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International audience; ackground: Familial hypercholesterolaemia (FH) is responsible for severe hypercholesterolaemia and premature cardiovascular morbidity and mortality. The first clinical event is typically an acute coronary syndrome. Unfortunately, FH is largely underdiagnosed in the general population.Aims: To assess the prevalence of clinical FH among patients with premature (aged≤50 years) acute myocardial infarction (MI) and compare it with FH prevalence in a control population.Methods: We reviewed in our database all patients with premature MI (aged≤50 years) referred to Ambroise Paré Hospital from 2014 to 2018. FH prevalence was estimated via the Dutch Lipid Clinic Network score, based on personal and family history of premature cardiovascular disease and low-density lipoprotein cholesterol concentrations. FH was "possible" with a score between 3 and 5 points, "probable" with a score between 6 and 8 and "definite" with a score above 8. FH prevalence in young patients with MI was then compared with FH prevalence in a general population of the same age from the CARVAR 92 prospective cohort.Results: Of the 457 patients with premature MI, 29 (6%) had "probable" or "definite" FH. In the CARVAR 92 cohort, 16 (0.16%) of 9900 subjects aged≤50 years had "probable" or "definite" FH. FH prevalence was 39 times greater among patients with premature MI than in the control population (P30-fold more common in patients referred for premature MI than in the general population; this highlights the need for FH screening after a first MI to enhance lipid-lowering therapy and allow early identification of family members.

International audience; Fabry disease (FD) is an X-linked genetic disease due to pathogenic variants in GLA. The phenotype varies depending on the GLA variant, alpha-galactosidase residual activity, patient's age and gender and, for females, X chromosome inactivation. Over 1000 variants have been identified, many through screening protocols more susceptible to disclose non-pathogenic variants or variants of unknown significance (VUS). This, together with the non-specificity of some FD symptoms, challenges physicians attempting to interpret GLA variants. The traditional way to interpreting pathogenicity is based on a combined approach using allele frequencies, genomic databases, global and disease-specific clinical databases, and in silico tools proposed by the American College of Medical Genetics and Genomics. Here, a panel of FD specialists convened to study how expertise may compare with the traditional approach. Several GLA VUS, highly controversial in the literature (p.Ser126Gly, p.Ala143Thr, p.Asp313Tyr), were re-analyzed through reviews of patients' charts. The same was done for pathogenic GLA variants with some specificities. Our data suggest that input of geneticists and physicians with wide expertise in disease phenotypes, prevalence, inheritance, biomarkers, alleles frequencies, disease-specific databases, and literature greatly contribute to a more accurate interpretation of the pathogenicity of variants, bringing a significant additional value over the traditional approach.

Background: The LDLR (low-density lipoprotein receptor) in the liver is the major determinant of LDL-cholesterol levels in human plasma. The discovery of genes that regulate the activity of LDLR helps to identify pathomechanisms of hypercholesterolemia and novel therapeutic targets against atherosclerotic cardiovascular disease. Methods: We performed a genome-wide RNA interference screen for genes limiting the uptake of fluorescent LDL into Huh-7 hepatocarcinoma cells. Top hit genes were validated by in vitro experiments as well as analyses of data sets on gene expression and variants in human populations. Results: The knockdown of 54 genes significantly inhibited LDL uptake. Fifteen of them encode for components or interactors of the U2-spliceosome. Knocking down any one of 11 out of 15 genes resulted in the selective retention of intron 3 of LDLR . The translated LDLR fragment lacks 88% of the full length LDLR and is detectable neither in nontransfected cells nor in human plasma. The hepatic expression of the intron 3 retention transcript is increased in nonalcoholic fatty liver disease as well as after bariatric surgery. Its expression in blood cells correlates with LDL-cholesterol and age. Single nucleotide polymorphisms and 3 rare variants of one spliceosome gene, RBM25 , are associated with LDL-cholesterol in the population and familial hypercholesterolemia, respectively. Compared with overexpression of wild-type RBM25 , overexpression of the 3 rare RBM25 mutants in Huh-7 cells led to lower LDL uptake. Conclusions: We identified a novel mechanism of posttranscriptional regulation of LDLR activity in humans and associations of genetic variants of RBM25 with LDL-cholesterol levels.

BACKGROUND A small proportion of familial hypercholesterolemia (FH) patients can adequately control this condition, although achieving the recommended targets for low-density lipoprotein cholesterol (LDL-c) levels remains a challenge. Proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) are new and potent lipid-lowering drugs. However, there is scarce literature on real-world data about their use in patients with FH. MATERIAL AND METHODS We examined the reduction in LDL-c levels from the baseline, after PCSK9i initiation in heterozygous familial hypercholesterolemia patients referred for lipoprotein apheresis in our regional lipid clinic. The study was conducted from March 2018 to September 2019, the period immediately after PCSK9i reimbursement was available in France. PCSK9i was added on top of the patients' maximal tolerated lipid-lowering regimens. RESULTS The study had 123 patients with heterozygous FH. The mean age of the patients was 59±11 years. The mean baseline LDL-c for all the participants was 277±78 mg/dl. It was 283±81 mg/dl in the PCSK9i monotherapy group (n=83), 247±68 mg/dl in the PCSK9i plus ezetimibe group (n=12), and 264±78 mg/dl in the PCSK9i plus statin and ezetimibe group (n=28). The mean decrease observed in the LDL-c level from baseline was 136±70 mg/dl (n=123), 125±60 mg/dl (n=83), 103±77 mg/dl (n=12), and 175±70 mg/dl (n=28), respectively. CONCLUSIONS An overall reduction of 49.1% from the baseline LDL-c was observed in the heterozygous FH population after PCSK9i initiation in a real-world experience. The group treated with PCSK9i ezetimibe plus statin showed further reduction of their LDL-c levels with a better responder rate, achieving the target 50% reduction in LDL-c from the baseline.

