An insertion/deletion polymorphism in intron 18 of the type B human natriuretic peptide receptor gene is not associated with cerebral infarction

Genetic Polymorphisms of the Natriuretic Peptide System in the Pathogenesis of Cardiovascular Disease: What Lies on the Horizon?

Background: The natriuretic peptide hormone family includes various proteins characterized by similar chemical structure and shared biological functions, with important effects on the cardiovascular system. Accordingly, these molecules are widely recognized as key clinical biomarkers in the diagnosis and monitoring of heart failure, hypertension, and coronary heart disease.

Content: Several single-nucleotide polymorphisms have been recently identified in genes associated with the natriuretic system. This review provides an overview of new insights into the functional role of these genetic variants, as well as their impact on cardiovascular physiopathology and drug response.

Conclusions: Noteworthy relationships between some specific polymorphisms and clinical correlates of cardiovascular disease have emerged. Nevertheless, future confirming studies are needed to substantiate the clinical relevance of such variants.

Natriuretic peptide receptor B signaling in the cardiovascular system: protection from cardiac hypertrophy

Natriuretic peptides (NP) represent a family of structurally homologous but genetically distinct peptide hormones involved in regulation of fluid and electrolyte balance, blood pressure, fat metabolism, cell proliferation, and long bone growth. Recent work suggests a role for natriuretic peptide receptor B (NPR-B) signaling in regulation of cardiac growth by either a direct effect on cardiomyocytes or by modulation of other signaling pathways including the autonomic nervous system. The research links NPR-B for the first time to a cardiac phenotype in vivo and underlines the importance of the NP in the cardiovascular system. This manuscript will focus on the role of NPR-B and its ligand C-type natriuretic peptide in cardiovascular physiology and disease and will evaluate these new findings in the context of the known function of this receptor, with a perspective on how future research might further elucidate NPR-B function.

Variable number of tandem repeat of the 5'-flanking region of type-C human natriuretic peptide receptor gene influences blood pressure levels in obesity-associated hypertension

The gene for natriuretic peptides receptor C (NPRC), which is a candidate susceptibility gene for essential hypertension (EH) or obese hypertension, plays a key role in the regulation of plasma levels and biological effects of natriuretic peptides. The aims of the present study were to find new genetic markers in the 5'-flanking region of the NPRC gene and to assess relationships between variants and phenotypes of EH, including EH in obese patients. Using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis, we discovered a novel six-nucleotide repeat polymorphism located 4 base pairs (bp) upstream of the major transcriptional initiation site. We performed association analysis of this variable number of tandem repeat (VNTR) in 242 EH patients and 212 normotensive controls (NT). Although no significant difference in overall frequency of VNTR was found between NT and EH groups, the blood pressure level of EH patients with the 5/6 genotype was significantly higher in obese subjects. This suggests that the VNTR of the 5'-flanking region of the NPRC gene influences blood pressure levels in obesity-associated hypertension.

The genetic contribution of the natriuretic peptide system to cardiovascular diseases

Three types of natriuretic peptides (NP) have been isolated: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). The NP family elicits a number of vascular, renal and endocrine effects that help to maintain blood pressure and extracellular fluid volume. These effects are mediated by the specific binding of NP to cell surface receptors that have been characterized, purified and cloned from cells of the vasculature, kidney, adrenal gland and brain. There are 3 subtypes of NP receptors: type A natriuretic peptide receptor (NPRA), type B natriuretic peptide receptor (NPRB), and type C natriuretic peptide receptor (NPRC). All 3 subtypes affect cellular second messenger activity. NPRA and NPRB are guanylyl cyclase receptors, and their activation increases cGMP levels. Activation of NPRC results in inhibition of adenylyl cyclase activity. Human NPRA has a high structural homology with human NPRB, and contains a highly-conserved guanylyl cyclase domain. ANP and BNP bind primarily to NPRA, which is found in the vasculature, causing vasodilation and inhibition of vascular smooth muscle cell proliferation. The present paper contains a review of NPs and their receptors and the genetic contribution of the NP system to cardiovascular diseases such as essential hypertension and myocardial infarction.

A simple and cost-effective method for rapid genotyping of insertion/deletion polymorphisms

We developed a simple method, based on the TaqMan technology, for fast genotyping of insertion/deletion polymorphisms of known location. The genotypes of 22 CEPH individuals, previously ascertained by conventional methods, were confirmed in the new assay without manual, time-consuming, post-PCR analysis. We propose to expand the application of TaqMan probes for population screening of insertion/deletion polymorphisms in which the exact endpoints of the insertion/deletion are known. The method can be applied to polymorphisms of any size and can be used for different applications such as diagnostics, genome variation, and species identification.

