB (33), and PCSK9 (4); 8 patients presented with homozygous FH. A detection rate of 41.5% was observed. A stricter biochemical criteria was shown to improve patient identification. Overall, we have identified 3.4% and 80% of all heterozygous and homozygous patients, respectively, estimated to exist in our country.ConclusionThe Portuguese FH Study has established the genetic diagnosis of FH in Portugal and is committed to continue the investigation of the genetic complexity of FH. Genetic diagnosis of FH should be expanded to include the study of all coding/flanking regions of APOB and functional in vitro studies, to improve the correct patient identification, and to avoid misdiagnosis.     

Homozygous familial hypercholesterolemia in a young woman with dual gene mutations of low-density lipoprotein receptor and proprotein convertase subtilisin/kexin type 9

A 28-year-old woman with a rare combination of homozygous LDLR and heterozygous PCSK9 mutations had a phenotype consistent with homozygous familial hypercholesterolemia. She reported a clinical history of coronary and extracoronary atherosclerosis treated with 3 coronary stenting procedures, one coronary bypass, and aortic and mitral valve replacements. Because the patient refused lipoprotein apheresis, lipid-lowering therapy with statins, ezetimibe, and evolocumab was started. The desired low-density lipoprotein cholesterol target was not achieved. Dose-escalated lomitapide therapy (up to 30 mg/d) was added, enabling achievement of low-density lipoprotein cholesterol levels of 45 mg/dL during 24 months' follow-up. During this period, no cardiovascular events or clinical evidence of side effects occurred. In this case, lomitapide has been used in combination with maximum-tolerated statin therapy to successfully treat a patient with a rare combination of mutations in both LDLR and PCSK9 genes.     

Mutational analysis in UK patients with a clinical diagnosis of familial hypercholesterolaemia: relationship with plasma lipid traits, heart disease risk and utility in relative tracing

As part of a randomised trial [Genetic Risk Assessment for Familial Hypercholesterolaemia (FH) Trial] of the psychological consequences of DNA-based and non-DNA-based diagnosis of FH, 338 probands with a clinical diagnosis of FH (46% with tendon xanthomas) were recruited. In the DNA-based testing arm (245 probands), using single-strand conformation polymorphism of all exons of the low-density lipoprotein receptor (LDLR) gene, 48 different pathogenic mutations were found in 62 probands (25%), while 7 (2.9%) of the patients had the R3500Q mutation in the apolipoprotein B (APOB) gene. Compared to those with no detected mutation, mean untreated cholesterol levels in those with the APOB mutation were similar, while in those with an LDLR mutation levels were significantly higher (None=9.15±1.62 vs LDLR=9.13±1.16 vs APOB=10.26±2.07 mmol/l p<0.001, respectively). Thirty seven percent of the detected mutations were in exon 3/4 of LDLR, and this group had significantly higher untreated cholesterol than those with other LDLR mutations (11.71±2.39 mmol/l vs 9.88±2.44 mmol/l, p=0.03), and more evidence of coronary disease compared to those with other LDLR or APOB mutations (36 vs 13% p=0.04). Of the probands with a detected mutation, 54 first-degree relatives were identified, of whom 27 (50%) had a mutation. Of these, 18 had untreated cholesterol above the 95th percentile for their age and gender, but there was overlap with levels in the non-carrier relatives such that 12% of subjects would have been incorrectly diagnosed on lipid levels alone. In the non-DNA-based testing arm (82 probands) only 19 of the 74 relatives identified had untreated cholesterol above the 95th percentile for their age and gender, which was significantly lower (p<0.0005) than the 50% expected for monogenic inheritance. These data confirm the genetic heterogeneity of LDLR mutations in the UK and the deleterious effect of mutations in exon 3 or 4 of LDLR on receptor function, lipids and severity of coronary heart disease. In patients with a clinical diagnosis of FH but no detectable mutation, there is weaker evidence for a monogenic cause compared with relatives of probands with LDLR mutations. This supports the usefulness of DNA testing to confirm diagnosis of FH for the treatment of hyperlipidaemia and for further cascade screening.     

