Angiotensin II type 1 receptor A1166C polymorphism and prophylactic indomethacin treatment induced ductus arteriosus closure in very low birth weight neonates

Mouse models of patent ductus arteriosus (PDA) and their relevance for human PDA

The ductus arteriosus (DA) is a unique fetal vascular shunt, which allows blood to bypass the developing lungs in utero. After birth, changes in complex signaling pathways lead to constriction and permanent closure of the DA. The persistent patency of the DA (PDA) is a common disorder in preterm infants, yet the underlying causes of PDA are not fully defined. Although limits on the availability of human DA tissues prevent comprehensive studies on the mechanisms of DA function, mouse models have been developed that reveal critical pathways in DA regulation. Over 20 different transgenic models of PDA in mice have been described, with implications for human DA biology. Similarly, we enumerate 224 human single-gene syndromes that are associated with PDA, including a small subset that consistently feature PDA as a prominent phenotype. Comparison and functional analyses of these genes provide insight into DA development and identify key regulatory pathways that may serve as potential therapeutic targets for the management of PDA.

Molecular Mechanisms Underlying Remodeling of Ductus Arteriosus: Looking beyond the Prostaglandin Pathway

The ductus arteriosus (DA) is a physiologic vessel crucial for fetal circulation. As a major regulating factor, the prostaglandin pathway has long been the target for DA patency maintenance or closure. However, the adverse effect of prostaglandins and their inhibitors has been a major unsolved clinical problem. Furthermore, a significant portion of patients with patent DA fail to respond to cyclooxygenase inhibitors that target the prostaglandin pathway. These unresponsive medical patients ultimately require surgical intervention and highlight the importance of exploring pathways independent from this well-recognized prostaglandin pathway. The clinical limitations of prostaglandin-targeting therapeutics prompted us to investigate molecules beyond the prostaglandin pathway. Thus, this article introduces molecules independent from the prostaglandin pathway based on their correlating mechanisms contributing to vascular remodeling. These molecules may serve as potential targets for future DA patency clinical management.

Molecular and Mechanical Mechanisms Regulating Ductus Arteriosus Closure in Preterm Infants

Failure of ductus arteriosus closure after preterm birth is associated with significant morbidities. Ductal closure requires and is regulated by a complex interplay of molecular and mechanical mechanisms with underlying genetic factors. In utero patency of the ductus is maintained by low oxygen tension, high levels of prostaglandins, nitric oxide and carbon monoxide. After birth, ductal closure occurs first by functional closure, followed by anatomical remodeling. High oxygen tension and decreased prostaglandin levels mediated by numerous factors including potassium channels, endothelin-1, isoprostanes lead to the contraction of the ductus. Bradykinin and corticosteroids also induce ductal constriction by attenuating the sensitivity of the ductus to PGE2. Smooth muscle cells of the ductus can sense oxygen through a mitochondrial network by the role of Rho-kinase pathway which ends up with increased intracellular calcium levels and contraction of myosin light chains. Anatomical closure of the ductus is also complex with various mechanisms such as migration and proliferation of smooth muscle cells, extracellular matrix production, endothelial cell proliferation which mediate cushion formation with the interaction of blood cells. Regulation of vessel walls is affected by retinoic acid, TGF-β1, notch signaling, hyaluronan, fibronectin, chondroitin sulfate, elastin, and vascular endothelial cell growth factor (VEGF). Formation of the platelet plug facilitates luminal remodeling by the obstruction of the constricted ductal lumen. Vasa vasorum are more pronounced in the term ductus but are less active in the preterm ductus. More than 100 genes are effective in the prostaglandin pathway or in vascular smooth muscle development and structure may affect the patency of ductus. Hemodynamic changes after birth including fluid load and flow characteristics as well as shear forces within the ductus also stimulate closure. Current pharmacological treatment for the closure of a patent ductus is based on the blockage of the prostaglandin pathway mainly through COX or POX inhibition, albeit with some limitations and side effects. Further research for new agents aiming ductal closure should focus on a clear understanding of vascular biology of the ductus.

