Familial hypercholesterolemia mutations in Petrozavodsk: no similarity to St. Petersburg mutation spectrum

A familial hypercholesterolemia registry as the main tool for adequate management of the disease

Familial hypercholesterolemia (FH) is the most common, but poorly diagnosed autosomal-dominant genetic disease which increases the cardio-vascular risk.

AIM

To evaluate the experience of FH registry conducted in Karelia Republic.

METHODS

FH registry in Karelia is existing from 2004, it includes 350 patients with heterozygous FH (110 with definite FH), the mean age is 48 ± 2.3 years. The genetic study was performed in 102 patients (29.1%).

RESULT

The creation of the registry has contributed to the active identification of FH, and now the estimated frequency of FH occurrence in Karelia may be 1:300, in patients with cardiovascular disease 1:10. We also analyzed genetic features of FH in our republic and found that the LDL-C level, above which the probability of LDL receptor mutation increases in Karelia, is 6.5 mmol/L. We analyzed risk factors of ischemic heart disease and the prognosis in FH.

CONCLUSION

The creation and maintenance of a registry is an effective way of organizing timely diagnosis and adequate treatment of FH patients.

Analysis of Clinical and Biochemical Characteristics of Patients With Genetically Confirmed Familial Hypercholesterolemia in Russian North Western District Residents

Aim      To compare results of clinical, laboratory, and genetic examination of patients with familial hypercholesterolemia (FHC).

Material and methods  112 patients aged 40.2±17.9 years (49 men) were examined. The gene of low-density lipoprotein receptor (LDLR) was analyzed and evaluated using the Dutch Lipid Clinic Network (DLCN) criterion of lipid score ≥6. The LDLR gene mutation was searched for using the conformational polymorphism analysis followed by sequencing of the DNA of isolated LDLR gene exons.

Results Mean variables of the blood lipid profile were total cholesterol (C), 10.12±2.32 mmol/l, LDL-C, 7.72±2.3 mmol/l. Corneal arcus was observed in 15 % of patients, tendon xanthomas in 31.8 %, and xanthelasma palpebrarum in 5.3 %. The types of LDLR gene mutations included missense mutations (42.8 %), mutations causing a premature termination of protein synthesis (41.1 %), and frameshift mutations (16.1 %). In the presence of a mutation in exon 4, patients with IHD compared to patients with no IHD had significantly higher levels of total C (10.88±2.08 mmol/l vs. 8.74±1.57 mmol/l, respectively, р=0.001) and LDL-C (8.60±2.14 mmol/l vs. 6.62±1.79 mmol/l, respectively, р=0.005). Patients with IHD compared to patients with no IHD and a mutation in LDLR gene exon 9 had only a higher LDL-C level (8.96±1.53 mmol/l vs. 6.92±1.59 mmol/l, respectively, р=0.022). A differentiated comparison of IHD patients using a logistic regression depending on the identified type of LDLR gene mutation produced formulas for calculating the odds ratio of IHD and myocardial infarction (MI) with adjustments for the patient’s age and baseline LDL.

Conclusion      The detection rate of the LDLR gene mutations was 42.8 % for missense mutations, 41.1 % for mutations causing a premature termination of protein synthesis, and 16.1 % for frameshift mutations. Blood lipid profiles did not differ between patients from different cities and with different types of LDLR gene mutations. Blood lipid profiles were different in IHD patients depending on the mutation type.

Analysis of the low density lipoprotein receptor gene (<i>LDLR</i>) mutation spectrum in Russian familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a very common human hereditary disease in Russia and in the whole world with most of mutations localized in the gene coding for the low density lipoprotein receptor (LDLR). The object of this review is to systematize the knowledge about LDLR mutations in Russia. With this aim we analyzed all available literature on the subject and tabulated the data. More than 1/3 (80 out of 203, i. e. 39.4 %) of all mutations reported from Russia were not described in other populations. To date, most LDLR gene mutations have been characterized in large cities: Moscow (130 entries), Saint Petersburg (50 entries), Novosibirsk (34 mutations) and Petrozavodsk (19 mutations). Other regions are poorly studied. The majority of pathogenic mutations (142 out of 203 reported here or 70 %) were revealed in single pedigrees; 61 variants of mutations were described in two or more genealogies; only 5 mutations were found in 10 or more families. As everywhere, missense mutations prevail among all types of nucleotide substitutions in LDLR, but the highest national specificity is imparted by frameshift mutations: out of 27 variants reported, 19 (or 70 %) are specific for Russia. The most abundant in mutations are exons 4 and 9 of the gene due to their largest size and higher occurrence of mutations in them. Poland,the Czech Republic, Italy and the Netherlands share the highest number of mutations with the Russian population. Target sequencing significantly accelerates the characterization of mutation spectra in FH, but due to the absence of systematic investigations in the regions, one may suggest that most of LDLR mutations in the Russian population have not been described yet.

