Identification and characterization of novel low-density lipoprotein receptor mutations of familial hypercholesterolaemia patients in Taiwan

Genetic Diagnosis of Familial Hypercholesterolemia in Asia

Familial hypercholesterolemia (FH) is a common genetic disease with an incidence of about 1 in 200-500 individuals. Genetic mutations markedly elevate low-density lipoprotein cholesterol and atherosclerotic cardiovascular disease (ASCVD) in FH patients. With advances in clinical diagnosis and genetic testing, more genetic mutations have been detected, including those in low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9), and so on. Globally, most FH patients remain undiagnosed, untreated, or inappropriately treated. Recently, there was a Global Call to Action by the Global Familial Hypercholesterolemia Community to reduce the health burden of FH. Asia, despite being the most populous continent with half of the global population, has low FH detection rates compared to Western countries. Therefore, we aimed to review the current status of FH genetic diagnosis in Asia to understand the gaps in FH diagnosis and management in this region.

Cascade screening for familial hypercholesterolemia-identification of the C308Y mutation in multiple family members and relatives for the first time in mainland China

Background

Familial hypercholesterolemia (FH), an autosomal dominant genetic disorder, is underdiagnosed and undertreated. The majority of FH cases are caused by low density lipoprotein receptor (LDL-R) gene mutations. The C308Y mutation in LDL-R results in approximately 70% loss of LDL-R activity, leading to the elevation of low density lipoprotein-cholesterol (LDL-C) and an increased risk of premature coronary heart disease (CHD). The aim of this study was to identify FH cases by cascade screening in family members and relatives of a 37-year old male with premature CHD and hypercholesterolemia.

Methods

Clinical exam, blood lipid profiling and genomic DNA sequencing of all exons of LDL-R were performed for the proband and his 14 family members and relatives. FH diagnosis was carried out using the Dutch Lipid Clinic Network (DLCN) criteria.

Results

Lipid profiling showed that 9 individuals, including the proband, had hypercholesterolemia. All these 9 subjects had a G > A substitution at nucleotide 986 in exon 7 resulting in the C308Y mutation as determined by DNA sequencing, and all those carrying the mutation were diagnosed as having definite FH under the DLCN criteria. However, most (7/9) did not have suggestive clinical manifestations of CHD.

Conclusions

The C308Y mutation was discovered in multiple family members and relatives for the first time in mainland China. Cascade screening is key for the confirmatory diagnosis of FH. Our hypothesis that the C308Y is a common variant in the population of Southern China origin warrants further validation by screening for the C308Y mutation in a large population.

Association between serum sulfatide and carotid intima media thickness in patients with familial hypercholesterolemia

There is a positive association between sulfatide and atherosclerosis in an animal model for human familial hypercholesterolemia. Carotid intima-media thickness (IMT) is thought to be a marker of atherosclerosis in humans. We investigated the relationship between sulfatide and carotid IMT in heterozygous familial hypercholesterolemia (FH) patients. Thirty-five genetically-verified heterozygous patients with FH and 34 healthy controls were recruited into our study. We measured serum sulfatide levels, the carotid IMT, and conventional cardiovascular risk factors including obesity parameters, blood pressure, fasting blood glucose, and lipid profiles. Subjects with heterozygous FH had significantly elevated serum sulfatide, elevated total cholesterol, low-density lipoprotein cholesterol, and increased carotid IMT compared with control subjects. In patients with FH, univariate analysis showed that serum sulfatide was significantly correlated with carotid IMT. Multiple linear regression analysis indicated that serum sulfatide was the only independent predictor of carotid IMT in patients with FH. Patients with heterozygous FH had significantly higher carotid IMT and the level of serum sulfatide was independently associated with atherosclerotic progression. (R: 0.720, R(2): 0.503, p < 0.001).

Detection of mutations and large rearrangements of the low-density lipoprotein receptor gene in Taiwanese patients with familial hypercholesterolemia

Familial hypercholesterolemia (FH) is commonly caused by mutations in the low-density lipoprotein receptor (LDLR), apolipoprotein B, and proprotein convertase subtilisin/kexin type 9 genes. The study aim was to investigate patients with FH in Taiwan, using molecular diagnostic methods, and compare the abnormalities in the small mutation and large DNA rearrangement subgroups. In total, 102 unrelated probands with FH were tested for mutations by exon-by-exon sequence analysis (EBESA) and multiple ligation-dependent probe amplification (MLPA). EBESA identified gene apolipoprotein B R3500W in 8 probands and 25 mis-sense, 5 nonsense, and 6 frameshift LDLR mutations in 52 probands; 11 were novel mutations. Of the 42 probands with mutations undetected by EBESA, 8 had abnormal MLPA patterns, including 2 with exon 6 to 18 deletions, 2 with exon 9 deletion, 1 with exon 6 to 8 deletions, 1 with exon 11 deletion, 1 with exon 3 to 5 duplications, and 1 with exon 7 to 12 duplications. Pedigree analysis showed mutation cosegregation with hypercholesterolemia in affected family members. Mean lipid profiles and rate of failure to lower LDL cholesterol <100 mg/dl in response to rosuvastatin/ezetimibe treatment were similar in groups with abnormal MLPA patterns and groups carrying nonsense or frameshift mutations. In conclusion, frequency of large LDLR rearrangement was approximately 8% in Taiwanese patients with FH. The response to statin drugs differed between probands with abnormal MLPA patterns and probands carrying mis-sense or undetected mutations.

