Familial Hypercholesterolemia Families Research Articles

Novel LDLR variants affecting low density lipoprotein metabolism identified in familial hypercholesterolemia.

Familial hypercholesterolemia (FH) is an autosomal dominant disease of lipid metabolism mainly caused by mutations in the low-density lipoprotein receptor (LDLR) gene. Genetic detection of patients with FH help with precise diagnosis and treatment, thus reducing the risk of coronary heart disease (CHD) and other related diseases. The study aimed to identify the causative gene mutations in a Chinese FH family and reveal the pathogenicity and the mechanism of these mutations. Whole exome sequencing was performed in a patient with severe lipid metabolism dysfunction seeking fertility guidance from a Chinese FH family. Two LDLR variants c.1875C > G (p.N625K; novel variant) and c.1448G > A (p.W483*) were identified in the family. Wildtype and mutant LDLR constructs were established by the site-direct mutagenesis technique. Functional studies were carried out by cell transfection to evaluate the impact of detected variants on LDLR activity. The two variants were proven to affect LDL uptake and binding, resulting in cholesterol clearance reduction to different degrees. According to The American College of Medical Genetics and Genomics (ACMG) Standards and Guidelines, the W483* variant was classified as "Pathogenic", while the N625K variant as "VUS". Our results provide novel experimental evidence of functional alteration by LDLR variants identified in our study and expand the mutational spectrum of LDLR mutation induced FH.

Identification of c.683_684insCTGCAAGGACAAATCTGACGA pathogenic variant of the low-density lipoprotein receptor gene in a patient with familial hypercholesterolemia: a case report

Familial hypercholesterolemia (FH) is one of the most common monogenic diseases that leads to the early development of atherosclerosis and is characterized by a poor prognosis. However, only about 1% of FH cases are diagnosed in Russia. The aim of this study was to determine the genetic defect in the FH family and conduct DNA diagnostics in the proband relatives. The study was performed on blood samples obtained with the informed consent of the patients. Polymerase chain reaction and polyacrylamide gel electrophoresis were used. We report c.683_684insCTGCAAGGA CAAATCTGACGA pathogenic variant of the low-density lipoprotein receptor (LDLR) gene for the first time in Russia and demonstrate its cosegregation in a family with high blood cholesterol. The c.683_684in sCTGCAAGGACAAATCTGACGA insertion is considered as a probable cause of FH.

A pragmatic clinical trial of cascade testing for familial hypercholesterolemia

We compared new cases detected per index case in familial hypercholesterolemia (FH) families with or without an identifiable monogenic etiology. We enrolled 52 FH probands with a pathogenic variant (FHg+) in LDLR, APOB, or PCSK9 and 73 probands without such a variant (FHg-). After direct contact by the study team, family members (FMs) of FHg+ probands could opt-in for genetic testing and FMs of FHg- probands were asked to provide a lipid profile. New cases were defined as presence of a pathogenic variant in FHg+ families and as low-density lipoprotein cholesterol ≥155 mg/dL in FHg- families. Of 71 FHg+ probands seen by a genetic counselor, 52 consented and identified 253 FMs (111 consented and were tested, yielding 48 new cases). Of 101 FHg- probands who received counseling, 73 consented and identified 295 FMs (63 consented and were tested, yielding 17 new cases). New case detection per index case was significantly greater in FHg+ than in FHg- families (0.92 vs 0.23), a result of higher cascade testing uptake (43.9 vs 21.4%) and yield (43.2 vs 27.0%) in the former. New case detection rate was significantly higher in FH families with a monogenic etiology than in those without such an etiology owing to greater uptake and yield of cascade testing.

Identification and functional characterization of two rare LDLR stop gain variants (p.C231* and p.R744*) in Saudi familial hypercholesterolemia patients.