Genetic variants associated with patent ductus arteriosus in extremely preterm infants

OBJECTIVE

Patent ductus arteriosus (PDA) is a commonly observed condition in preterm infants. Prior studies have suggested a role for genetics in determining spontaneous ductal closure. Using samples from a large neonatal cohort we tested the hypothesis that common genetic variations are associated with PDA in extremely preterm infants.

STUDY DESIGN

Preterm infants (n = 1013) enrolled at NICHD Neonatal Research Network sites were phenotyped for PDA. DNA was genotyped for 1634 single nucleotide polymorphisms (SNPs) from candidate genes. Analyses were adjusted for ancestral eigenvalues and significant epidemiologic variables.

RESULTS

SNPs in several genes were associated with the clinical diagnosis of PDA and with surgical ligation in extremely preterm neonates diagnosed with PDA (p < 0.01). None of the associations were significant after correction for multiple comparisons.

CONCLUSION

We identified several common genetic variants associated with PDA. These findings may inform further studies on genetic risk factors for PDA in preterm infants.

Genetics of the patent ductus arteriosus (PDA) and pharmacogenetics of PDA treatment

Patent ductus arteriosus (PDA) is a frequent, complex, and difficult to treat clinical syndrome among preterm infants in the neonatal intensive care unit. In addition to known clinical risk factors, there are emerging data about genetic predisposition to PDA in both animal and human models. Clinical response and toxicity from drugs used to treat PDA are highly variable. Developmental and genetic aspects of pharmacokinetics and pharmacodynamics influence exposure and response to pharmacologic therapies. Given the variable efficacy and toxicity of known drug therapies, novel therapeutic targets for PDA treatment offer the promise of precision medicine. This review addresses the known genetic contributions to prolonged ductal patency, variability in response to drug therapy for PDA, and potential novel drug targets for future PDA treatment discovery.

Yap/Taz transcriptional activity is essential for vascular regression via Ctgf expression and actin polymerization

Vascular regression is essential to remove redundant vessels during the formation of an efficient vascular network that can transport oxygen and nutrient to every corner of the body. However, no mechanism is known to explain how major blood vessels regress during development. Here we use the dorsal part of the caudal vein plexus (dCVP) in Zebrafish to investigate the mechanism of regression and discover a new role of Yap/Taz in vascular regression. During regression, Yap/Taz is activated by blood circulation in the endothelial cells. This leads to induction of Ctgf and actin polymerization. Interference with Yap/Taz activation decreased Ctgf production, which decreased actin polymerization and vascular regression. These results implicate a novel role of Yap/Taz in vascular regression.

Genetic Modifiers of Patent Ductus Arteriosus in Term Infants

OBJECTIVE

To identify single-nucleotide polymorphisms (SNPs) in specific candidate genes associated with patent ductus arteriosus in term infants.

STUDY DESIGN

We conducted an initial family-based, candidate gene study to analyze genotype data from DNA samples obtained from 171 term infants and their parents enrolled in the National Birth Defects Prevention Study (NBDPS). We performed transmission disequilibrium testing (TDT) using a panel of 55 SNPs in 17 genes. Replication of SNPs with P < .1 in the NBDPS trios was performed with a case-control strategy in an independent population.

RESULTS

TDT analysis of the NBDPS trios resulted in 6 SNPs reaching the predetermined cutoff (P < .1) to be included in the replication study. These 6 SNPs were genotyped in the independent case-control population. A SNP in TGFBR2 was found to be associated with term patent ductus arteriosus in both populations after we corrected for multiple comparisons. (rs934328, TDT P = 2 × 10(-4), case-control P = 6.6 × 10(-5)).

CONCLUSIONS

These findings confirm the importance of the transforming growth factor-beta pathway in the closure of the term ductus arteriosus and may suggest new therapeutic targets.

