A Novel Missense Mutation, F826Y, in the Mineralocorticoid Receptor Gene in Japanese Hypertensives: Its Implications for Clinical Phenotypes

An overview of the classical and tissue-derived renin-angiotensin-aldosterone system and its genetic polymorphisms in essential hypertension

The renin-angiotensin-aldosterone system (RAAS) is a specific hormonal cascade implicated in the blood pressure control and sodium balance regulation. Several components of this pathway have been identified including renin, angiotensinogen, angiotensin-converting enzyme, angiotensins with a wide range of distinct subtypes and receptors, and aldosterone. The RAAS is not only confined to the systemic circulation but also exists locally in specific tissues such as the heart, brain, and blood vessels with a particular paracrine action. Alteration of RAAS function can contribute to the development of hypertension and the emergence of its associated end-organ damage. Genotypic variations of the different genes of RAAS cascade have been linked to the susceptibility to essential hypertension. Accordingly, to understand the pathogenesis of essential hypertension and its related complications, deep insight into the physiological and genetic aspects of RAAS with its different components and pathways is necessary. In this review, we aimed to illustrate the physiological and genetic aspects of RAAS and the underlying mechanisms which link this system to the predisposition to essential hypertension.

Genetics talks to epigenetics? The interplay between sequence variants and chromatin structure

Transcription is regulated by two major mechanisms. On the one hand, changes in DNA sequence are responsible for genetic gene regulation. On the other hand, chromatin structure regulates gene activity at the epigenetic level. Given the fundamental participation of these mechanisms in transcriptional regulation of virtually any gene, they are likely to co-regulate a significant proportion of the genome. The simple concept behind this idea is that a mutation may have a significant impact on local chromatin structure by modifying DNA methylation patterns or histone type recruitment. Yet, the relevance of these interactions is poorly understood. Elucidating how genetic and epigenetic mechanisms co-participate in regulating transcription may assist in some of the unresolved cases of genetic variant-phenotype association. One example is loci that have biologically predictable functions but genotypes that fail to correlate with phenotype, particularly disease outcome. Conversely, a crosstalk between genetics and epigenetics may provide a mechanistic explanation for cases in which a convincing association between phenotype and a genetic variant has been established, but the latter does not lie in a promoter or protein coding sequence. Here, we review recently published data in the field and discuss their implications for genetic variant-phenotype association studies.

Relationship of aldosterone synthase gene (C-344T) and mineralocorticoid receptor (S810L) polymorphisms with gestational hypertension

The extent of genetic influence in the aetiology of gestational hypertension has not been completely determined. The aim of this study was to analyse the relationship between aldosterone levels and the -344T/C polymorphism of the aldosterone synthase gene (CYP11B2) and to investigate the frequency of the S810L mutation of mineralocorticoid receptor (MR) in gestational hypertension. One hundred women with pregnancy-induced hypertension and 100 with normal pregnancy were studied to measure serum aldosterone and progesterone levels and for the genotypification of the -344T/C polymorphism of CYP11B2 gene and the S810L mutation of MR by RFLP-PCR and SSP, respectively. Serum aldosterone levels were reduced (<0.000001) and serum progesterone levels increased (<0.000001) in gestational hypertensive women as compared with normal pregnant women. The -344T/C of CYP11B2 genotypic frequencies were similar in the hypertensive and normotensive pregnant women. The 810L-mutated allele of MR was found in 12% of the hypertensive and 9.4% of the normotensive pregnant women. In contrast to the observations made in preeclampsia, the genotype of -344T/C of CYP11B2 was neither related with gestational hypertension nor with aldosterone levels at delivery. The frequency of the S810L mutation was similar in the hypertensive and normotensive women but higher than observed in other reports.

Association of a mineralocorticoid receptor gene polymorphism with hypertension in a Spanish population

BACKGROUND

To assess the association of polymorphisms and haplotypes of the mineralocorticoid receptor (MR) (NR3C2) gene to the risk of essential hypertension (HTN) in a Spanish population.