Familial hypercholesterolemia (FH) is a globally underdiagnosed inherited metabolic disorder. Owing to limited published data from Arab world, this study was conducted with the aim of identifying the genetic and molecular basis of FH in highly consanguineous Saudi population. We performed clinical screening, biochemical profiling, whole exome sequencing and variant segregation analysis of two Saudi FH families. Additionally, 500 normolipic individuals were screened to ensure the absence of FH variant in general Saudi population. Functional characterization of FH variants on secondary structure characteristics of RNA and protein molecules was performed using different bioinformatics modelling approaches. WES analysis identified two independent rare LDLR gene stop gain variants (p.C231* and p.R744*) consistent to the clinical presentation of FH patients from two different families. RNAfold analysis has shown that both variants were predicted to disturb the free energy dynamics of LDLR mRNA molecule and destabilize its folding pattern and function. PSIPRED based structural modelling analysis has suggested that both variants bring drastic changes disturbing the secondary structural elements of LDLR molecule. The p.C231* and p.R744* variants are responsible for partial or no protein product, thus they are class 1 variants causing loss of function (LoF) LDLR variants. This study highlights the effectiveness of the WES, sanger sequencing, and computational analysis in expanding FH variant spectrum in culturally distinct populations like Saudi Arabia. Genetic testing of FH patients is very essential in better clinical diagnosis, screening, treatment, and management and prevention of cardiovascular disease burden in the society.

A Comprehensive Analysis of Genomics and Metagenomics in a Heterozygote Familial Hypercholesterolemia Family.

Familial hypercholesterolemia (FH) is an inherited rare disease leading to markedly elevated low-density lipoprotein cholesterol (LDL-C) levels and increased risk for cardiovascular event. Gut microbiota has been implicated as a pivotal contributing factor in hyperlipidemia, however, its role in FH remains elusive. We performed whole-exome and metagenomics sequencing on a family with 22 members in which myocardial infarctions occurred at a young age with unclear etiology. We confirmed the missense mutation of LDLR c.1723C>T accounted for the abnormal cholesterol metabolism in the family through co-segregation analysis. In addition, Prevotella dentalis was found elevated and strongly associated with LDL-C level in FH family members with mutation of LDLR c.1723C>T compared to unaffected members with hyperlipidemia. Overall, our work suggests that whole-exome sequencing can facilitate identification of disease-causing variants and enable preventive treatment of FH. Our metagenomics analysis provides early insights into potential contributions of host-microbe interactions in genetic and common hypercholesterolemia.

Molecular screening of familial hypercholesterolemia in Icelanders

Familial hypercholesterolemia (FH) is a monogenic disease characterized by a lifelong exposure to high LDL-C levels that can lead to early onset coronary heart disease (CHD). The main causes of FH identified to date include loss-of-function mutations in LDLR or APOB, or gain-of-function mutations in PCSK9. Early diagnosis and genetic testing of FH suspects is critical for improved prognosis of affected individuals as lipid lowering treatments are effective in preventing CHD related morbidity and mortality. In the present study, we carried out a comprehensive screening, using a next-generation sequencing (NGS) panel, for FH culprit mutations in two Icelandic studies representative of either FH families or the general population. We confirmed all previously known mutations in the FH families, and identified two subjects that had been misdiagnosed clinically at young age. We identified six new mutations in the Icelandic FH families and detected three pathogenic mutations in the general population-based study. The application of the NGS panel revealed substantial diagnostic yields in identifying pathogenic mutations, or 68.2% of those with definite clinical diagnosis of FH in the family material and 5.6-fold enrichment in the population-based genetic testing.

A systematic review of LDLR, PCSK9, and APOB variants in Asia

Background and aimsGenetic identification is a public health care concern for management of familial hypercholesterolemia (FH) associated cardiovascular morbidity and mortality. This study presents the spectrum and distribution of LDLR, APOB, PCSK9 gene mutations in Asia. MethodsDatabases were searched for English papers from 1950 to 2019. The spectrum of the variants was investigated in 8994 FH families in 48 Asian countries. We determined the frequency of variants, zygosity, and clinical features. ResultsTwenty countries have studied LDLR variants. A total of 629 mutations were reported and twenty variants were accounted as common variants in different populations. China, Japan, India and Taiwan constituted 68% of published articles. The most frequent mutation was reported in Japan but was not common in other countries. Other missense variants accounted for 50% of the mutations, frameshifts 19%, and nonsense 11%. The pooled frequency of variation was estimated in 1867 individuals. Approximately 67% of Iranian families were homozygous.,The common variant was p.Ser130Ter. p.Arg3527Trp in APOB was common among 184 heterozygous patients; the common variant of PCSK9 was p.Glu32Lys. ConclusionsThis is the first systematic review of LDLR, APOB, PCSK9 mutations in FH patients in Asia. These findings underscore the need to fill in the gap of studies on different populations in Asia. It also underlies the importance of early detection and management to decrease atherosclerosis and cardiovascular risk in different ethnicities.