Identification of differentially regulated genes in human patent ductus arteriosus

In order to identify differentially expressed genes that are specific to the ductus arteriosus, 18 candidate genes were evaluated in matched ductus arteriosus and aortic samples from infants with coarctation of the aorta. The cell specificity of the gene's promoters was assessed by performing transient transfection studies in primary cells derived from several patients. Segments of ductus arteriosus and aorta were isolated from infants requiring repair for coarctation of the aorta and used for mRNA quantitation and culturing of cells. Differences in expression were determined by quantitative PCR using the ΔΔCt method. Promoter regions of six of these genes were cloned into luciferase reporter plasmids for transient transfection studies in matched human ductus arteriosus and aorta cells. Transcription factor AP-2b and phospholipase A2 were significantly up-regulated in ductus arteriosus compared to aorta in whole tissues and cultured cells, respectively. In transient transfection experiments, Angiotensin II type 1 receptor and Prostaglandin E receptor 4 promoters consistently gave higher expression in matched ductus arteriosus versus aorta cells from multiple patients. Taken together, these results demonstrate that several genes are differentially expressed in ductus arteriosus and that their promoters may be used to drive ductus arteriosus-enriched transgene expression.

Single nucleotide polymorphisms in AGTR1, TFAP2B, and TRAF1 are not associated with the incidence of patent ductus arteriosus in Japanese preterm infants

BACKGROUND

Persistent patent ductus arteriosus (PDA) is a frequent complication in preterm infants. Single nucleotide polymorphisms (SNP) in several genes, including angiotensin II receptor, type 1 (AGTR1), transcription factor AP-2 beta (TFAP2B) and tumor necrosis factor receptor-associated factor 1 (TRAF1), have been reported to be associated with PDA in preterm infants. The aim of this study was to evaluate the relationships between PDA in preterm infants and polymorphisms in AGTR1, TFAP2B and TRAF1 in the Japanese population.

METHODS

The subjects consisted of 107 preterm infants with gestational age <32 weeks. Extremely low-birthweight infants were treated with prophylactic indomethacin during the first 24 h after birth. Five SNP, namely, rs5186 in AGTR1, rs987237 and rs6930924 in TFAP2B, and rs1056567 and rs10985070 in TRAF1, were genotyped using TaqMan SNP genotyping assays.

RESULTS

There were no significant differences in the distributions of the genotypes and allele frequencies of all studied SNP between the PDA group (n = 46) and the non-PDA group (n = 61).

CONCLUSIONS

There were no significant associations between the studied SNP and the incidence of PDA in Japanese preterm infants. These SNP may not be clinically important predisposing factors for PDA in Japanese preterm infants.

Very Low Birth Weight Monochorionic Diamniotic Twins as a Risk Factor for Symptomatic Patent Ductus Arteriosus

BACKGROUND

Some prior studies have shown that symptomatic patent ductus arteriosus (sPDA) is highly familial. Although it is estimated that both genetic and environmental factors may contribute to sPDA, evidence is still lacking.

OBJECTIVE

The aim of this study was to determine the risk factors for sPDA, focusing on the genetic and in utero environment by analyzing very low birth weight (VLBW) singletons and twins.

METHODS

This retrospective case-control study reviewed the medical records of 445 VLBW infants (25 weeks ≤ gestational age <32 weeks, 600 g ≤ birth weight <1,500 g) and compared the incidence of sPDA among monochorionic diamniotic (MD) twins (n = 65), dichorionic diamniotic (DD) twins (n = 66), and singletons (n = 314).

RESULTS

Stepwise multiple regression analysis showed that twin siblings (p = 0.001), gestational week (p < 0.001), antenatal steroid use (p = 0.021), and premature rupture of membranes (p = 0.002) were independent predictors of sPDA. Incidence of sPDA in MD twin siblings was significantly higher than that in singletons (p < 0.01), whereas no significant difference was found between singletons and DD twins or between MD and DD twins.

CONCLUSIONS

The current results show that being a VLBW MD twin is an independent risk factor for sPDA, and that both genetic and in utero environmental factors may contribute to its development.

Effects of Advancing Gestation and Non-Caucasian Race on Ductus Arteriosus Gene Expression

OBJECTIVE

To identify genes affected by advancing gestation and racial/ethnic origin in human ductus arteriosus (DA).