Genomic microarrays in human genetic disease and cancer

Alterations in the genome that lead to changes in DNA sequence copy number are a characteristic of solid tumors and are found in association with developmental abnormalities and/or mental retardation. Comparative genomic hybridization (CGH) can be used to detect and map these changes. Recent improvements in the resolution and sensitivity of CGH have been possible through implementation of microarray-based CGH (array CGH). Here we discuss the performance characteristics of different array platforms and review some of the recent applications of array CGH in cancer and medical genetics.

Haplotype analysis of the prostacyclin synthase gene and essential hypertension

Previously, we discovered 3 polymorphisms in the prostacyclin synthase (PGIS) gene: 1) T-192G, in the 5-flanking region, a novel single-nucleotide polymorphism (SNP) that is not associated with essential hypertension (EH); 2) a variable number of tandem repeat (VNTR) polymorphism, 6 nucleotides upstream from the ATG start codon, that is associated with risk of cerebral infarction; and 3) C1117A, in exon 8, an SNP that does not cause an amino acid change in codon 373, and that is associated with risk of myocardial infarction (MI). The purpose of the present study was to establish haplotypes of the PGIS gene consisting of these 3 polymorphisms, and to assess the association between these haplotypes and EH. We detected 19 haplotypes. There was no significant difference in the overall distribution of haplotypes between EH and normotensive subjects. To summarize, we successfully identified haplotypes of the PGIS gene, and these haplotypes were not associated with EH.

A novel variable number of tandem repeat polymorphism of the renin gene and essential hypertension

The aims of the present study were to find new genetic markers of essential hypertension (EH) and to investigate relationships between EH and polymorphisms of the renin gene. Using single strand conformation polymorphism, we discovered a new variable number of tandem repeat (VNTR) polymorphism in intron 7 that is 18 bp upstream from the boundary with exon 8. Nucleotide sequencing revealed that this VNTR polymorphism is a tandem repeat of the 4-nucleotide sequence TCTG. There were 6 alleles of this VNTR polymorphism, ranging from 7 repeats to 12 repeats. We analyzed the association between EH and this VNTR polymorphism. There was no significant difference in the overall distribution of this VNTR polymorphism between the EH and normotensive subjects. In summary, we discovered a novel VNTR polymorphism in the renin gene, and this polymorphism was not associated with EH.

Alu-repeat polymorphism in the gene coding for tissue-type plasminogen activator and the risk of hypertension in a Chinese Han population

Accumulating data support an association between hypertension and impaired fibrinolytic potential abnormalities in endogenous fibrinolysis. The present study examined whether there was an association between essential hypertension and either a polymorphism in the gene coding for t-PA or the plasma concentration of t-PA antigen. Chinese hypertensive subjects (n = 126) and normotensive controls (n = 102; sex- and age-matched with hypertensives) were recruited from among the outpatients of FuWai Hospital. The distributions of the II, ID, and DD genotypes of the t-PA gene in hypertensive patients (0.15, 0.49, 0.36) were similar to those in control subjects (0.11, 0.51, 0.38; p = 0.626). No significant difference in overall allele frequencies was found between the hypertension and control groups (p = 0.656). The allelic frequencies were in Hardy-Weinberg equilibrium. There was no evidence of an association between the level of t-PA antigen and risk of hypertension. Thus, in this case control study, neither the presence of the insertion allele of the Alu-repeat polymorphism of the t-PA nor the level of t-PA antigen were associated with the risk of essential hypertension.

A novel missense mutation of exon 3 in the type A human natriuretic peptide receptor gene: possible association with essential hypertension

The natriuretic peptide (NP) family is involved in regulation of blood pressure and fluid volume. We recently characterized the exon/intron organization of the human type A NP receptor (hNPRA) gene. The aim of this study was to isolate the genetic markers according to the organization of this gene, and to study the association between this gene and essential hypertension. Using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis, we identified a novel missense mutation, M3411, consisting of a methionine (ATG) to isoleucine (ATC) substitution at nucleotide 1023 in exon 3. Computer-aided three-dimensional structural analysis suggested that M341 exists in the loop between two alpha-helices, and that the mutation may influence receptor activities by altering the conformation of the alpha-helices. We performed an association study of the mutation in 210 essential hypertension (EH) patients and 210 normotensive controls. The overall distribution of alleles was not significantly different between the control and EH groups. However, the C/C homozygous genotype was found only in the EH group. The ratio of plasma brain natriuretic peptide (BNP)/mean blood pressure of the C/C genotype was significantly higher than that of the G/G genotype or the G/C genotype. We conclude that the significance of homozygous M3411 mutation in exon 3 is worth investigating for its possible association with EH.

Association study between a novel single nucleotide polymorphism of the promoter region of the prostacyclin synthase gene and essential hypertension

The purpose of this study was to investigate whether an association exists between the promoter region of the prostacyclin synthase gene and essential hypertension (EH). Using the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method, we discovered a novel single nucleotide polymorphism (SNP), T-192G, in the 5'-flanking region. We performed an association study using the SNP in 200 patients and 200 controls. The allele frequency distribution in the two groups was not significantly different. Thus, this SNP in the PGIS gene is not associated with EH.