Relation of C-reactive protein and carotid intima media thickness in Taiwanese with familial hypercholesterolemia

The aim of this study was to investigate the potential relationships between the carotid intima media thickness (carotid IMT), high sensitive C-reactive protein (hsCRP), and cholesterol burden in heterozygous familial hypercholesterolemia (FH) subjects. Thirty-two genetically-verified heterozygous patients with FH and 34 healthy controls were recruited into our study in Taiwan. We measured conventional risk factors, hsCRP, and carotid IMT of study subjects. The cholesterol-year score was used to estimate the lifetime cholesterol burden. Subjects with heterozygous FH had significantly elevated total cholesterol, elevated low-density lipoprotein cholesterol, and increased carotid IMT compared with control subjects. Carotid IMT correlated well with the cholesterol-year score. In patients with FH, univariate analysis showed that hsCRP was highly correlated with carotid IMT. Multiple linear regression analysis indicated that hsCRP was the only independent predictor of carotid IMT in patients with FH. In conclusion, patients with heterozygous FH had significantly higher carotid IMT and the level of hsCRP was independently associated with atherosclerotic progression. (R: 0.639, R(2): 0.408, p <0.001).

LDLR and ApoB are major genetic causes of autosomal dominant hypercholesterolemia in a Taiwanese population

BACKGROUND/PURPOSE

Autosomal dominant hypercholesterolemia (ADH) is an autosomal dominant inherited disease characterized by an increase in low-density lipoprotein cholesterol levels and premature coronary heart disease, which can be caused by mutations in genes encoding the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB) and proprotein convertase subtilisin/kexin type 9 (PCSK9). There is scant information with regard to the role played by each gene in the Taiwanese ADH population, especially the newly discovered PCSK9 gene.

METHODS

We used coupling heteroduplex analysis based on a denaturing high performance liquid chromatography system and DNA sequencing to screen for the LDLR gene, APOB gene and PCSK9 gene in 87 ADH cases recruited from 30 unrelated Taiwanese families.

RESULTS

We did not find any mutation-causing variant of the PCSK9 gene in our cases and thus excluded PCSK9 as the major culprit mutation in these families. On the other hand, we identified six previously reported LDLR gene mutations (C107Y, D69N, R385W, W462X, G170X, V408M), two novel LDLR gene mutations (FsG631 and splice junction mutation of intron 10), and one known mutation (R3500W) and one novel missense mutation (T3540M) in the APOB gene that were present in 55 members from 18 ADH families (60%). R3500W, rather than R3500Q, could be the principle mutation responsible for familial defective apolipoprotein B in Taiwanese.

CONCLUSION

The results of our study reveal a characteristic mutation pattern of ADH in Taiwan, mainly in the LDLR and APOB genes. However, PCSK9 gene mutation may not be a major cause of ADH in our study population.

Relation of coronary artery calcium to flow-mediated dilation and C-reactive protein levels in asymptomatic patients with heterozygous familial hypercholesterolemia

The extent of coronary artery calcium (CAC) is correlated with coronary artery disease prognosis. However, the relation of CAC to endothelial function and high-sensitivity C-reactive protein (hs-CRP) in patients with asymptomatic heterozygous familial hypercholesterolemia (FH) requires clarification. The study aim was to investigate the relations among CAC, endothelial function, and hs-CRP in patients with asymptomatic heterozygous FH. Thirty-two patients with asymptomatic heterozygous FH (mean age 42 years) and 34 healthy control subjects (mean age 36 years) were enrolled. We measured CAC by electron-beam computed tomography and endothelial function by flow-mediated dilation of the brachial artery. A higher percentage of patients with FH had a positive CAC score compared with the control group. Comparing the FH group with detectable CAC (CAC score >0) and undetectable CAC (CAC score of 0), we found higher hs-CRP levels (0.29 +/- 0.23 vs 0.07 +/- 0.08 mg/dl, p = 0.001) and reduced flow-mediated dilation (0.04 +/- 0.03 vs 0.08 +/- 0.03, p = 0.005) in the detectable CAC group. Multivariate analysis showed an independent correlation of hs-CRP with detectable CAC (relative risk 5.034, 95% confidence interval 1.525 to 16.613, p = 0.04). In conclusion, FH subjects with positive CAC scores have decreased flow-mediated dilation and increased hs-CRP levels. Furthermore, hs-CRP level is the only independent predictor of the presence of CAC.