STUDY DESIGN

We collected 3 sets of DA tissue (n = 93, n = 89, n = 91; total = 273 fetuses) from second trimester pregnancies. We examined four genes, with DNA polymorphisms that distribute along racial lines, to identify "Caucasian" and "non-Caucasian" DA. We used real time polymerase chain reaction to measure RNA expression of 48 candidate genes involved in functional closure of the DA, and used multivariable regression analyses to examine the relationships between advancing gestation, "non-Caucasian" race, and gene expression.

RESULTS

Mature gestation and non-Caucasian race are significant predictors for identifying infants who will close their patent DA when treated with indomethacin. Advancing gestation consistently altered gene expression in pathways involved with oxygen-induced constriction (eg, calcium-channels, potassium-channels, and endothelin signaling), contractile protein maturation, tissue remodeling, and prostaglandin and nitric oxide signaling in all 3 tissue sets. None of the pathways involved with oxygen-induced constriction appeared to be altered in "non-Caucasian" DA. Two genes, SLCO2A1 and NOS3, (involved with prostaglandin reuptake/metabolism and nitric oxide production, respectively) were consistently decreased in "non-Caucasian" DA.

CONCLUSIONS

Prostaglandins and nitric oxide are the most important vasodilators opposing DA closure. Indomethacin inhibits prostaglandin production, but not nitric oxide production. Because decreased SLCO2A1 and NOS3 expression can lead to increased prostaglandin and decreased nitric oxide concentrations, we speculate that prostaglandin-mediated vasodilation may play a more dominant role in maintaining the "non-Caucasian" patent DA, making it more likely to close when inhibited by indomethacin.

Mechanisms for ductus arteriosus closure

Closure of the ductus arteriosus at birth is a complex phenomenon being conditioned by antenatal events and progressing in preprogrammed steps. Functional at first, narrowing of the vessel is determined by 2 overlapping processes--removal of the prostaglandin E(2)-based relaxation sustaining prenatal patency and activation of a constrictor mechanism by the natural rise in blood oxygen tension. Two schemes have been proposed for oxygen action--one involving a cytochrome P450 hemoprotein (sensor)/endothelin-1 (effector) complex and the other a set of voltage-gated K(+) channels. These proposals, however, are not mutually exclusive. Structural closure follows the constriction through a remodeling process initiated antenatally with the development of intimal cushions and completed postnatally by a host of humoral and mechanical stimuli. Research in this area has already provided clinical applications. Nevertheless, management of premature infants with persistent ductus remains troublesome and calls for an alternative approach to the prostaglandin E(2) inhibitors now in use. Studies in progress on the oxygen-sensing system may lead to a definitive solution for this problem.

Genetics of patent ductus arteriosus susceptibility and treatment

The ductus arteriosus is a vital fetal structure designed to close shortly after birth. Although many physiologic and pharmacologic investigations have characterized the closure of this structure, genetic studies of persistent patency of the ductus arteriosus (patent ductus arteriosus, PDA) are relatively recent. Progress in the identification of specific genes associated with PDA is well behind that of many adult-onset diseases because of several reasons ranging from the lack of large biorepositories for this unique population to the belief that any genetic contribution to PDA is minimal. Viewing the PDA as a complex, developmentally influenced disease with both genetic and environmental risk factors has resulted in initial successes in some genetic studies. We will introduce several genetic approaches, which have been or are currently being applied to the study of PDA, that have been successful in identifying polymorphisms associated with adult diseases. Genetic investigations of PDA will be discussed with respect to heritability, in general, and to specific risk genes. Several animal models that have been used to study PDA-related genes will also be presented. Further advances in discovering genetic variation causing PDA will drive the more rational use of current therapies, and may help identify currently unknown targets for future therapeutic manipulation.

