The D9N, N291S and S447X variants in the lipoprotein lipase (LPL) gene are not associated with Type III hyperlipidemia

Genetic risk score in patients with the APOE2/E2 genotype as a predictor of familial dysbetalipoproteinemia

BACKGROUND

Familial dysbetalipoproteinemia (FD) is an autosomal recessive (rarely dominant) inherited disorder that is almost exclusively associated with the apolipoprotein E gene (APOE) variability. Nonetheless, only a small proportion of APOE2/E2 subjects develop the phenotype for mixed dyslipidemia; the context of other trigger metabolic or genetic factors remains unknown.

METHODS

One hundred and one patients with FD and eighty controls (all APOE2/E2 homozygotes; rs429358) were screened for 18 single-nucleotide polymorphisms (SNPs) within the genes involved in triglyceride metabolism.

RESULTS

Two SNPs were significantly associated with the FD phenotype (rs439401 within APOE; P < 0.0005 and rs964184 within ZPR1/APOA5/A4/C3/A1 gene cluster; P < 0.0001). Unweighted genetic risk scores - from these two SNPs (GRS2), and, also, additional 13 SNPs with P-value below 0.9 (GRS15) - were created as an additional tool to improve the risk estimation of FD development in subjects with the APOE2/E2 genotype. Both GRS2 and GRS15 were significantly (P < 0.0001) increased in patients and both GRSs discriminated almost identically between the groups (P = 0.86). Subjects with an unweighted GRS2 of three or more had an almost four-fold higher risk of FD development than other individuals (odds ratio (OR) 3.58, 95% confidence interva (CI): 1.78-7.18, P < 0.0005).

CONCLUSIONS

We identified several SNPs that are individual additive factors influencing FD development. The use of unweighted GRS2 is a simple and clinically relevant tool that further improves the prediction of FD in APOE2/E2 homozygotes with corresponding biochemical characteristics.

The influence of LPL S447X variants and obesity on lipid profile, oxidative stress, and the risk of T2DM: A case-control study

Aims

The present study aimed to investigate the association between lipoprotein lipase (LPL) S447X polymorphism and type 2 diabetes mellitus (T2DM), obesity, lipid profile, and oxidative stress parameters in a population from the Kurdistan region of Iraq.

Method

We studied 250 adults (51% female and 49% male) aged 45-65 years in four groups, obese and normal body mass index (BMI) diabetic patients versus healthy normal BMI and obese individuals as controls. Lipid profile and oxidative stress parameters were analyzed by colorimetric assay. The LPL S447X genotypes were detected by polymerase chain reaction (PCR)-restriction fragment length polymorphism.

Results

We found that the obese diabetic group had higher levels of triglycerides (TG), cholesterol, and low-density lipoprotein-cholesterol, and lower level of high-density lipoprotein-cholesterol than other groups. Obese diabetic patients had higher anthropometric indices than nonobese diabetic patients, obese and normal BMI controls. The levels of TG and total oxidative status (TOS) were significantly lower and higher, respectively, in normal BMI controls than in obese controls. Obese diabetic patients had a lower level of total antioxidant capacity than nondiabetic obese controls. The level of TOS was lower in nondiabetic controls compared to the patient groups. Obese diabetic patients had the highest TOS and malondialdehyde levels. The LPL SX genotype was associated with decreased the risk of T2DM by 79% (odds ratio [OR] = 0.21; 95% confidence interval [CI]: 0.05-0.81, p = 0.03). Also, the presence of this genotype reduced the risk of obesity by 39% (OR = 0.61; 95% CI: 0.07-4.90, p = 0.6). In all individuals, the presence of the SX genotype was associated with significantly lower levels of fasting blood sugar (FBS) and TOS.

Conclusion

We report the influence of obesity on lipid profile in diabetic and nondiabetic individuals and the effect of LPL SX genotype on decreased risk of T2DM and reduced levels of FBS and TOS.

Familial dysbetalipoproteinemia: highly atherogenic and underdiagnosed disorder

Familial dysbetalipoproteinemia (FD) is a genetic, highly atherogenic disorder. The penetrance of FD depends on the patient’s lifestyle and concomitant diseases. Despite the fact that FD was described almost half a century ago, it is still insufficiently studied and is extremely rarely diagnosed. In actual clinical practice, physicians do not have clear understanding of clinical course and genetic basis of FD. The aim was to present the most complete, but at the same time a critical review with a modern view on FD. We analyzed Russian and foreign publications from following electronic databases: PubMed, eLIBRARY, Google Scholar. As a result, the phenotypic features and genetic variability of the disease were considered and the main issues of diagnosis and treatment of patients with FD were discussed. The data presented will help the clinician to timely suspect the FD, conduct a full range of investigations and prescribe evidence-based lipid-lowering therapy.