The benign c.344G > A: p.(Arg115His) variant in the LDLR gene interpreted from a pedigree-based genetic analysis of familial hypercholesterolemia

BackgroundWe previously identified the c.344G > A: p.(Arg115His) variant in the low-density lipoprotein receptor (LDLR) gene, which was interpreted as “conflicting interpretations of pathogenicity” in ClinVar, based on a genetic analysis of patients with familial hypercholesterolemia (FH). However, whether this variant affects the pathophysiology of FH remains unclear. Therefore, our aim was to annotate the c.344G > A: p.(Arg115His) variant in the LDLR gene in FH. We present 2 families harboring the c.344G > A: p.(Arg115His) variant in the LDLR gene.MethodsGenetic analyses were performed for the coding regions and the exon-intron boundary sequence of the LDLR and proprotein convertase subtilisin/kexin type 9 (PCSK9) genes in 2 FH families. Next, the family without pathogenic variants in the LDLR and PCSK9 genes was screened by whole-exome sequencing. Detailed clinical and biochemical data were gathered from family members.ResultsIn one family, the index case had biallelic c.1567G > A: p.(Val523Met) and c.344G > A: p.(Arg115His) variants in the LDLR gene, while the sibling had only the c.1567G > A: p.(Val523Met) variant in the LDLR gene. There was no difference in the FH phenotype between the siblings. In another family, the index case and the sibling had no pathogenic variants in the LDLR, PCSK9, and apolipoprotein B (APOB) genes, but the sibling’s wife with nonFH had the c.344G > A: p.(Arg115His) variant in the LDLR gene. The sibling and his wife had 4 children, including an unaffected child and an affected child who had the c.344G > A: p.(Arg115His) variant in the LDLR gene. In addition, the allele frequency of the c.344G > A: p.(Arg115His) variant (0.0023–0.0043) in Japanese and East Asian populations is relatively high compared with that of the other LDLR pathogenic variants (0.0001–0.0008).ConclusionsThe c.344G > A: p.(Arg115His) variant in the LDLR gene is interpreted as benign in individuals with FH.

In search of a genetic explanation for LDLc variability in an FH family: common SNPs and a rare mutation in MTTP explain only part of LDL variability in an FH family

We previously identified a highly consanguineous familial hypercholesterolemia (FH) family demonstrating segregation of the JD Bari mutation in the LDL receptor as well as a putative cholesterol-lowering trait. We aimed to identify genes related to the latter effect. LDL cholesterol (LDLc) values were normalized for FH affectation status, age, and gender. Using genome-wide SNP data, we examined whether known SNPs gleaned from a genome-wide association study could explain the variation observed in LDLc. Four individuals with markedly reduced LDL levels underwent whole exome sequencing. After prioritizing all potential mutations, we identified the most promising candidate genes and tested them for segregation with the lowering trait. We transfected a plasmid carrying the top candidate mutation, microsomal triglyceride transfer protein (MTTP) R634C, into COS-7 cells to test enzymatic activity. The SNP score explained 3% of the observed variability. MTTP R634C showed reduced activity (49.1 nmol/ml) compared with the WT allele (185.8 nmol/ml) (P = 0.0012) and was marginally associated with reduced LDLc in FH patients (P = 0.05). Phenotypic variability in a FH pedigree can only partially be explained by a combination of common SNPs and a rare mutation and a rare variant in the MTTP gene. LDLc variability in FH patients may have nongenetic causes.

A xanthomatosis-susceptibility gene may exist in a Syrian family with familial hypercholesterolemia.