International audience; Apolipoprotein E (apoE) is a major apolipoprotein involved in lipoprotein metabolism. It is a polymorphic protein and different isoforms are associated with variations in lipid and lipoprotein levels and thus cardiovascular risk. The isoform apoE4 is associated with an increase in LDL-cholesterol levels and thus a higher cardiovascular risk compared to apoE3. Whereas, apoE2 is associated with a mild decrease in LDL-cholesterol levels. In the presence of other risk factors, apoE2 homozygotes could develop type III hyperlipoproteinemia (familial dysbetalipoproteinemia or FD), an atherogenic disorder characterized by an accumulation of remnants of triglyceride-rich lipoproteins. Several rare APOE gene variants were reported in different types of dyslipidemias including FD, familial combined hyperlipidemia (FCH), lipoprotein glomerulopathy and bona fide autosomal dominant hypercholesterolemia (ADH). ADH is characterized by elevated LDL-cholesterol levels leading to coronary heart disease, and due to molecular alterations in three main genes: LDLR, APOB and PCSK9. The identification of the APOE-p.Leu167del variant as the causative molecular element in two different ADH families, paved the way to considering APOE as a candidate gene for ADH. Due to non mendelian interacting factors, common genetic and environmental factors and perhaps epigenetics, clinical presentation of lipid disorders associated with APOE variants often strongly overlap. More studies are needed to determine the spectrum of APOE implication in each of the diseases, notably ADH, in order to improve clinical and genetic diagnosis, prognosis and patient management. The purpose of this review is to comment on these APOE variants and on the molecular and clinical overlaps between dyslipidemias.

International audience; Familial hypercholesterolemia (FH) is caused by mutations in LDLR (low-density lipoprotein receptor), APOB (apolipoprotein B), PCSK9 (proprotein convertase subtilisin/kexin type 9), or APOE (apolipoprotein E) genes in approximately 80% of the cases. Polygenic forms of hypercholesterolemia may be present among patients clinically diagnosed with FH but with no identified mutation (FH mutation-negative (FH/M-)). To address whether polygenic forms may explain phenocopies in FH families, we calculated a 6-single-nucleotide polymorphism (SNP) genetic risk score (GRS) in all members from five French FH families where a mutation was identified (FH/M+) as well as some phenocopies (FH/M-). In two families, three FH/M- patients present a high GRS suggesting a polygenic hypercholesterolemia for these phenocopies. However, a high GRS is also observed in nine FH/M+ patients and in four unaffected relatives from three families. These observations indicate that the GRS does not seem to be a good diagnostic tool at the individual level. Nevertheless, the GRS seems to be a contributor of the severity of hypercholesterolemia since patients who cumulate a mutation and a high GRS exhibit higher low-density lipoprotein cholesterol levels when compared to patients with only FH (p = 0.054) or only polygenic hypercholesterolemia (p = 0.0039). In conclusion, the GRS can be used as a marker of the severity of hypercholesterolemia but does not seem to be a reliable tool to distinguish phenocopies within FH families.

International audience; BACKGROUND: Abetalipoproteinemia, a recessive disease resulting from deleterious variants in MTTP (microsomal triglyceride transfer protein), is characterized by undetectable concentrations of apolipoprotein B, extremely low levels of low-density lipoprotein cholesterol in the plasma, and a total inability to export apolipoprotein B-containing lipoproteins from both the intestine and the liver. OBJECTIVE: To study lipid absorption after a fat load and liver function in 7 heterozygous relatives from 2 abetalipoproteinemic families, 1 previously unreported. RESULTS: Both patients are compound heterozygotes for p.(Arg540His) and either c.708\₇09del p.(His236Glnfs*11) or c.1344+3\₁344+6del on the MTTP gene. The previously undescribed patient has been followed for 22 years with ultrastructure analyses of both the intestine and the liver. In these 2 families, 5 relatives were heterozygous for p.(Arg540His), 1 for p.(His236Glnfs*11) and 1 for c.1344+3\₁344+6del. In 4 heterozygous relatives, the lipid absorption was normal independent of the MTTP variant. In contrast, in 3 of them, the increase in triglyceride levels after fat load was abnormal. These subjects were additionally heterozygous carriers of Asp2213 APOB in-frame deletion, near the cytidine mRNA editing site, which is essential for intestinal apoB48 production. Liver function appeared to be normal in all the heterozygotes except for one who exhibited liver steatosis for unexplained reasons. CONCLUSION: Our study suggests that a single copy of the MTTP gene may be sufficient for human normal lipid absorption, except when associated with an additional APOB gene alteration. The hepatic steatosis reported in 1 patient emphasizes the need for liver function tests in all heterozygotes until the level of risk is established.

Introduction: The identification by Abifadel et al. in 2003 of the first mutations of PCSK9 was the major breakthrough in the cholesterol field that led to a new therapeutic target. This discovery paved the way to new lipid lowering drugs reducing LDL-cholesterol levels through the inhibition of PCSK9. Two anti-PCSK9 monoclonal antibodies have received FDA and EMA approvals: Alirocumab and Evolocumab. Areas covered: This article reviews the different strategies that are pursued to modulate the functional activity of PCSK9 for lowering LDL-cholesterol levels. It also provides a brief overview of the patents related to PCSK9 from 2011 until the end of 2015. This review is addressed to researchers from academia and pharmaceutical companies who are engaged in PCSK9 research/cholesterol regulation. Readers will gain an up-to-date overview of the different strategies that have been investigated to reduce PCSK9, focusing on anti-PCSK9 monoclonal antibodies and the related clinical trials. Expert opinion: Anti-PCSK9 antibodies are a new class of lipid lowering drugs with promising results in reducing LDL-cholesterol. Long-term ongoing studies investigating on a large scale the efficacy and safety of the anti-PCSK9 antibodies and their cardiovascular outcomes are eagerly awaited.