Patterns of gene expression in the ductus arteriosus are related to environmental and genetic risk factors for persistent ductus patency

Three independent risk factors (immature gestation, absence of antenatal glucocorticoid exposure, and presence of the rs2817399(A) allele of the gene TFAP2B) are associated with patent ductus arteriosus (PDAs) that fail to close during prostaglandin inhibition. We hypothesized that these three factors may affect a common set of genes that increase the risk of persistent PDA after birth. We studied baboon ductus from term, preterm, and glucocorticoid-treated preterm fetuses and found that both immature gestation and absence of antenatal glucocorticoid exposure decreased RNA expression of calcium- and potassium-channel genes involved in oxygen-induced constriction, and phosphodiesterase genes (that modulate cAMP/cGMP signaling). Ductus obtained from second trimester human pregnancies were genotyped for TFAP2B polymorphisms. When present, the rs2817399(A) allele also was associated with decreased expression of calcium- and potassium-channel genes. In contrast, alleles of two other TFAP2B polymorphisms, rs2817419(G) and rs2635727(T), which are not related to the incidence of PDA after birth, had no effect on RNA expression. In conclusion, three calcium- and potassium-channel genes (CACNA1G/ alpha1G, CACNB 2/CaL-beta2, and KCNA2/ Kv1.2) were similarly affected by each of the PDA risk factors. We speculate that these channels may play a significant role in closing the preterm ductus during prostaglandin inhibition and may be potential targets for future pharmacologic manipulations.

Inadvertent relaxation of the ductus arteriosus by pharmacologic agents that are commonly used in the neonatal period

Premature birth and disruption of the normal maturation process leave the immature ductus arteriosus unable to respond to postnatal cues for closure. Strategies that advocate conservative management of the patent ductus arteriosus (PDA) in premature infants are dependent on identification of the symptomatic PDA and understanding the risk factors that predispose to PDA. Exposure of premature infants to unintended vasodilatory stimuli may be one of the risk factors for PDA that is under recognized. In this article, we summarize the clinical factors that are associated with PDA and review commonly used neonatal drugs for their vasodilatory properties. Data demonstrating relaxation of the ductus arteriosus by gentamicin and other aminoglycoside antibiotics, by cimetidine and other H2 receptor antagonists, and by heparin are provided as examples of neonatal therapies that have unanticipated effects that may promote PDA.

Determination of genetic predisposition to patent ductus arteriosus in preterm infants

OBJECTIVE

Patent ductus arteriosus is a common morbidity associated with preterm birth. The incidence of patent ductus arteriosus increases with decreasing gestational age to approximately 70% in infants born at 25 weeks' gestation. Our major goal was to determine if genetic risk factors play a role in patent ductus arteriosus seen in preterm infants.

METHODOLOGY

We investigated whether single-nucleotide polymorphisms in genes that regulate smooth muscle contraction, xenobiotic detoxification, inflammation, and other processes are markers for persistent patency of ductus arteriosus. Initially, 377 single-nucleotide polymorphisms from 130 genes of interest were evaluated in DNA samples collected from 204 infants with a gestational age of <32 weeks. A family-based association test was performed on genotyping data to evaluate overtransmission of alleles.

RESULTS

P values of <.01 were detected for genetic variations found in 7 genes. This prompted additional analysis with an additional set of 162 infants, focusing on the 7 markers with initial P values of <.01, and 1 genetic variant in the angiotensin II type I receptor previously shown to be related to patent ductus arteriosus. Of the initial positive signals, single-nucleotide polymorphisms in the transcription factor AP-2 beta and tumor necrosis factor receptor-associated factor 1 genes remained significant. Additional haplotype analysis revealed genetic variations in prostacyclin synthase to be associated with patent ductus arteriosus. An angiotensin II type I receptor polymorphism previously reported to be associated with patent ductus arteriosus after prophylactic indomethacin administration was not associated with the presence of a patent ductus arteriosus in our population.

CONCLUSIONS

Overall, our data support a role for genetic variations in transcription factor AP-2 beta, tumor necrosis factor receptor-associated factor 1, and prostacyclin synthase in the persistent patency of the ductus arteriosus seen in preterm infants.