Familial hypercholesterolemia (FH) is an autosomal-dominant inherited disorder characterized by high serum low-density lipoprotein (LDL)-cholesterol concentrations, xanthoma formation, and premature atherosclerosis. Homozygous individuals die of vascular disease as children or young adults; heterozygous persons are at high risk for premature cardiovascular death. Mutations in the LDL-receptor gene are responsible for FH. We studied 49 members of a consanguineous Syrian kindred containing 6 homozygous individuals from the same pedigree. Half of the homozygotes had giant xanthomas, while half did not, even though their LDL-cholesterol concentrations were elevated to similar degrees (> 14 mmol/l). Heterozygous FH individuals from this family were also clearly distinguishable with respect to xanthoma size. We performed DNA analysis and were successful in identifying a hitherto not described mutation in this family's LDL receptor. DNA sequence analysis of the LDL-receptor gene revealed a T to C substitution at nucleotide 1,999 in codon 646 of exon 14. We next conducted a segregation analysis, which suggests that a susceptibility gene may explain the formation of giant xanthomas in this family. We raise the hypothesis that the appearance of giant xanthomas in this FH family is controlled by a second gene acting in an autosomal-dominant or recessive fashion. Elucidation of this 'xanthoma' gene may shed additional light on LDL-cholesterol deposition.

Cascade screening for familial hypercholesterolemia: Practical consequences

Familial Hypercholesterolemia (FH) is an autosomal dominant disorder mainly caused by mutations in the LDLR gene, resulting in elevated serum cholesterol levels and elevated risk of premature cardiovascular disease (CVD). Timely treatment with lipid lowering medication can lower the risk of CVD to the same level of the normal population. Currently the incidence of FH is estimated at 1 in 240 persons in the Caucasian population. A diagnosis of FH can be made on the basis of clinical criteria (including LDL cholesterol and family history) or DNA testing. When a mutation is known within a family an unequivocal diagnosis can be made by DNA testing in family members at any age. Genetic cascade screening is a cost-effective way to identify patients and prevent CVD. Between 1994 until 2014 a nationwide and government subsidized cascade screening program functioned to identify FH patients in the Netherlands. During this time more than 28,000 patients with FH have been identified and entered in a central, national database. Since 2014 cascade screening has been integrated in the regular Dutch health care system. Screening, counseling and treatment are now integrated in the care as a whole of FH patients and families, coordinated by the treating physician, while the national FH database is still maintained. However, since cascade screening by actively approaching family members cannot be applied anymore because of new regulations within the healthcare system, the number of family members participating in the cascade screening program, has plummeted. With this review we would like to highlight the practical consequences of implementing and executing a cascade screening program with a special focus on the lessons learned in the Netherlands.

Mutation detection in Chinese patients with familial hypercholesterolemia.

BackgroundFamilial hypercholesterolemia (FH) is the first molecularly and clinically characterized genetic disease of lipid metabolism. It is an autosomal dominant disorder with significantly elevated levels of total cholesterol and low density of lipoprotein cholesterol in serum, which would lead to extensive xanthomas and premature coronary heart disease. Mutations in low density lipoprotein receptor (LDLR), proprotein convertase subtilisin/kexin type 9 and Apo lipoprotein B-100 (APOB) have been identified to be the underlying cause of this disease.MethodsGenetic testing and reports of the mutations in the Chinese population are still limited. In this study, 11 unrelated Chinese FH families were enrolled to detect the candidate gene variants by DNA direct sequencing.Results and conclusionWe identified 12 mutations (11 in LDLR and one in APOB) in ten FH families. Three novel LDLR mutations (c.516C>A/p.D172E, c.1720C>A/p.R574S and c.760C>T/p.Q254X) were identified and co-segregated with the affected individuals in the families. Our discoveries not only further supports the significant role of LDLR in FH, but also expands the spectrum of LDLR mutations. These new insights will contribute to the genetic diagnosis and counseling of FH patients.