International audience; Background and aims: Cardiovascular risk is high in heterozygous familial hypercholesterolemia (HeFH). The objective of this study was to describe recurrent cardiovascular events in selected patients with HeFH attending lipid clinics in France. Methods: We included 781 patients with a clinical (Dutch Lipid Clinic Network score \textgreater= 6) or genetic diagnosis of HeFH who had experienced a first cardiovascular event (myocardial infarction, percutaneous coronary intervention or coronary bypass, unstable angina, stroke, peripheral arterial revascularization or cardiovascular death) and were enrolled in the French Familial Hypercholesterolemia Registry (November 2015 to March 2018). Results: The first cardiovascular event occurred at the mean age of 47 years (interquartile range 39-55) in a predominantly male population (72%); 48% of patients were on statin therapy. Overall, 37% of patients had at least one recurrent cardiovascular event (mean of 1.8 events per patient), of which 32% occurred in the 12 months after the index event; 55% of events occurred \textgreater 3 years after the first event. Mean LDL-C at the last clinic visit was 144 +/- 75 mg/dL (132 +/- 69 mg/dL for patients on high-potency statin therapy and 223 +/- 85 mg/dL for untreated patients). Conclusions: The rate of recurrent cardiovascular events was high in French patients with HeFH in secondary prevention. The detection of FH during childhood is crucial to prevent CV events at a young age by early initiating statin therapy. There is a clear urgent need to expand the actual very small target population which can be treated with the PCSK9 inhibitor in France.

Background The Middle East region is characterized by low levels of high-density lipoprotein cholesterol (HDL-C). To date, no genetic study has investigated the cause of low HDL-C in the Lebanese population. Objective Our objective was to study the genetic causes for hypoalphalipoproteinemia in a Lebanese family with extremely low HDL-C levels. Methods We sequenced the ABCA1 gene and evaluated cholesterol efflux, inflammatory, and metabolic profiles in the proband and his family. Results We identified the first Lebanese pathogenic variant in ABCA1 gene causing Tangier disease in a consanguineous family. The proband carried a novel homozygous pathogenic variant p.Gly592Asp in exon 14 of ABCA1, which segregated with the disease in the family. Functional study of the p.Gly592Asp pathogenic variant revealed that lipid-free apolipoprotein A-I–dependent cholesterol efflux was completely abolished in cholesterol-loaded human monocytes-derived macrophages isolated from the proband when compared to controls. Systemic inflammatory and metabolic assessments showed that plasma cytokines (MCP-1, MIP-1α, IL-6, CRP, TNF-α), adhesion molecules (ICAM-1, VCAM-1, E-selectin), inflammatory soluble receptors (sIL-6r, sTNFRI, sTNFRII), and metabolic markers (Insulin, C-peptide) were elevated in the proband when compared to controls. Noninvasive cardiovascular investigation revealed the presence of premature artery lesions in the proband. Conclusions It is the first case of Tangier disease reported in Lebanon harboring a novel pathogenic variant in ABCA1. Further genetic research is needed in the Middle East where the consanguinity rate is elevated, to understand the cause of the highly prevalent dyslipidemia. This will help guiding the early diagnosis, management, and prevention of cardiovascular complications.

Autosomal dominant hypercholesterolemia (ADH) is characterized by elevated LDL-C levels leading to coronary heart disease. Four genes are implicated in ADH: LDLR, APOB, PCSK9 and APOE. Our aim was to identify new mutations in known genes, or in new genes implicated in ADH. Thirteen French families with ADH were recruited and studied by exome sequencing after exclusion, in their probands, of mutations in the LDLR, PCSK9 and APOE genes and fragments of exons 26 and 29 of APOB gene. We identified in one family a p.Arg50Gln mutation in the APOB gene, which occurs in a region not usually associated with ADH. Segregation and in-silico analysis suggested that this mutation is disease causing in the family. We identified in another family with the p.Ala3396Thr mutation of APOB, one patient with a severe phenotype carrying also a mutation in PCSK9: p.Arg96Cys. This is the first compound heterozygote reported with a mutation in APOB and PCSK9. Functional studies proved that the p.Arg96Cys mutation leads to increased LDL receptor degradation. This work shows that Next-Generation Sequencing (exome, genome or targeted sequencing) are powerful tools to find new mutations and identify compound heterozygotes, which will lead to better diagnosis and treatment of ADH.

BACKGROUND: Familial hypercholesterolemia (FH) is a common autosomal dominant disease associated with premature coronary heart disease (CHD). Studies tend to show that patients with FH associated with an identified mutation (mutation+ FH) are at higher risk than patients without an identified mutation (mutation– FH). We compared the clinical and biological profile and the risk of CHD in patients with mutation+ FH and mutation– FH. HYPOTHESIS: In addition to LDL‐C, a pathogenic mutation predicts premature CHD in FH. METHODS: We successively included all patients with suspected FH (LDL‐C > 190 mg/dL if age > 18 years; LDL‐C > 160 mg/dL if age

International audience; The c.61\₆3dupCTG (L10) allele of rs72555377 polymorphism in PCSK9 has been reported to be associated with low-density lipoprotein-cholesterol (LDL-C) levels and with a decreased risk of coronary artery disease (CAD). We investigated the effect of two known alleles for rs72555377, L10 and L11, on the risk of CAD in a Tunisian cohort (218 patients diagnosed by angiography and 125 control subjects). Two subgroups of patients were defined by their level of stenosis: >= 50% for CAD and = 50% in two or three major coronary arteries (0.210 vs 0.125, p = 0.028). Multiple regression analysis showed that the L10 allele was significantly associated with a reduced risk of CAD (p = 0.049, OR = 0.51[0.26-1.00]), and with its reduced severity (p = 0.045, OR = 0.44[0.20-0.98]). The L10 allele is associated with a reduced risk and severity of CAD, seemingly independently of its LDL-lowering effect, suggesting a direct effect of PCSK9 on atherogenesis.

Background The identification of mutations in PCSK9 (proprotein convertase subtilisin kexin9) in autosomal dominant hypercholesterolemia (ADH), has revealed the existence of a new player in cholesterol homeostasis. PCSK9 has been shown to enhance the degradation of the LDL receptor (LDLR) at the cell surface. Gain-of-function mutations of PCSK9 induce ADH and are very rare, but their identification is crucial in studying PCSK9's role in hypercholesterolemia, its detailed trafficking pathway and its impact on the LDLR. Methods In order to identify new mutations and understand the exact mechanisms of action of mutated PCSK9, PCSK9 was sequenced in 75 ADH patients with no mutations in the LDLR or APOB genes. Functional analyses in cell culture were conducted and the impact of novel PCSK9 mutations on the quantitative and qualitative features of lipoprotein particles and on the HDL-mediated cellular cholesterol efflux was studied. Results Among these 75 ADH probands with no mutations in the LDLR or APOB genes, four gain-of-function mutations of PCSK9 were identified, of which two were novel: the p.Leu108Arg and the p.Asp35Tyr substitutions. In vitro studies of their consequences on the activity of PCSK9 on cell surface levels of LDLR showed that the p.Leu108Arg mutation clearly results in a gain-of-function, while the p.Asp35Tyr mutation created a novel Tyr-sulfation site, which may enhance the intracellular activity of PCSK9. Conclusion These data further contribute to the characterization of PCSK9 mutations and to better understanding of the impact on cholesterol metabolism of this new therapeutic target.