Identification of mutations in the lipoprotein lipase (LPL) and apolipoprotein C-II (APOC2) genes using denaturing high performance liquid chromatography (DHPLC)

BACKGROUND

Endothelial lipoprotein lipase (LPL) hydrolyzes triglycerides of chylomicrons and very low density lipoproteins, releasing free fatty acids for local and systemic use. Mutations in the LPL gene or its cofactor APOC2 may result in a decrease or complete loss of enzyme function and subsequently to type I hyperlipoproteinemia.

METHODS

We used PCR to amplify all exons and the promoter region of LPL and APOC2. Nine blinded DNA samples with known LPL mutations were used as positive controls. In addition, nine patients from our lipid clinic and twelve healthy subjects were analyzed. DNA was screened for sequence variants by denaturing HPLC (DHPLC) followed by direct sequencing of PCR fragments showing distinct elution profiles.

RESULTS

All LPL sequence variants in the positive controls (D9N, V69L, delAACTG386, I225T, N291S, and S447X) were correctly identified. In the remaining patients, additional variants were detected in LPL and APOC2. These variants were also present in healthy subjects, indicating that they constituted silent variation with no relevant effect on plasma triglycerides, at least in the heterozygous state.

CONCLUSIONS

A semi-automated DHPLC screening method was developed for the detection of sequence variants in the LPL and APOC2 genes. Our results demonstrate that the method was robust and sensitive.

Rare variants in the lipoprotein lipase (LPL) gene are common in hypertriglyceridemia but rare in Type III hyperlipidemia

OBJECTIVE

Genomewide association studies (GWAS) have shown that variation in the lipoprotein lipase gene (LPL) is associated with plasma triglyceride levels but that common variants account for only 1.25% of the variance. The aim of this study was to determine the frequency of rare variants in the LPL gene in patients with various forms of hypertriglyceridemia.

METHODS

The DNA sequence of the exons plus exon/intron boundaries of the LPL gene of 313 patients with triglycerides above the 95th percentile for age and sex (107 of whom had triglycerides above 875 mg/dl) and 121 patients with Type III hyperlipidemia was determined.

RESULTS

Twenty rare variants were detected of which seven have been previously reported. All of the rare variants were present as heterozygotes. Sixteen were missense mutations, two were short deletion mutants and there were single nonsense and insertion mutations. Fifteen of the missense mutations resulted in an amino acid change. There were 13 patients (12.1%) with triglycerides above 875 mg/dl and 10 patients (4.9%) with moderately elevated triglycerides, who were carriers of at least one rare, non-synonymous mutation in the LPL gene. Of the patients with Type III HLP, two were carriers of rare variants.

CONCLUSION

Rare mutations in the LPL gene are frequent in patients with elevated triglycerides.

The expression of type III hyperlipoproteinemia: involvement of lipolysis genes

Type III hyperlipoproteinemia (HLP) is mainly found in homozygous apolipoprotein (APO) E2 (R158C) carriers. Genetic factors contributing to the expression of type III HLP were investigated in 113 hyper- and 52 normolipidemic E2/2 subjects, by testing for polymorphisms in APOC3, APOA5, HL (hepatic lipase) and LPL (lipoprotein lipase) genes. In addition, 188 normolipidemic Dutch control panels (NDCP) and 141 hypertriglyceridemic (HTG) patients were genotyped as well. No associations were found for four HL gene polymorphisms and two LPL gene polymorphisms and type III HLP. The frequency of the rare allele of APOC3 3238 G>C and APOA5 -1131 T>C (in linkage disequilibrium) was significantly higher in type III HLP patients when compared with normolipidemic E2/2 subjects, 15.6 vs 6.9% and 15.1 vs 5.8%, respectively, (P<0.05). Furthermore, the frequencies of the APOA5 c.56 G>C polymorphism and LPL c.27 G>A mutation were higher in type III HLP patients, though not significant. Some 58% of the type III HLP patients carried either the APOA5 -1131 T>C, c.56 G>C and/or LPL c.27 G>A mutation as compared to 27% of the normolipidemic APOE2/2 subjects (odds ratio 3.7, 95% confidence interval=1.8-7.5, P<0.0001). The HTG patients showed similar allele frequencies of the APOA5, APOC3 and LPL polymorphisms, whereas the NDCP showed similar allele frequencies as the normolipidemic APOE2/2. Patients with the APOC3 3238 G>C/APOA5 -1131 T>C polymorphism showed a more severe hyperlipidemia than patients without this polymorphism. Polymorphisms in lipolysis genes associate with the expression and severity of type III HLP in APOE2/2.