METHODS

This is a population-based study which included 1,502 subjects (748 women) >18 years old. Twenty-four polymorphisms of NR3C2 gene were analyzed by using SNPlex (Genotyping System based on OLA/PCR technology).

RESULTS

Alleles of the single-nucleotide polymorphism (SNP) rs5522 were significantly associated with the risk of HTN, both in the recessive and codominant models adjusted by age, gender, and body mass index (BMI). Genotype GG of the rs5522 showed to be protective against HTN odds ratio (OR) 0.10 (0.02-0.56), P < 0.01. One haplotype, which included the G allele of the rs5522, was also associated with reduced risk of HTN and four haplotypes which included the A allele were associated with increased risk of HTN. When the 24-h urinary sodium excretion and the estimated glomerular filtration rate (eGFR) were added, they did not reduce the significance level. Interaction between genotypes of the rs5522 and quartiles of 24-h sodium excretion has been observed. In subjects with the AA genotype, those with higher urinary sodium excretion had the lowest risk to be hypertensive.

CONCLUSION

A functional polymorphism of the NR3C2 gene was associated with risk of HTN. The data provided in this study seems to give credit to the hypothesis of the participation of MR gene in the development of HTN, although further studies are necessary to better assess its real impact.

Genetic variants in PCSK9 in the Japanese population: Rare genetic variants in PCSK9 might collectively contribute to plasma LDL cholesterol levels in the general population

The aim of this study was to investigate whether plasma low-density lipoprotein cholesterol (LDL-C) levels in the general population are influenced by rare sequence variations in the PCSK9 gene. We sequenced the promoter and coding regions of the PCSK9 gene in individuals from the general population (n=3655) with the lowest (n=78) and highest (n=96) LDL-C levels and in individuals taking antihypercholesterolemia medication (n=96). We identified 33 sequence variants in the PCSK9 gene among which 24 were specific for Japanese. Statistical analysis showed that one missense mutation, R93C, was associated with low LDL-C levels. The other variants had no association with LDL-C levels or the numbers of individuals with the variants were too small for statistical analysis. A comparison of the numbers of individuals with nonsynonymous mutations between the low LDL-C and high LDL-C/treatment groups found that four missense mutations and one nonsense mutation were identified only in the low LDL-C group and six missense mutations were identified only in the high LDL-C/treatment group. As we have analyzed groups at opposite ends of the LDL-C spectrum, it is likely that some of these nonsynonymous mutations may be associated with either low or high LDL-C in the Japanese population. Based on the extremely high frequencies of the nonsynonymous mutations in PCSK9 compared with those of LDLR or apoB-100, PCSK9 mutations could be important factors that cumulatively influence plasma LDL-C levels in the general population.

Association of Genetic Polymorphisms of Endothelin-Converting Enzyme-1 Gene with Hypertension in a Japanese Population and Rare Missense Mutation in Preproendothelin-1 in Japanese Hypertensives

Endothelin-1 (EDN1), a 21-amino acid peptide, is a potent vasoconstrictor with various pharmacological responses. EDN1 is synthesized from a 212-amino acid precursor protein, preproEDN1, through multiple proteolytic steps. Endothelin-converting enzyme (ECE) cleaves a Trp73-Val74 peptide bond in big-EDN1 to give rise to mature EDN1. In this study, we examined the possible association of genetic variations in ECE1 with hypertension in a general Japanese population and searched for missense mutations in and around the EDN1 polypeptide. We genotyped 5 single nucleotide polymorphisms (SNPs) in the ECE1 gene in 1,873 individuals from a general Japanese population and identified one SNP associated with hypertension in women (rs212528: TT vs. TC+CC: odds ratio=1.40; 95% confidence intervals: 1.04-1.89; p=0.026), after adjusting for confounding factors. The systolic blood pressure in women with the CC genotype was 6.44 mmHg higher than that in those with the TT genotype (p=0.007), after adjusting for the same factors. Next, to identify the missense mutations that may influence the biological activity of EDN1, we sequenced the genomic region that encodes EDN1 in 942 Japanese hypertensive patients. We identified a novel missense mutation, G36R, in one hypertensive patient, but no mutations were observed in EDN1. A gene polymorphism in EDN1, Lys198Asn, has been reported to be associated with hypertension in obese subjects. Taken together, these findings reveal that the EDN-ECE pathway is an important system involved in essential hypertension in Japanese.