Background Autosomal dominant hypercholesterolemia (ADH) is commonly caused by mutations in the low-density lipoprotein (LDL) receptor gene ( LDLR ), in the apolipoprotein B-100 gene ( APOB ), or in the proprotein convertase subtilisin kexine 9 gene ( PCSK9 ). ADH subjects carrying a mutation in LDLR present highly variable plasma LDL-cholesterol (LDL-C). This variability might be due to environmental factors or the effect of some modifying genes such as PCSK9 and APOE . Aims We investigated the molecular basis of thirteen Tunisian ADH families and attempted to determine the impact of PCSK9 and APOE gene variations on LDL-cholesterol levels and on the variable phenotypic expression of the disease. Methods and results Fifty six subjects were screened for mutations in the LDLR gene through direct sequencing. The causative mutation was found to segregate with the disease in each family and a new frameshift mutation, p.Met767CysfsX21, was identified in one family. The distribution of total- and LDL-cholesterol levels, adjusted for age and gender, among homozygous and heterozygous ADH patients varied widely. Within seven families, nine subjects presented low LDL-cholesterol levels despite carrying a mutation in the LDLR gene. To identify the molecular actors underlying this phenotypic variability, the PCSK9 gene was screened using direct sequencing and/or enzymatic restriction analysis, and the apo E genotypes were determined. A new missense variation (p.Pro174Ser) in the PCSK9 gene was identified and characterized as a new putative loss-of-function mutation. Conclusion Genetic variations in PCSK9 and APOE genes could explain only part of the variability observed in the phenotypic expression in Tunisian ADH patients carrying mutations in the LDLR gene. Other genetic variants and environmental factors very probably act to fully explain this phenotypic variability.

Supplemental Digital Content is available in the text., Background— Patients with PCSK9 gene gain of function (GOF) mutations have a rare form of autosomal dominant hypercholesterolemia. However, data examining their clinical characteristics and geographic distribution are lacking. Furthermore, no randomized treatment study in this population has been reported. Methods and Results— We compiled clinical characteristics of PCSK9 GOF mutation carriers in a multinational retrospective, cross-sectional, observational study. We then performed a randomized placebo-phase, double-blind study of alirocumab 150 mg administered subcutaneously every 2 weeks to 13 patients representing 4 different PCSK9 GOF mutations with low-density lipoprotein cholesterol (LDL-C) ≥70 mg/dL on their current lipid-lowering therapies at baseline. Observational study: among 164 patients, 16 different PCSK9 GOF mutations distributed throughout the gene were associated with varying severity of untreated LDL-C levels. Coronary artery disease was common (33%; average age of onset, 49.4 years), and untreated LDL-C concentrations were higher compared with matched carriers of mutations in the LDLR (n=2126) or apolipoprotein B (n=470) genes. Intervention study: in PCSK9 GOF mutation patients randomly assigned to receive alirocumab, mean percent reduction in LDL-C at 2 weeks was 62.5% (P

Autosomal dominant hypercholesterolemia (ADH) is characterized by isolated increase in plasmatic low-density lipoprotein (LDL) cholesterol levels associated with high risk of premature cardiovascular disease. Mutations in LDLR, APOB, and PCSK9 genes have been shown to cause ADH. We now report further genetic heterogeneity of ADH through the study of a large French family in which the involvement of these three genes was excluded. A genome-wide scan mapped the disease-causing gene, named HCHOLA4, at 16q22.1 in a 7.89-Mb interval containing 154 genes with a maximum LOD score of 3.9. To reduce the linked region, we genotyped 18 smaller non-LDLR/non-APOB/non-PCSK9-ADH families at the HCHOLA4 locus. Six families did not exclude linkage to the locus, but none allowed reduction of the disease interval. The 154 regional genes were sorted according to the function of the encoded protein and tissue expression profiles, and 57 genes were analyzed through sequencing of their coding region and close flanking intronic parts. No disease-causing mutation was identified in these families, particularly in the LCAT gene. Finally, our results also show the existence of other ADH genes as nine families were neither linked to LDLR, APOB, and PCSK9 genes nor to the new HCHOLA4 locus.

Autosomal dominant hypercholesterolemia (ADH), a major risk for coronary heart disease, is associated with mutations in the genes encoding the low-density lipoproteins receptor (LDLR), its ligand apolipoprotein B (APOB) or PCSK9 (Proprotein Convertase Subtilin Kexin 9). Familial hypercholesterolemia (FH) caused by mutation in the LDLR gene is the most frequent form of ADH. The incidence of FH is particularly high in the Lebanese population presumably as a result of a founder effect. In this study we characterize the spectrum of the mutations causing FH in Lebanon: we confirm the very high frequency of the LDLR p.Cys681X mutation that accounts for 81.5 % of the FH Lebanese probands recruited and identify other less frequent mutations in the LDLR. Finally, we show that the p.Leu21dup, an in frame insertion of one leucine to the stretch of 9 leucines in exon 1 of PCSK9, known to be associated with lower LDL-cholesterol levels in general populations, is also associated with a reduction of LDL-cholesterol levels in FH patients sharing the p.C681X mutation in the LDLR. Thus, by studying for the first time the impact of PCSK9 polymorphism on LDL-cholesterol levels of FH patients carrying a same LDLR mutation, we show that PCSK9 might constitute a modifier gene in familial hypercholesterolemia. © 2009 Wiley-Liss, Inc.