Genetic Diagnostic Approaches in Familial Hypercholesterolemia Evaluation

Familial hypercholesterolemia (FH) manifested as atherosclerosis is a major cause of coronary heart disease. Different scoring systems based on clinical and paraclinical data are currently used, but the FH diagnosis should be made only in the presence of the causative genetic defect. In the present study, 12 symptomatic (previously diagnosed with atherosclerosis) and asymptomatic family members were investigated. Serum lipids were measured using commercial reagents. A genetic investigation was performed by Sanger sequencing using commercial reagents and custom primers, while copy number variations and a selected set of 40 point mutations were evaluated using in vitro diagnostic medical devices. For the investigated patients, serum lipids were within the reference range, due to the fact that the subjects were following lipid-lowering therapy, and smoking was the only identifiable additional risk factor. Four benign exon variants and three intron variants situated within the low-density lipoprotein cholesterol receptor gene were identified by Sanger sequencing. No copy number variations and none of the 40 investigated point mutations were determined. Although independently considered benign, the combined effect of the identified genetic conditions could be pathogenic under the influence of additional risk factors. Even in the presence of a diagnosis made using clinical scores, the molecular diagnosis is often challenging, attesting to the complexity of FH genetic etiology.

Molecular Genetic Approach and Evaluation of Cardiovascular Events in Patients with Clinical Familial Hypercholesterolemia Phenotype from Romania

This study identifies the genetic background of familial hypercholesterolemia (FH) patients in Romania and evaluates the association between mutations and cardiovascular events. We performed a prospective observational study of 61 patients with a clinical diagnosis of FH selected based on Dutch Lipid Clinic Network (DLCN) and Simon Broome score between 2017 and 2020. Two techniques were used to identify mutations: multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing. The mutation rate was 37.7%, i.e., 23 patients with mutations were identified, of which 7 subjects had pathogenic mutations and 16 had polymorphisms. Moreover, 10 variants of the low-density lipoprotein receptor (LDLR) gene were identified in 22 patients, i.e., one variant of the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene in six patients, and one variant of the apolipoprotein B (APOB) gene in three patients. Of the LDLR gene variants, four were LDLR pathogenic mutations (c.81C > G, c.502G > A, c.1618G > A mutations in exon 2, exon 4, exon 11, and exon 13–15 duplication). The PCSK9 and APOB gene variants were benign mutations. The pathogenic LDLR mutations were significant predictors of the new cardiovascular events, and the time interval for new cardiovascular events occurrence was significantly decreased, compared to FH patients without mutations. In total, 12 variants were identified, with four pathogenic variants identified in the LDLR gene, whereas 62.3% of the study population displayed no pathological mutations.

The LDLR, APOB, and PCSK9 Variants of Index Patients with Familial Hypercholesterolemia in Russia

Familial hypercholesterolemia (FH) is a common autosomal codominant disorder, characterized by elevated low-density lipoprotein cholesterol levels causing premature atherosclerotic cardiovascular disease. About 2900 variants of LDLR, APOB, and PCSK9 genes potentially associated with FH have been described earlier. Nevertheless, the genetics of FH in a Russian population is poorly understood. The aim of this study is to present data on the spectrum of LDLR, APOB, and PCSK9 gene variants in a cohort of 595 index Russian patients with FH, as well as an additional systematic analysis of the literature for the period of 1995-2020 on LDLR, APOB and PCSK9 gene variants described in Russian patients with FH. We used targeted and whole genome sequencing to search for variants. Accordingly, when combining our novel data and the data of a systematic literature review, we described 224 variants: 187 variants in LDLR, 14 variants in APOB, and 23 variants in PCSK9. A significant proportion of variants, 81 of 224 (36.1%), were not described earlier in FH patients in other populations and may be specific for Russia. Thus, this study significantly supplements knowledge about the spectrum of variants causing FH in Russia and may contribute to a wider implementation of genetic diagnostics in FH patients in Russia.

Familial Hypercholesterolemia in Russia: Three Decades of Genetic Studies

The first studies of familial hypercholesterolemia (FH) in Russia go back to late 1980-ies. For more than 10 years the research in this field was carried out in Saint-Petersburg, the megapolis in the North-West Russia. Studies were focused on the search for causative mutations in low-density lipoprotein receptor gene (LDLR). Gradually the research was spread to Petrozavodsk in Karelia and in the XXI century two more centers contributed in investigations of genetics of FH, i.e., in Moscow and Novosibirsk. The best studied is the spectrum of mutations in LDLR, though genetic abnormalities in APOB and PCSK9 genes were also considered. Despite that some 40% mutations in LDLR found in Saint-Petersburg and Moscow are referred to as specific for Russian population, and this proportion is even higher in Karelia (ca. 70%), rapid introduction of NGS and intensifying genetic research all over the world result in continuous decrease of these numbers as "Slavic" mutations become documented in other countries. The samplings of genetically characterized patients in Russia were relatively small, which makes difficult to specify major mutations reflecting the national specificity of FH. Moreover, the majority of studies accomplished so far did not explore possible associations of certain mutations with ethnic origin of patients. By now the only exception is the study of Karelian population showing the absence of typical Finnish mutations in the region that borders on Finland. It can be concluded that the important primary research partly characterizing the mutation spectrum in FH patients both in the European and Siberian parts of Russia has been done. However, it seems likely that the most interesting and comprehensive genetic studies of FH in Russia, concerning various mutations in different genes and the variety of ethnic groups in this multi-national country, are still to be undertaken.