Genetic identification of familial hypercholesterolemia within whole genome sequences in 6820 newborns

Familial hypercholesterolemia (FH) is defined as a monogenic disease, characterized by elevated low-density lipoprotein cholesterol (LDL-C) levels. FH remains underdiagnosed and undertreated in Chinese. We whole-genome sequenced 6820 newborns from Qingdao of China to investigate the FH-related gene (LDLR, APOB, PCSK9) mutation types, carrier ratio and genotype–phenotype correlation. In this study, the prevalence of FH in Qingdao of China was 0.47% (95% CI: 0.32%–0.66%). The plasma lipid levels of FH-related gene mutation carriers begin to increase as early as infant. T-CHO and LDL-C of FH infants was higher by 48.1% (p < 0.001) and 42.9% (p < 0.001) relative to non-FH infants. A total of 22 FH infants and their parent participate in further studies. The results indicated that FH infant parent noncarriers have the normal plasma lipid level, while T-CHO and LDL-C increased in FH infants and FH infant parent carriers, but no difference between the groups. This highlights the importance of genetic factors. In conclusion, the spectrum of FH-causing mutations in the newborns of Qingdao, China was described for the first time. These data can serve as a considerable dataset for next-generation sequencing analysis of the Chinese population with FH and potentially helping reform regional policies for early detection and prevention of FH.     

Screening for point mutations in the LDL receptor gene in Bulgarian patients with severe hypercholesterolemia

Familial hypercholesterolemia (FH) is a common, autosomal dominant disorder of lipid metabolism, caused by defects in the receptor-mediated uptake of LDL (low-density lipoproteins) due to mutations in the LDL receptor gene (LDLR). Mutations underlying FH in Bulgaria are largely unknown. The aim of the present study was to provide information about the spectrum of point mutations in LDLR in a sample of 45 Bulgarian patients with severe hypercholesterolemia. Exons 3, 4, 6, 8, 9, and 14, previously shown to be mutational hot spots in LDLR, were screened using PCR-single-strand conformation polymorphism (SSCP). Samples with abnormal SSCP patterns were sequenced. Three different, hitherto undescribed point mutations (367T>A, 377T>A, 917C>A) and two previously described mutations (858C>A and 1301C>T) in eight unrelated patients were identified; four of the detected point mutations being missense mutations and one, a nonsense mutation. One of the newly described point mutations (917C>A) is a base substitution at a nucleotide position, at which two other different base substitutions have already been reported. Thus, all three possible base substitutions at this nucleotide position have been detected, making it a hot spot for point mutations causing FH. This is the first such mutational hot spot described in exon 6 of LDLR.     

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

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

Predominance of a 6 bp deletion in exon 2 of the LDL receptor gene in Africans with familial hypercholesterolaemia

In South Africa, the high prevalence of familial hypercholesterolaemia (FH) among Afrikaners, Jews, and Indians as a result of founder genes is in striking contrast to its reported virtual absence in the black population in general. In this study, the molecular basis of primary hypercholesterolaemia was studied in 16 Africans diagnosed with FH. DNA analysis using three screening methods resulted in the identification of seven different mutations in the coding region of the low density lipoprotein (LDLR) gene in 10 of the patients analysed. These included a 6 bp deletion (GCGATG) accounting for 28% of defective alleles, and six point mutations (D151H, R232W, R385Q, E387K, P678L, and R793Q) detected in single families. The Sotho patient with missense mutation R232W was also heterozygous for a de novo splicing defect 313+1G→A. Several silent mutations/polymorphisms were detected in the LDLR and apolipoprotein B genes, including a base change (g→t) at nucleotide position −175 in the FP2 LDLR regulatory element. This promoter variant was detected at a significantly higher (p<0.05) frequency in FH patients compared to controls and occurred in cis with mutation E387K in one family. Analysis of four intragenic LDLR gene polymorphisms showed that the same chromosomal background was identified at this locus in the four FH patients with the 6 bp deletion. Detection of the 6 bp deletion in Xhosa, Pedi, and Tswana FH patients suggests that it is an ancient mutation predating tribal separation approximately 3000 years ago.