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by mutations in the low-density lipoprotein receptor ( LDLR ), apolipoprotein B ( APOB ), and proprotein convertase subtilisin/kexin type 9 ( PCSK9 ) genes. In previous studies, we have identified novel mutations in Tunisian FH families. In this study, we have extended our investigation to additional families. Five unrelated probands were screened for mutations in the LDLR and APOB genes, using direct sequencing and enzymatic restriction. We identified two novel LDLR mutations: a missense mutation in exon 7: p.Gly343Cys (c.1027G>T), and a nonsense mutation in exon 17: p.Lys816X (c.2446A>T). Using the PolyPhen and SIFT prediction computer programs the p.Gly343Cys is predicted to have a deleterious effect on LDL receptor activity. The missense mutation we found in exon 3, p.Cys89Trp (c.267C>G), has previously been identified in patients from United Kingdom and Spain, and is reported here for the first time in the Tunisian population. Finally, the framshift mutation in exon 10, p.Ser493ArgfsX44, is reported here for the fourth and fifth time in Tunisian families. The latter is the most frequent FH-causing mutation in Tunisia. These LDLR gene mutations enrich the spectrum of mutations causing FH in the Tunisian population. The framshift mutation, p.Ser493ArgfsX44, seems to be a founder mutation in this population.

Autosomal dominant hypercholesterolemia (ADH) is characterized by isolated elevation of plasmatic low-density lipoprotein cholesterol associated with high risk of premature cardiovascular complications. More than 1000 mutations in the LDLR gene and 9 in the APOB gene have been implicated. We have shown further heterogeneity with the discovery of missense mutations in the PCSK9 gene resulting in ADH. Different studies have tried to evaluate the respective contribution of mutations in each gene to the disease, but results were not always in agreement. After a brief overview of mutations reported for each gene, strategies and results of these different studies are reviewed and analyzed. Altogether, numerous reports give evidence for the existence of a greater level of genetic heterogeneity in ADH and the involvement of still unknown genes.

Familial hypercholesterolemia (FH) is a genetic disorder mainly caused by defects in the low-density lipoprotein receptor (LDLR) gene, although it can also be due to alterations in the gene encoding apolipoprotein B (familial defective apoB or FDB) or in other unidentified genes. In Morocco, the molecular basis of FH is unknown. To obtain information on this issue, 27 patients with FH from eight unrelated families were analyzed by screening the LDLR (PCR-SSCP and Southern blot) and apoB genes (PCR and restriction enzyme digestion analysis). None of the patients carried either the R3500Q or the R3531C mutation in the apoB gene. By contrast, seven mutations in the LDLR gene were identified, including five missense mutations on exons 4, 6, 8, and 14 (C113R, G266C, A370T, P664L, C690S) and two large deletions (FH Morocco-1 and FH Morocco-2). The two major rearrangements and the missense mutation G266C are novel mutations and could well be causative of FH in the Moroccan population. This study has yielded preliminary information on the mutation spectrum of the LDLR gene among patients with FH in Morocco.

Familial hypercholesterolemia (FH), a frequent monogenic condition complicated by premature cardiovascular disease, is characterized by high allelic heterogeneity at the low-density lipoprotein receptor (LDLR) locus. Despite more than a decade of genetic testing, knowledge about intronic disease-causing mutations has remained limited because of lack of available genomic sequences. Based on the finding from bioinformatic analysis that Alu repeats represent 85% of LDLR intronic sequences outside exon-intron junctions, we designed a strategy to improve the exploration of genomic regions in the vicinity of exons in 110 FH subjects from an admixed population. In the first group of 42 patients of negative mutation carriers, as previously established by former screening strategies (denaturing gradient gel electrophoresis, DNA sequencing with former primers overlapping splice-sites, Southern Blotting), about half (n=22) were found to be carriers of at least one heterozygous mutation. Among a second group of 68 newly recruited patients, 27% of mutation carriers (n=37) had a splicing regulatory mutation. Overall, out of the 54 mutations identified, 13 were intronic, and 18 were novel, out of which nearly half were intronic. Two novel intronic mutations (IVS8–10G→A within the polypyrimidine tract and IVS7+10G→A downstream of donor site) might create potential aberrant splice sites according to neural-network computed estimation, contrary to 31 common single nucleotide variations also identified at exon-intron junctions. This new strategy of detecting the most likely disease-causing LDLR mutations outside of Alu-rich genomic regions reveals that intronic mutations may have a greater impact than previously reported on the molecular basis of FH. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00439-002-0813-4

A decade after our discovery of the involvement of proprotein convertase subtilisin/kexin type 9 (PCSK9) in cholesterol metabolism through the identification of the first mutations leading to hypercholesterolemia, PCSK9 has become one of the most promising targets in cholesterol and cardiovascular diseases. This challenging work in the genetics of hypercholesterolemia paved the way for a plethora of studies around the world allowing the characterization of PCSK9, its expression, its impact on reducing the abundance of LDL receptor, and the identification of loss-of-function mutations in hypocholesterolemia. We highlight the different steps of this adventure and review the published clinical trials especially those with the anti-PCSK9 antibodies evolocumab (AMG 145) and alirocumab (SAR236553/REGN727), which are in phase III trials. The promising results in lowering LDL cholesterol levels raise hope that the PCSK9 adventure will lead, after the large and long-term ongoing phase III studies evaluating efficacy and safety, to a new anticholesterol pharmacological class.

Background— Exome sequencing is a promising tool for gene mapping in Mendelian disorders. We used this technique in an attempt to identify novel genes underlying monogenic dyslipidemias. Methods and Results— We performed exome sequencing on 213 selected family members from 41 kindreds with suspected Mendelian inheritance of extreme levels of low-density lipoprotein cholesterol (after candidate gene sequencing excluded known genetic causes for high low-density lipoprotein cholesterol families) or high-density lipoprotein cholesterol. We used standard analytic approaches to identify candidate variants and also assigned a polygenic score to each individual to account for their burden of common genetic variants known to influence lipid levels. In 9 families, we identified likely pathogenic variants in known lipid genes ( ABCA1 , APOB , APOE , LDLR, LIPA , and PCSK9 ); however, we were unable to identify obvious genetic etiologies in the remaining 32 families, despite follow-up analyses. We identified 3 factors that limited novel gene discovery: (1) imperfect sequencing coverage across the exome hid potentially causal variants; (2) large numbers of shared rare alleles within families obfuscated causal variant identification; and (3) individuals from 15% of families carried a significant burden of common lipid-related alleles, suggesting complex inheritance can masquerade as monogenic disease. Conclusions— We identified the genetic basis of disease in 9 of 41 families; however, none of these represented novel gene discoveries. Our results highlight the promise and limitations of exome sequencing as a discovery technique in suspected monogenic dyslipidemias. Considering the confounders identified may inform the design of future exome sequencing studies.