Heritability of bronchopulmonary dysplasia, defined according to the consensus statement of the national institutes of health

OBJECTIVE

The goal was to determine the magnitude of genetic effects on susceptibility and risk factors for bronchopulmonary dysplasia by using the clinically validated National Institutes of Health consensus definition as a demonstrated proxy for long-term respiratory and neurodevelopmental outcomes in extremely low birth weight infants.

METHODS

We analyzed clinical data from twin pairs born at </=30 completed weeks of gestation in British Columbia, Canada, between 1993 and 2006. Differences in correlations between monozygotic and dizygotic twin pairs and model-fitting approaches were used to quantify the relative contributions of genetic, shared environmental, and nonshared environmental effects.

RESULTS

Among 318 twins of known zygosity, monozygotic twin pair similarities were greater than those observed for dizygotic pairs, which suggests significant heritability for bronchopulmonary dysplasia. Model-fitting analyses confirmed that genetic effects accounted for 82% and 79% of the observed variance in bronchopulmonary dysplasia susceptibility, defined on the basis of the need for supplemental oxygen at 36 weeks or the National Institutes of Health consensus definition, respectively. Variations in rates of hemodynamically significant patent ductus arteriosus were largely accounted for by genetic effects, whereas the observed variability in susceptibility to blood-borne bacterial infections was largely attributable to environmental factors, both common and unique to each infant.

CONCLUSIONS

Susceptibility to bronchopulmonary dysplasia and persistence of patent ductus arteriosus are both significantly heritable. Our study strengthens the case for investigating genetic risk stratification markers useful for predicting the most significant long-term respiratory and neurodevelopmental consequences of bronchopulmonary dysplasia in premature neonates.

The extent to which genotype information may add to the prediction of disturbed perinatal adaptation: none, minor, or major?

Studies have been performed to describe the significance of genetic polymorphisms in complications associated with disturbed perinatal adaptation. Due to the large number of interacting factors, the results of classic statistical methods are often inconsistent. The random forest technique (RFT) is a robust nonparametric statistical approach that overcomes this problem through the calculation of the importance of each factor. We used RFT to reanalyze the importance of 24 genetic polymorphisms in the classification of preterm infants (birth weight, 680-1460 g, n = 100) to affected and unaffected groups according to the presence of acute perinatal complications. The accuracy of classification was between 0.5 and 0.8 for each complication when only birth data were considered. However, when genetic polymorphisms with the highest importance scores (ISs) were included in the analysis, the accuracy of classification according overall morbidity, necrotizing enterocolitis (NEC), acute renal failure (ARF), infant respiratory distress syndrome (IRDS), cardiac failure (CF), and patent ductus arteriosus (PDA) improved from 0.69, 0.60, 0.70, 0.72, 0.68, and 0.57 to 0.77, 0.70, 0.76, 0.77, 0.76, and 0.64, respectively. Our findings suggest that genetic polymorphisms identified by RFT as predictors may improve the risk assessment of preterm infants. RFT is a suitable tool to develop risk factor patterns in this population.

Dysplasia: a review

Bronchopulmonary dysplasia (BPD) is a common perinatal complication of very low birth weight preterm infants with a significant risk of long-term disability and morbidity. While clinical conditions such as prematurity and mechanical ventilation are its major risk factors, studies suggest that there is an individual susceptibility to BPD. This comprehensive review summarizes data collected about the implication of genetic polymorphisms in BPD and in its risk factors. Some studies have directly related the risk of BPD to genotype. Indeed, carrier states of genetic variants of cytokines (IFNgamma T+874A), adhesion molecules (L-selectin-Pro213Ser), elements of renin-angiotensin system (ACE-I/D), antioxidant enzymes (GST-P1 Val105Ile), and surfactant proteins (SPA1, SPB intron 4) has been identified as risk factors to BPD. Other studies investigated the role of genotype in BPD risk factors. Premature birth has been linked to carrier states of genetic variants with an impact on immune status (such as IL-6 G(-174)C, MBL2 54G/A, VEGF G+405C, HSP72 A+1267G genes) and matrix metalloproteases. Fetal inflammatory response syndrome, a major determinant of BPD is also affected by genotype (including LTalpha A+250G). Disturbed intrauterine lung development and vascularization may also contribute to BPD; these processes may be impaired in the presence of some rare genetic mutations. Furthermore, there is also a genetic component in the susceptibility to other perinatal adaptational disturbances such as respiratory distress syndrome that are associated with an increased need for mechanical ventilation, and, hence, with lung damage. The genetic variants presented in this article may help to identify infants at risk for BPD.