Keywords: apolipoprotein B; hypercholesterolaemia; low density lipoprotein receptor; mutation     

Homozygous familial hypercholesterolemia: The c.1055G>A mutation in the LDLR gene and clinical heterogeneity

Familial hypercholesterolemia (FH) is a world public health issue because of its high frequency, morbidity, and mortality. FH is characterized by elevated plasma low-density lipoprotein cholesterol (LDL-C) levels and a high risk for premature cardiovascular disease. We report an 8-year-old male with homozygous familial hypercholesterolemia. The clinical and biochemical characteristics of this case were bilateral corneal arcus, xanthomas in several body parts, severe stenosis of the left carotid artery and serum total cholesterol levels of 782.0 mg/dL and 715.0 mg/dL LDL-C. The initial treatment was atorvastatin (40 mg) and ezetimibe (20 mg), with no satisfactory response. LDLR gene was analyzed and homozygosity for c.1055G>A mutation was observed, resulting in an amino acid change from cysteine to tyrosine in codon 352 (p.Cys352Tyr). This mutation is known as Mexico 2 and has only been observed in the Mexican population. Both parents and siblings were carriers of the same mutation, but the paternal grandmother and the father of the index case showed the phenomenon of incomplete penetrance. With the analysis 5 polymorphisms (rs1003723C>T, rs5930A>G, rs688C>T, rs5929T>C and rs5927A>G), a common ancestor for the mutation can be suggested and linkage to TGTCG haplotype.     

Premature coronary heart disease and autosomal dominant hypercholesterolemia: Increased risk in women with LDLR mutations

BackgroundFor patients with autosomal dominant hypercholesterolemia (ADH), it remains unclear whether differences exist in the risk of premature coronary heart disease (CHD) between patients with confirmed mutations in low-density lipoprotein receptor (LDLR) vs those without detectable mutations.ObjectiveThis study sought to assess the risk of premature CHD in ADH patients with mutations in LDLR (referred to as familial hypercholesterolemia [FH]) vs those without detectable mutations (unexplained ADH), stratified by sex.MethodsComparative study of premature CHD in a multiethnic cohort of 111 men and 165 women meeting adult Simon–Broome criteria for ADH.ResultsWomen with FH (n = 51) had an increased risk of premature CHD compared with unexplained ADH women (n = 111; hazard ratio [HR], 2.74; 95% confidence interval, 1.40–5.34; P = .003) even after adjustment for lipid levels and traditional CHD risk factors (HR, 2.53 [1.10–5.83]; P = .005). Men with FH (n = 42), in contrast, had a similar risk of premature CHD when compared with unexplained ADH men (n = 66; unadjusted: HR, 1.48 [0.84–2.63]; P = .18; adjusted: HR, 1.04 [0.46–2.37]; P = .72). To address whether mutation status provides additional information beyond LDL-cholesterol level, we analyzed premature CHD risk for FH vs unexplained ADH at various percentiles of LDL-cholesterol: the risk ratios were significant for women at 25th percentile (HR, 4.90 [1.69–14.19]) and 50th percentile (HR, 3.44 [1.42–8.32]) but not at 75th percentile (HR, 1.99 [0.95–4.17]), and were not significant for men at any percentile.ConclusionsOur findings suggest that genetic confirmation of ADH may be important to identify patient's risk of CHD, especially for female LDLR mutation carriers.     