Autosomal dominant type IIa hypercholesterolaemia (ADH) is characterised by an elevation of total plasma cholesterol associated with increased LDL particles. Numerous different molecular defects have been identified in the LDL receptor (LDLR) and few specific mutations in the apolipoprotein B (APOB) gene resulting in familial hypercholesterolaemia and familial defective apoB-100 respectively. To estimate the respective contribution of LDLR, APOB and other gene defects in this disease, we studied 33 well characterised French families diagnosed over at least three generations with ADH through the candidate gene approach. An estimation of the proportions performed with the HOMOG3R program showed that an LDLR gene defect was involved in approximately 50% of the families (P = 0.001). On the other hand, the estimated contribution of an APOB gene defect was only 15%. This low estimation of ADH due to an APOB gene defect is further strengthened by the existence of only two probands carrying the APOB (R3500Q) mutation in the sample. More importantly and surprisingly, 35% of the families in the sample were estimated to be linked to neither LDLR nor APOB genes. These data were confirmed by the exclusion of both genes through direct haplotyping in three families. Our results demonstrate that the relative contributions of LDLR and APOB gene defects to the disease are very different. Furthermore, our results also show that genetic heterogeneity is, generally, underestimated in ADH, and that at least three major groups of defects are involved. At this point, the contribution of the recently mapped FH3 gene to ADH cannot be assessed nor its importance in the group of 'non LDLR/non APOB' families.

Mutations in the LDL receptor gene (LDLR) cause familial hypercholesterolemia (FH), a common autosomal dominant disorder. The LDLR database is a computerized tool that has been developed to provide tools to analyse the numerous mutations that have been identified in the LDLR gene. The second version of the LDLR database contains 140 new entries and the software has been modified to accommodate four new routines. The analysis of the updated data (350 mutations) gives the following informations: (i) 63% of the mutations are missense, and only 20% occur in CpG dinucleotides; (ii) although the mutations are widely distributed throughout the gene, there is an excess of mutations in exons 4 and 9, and a deficit in exons 13 and 15; (iii) the analysis of the distribution of mutations located within the ligand-binding domain shows that 74% of the mutations in this domain affect a conserved amino-acid, and that they are mostly confined in the C-terminal region of the repeats. Conversely, the same analysis in the EGF-like domain shows that 64% of the mutations in this domain affect a non-conserved amino-acid, and, that they are mostly confined in the N-terminal half of the repeats. The database is now accessible on the World Wide Web at http://www.umd.necker.fr

Autosomal Dominant Hypercholesterolemia (ADH) is due to defects in the LDL receptor gene (LDLR), the apolipoprotein B-100 gene (APOB) or the proprotein convertase subtilisin/kexin type 9 gene (PCSK9). The aim of this study was to identify and to characterize the ADH-causative mutations in two Tunisian families. Analysis of the LDLR gene was performed by direct sequencing, multiplex ligation-dependent probe amplification (MLPA) and by long range PCR and sequencing. The PCSK9 gene was analysed by direct sequencing and the APOB gene was screened for the most common mutation: p.Arg3527Gln. In the LDLR gene, we found two large deletions and characterized their exact extent and breakpoint sequences. The first one is a deletion of 12,684 bp linking intron 1 to intron 5: g.11205052_11217736del12684. The second deletion spans 2364 bp from intron 4 to 6: g.11216885_11219249del2364. Sequence analysis of each deletion breakpoint indicates that intrachromatid non-allelic homologous recombination (NAHR) between Alu elements is involved. These two large rearrangements in the LDLR gene are the first to be described in the Tunisian population, increasing the spectrum of ADH-causative mutations.

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.

Abetalipoproteinemia (ABL) is an inherited disease characterized by the defective assembly and secretion of apolipoprotein B-containing lipoproteins caused by mutations in the microsomal triglyceride transfer protein large subunit (MTP) gene (MTTP). We report here a female patient with an unusual clinical and biochemical ABL phenotype. She presented with severe liver injury, low levels of LDL-cholesterol, and subnormal levels of vitamin E, but only mild fat malabsorption and no retinitis pigmentosa or acanthocytosis. Our objective was to search for MTTP mutations and to determine the relationship between the genotype and this particular phenotype. The subject exhibited compound heterozygosity for two novel MTTP mutations: one missense mutation (p.Leu435His) and an intronic deletion (c.619-5_619-2del). COS-1 cells expressing the missense mutant protein exhibited negligible levels of MTP activity. In contrast, the minigene splicing reporter assay showed an incomplete splicing defect of the intronic deletion, with 26% of the normal splicing being maintained in the transfected HeLa cells. The small amount of MTP activity resulting from the residual normal splicing in the patient explains the atypical phenotype observed. Our investigation provides an example of a functional analysis of unclassified variations, which is an absolute necessity for the molecular diagnosis of atypical ABL cases.-Di Filippo, M., H. Crehalet, M. E. Samson-Bouma, V. Bonnet, L. P. Aggerbeck, J-P. Rabes, F. Gottrand, G. Luc, D. Bozon, and A. Sassolas. Molecular and functional analysis of two new MTTP gene mutations in an atypical case of abetalipoproteinemia. J. Lipid Res. 2012. 53: 548-555.

