Identification of two LDL receptor mutations causing familial hypercholesterolemia in Indian subjects

Obesity: An Impact with Cardiovascular and Cerebrovascular Diseases

The authors sought to correlate the complex sequel of obesity with various parameters known to develop metabolic syndrome viz. insulin resistance, dyslipidemia, hypertension etc., as these anomalies are linked to vascular atherosclerosis and outbreak of cardiovascular and cerebrovascular diseases.  A comprehensive online survey using MEDLINE, Scopus, PubMed and Google Scholar was conducted for relevant journals from 1970 till present time (2023) with key search terms like: 'obesity', 'leptin', type-2 diabetes', 'atherosclerosis', 'cardiovascular and cerebrovascular diseases'. The findings of the reports were compared and correlated. The information was then collated for developing this review. Reports showed that in human obesity, hyper-leptinemia could induce hyperglycemia, which in turn templates hypercholesterolemia. Persisting hypercholesterolemia over a period of time may en-route atherosclerosis in blood vessels. Thus obesity has been considered as a template for originating hyperglycemia, hypercholesterolemia and outbreak of vascular atherogenesis or in other words, obesity in long run can trigger atherosclerosis and its related disorders e.g. heart attack and stroke. Literature survey shows that primarily, co-morbidities of human obesity start with leptin and insulin resistance and then multiplies with metabolic irregularities to an extreme that results in pathogenesis of heart attack and stroke. Atherosclerosis associated cardiovascular and cerebrovascular events are independent risks of obese subjects and particularly in the cases of persisting obesity.

Screening of PCSK9 and LDLR genetic variants in Familial Hypercholesterolemia (FH) patients in India

Familial Hypercholesterolemia (FH) is an autosomal, dominant, inherited disorder characterized by severely elevated LDL-cholesterol (LDL-C) levels with high risk for Coronary Artery Disease (CAD). There are limited genetic studies especially on genes other than Low Density Lipoprotein receptor (LDLR) conducted in Indian population. Thus, our aim was to screen the entire Proprotein Convertase Subtilisin/Kexin type 9 gene (PCSK9) gene & hotspot exons 3, 4 and 9 of LDLR gene in FH cases and controls. 50 FH cases were categorized into definite, probable and possible cases according to Dutch Lipid Network Criteria (DLNC) who were gender matched with 50 healthy controls. All 12 exons of PCSK9, and hotspot exons 3, 4 & 9 of LDLR gene were screened through High Resolution Melt (HRM) curve analysis. Enzyme linked immunosorbent assay was performed to measure circulating PCSK9 levels. Total cholesterol and LDL-C were significantly high in all three groups of cases. Total 8 nonpathogenic variants in exon 1, 5, 7 and 9 of the PCSK9 gene were detected. In LDLR gene, 3 known pathogenic and 1 benign variant were found in exon 3 & 4. In FH cases, PCSK9 levels were significantly high compared to controls (P = 0.0001), and were directly correlated to LDL-C (P = 0.0001) and Total Cholesterol (P = 0.0001). Our study is first to screen the entire PCSK9 gene in western part of India. Since no pathogenic variants were identified, it is possible that PCSK9 variants are clinically less relevant. However, 3 known pathogenic variants were found in the LDLR gene. These findings support our understanding of the genetic spectrum of FH in India.

Low-density lipoprotein receptor gene mutation at Exon 2 and 4 in premature coronary artery disease in our population

Objective

To determine the frequency of mutations in Low density lipoprotein receptor gene at exon 2 and 4 and its association with premature coronary artery disease (PCAD).

Methods

A case-control study was conducted at Armed Forces Institute of Cardiology and Chemical Pathology department of Army Medical College Rawalpindi for a period of six months from June 2017 to December 2017. A sample size of 50 (40 patients, 10 controls) with 5% significance and 95% confidence interval was calculated with 4:1 case to control ratio. Consecutive sampling was used for distribution of participants into both groups. .Diagnosed patients of premature coronary artery disease that is any cardiac event before the age of 45 in males and 50 in females were taken as cases. Controls were healthy males less than 45 years of age and females less than 50 years. Patients with diabetes mellitus, thyroid illnesses, any acute infection, low white blood cells count and kidney disorders were excluded. A total of fasting 10ml blood was withdrawn from each patient. 5ml was utilized for the routine blood tests and the rest 5ml was used for further genetic analysis.

Results

Total 50 participants were included in study. Mean age of participants in years was 42.48 ± 4.02 SD. Mean total cholesterol (TC) (mmol/l) were higher among cases (4.91±0.64 SD) than controls (4.22±0.66 SD). Serum triglyceride(Tg) (mmol/l) and low-density lipoprotein(LDL) (mmol/l) was also high among cases (2.07±0.58; 2.84±0.46) than controls (1.99±0.24; 1.98±0.32). One synonymous mutation in exon 2 of low-density lipoprotein receptor gene (LDLR) and one non-synonymous mutation in exon 4 (LDLR gene) were identified in our population in four patients among the forty cases. Data was analyzed by Statistical Package for the Social Science (SPSS) 21 version and a p-value of less than 0.05 was taken as significant.

Conclusion

Glutamic acid (E) is replaced by Lysine (K) at position number 207 (E207K) mutation at exon 4 of low-density lipoprotein receptor (LDLR) gene may be the causative genetic basis of premature coronary artery disease among Pakistani population. The identified synonymous mutation at exon 2 was not causative as there is no change in the amino acid.