Molecular Spectrum of Autosomal Dominant Hypercholesterolemia in France

Autosomal Dominant Hypercholesterolemia (ADH), characterized by isolated elevation of plasmatic LDL cholesterol and premature cardiovascular complications, is associated with mutations in 3 major genes: LDLR (LDL receptor), APOB (apolipoprotein B) and PCSK9 (proprotein convertase subtilisin‐kexin type 9). Through the French ADH Research Network, we collected molecular data from 1358 French probands from eleven different regions in France. Mutations in the LDLR gene were identified in 1003 subjects representing 391 unique events with 46.0% missense, 14.6% frameshift, 13.6% splice, and 11.3% nonsense mutations, 9.7% major rearrangements, 3.8% small in frame deletions/insertions, and 1.0% UTR mutations. Interestingly, 175 are novel mutational events and represent 45% of the unique events we identified, highlighting a specificity of the LDLR mutation spectrum in France. Furthermore, mutations in the APOB gene were identified in 89 probands and in the PCSK9 gene in 10 probands. Comparison of available clinical and biochemical data showed a gradient of severity for ADH‐causing mutations: FH=PCSK9>FDB>‘Others’ genes. The respective contribution of each known gene to ADH in this French cohort is: LDLR 73.9%, APOB 6.6%, PCSK9 0.7%. Finally, in 19.0% of the probands, no mutation was found, thus underscoring the existence of ADH mutations located in still unknown genes. © 2010 Wiley‐Liss, Inc.     

A novel LDLR mutation, H190Y, in a Utah kindred with familial Hypercholesterolemia

Heterozygous familial hypercholesterolemia (FH) is a serious disorder causing twice normal low-density lipoprotein (LDL) cholesterol levels early in childhood and very early coronary disease in both men and women. Treatment with multiple medications together with diet can normalize cholesterol levels in many persons with FH and prevent or delay the development of coronary atherosclerosis. Previously published blood cholesterol criteria greatly under-diagnosed new cases of FH among members of known families with FH and over-diagnosed FH among participants of general population screening. Thus, there is a need for accurate and genetically validated criteria for the early diagnosis of heterozygous FH. In the course of investigations of coronary artery disease in Utah, we identified a family whose proband showed elevated plasma levels of LDL cholesterol. To carry out molecular genetic diagnosis of the disease, we screened DNA samples for mutations in all 18 exons and the exon-intron boundaries of the LDL receptor gene (LDLR). Novel point mutations were identified in the proband: a C-to-T transversion at nucleotide position 631, causing substitution of tyrosine for histidine at codon 190 in exon 4 of the LDLR gene. The mutant allele-specific amplification method was used to examine 12 members of the family recruited for the diagnosis. This method helped to unequivocally diagnose 7 individuals as heterozygous for this particular LDLR mutation, while excluding the remaining 5 individuals from carrier status with FH. Received: March 29, 1999 / Accepted: June 18, 1999     

Novel APOB nonsense variant related to familial hypobetalipoproteinemia and hepatic steatosis: A case report and review

Hereditary familial hypobetalipoproteinemia (FHBL) is a syndrome caused by variants in the APOB gene, that cause a defect in the secretion and mobilization of liver lipids to peripheral tissues, associated with the synthesis of truncated ApoB100 apolipoproteins. This condition causes significant reduction in total cholesterol (TC), low-density lipoproteins (LDL), very low-density proteins (VLDL) and serum triglyceride levels, with unchanged high-density lipoprotein (HDL) cholesterol levels. Herein we present the case of a middle-aged woman diagnosed with FHBL and hepatic steatosis, heterozygous for c.4698C>A; (p.Tyr1566Ter) variant in APOB. The variant presented herein showed high expressiveness in the two generations of individuals analyzed and has not yet being described in the medical literature. Early diagnosis and screening for associated metabolic comorbidities such as metabolic fatty liver disease and its subsequent progression to fibrosis are the two main goals in the treatment of this condition, in order to prevent medium to long term potential complications.