The molecular basis of myotonic dystrophy (DM) has been characterised. All DM mutations characterised to date appear as an unstable elongation of a fragment containing a tandem repeat of a CTG motif, which can be visualised in both EcoRI and BamHI digests. It has been shown that the fragment is polymorphic in the normal population. Another 1 kb insertion/deletion polymorphism located near the unstable CTG repeat region has been identified. The 1 kb insertion allele is present in all DM patients. These different polymorphic systems can be distinguished using cDNA25 and BamHI, because this enzyme cuts between the site of the 1 kb insertion and the CTG repeat. We thus haplotyped DM patients from 72 French families and clearly showed that all chromosomes (100%) with the DM mutation carried the 1 kb insertion as well. In addition to this association, we detected significant linkage disequilibrium between the DM locus and D19S63 for which allelic frequencies were different from other European populations. Our results in the French DM population are thus in agreement with the hypothesis that the CTG expansion occurred on one or a few ancestral chromosomes carrying the large 1 kb insertion allele.

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.

Hypercholesterolemia is one of the major causes of coronary heart disease (CHD). The genes encoding the low-density lipoprotein receptor and its ligand apolipoprotein B, have been the two genes classically implicated in autosomal dominant hypercholesterolemia (ADH). Our discovery in 2003 of the first mutations of the proprotein convertase subtilisin kexin 9 gene (PCSK9) causing ADH shed light on an unknown actor in cholesterol metabolism that since then has been extensively investigated. Several PCSK9 variants have been identified, some of them are gain-of-function mutations causing hypercholesterolemia by a reduction of low-density lipoprotein (LDL) receptor levels; while others are loss-of-function variants associated with a reduction of LDL-cholesterol (LDL-C) levels and a decreased risk of CHD. In this review, we focus on reported variants, and their biological, clinical, and functional relevance. We also highlight the spectrum of hypercholesterolemia or hypobetalipoproteinemia phenotypes that are already associated with mutations in PCSK9. Finally, we present future prospects concerning this therapeutic target that might constitute a new approach to reduce cholesterol levels and CHD, and enhance the effectiveness of other lipid-lowering drugs.

International audience; Background: Our discovery in 2003 of the first mutations of PCSK9 gene causing autosomal dominant hypercholesterolaemia (ADH) shed light on an unknown factor that strongly influences the level of circulating low density lipoprotein cholesterol (LDL-C). PCSK9 gain of function mutations cause hypercholesterolaemia by a reduction of LDL receptor levels, while PCSK9 loss of function variants are associated with a reduction of LDL-C values and a decreased risk of coronary heart disease. METHODS AND RESULTS: We report an insertion of two leucines (p.L21tri also designated p.L15_L16ins2L) in the leucine stretch of the signal peptide of PCSK9 that is found in two of 25 families with familial combined hyperlipidaemia (FCHL). This mutant is associated with high total cholesterol and LDL-C values in these families and is found also in a patient with familial hypercholesterolaemia and her father. CONCLUSION: PCSK9 variants might contribute to FCHL phenotype and are to be taken into consideration in the study of this complex and multigenic disease with other genes implicated in dyslipidaemia.

Background Familial hypercholesterolemia (FH) is an autosomal dominant inherited disease caused by mutations in either the low-density lipoprotein receptor, the apolipoprotein B or the proprotein convertase subtilisin/kexin type 9 genes. It is characterized by a high concentration of low-density lipoprotein (LDL), which frequently gives rise to premature coronary disease. In this study, we report a novel splice site mutation of the LDL receptor gene in a Tunisian family. Methods Seven patients from the family were screened for mutations in the LDLR gene and the apoB gene, using direct sequencing. RT-PCR and study on cultured skin fibroblast were realised to characterize the effect of novel mutation. Results Direct sequencing of the promoter and 18 exons reveals a G > A substitution in the splice site junction of intron 8 (c.1186 + 1 G > A). Study on cultured skin fibroblasts showed a residual activity of 10% of the LDL receptor. Reverse transcription, amplification and direct sequencing of RNA from patient's lymphocytes reveal a deletion of the final 51 bp of exon 8 preserving the reading frame. Conclusions The study identified a novel splice mutation c.1186 + 1 G > A in the LDL receptor gene. It causes the utilization of a new cryptic donor splice site 51 bp downstream from the normal site.

Background Familial hypercholesterolemia (FH) and familial defective apolipoprotein B-100 (FDB) are relatively common lipid disorders caused by mutations of the low-density lipoprotein receptor (LDLR) and apolipoprotein B (apoB) genes, respectively. A third locus on chromosome 1p34.1–p32 was recently linked to FH and the responsible gene has been identified [protein convertase subtilisin/kexin type 9 (PCSK9)]. Methods We assessed the contribution of the LDLR, apoB, and PCSK9 genes as cause of FH in Mexico. Forty six unrelated probands, as well as 68 affected and 60 healthy relatives, were included. Results All index cases were diagnosed as having heterozygous autosomal dominant FH. Seventeen of the 46 index cases had LDLR gene mutations, four of which were novel (Fs92ter108, C268R, Q718X, and Fs736ter743); and only one patient had an apoB mutation (R3500Q). We sequenced the PCSK9 gene in the remainder of the 28 probands with no identified LDLR or APOB gene defects; however, no PCSK9 mutations were found, including one large kindred with positive linkage to the 1p34.1–32 locus (multipoint LOD score of 3.3) and two small pedigrees. Linkage was excluded from these three loci in at least four kindreds suggesting that other yet uncharacterized genes are involved. Conclusions Our results underline substantial genetic heterogeneity for FH in the Mexican population.

Mutations in the LDL receptor gene (LDLR) cause familial hypercholesterolemia (FH), one of the most frequent hereditary dominant disorders. The protein defect was identified in 1973, the gene was localized by in situ hybridization in 1985, and since, a growing number of mutations have been reported. The UMD-LDLR database is customized software that has been developed to list all mutations, and also to provide means to analyze them at the nucleotide and protein levels. The database has been recently modified to fulfill the recommendations of the Nomenclature Working Group for human gene mutations. However, in the current version, both the nomenclature and usual LDLR gene mutation names are reported since the latter are more commonly used. The software has also been modified to accommodate the splicing mutations and alleles that carry two nucleotide variations. The current version of UMD-LDLR contains 840 entries, of which 490 are new entries. Point mutations account for 90% of all mutations in the LDLR gene; the remaining are mostly major rearrangements, due to the presence of Alu sequences. Three new routines have been implemented in the software, thus giving users access to 13 sorting tools. In addition to the database, a Web site containing information about polymorphisms, major rearrangements, and promoter mutations is available. Both are accessible to the scientific community (www.umd.necker.fr) and should help groups working on LDLR to check their mutations and identify new ones, and greatly facilitate the understanding of functional classes/genotype relationships and of genotype/phenotype correlations.