Lipid phenotype and heritage pattern in families with genetic hypercholesterolemia not related to LDLR, APOB, PCSK9, or APOE

A substantial proportion of individuals clinically diagnosed as familial hypercholesterolemia (FH) do not carry pathogenic mutations in candidate genes. Whether in them the high cholesterol trait is transmitted monogenically has not been studied. We assessed the inheritance pattern, penetrance, and expression of high low-density lipoprotein (LDL)-cholesterol (LDLc) in families with genetic hypercholesterolemia (GH) without known causative mutations (non-FH-GH). The study included probands with a clinical diagnosis of FH and their families attending 2 lipid clinics in Spain. Inclusion criteria for probands were LDLc >95th percentile, triglycerides <90th percentile, at least 1 first-degree family member with LDLc >90th percentile, >5 points in the Dutch Lipid Clinic Network criteria score, and absence of mutations in LDLR, APOB, PCSK9 or APOE. Eleven FH families with a LDLR mutation were also examined for comparison. We analyzed 49 non-FH-GH probands and 277 first-and second-degree relatives. LDLc was >90th percentile in 37.8% of blood relatives, at concentrations similar to those of probands. LDLc had a normal distribution in non-FH-GH families, in contrast with a bimodal distribution in FH families. When a dominant model was tested, family-based association tests gave much lower heritability values for total cholesterol and LDLc in non-FH-GH (0.39 and 0.32, respectively) than in FH (0.78 and 0.61, respectively). Non-FH-GH families have a milder lipid phenotype than genetically defined FH. The heritage pattern of LDLc in non-FH-GH does not fit with a monogenic disorder. Our findings support the concept that most non-FH-GHs are polygenic hypercholesterolemias.

Erratum: Identification of the gene defect responsible for severe hypercholesterolaemia using whole-exome sequencing

Familial hypercholesterolaemia (FH) is a serious genetic metabolic disease. We identified a specific family in which the proband had typical homozygous phenotype of FH, but couldn’t detect any mutations in usual pathogenic genes using traditional sequencing. This study is the first attempt to use whole exome sequencing (WES) to identify the pathogenic genes in Chinese FH. The routine examinations were performed on all parentage members, and WES on 5 members. We used bioinformatics methods to splice and filter out the pathogenic gene. Finally, Sanger sequencing and cDNA sequencing were used to verify the candidate genes. Half of parentage members had got hypercholesterolaemia. WES identified LDLR IVS8[−10] as a candidate mutation from 222,267 variations. The Sanger sequencing showed proband had a homozygous mutation inherited from his parents, and this loci were cosegregated with FH phenotype. The cDNA sequencing revealed that this mutations caused abnormal shearing. This mutation was first identified in Chinese patients, and this homozygous mutation is a new genetic type of FH. This is the first time that WES was used in Chinese FH patients. We detected a novel genetic type of LDLR homozygous mutation. WES is powerful tools to identify specific FH families with potentially pathogenic gene mutations.

Identification of the gene defect responsible for severe hypercholesterolaemia using whole-exome sequencing.

Familial hypercholesterolaemia (FH) is a serious genetic metabolic disease. We identified a specific family in which the proband had typical homozygous phenotype of FH, but couldn’t detect any mutations in usual pathogenic genes using traditional sequencing. This study is the first attempt to use whole exome sequencing (WES) to identify the pathogenic genes in Chinese FH. The routine examinations were performed on all parentage members, and WES on 5 members. We used bioinformatics methods to splice and filter out the pathogenic gene. Finally, Sanger sequencing and cDNA sequencing were used to verify the candidate genes. Half of parentage members had got hypercholesterolaemia. WES identified LDLR IVS8[−10] as a candidate mutation from 222,267 variations. The Sanger sequencing showed proband had a homozygous mutation inherited from his parents, and this loci were cosegregated with FH phenotype. The cDNA sequencing revealed that this mutations caused abnormal shearing. This mutation was first identified in Chinese patients, and this homozygous mutation is a new genetic type of FH. This is the first time that WES was used in Chinese FH patients. We detected a novel genetic type of LDLR homozygous mutation. WES is powerful tools to identify specific FH families with potentially pathogenic gene mutations.

Genetics of familial hypercholesterolemia.

Familial hypercholesterolemia (FH) is a genetic disorder characterized by elevated low-density lipoprotein (LDL) cholesterol and premature cardiovascular disease, with a prevalence of approximately 1 in 200-500 for heterozygotes in North America and Europe. Monogenic FH is largely attributed to mutations in the LDLR, APOB, and PCSK9 genes. Differential diagnosis is critical to distinguish FH from conditions with phenotypically similar presentations to ensure appropriate therapeutic management and genetic counseling. Accurate diagnosis requires careful phenotyping based on clinical and biochemical presentation, validated by genetic testing. Recent investigations to discover additional genetic loci associated with extreme hypercholesterolemia using known FH families and population studies have met with limited success. Here, we provide a brief overview of the genetic determinants, differential diagnosis, genetic testing, and counseling of FH genetics.