Identification of novel variants in the LDLR gene in Russian patients with familial hypercholesterolemia using targeted sequencing

Familial hypercholesterolemia (FH) is caused by mutations in various genes, including the LDLR, APOB and PSCK9 genes; however, the spectrum of these mutations in Russian individuals has not been fully investigated. In the present study, mutation screening was performed on the LDLR gene and other FH-associated genes in patients with definite or possible FH, using next-generation sequencing. In total, 59 unrelated patients were recruited and sorted into two separate groups depending on their age: Adult (n=31; median age, 49; age range, 23-70) and children/adolescent (n=28; median age, 11; age range, 2-21). FH-associated variants were identified in 18 adults and 25 children, demonstrating mutation detection rates of 58 and 89% for the adult and children/adolescent groups, respectively. In the adult group, 13 patients had FH-associated mutations in the LDLR gene, including two novel variants [NM_000527.4: c.433_434dupG p.(Val145Glyfs*35) and c.1186G>C p.(Gly396Arg)], 3 patients had APOB mutations and two had ABCG5/G8 mutations. In the children/adolescent group, 21 patients had FH-causing mutations in the LDLR gene, including five novel variants [NM_000527.4: c.325T>G p.(Cys109Gly), c.401G>C p.(Cys134Ser), c.616A>C p.(Ser206Arg), c.1684_1691delTGGCCCAA p.(Pro563Hisfs*14) and c.940+1_c.940+4delGTGA], and 2 patients had APOB mutations, as well as ABCG8 and LIPA mutations, being found in different patients. The present study reported seven novel LDLR variants considered to be pathogenic or likely pathogenic. Among them, four missense variants were located in the coding regions, which corresponded to functional protein domains, and two frameshifts were identified that produced truncated proteins. These variants were observed only once in different patients, whereas a splicing variant in intron 6 (c.940+1_c.940+4delGTGA) was detected in four unrelated individuals. Previously reported variants in the LDLR, APOB, ABCG5/8 and LIPA genes were observed in 33 patients. The LDLR p.(Gly592Glu) variant was detected in 6 patients, representing 10% of the FH cases reported in the present study, thus it may be a major variant present in the Russian population. In conclusion, the present study identified seven novel variants of the LDLR gene and broadens the spectrum of mutations in FH-related genes in the Russian Federation.

Genetics of Familial Hypercholesterolemia: New Insights

Familial hypercholesterolemia (FH) is one of the most common monogenic diseases, leading to an increased risk of premature atherosclerosis and its cardiovascular complications due to its effect on plasma cholesterol levels. Variants of three genes (LDL-R, APOB and PCSK9) are the major causes of FH, but in some probands, the FH phenotype is associated with variants of other genes. Alternatively, the typical clinical picture of FH can result from the accumulation of common cholesterol-increasing alleles (polygenic FH). Although the Czech Republic is one of the most successful countries with respect to FH detection, approximately 80% of FH patients remain undiagnosed. The opportunities for international collaboration and experience sharing within international programs (e.g., EAS FHSC, ScreenPro FH, etc.) will improve the detection of FH patients in the future and enable even more accessible and accurate genetic diagnostics.

Cholesterol Levels in Genetically Determined Familial Hypercholesterolaemia in Russian Karelia

Familial hypercholesterolaemia (FH) is a rare disease that tends to be diagnosed lately. In Russia, the genetic and phenotypic characteristics of the disease are not well defined. We investigated 102 patients with definite FH. In 52 of these patients (50.9%) genetic analysis was performed, revealing pathogenic mutations of the low density lipoprotein (LDL) receptor gene in 22 patients. We report here five mutations of the LDL receptor gene found in the Karelian FH sample for the first time. The detection rate of mutations in definite FH patients was 42.3%. Two groups of patients with a definite diagnosis of FH according to the Dutch Lipid Clinic Network criteria were compared: the first group had putatively functionally important LDL receptor gene mutations, while in the second group LDL receptor gene mutations were excluded by single-strand conformation polymorphism analysis. Total and LDL cholesterol levels were higher in the group with LDL receptor mutations compared to the mutation-free population. The frequency of mutations in patients with LDL cholesterol > 6.5 mmol/L was more than 3 times higher than that in patients with LDL < 6.5 mmol/L. Total and LDL cholesterol levels and the frequency of coronary heart disease and myocardial infarction were higher in the group with definite FH compared to groups with probable and possible FH. Cholesterol figures in FH patients of different age and sex from the Karelian population were comparable.