Abstract —Familial hypercholesterolemia and familial ligand-defective apolipoprotein B-100 (FDB) are dominantly inherited disorders leading to impaired low-density lipoprotein receptor (LDLR) and apolipoprotein B-100 (APOB) interaction, plasma LDL elevation, and hypercholesterolemia. We previously identified the first French FDB-R3531C proband, a woman with very high total cholesterol, in a group of type IIa hypercholesterolemic families. We report here the investigation of her family at large that revealed the total absence of cosegregation with hypercholesterolemia. Six of the 10 subjects heterozygous for the R3531C mutation had plasma cholesterol lower than the 97.5th percentile for their age and gender, and mean cholesterol levels were not significantly different between affected and unaffected persons. Furthermore, 2 family members with similar high LDL-cholesterol levels were not carriers of the R3531C substitution, suggesting the implication of another mutation. Segregation analysis of the LDLR gene revealed statistically significant genetic linkage with hypercholesterolemia, and analysis of the proband LDLR gene led to the identification of the 664 proline to leucine defective mutation and its detection in all 6 hypercholesterolemic-related members of this family. Therefore, our results show that the family presents with familial hypercholesterolemia and give evidence that the R3531C substitution in the APOB gene is not an allelic variant leading to FDB. Furthermore, thorough analysis of our data suggests that the APOB-R3531C mutation enhances the hypercholesterolemic effect of the LDLR-P664L defect, suggesting that it is a susceptibility mutation.

The low-density lipoprotein receptor (LDLr) plays a pivotal role in cholesterol homeostasis. Mutations in the LDLr gene (LDLR), which is located on chromosome 19, cause familial hypercholesterolemia (FH), an autosomal dominant disorder characterized by severe hypercholesterolemia associated with premature coronary atherosclerosis. To date almost 300 mutations have been identified in the LDLR gene. To facilitate the mutational analysis of the LDLR gene, and promote the analysis of the relationship between genotype and phenotype, a software package along with a computerized database (currently listing 210 entries) have been created.

Myotonic dystrophy (DM) is an autosomal dominant neuromuscular disease. The mutation has been identified as an unstable trinucleotide CTG repeat in a sequence encoding a putative cAMP-dependent protein kinase. The CTG repeat varies in length between affected siblings, and generally increases through generations in parallel with increasing severity of the disease. Congenital myotonic dystrophy, which represents the most severe phenotype, is exclusively maternally inherited. In this report, we show, by Northern blot analysis, that no mutated enlarged transcript is detectable in a 20-week-old DM fetus and in two congenitally affected infants. Furthermore, in skeletal and cardiac muscle of the DM fetus, we observed by RNA analysis, including Northern blot and RT-PCR, an unexpectedly low expression of the paternal wild type allele. Varying degrees of expression of the mutant and/or the normal allele might therefore account for the characteristic features of the congenital form and the extreme variability of the disease.

Autosomal dominant hypercholesterolemia (ADH) is a frequent (1/500) monogenic inherited disorder characterized by isolated elevation of LDL leading to premature cardiovascular disease. ADH is known to result from mutations at two main loci: LDLR (encoding the low density lipoprotein receptor), and APOB (encoding apolipoprotein B100), its natural ligand. We previously demonstrated that ADH is also caused by mutations of the PCSK9 (proprotein convertase subtilisin/kexin type 9) gene that encodes Narc-1 (neural apoptosis-regulated convertase 1). However, the role of this novel disease locus as a cause of hypercholesterolemia remains unclear. In the present study, we analysed the PCSK9 coding region and intronic junctions in 130 adult or pediatric patients with ADH, previously found as being non LDLR/non APOB mutation carriers. Four novel heterozygous missense variations were found: c.654A>T (p.R218S), c.1070G>A (p.R357H), c.1405C>T (p.R469W), and c.1327G>A (p.A443T). All mutations were absent in 340 normolipidemic controls. Except for the A443T, all mutations are nonconservative and modify a highly conserved residue. Segregation with hypercholesterolemia is incomplete in one pedigree. Type and severity of hyperlipidemia and of cardiovascular disease could vary among subjects from the same family. Finally, the proband carrying the R357H mutation exhibited very high plasma cholesterol during pregnancy, whereas the proband carrying the p.R469W mutation exhibited a severe phenotype of hypercholesterolemia in combination with a LDLR mutation resulting from a frameshift at residue F382 (1209delC). These observations suggest that variations in PCSK9 are a rare cause of non LDLR/non APOB ADH (∼ 2.3%) and that additional environmental or genetic factors may contribute to the phenotype caused by PCSK9 missense mutations in humans. © 2005 Wiley-Liss, Inc.

Autosomal dominant hypercholesterolemia (ADH), one of the most frequent hereditary disorders, is characterized by an isolated elevation of LDL particles that leads to premature mortality from cardiovascular complications. It is generally assumed that mutations in the LDLR and APOB genes account for ADH. We identified one large French pedigree (HC2) and 12 additional white families with ADH in which we excluded linkage to the LDLR and APOB, implicating a new locus we named "FH3." A LOD score of 3.13 at a recombination fraction of 0 was obtained at markers D1S2892 and D1S2722. We localized the FH3 locus to a 9-cM interval at 1p34.1-p32. We tested four regional markers in another set of 12 ADH families. Positive LOD scores were obtained in three pedigrees, whereas linkage was excluded in the others. Heterogeneity tests indicated linkage to FH3 in approximately 27% of these non-LDLR/non-APOB ADH families and implied a fourth locus. Radiation hybrid mapping located four candidate genes at 1p34.1-p32, outside the critical region, showing no identity with FH3. Our results show that ADH is genetically more heterogeneous than conventionally accepted.