Genetic variation in the promoter region of the beta2 bradykinin receptor gene is associated with essential hypertension in a Chinese Han population

The present study examined whether a genetic variant (-58T/C) in the promoter region of the human beta2 bradykinin receptor gene was genetically involved in essential hypertension. Chinese hypertensive subjects (n = 120) and normotensive controls (n = 98; sex- and age-matched with hypertensives) were recruited from the outpatients of Fu Wai hospital. Distribution of the -58T/C polymorphism was determined in patients and controls by means of PCR, SSCP, cloning and sequencing. The allelic frequencies were 0.56 for the C allele and 0.44 for the T allele in hypertensive subjects, and 0.46 for the C allele and 0.54 for the T allele in normotensive subjects. The allelic frequencies were in Hardy-Weinberg equilibrium. Significant differences between hypertensive and normotensive subjects were seen in the genotypes distribution (p = 0.045) and allelic frequencies (p = 0.033). These results suggested that -58C allele of the human beta2 bradykinin receptor gene may be an independent risk factor for essential hypertension in the Chinese Han population.

Association study between the variants of the human ANP gene and essential hypertension

Variants of atrial natriuretic peptide (ANP) are reported to be more common in blacks with hypertension than in normotensive controls and constitute an independent risk factor for cerebral infarction. The purpose of the present study was to investigate the role of ANP in the pathogenesis of essential hypertension (EH) in the Japanese. We investigated 2 previously reported ANP gene markers, G1837A and T2238C, for their possible associations with EH. A total of 233 individuals with EH and 213 age-matched normotensive (NT) control subjects were studied. The frequencies of the G and A alleles were 0.09 (42/466) and 0.91 (424/466), respectively, for the NT group and 0.11 (47/426) and 0.89 (379/426), respectively, for the EH group. These frequencies did not differ significantly between the two groups. The frequencies of the T and C alleles were 0.024 (11/466) and 0.97 (455/466), respectively, for the NT group and 0.03 (13/426) and 0.97 (413/426), respectively, for the EH group. These frequencies also did not differ significantly between the two groups. Neither G1837A nor the T2238C polymorphism of the ANP gene was associated with EH. Our findings do not support the hypothesis that the G1837A and T2238C polymorphisms of the ANP gene are markers for EH in the Japanese.

Frequent germline deletion polymorphism of chromosomal region 8p12-p21 identified as a recurrent homozygous deletion in human tumors

A number of carcinomas show high frequency of loss of heterozygosity (LOH) at chromosome 8p, suggesting that putative tumor suppressor genes are present in this region. While searching for homozygous deletions in a panel of pancreatic and biliary tumors, we discovered a homozygous deletion at the microsatellite AFMa224wh5 in chromosome region 8p12-p21. We applied a six-step algorithm comprising germline analysis, breakpoint sequencing, population screening, online gene mapping, allelic discrimination of tumor-associated LOH, and family history analysis. The results indicated that the deletion was likely due to a normal 102-bp deletion polymorphism present in nearly 10% of the study population, not likely to involve a recessive cancer-associated gene. Researchers need to be aware that germline insertion/deletion polymorphisms can affect the results of positional cloning efforts in human neoplasms. This problem would be accentuated in studies of cell lines where a paired sample of constitutional DNA is often unavailable.

A frequent deletion polymorphism on chromosome 22q13 identified by representational difference analysis of ovarian cancer

Sizable homozygous deletions (>100 bp) of genomic DNA in cancer cells are typically interpreted as an indication of the location of a tumor suppressor gene. In an effort to identify novel ovarian growth-suppressing genes, we performed representational difference analysis (RDA) of ovarian cancer cells. One of the RDA probes identified a 276-bp region of chromosome 22q deleted in 47% of the ovarian cancer cell lines examined. This small deletion was also found in the genomic DNA of 25% of colon cancer cell lines examined and, surprisingly, in 18% of the blood DNA samples from healthy controls. The deleted allele, which was named u22q, has a frequency of approximately 50% in the population and is in Hardy-Weinberg equilibrium with the intact allele. The deleted DNA sequence is flanked by direct repeats and likely originated through a slipped mispairing mechanism. The deletion did not encompass known transcripts or expressed sequence tags. It therefore appears likely that u22q represents a common polymorphism, often hemizygous in ovarian cancer because of a high rate of LOH of chromosome 22q. These findings provide an example of a sizable homozygous deletion that does not appear to be associated with disease. Such a finding provides a cautionary tale for positional cloning projects initiated exclusively on the basis of the identification of homozygous deletions. The possibility that the deletions in question may be constitutive should always be considered since it is probable that the genome contains a large number deletions/insertions of various sizes.