Genetic variations of HSD11B2 in hypertensive patients and in the general population, six rare missense/frameshift mutations

Mutations in the gene encoding 11beta-hydroxysteroid dehydrogenase type 2, HSD11B2, cause a rare monogenic juvenile hypertensive syndrome called apparent mineralocorticoid excess (AME). In AME, defective HSD11B2 enzyme activity results in overstimulation of the mineralocorticoid receptor (MR) by cortisol, causing sodium retention, hypokalemia, and salt-dependent hypertension. Here, we have studied whether genetic variations in HDS11B2 are implicated in essential hypertension in Japanese hypertensives and the general population. By sequencing the entire coding region and the promoter region of HDS11B2 in 953 Japanese hypertensives, we identified five missense mutations in 11 patients (L14F, n = 5; R74H, n = 1; R147H, n = 3; T156I, n = 1; R335H, n = 1) and one novel frameshift mutation (4884Gdel, n = 1) in a heterozygous state, in addition to 19 genetic variations. All genetic variations identified were rare, with minor allele frequencies less than 0.005. Four of 12 patients with the missense/frameshift mutations showed renal failure. Four missense mutations, L14F, R74H, R147H, and R335H, were successfully genotyped in the general population, with a sample size of 3,655 individuals (2,175 normotensives and 1,480 hypertensives). Mutations L14F, R74H, R147H, and R335H were identified in hypertensives (n = 6, 8, 3, and 0, respectively) and normotensives (n = 8, 12, 5, and 0, respectively) with a similar frequency, suggesting that these missense mutations may not strongly affect the etiology of essential hypertension. Since the allele frequency of all of the genetic variations identified in this study was rare, an association study was not conducted. Taken together, our results indicate that missense mutations in HSD11B2 do not substantially contribute to essential hypertension in Japanese.

Association of Sixty-One Non-Synonymous Polymorphisms in Forty-One Hypertension Candidate Genes with Blood Pressure Variation and Hypertension

We previously selected a group of hypertension candidate genes by a key word search using the OMIM database of NCBI and validated 525 coding single nucleotide polymorphisms (SNPs) in 179 hypertension candidate genes by DNA sequencing in a Japanese population. In the present study, we examined the association between 61 non-synonymous SNPs and blood pressure variations and hypertension. We used DNA samples taken from 1,880 subjects in the Suita study, a population-based study using randomly selected subjects. Analyses of covariance adjusting for age, body mass index, hyperlipidemia, diabetes, smoking, drinking, and antihypertensive medication revealed that 17 polymorphisms in 16 genes (APOB, CAST, CLCNKB, CTNS, GHR, GYS1, HF1, IKBKAP, KCNJ11, LIPC, LPL, P2RY2, PON2, SLC4A1, TRH, VWF) were significantly associated with blood pressure variations. Multivariate logistic regression analysis with adjustment for the same factors revealed that 11 polymorphisms in 11 genes (CAST, CTLA4, F5, GC, GHR, LIPC, PLA2G7, SLC4A1, SLCI8A1, TRH, VWF) showed significant associations with hypertension. Five polymorphisms in five genes, CAST(calpastatin), LIPC (hepatic lipase), SLC4A1 (band 3 anion transporter), TRH (thyrotropin-releasing hormone), and VWF (von Willebrand factor), were significantly associated with both blood pressure variation and hypertension. Thus, our study suggests that these five genes were susceptibility genes for essential hypertension in this Japanese population.