Genetic analysis of Indian subjects with clinical features of possible type IIa hypercholesterolemia

We performed genetic analysis in 55 patients with clinical features of possible type IIa hypercholesterolemia and 76 normolipemic healthy subjects for mutations and polymorphisms in the low-density lipoprotein (LDL) receptor (LDLR), apolipoprotein B-100 (APOB), apolipoprotein E (APOE), and hepatic lipase (LIPC) genes to elucidate the important genetic factors that can influence cholesterol levels in our population. None of the subjects showed mutations in part of exon 26 of the APOB gene, whereas two class 5 mutations were identified in exon 9 of the LDLR gene. First, an E387K mutation was observed in a Gujarati family in which both the parents were heterozygous for the mutation. Second, a L393R mutation was observed in a 38-year-old female. We found no correlation between LIPC -514C/T genotypes and cholesterol levels whereas the apoepsilon4 allele frequency was significantly higher in cases and the apoE4 genotype was found to influence total cholesterol levels.

Update of the molecular basis of familial hypercholesterolemia in The Netherlands

Autosomal-dominant hypercholesterolemia (ADH) has been identified as a major risk factor for coronary vascular disease (CVD) and is associated with mutations in the low-density lipoprotein receptor (LDLR) and the apolipoprotein B (APOB) gene. Since 1991 DNA samples from clinically diagnosed ADH patients have been routinely analyzed for the presence of LDLR and APOB gene mutations. As of 2001, 1,641 index patients (164 index patients per year) had been identified, while from 2001 onward a more sensitive, high-throughput system was used, resulting in the identification of 1,177 new index patients (average=294 index patients per year). Of these 1,177 index cases, 131 different causative genetic variants in the LDLR gene and six different causative mutations in the APOB gene were new for the Dutch population. Of these 131 mutations, 83 LDLR and four APOB gene mutations had not been reported before. The inclusion of all 2,818 index cases into the national screening program for familial hypercholesterolemia (FH) resulted in the identification of 7,079 relatives who carried a mutation that causes ADH. Screening of the LDLR and APOB genes in clinically diagnosed FH patients resulted in approximately 77% of the patients being identified as carriers of a causative mutation. The population of patients with ADH was divided into three genetically distinct groups: carriers of an LDLR mutation (FH), carriers of an APOB mutation (FDB), and non-LDLR/non-APOB patients (FH3). No differences were found with regard to untreated cholesterol levels, response to therapy, and onset of CVD. However, all groups were at an increased risk for CVD. Therefore, to ultimately identify all individuals with ADH, the identification of new genes and mutations in the genes that cause ADH is of crucial importance for the ongoing national program to identify patients with ADH by genetic cascade screening.

Gene polymorphism and coronary risk factors in Indian population

Asian Indians who have settled overseas and those in urban India have increased risk of coronary events. Reasons for this increased risk are thought to be genetic but are yet unclear. Advances in molecular cardiology have revealed a number of single nucleotide polymorphisms associated with atherosclerosis. In this review, gene polymorphisms that have been associated with coronary diseases among Indians are discussed. Topics include the genes involved in hyperlipidemia, hypertension, and homocysteine. Mutations in the low-density lipoprotein receptor (LDLR) gene resulting in familial hypercholesterolemia have strong association with premature atherosclerosis. Common polymorphism of the apolipoproteins (apo) B-100 and E genes have been associated with variation in lipid and lipoprotein levels. Recently identified polymorphisms in the apoC3 (T-455C, C-482T), and cholesteryl ester transfer protein (CETP) (B1/B2 allele) genes are associated with increased triglycerides and reduced high-density lipoprotein (HDL)-levels, a feature now also common among Asian Indians. Angiotensin-converting enzyme-deletion (DD) polymorphism has been shown to influence beta-blocker therapy in heart failure. Mutations in methylenetetrahydrofolate reductase (C667T), cystathionine beta-synthase (T833C), and methionine synthase (A2756G) genes cause hyperhomocysteinemia, an independent risk factor for atherothrombosis. As the genetics of atherosclerosis continues to evolve, these factors along with the newer emerging factors may become a part of the routine assessment, aiding prediction of future coronary events.

Molecular basis of familial hypercholesterolemia: An Indian experience

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by a multitude of low-density lipoprotein (LDL) receptor gene mutations. The LDL receptor is a cell surface trans-membrane protein that mediates the uptake & lysosomal degradation of plasma LDI., thereby providing cholesterol to cells. Affected individuals have elevated plasma levels of LDL, which causes premature coronary atherosclerosis. FH has an estimated worldwide prevalence of 0.2%. In some subpopulations there is an increased frequency of FH and specific LDL receptor mutations are found to be common due to 'founder gene effect'. Overall, more than 300 naturally occurring LDL receptor mutations have been described. To data upto ten LDL receptor gene mutations have been identified in Indians in South Africa, suggesting increased incidence of FH among Indians. Most mutations have occurred at CpG dinucleotide, a mutational hotspot in human genetic disease. In our study in 25 hypercholesterolemic subjects we have identified two novel insertion mutations in two patients. But the mutations underlying FH are still undefined in the majority of cases. Mutational heterogeneity on the other-hand has complicated disease diagnosis at DNA level. These findings warrant application of a generalized mutation screening method in search for new LDL receptor gene defects.