Novel and recurrent LDLR gene mutations in Pakistani hypercholesterolemia patients

The majority of patients with the autosomal dominant disorder familial hypercholesterolemia (FH) carry novel mutations in the low density lipoprotein receptor (LDLR) that is involved in cholesterol regulation. In different populations the spectrum of mutations identified is quite different and to date there have been only a few reports of the spectrum of mutations in FH patients from Pakistan. In order to identify the causative LDLR variants the gene was sequenced in a Pakistani FH family, while high resolution melting analysis followed by sequencing was performed in a panel of 27 unrelated sporadic hypercholesterolemia patients. In the family a novel missense variant (c.1916T > G, p.(V639G)) in exon 13 of LDLR was identified in the proband. The segregation of the identified nucleotide change in the family and carrier status screening in a group of 100 healthy subjects was done using restriction fragment length polymorphism analysis. All affected members of the FH family carried the variant and none of the non-affected members nor any of the healthy subjects. In one of the sporadic cases, two sequence changes were detected in exon 9, one of these was a recurrent missense variant (c.1211C > T; p.T404I), while the other was a novel substitution mutation (c.1214 A > C; N405T). In order to define the allelic status of this double heterozygous individual, PCR amplified fragments were cloned and sequenced, which identified that both changes occurred on the same allele. In silico tools (PolyPhen and SIFT) were used to predict the effect of the variants on the protein structure, which predicted both of these variants to have deleterious effect. These findings support the view that there will be a novel spectrum of mutations causing FH in patients with hypercholesterolaemia from Pakistan.

Identification of a recurrent insertion mutation in the LDLR gene in a Pakistani family with autosomal dominant hypercholesterolemia

Familial Hypercholesterolemia (FH) results in elevated levels of blood lipids including total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) with normal triglycerides (TG). This disease is one of the major contributors towards an early onset of coronary heart disease (CHD). The aim of the present study was to identify the genes responsible for causing FH in Pakistani population, for this purpose a large consanguineous FH family was selected for genetic analysis. Serum lipid levels, including TC, TG, LDL-C and high density lipoprotein cholesterol (HDL-C), were determined in patients and healthy controls. In order to find the causative mutation in this family, direct sequencing of the low density lipoprotein receptor (LDLR) gene was performed. In addition the part of the Apolipoprotein-B (APOB) gene containing the mutations R3500Q and R3500W was also sequenced. Affected individuals of the family were found to have raised TC and LDL-C levels. Sequencing revealed an insertion mutation (c.2416_2417InsG) in exon 17 of the LDLR gene in all the affected individuals of the family. Common FH causing APOB mutations were not present in this family. Heterozygous individuals had TC levels ranging from ~300-500 mg/dl and the only homozygous individual with typical xanthomas had TC levels exceeding 900 mg/dl. This is the first report of a known LDLR gene mutation causing FH in the Pakistani population. Despite a large heterogeneity of LDLR mutations there are still some common mutations which are responsible for FH throughout the world.

Two mutations in LDLR gene were found in two Chinese families with familial hypercholesterolemia

Familial hypercholesterolemia (FH) (OMIM 143890) is an autosomal dominantly inherited disease mainly caused by mutations of the gene encoding the low density lipoprotein receptor (LDLR) and Apolipoprotein (Apo) B. First the common mutation R3500Q in ApoB gene was determined using PCR/RFLP method. Then the LDLR gene was screened for mutations using Touch-down PCR, SSCP and sequencing techniques. Furthermore, the secondary structure of the LDLR protein was predicted with ANTHEPROT5.0. The R3500Q mutation was absent in these two families. A heterozygous p.W483X mutation of LDLR gene was identified in family A which caused a premature stop codon, while a homozygous mutation p.A627T was found in family B. The predicted secondary structures of the mutant LDLR were altered. We identified two known mutations (p.W483X, p.A627T) of the LDLR gene in two Chinese FH families respectively.

Limited mutational heterogeneity in the LDLR gene in familial hypercholesterolemia in Tunisia

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.