Impact of common genetic variation on neonatal disease and outcome

The main aim of identifying gene-environment interactions is to provide insight into mechanisms of disease development and to identify patients with an inherent vulnerability to certain conditions. This in turn may allow patients to be targeted with individualised treatment based on the knowledge of their inborn susceptibility to specific conditions. This review describes the possible effects of common genetic variation on outcome in various conditions affecting the neonate. It focuses predominantly on studies of positive association rather than non-association to illustrate this potential influence and to highlight the potential for further study and intervention. The shortcomings of published association studies and the place of such studies in future research are also discussed.

Management of acute renal failure in the newborn

Acute renal failure is common in the neonatal period. It is usually manifest by abnormal biochemistry and decreased urine output (<1 ml/kg/h), but non-oliguric renal failure is also common. A detailed understanding of the common pathophysiological mechanisms is rarely needed but an understanding of the common aetiologies (pre-renal, renal and post-renal) will enable the clinician to approach the problem in a logical manner. A standard approach to fluid and electrolyte management is described, along with a practical approach to the investigation and management of renal failure. A working understanding of the principles of peritoneal dialysis is important and a brief overview of the role of haemodialysis in neonatal renal failure is provided.

Angiotensin-converting enzyme DD genotype is preventive against circulatory failure in very-low-birthweight neonates

We studied the association between genetic polymorphisms of the renin-angiotensin system and the risk for circulatory failure (CF) during the first three postnatal days in 104 very-low-birthweight preterm infants.

CONCLUSION

Infants with angiotensin-converting enzyme DD genotype were protected against CF (adjusted OR 0.41, 95% CI 0.19-0.89).

Angiotensin II type-1 receptor A1166C polymorphism is associated with increased risk of ischemic stroke in hypertensive smokers

Recent observations revealed a novel role of angiotensin-converting enzyme 2 and the angiotensin II type-1 receptor (AT1R) in lung injury, thereby extending knowledge about the functions of the angiotensin system. Angiotensin II, whose target is the AT1R, is a potent vasoconstrictor. Accordingly, an imbalance leading to enhanced activity of the angiotensin II-AT1R axis is postulated to contribute to both circulatory disturbances and lung injury. In this context, a functional single-nucleotide polymorphism, AT1R A1166C, which leads to enhanced responsiveness of the AT1R, has been postulated as a candidate susceptibility factor for ischemic stroke. The aim of our study was to investigate its occurrence in ischemic stroke and to analyze its possible synergistic associations with clinical risk factors. Genetic and clinical data on 308 consecutive patients with acutely developing ischemic stroke were analyzed. A total of 272 stroke and neuroimaging alteration-free subjects served as a control group. Univariate and logistic regression statistical approaches were used. Alone, the AT1R 1166C allele did not pose a risk of stroke. In hypertensive smokers, however, it was associated with an increased risk of ischemic stroke (OR 22.3, 95% CI 5.8-110.2, p<0.001). Further subgroup analysis revealed the same association for both small-vessel (OR 24.3, 95% CI 6.1-121.1, p<0.001) and large-vessel (OR 21.3, 95% CI 4.6-81.1, p<0.001) infarction. On a pathophysiological basis, our results suggest the possibility that the AT1R A1166C polymorphism might give rise to ischemic stroke indirectly via an unfavorable effect on the cardiorespiratory function.

Genetic polymorphisms and risk for acute renal failure in preterm neonates

Acute renal failure (ARF) affects about 10% of severely ill neonates. Recent studies have shown that genetic polymorphisms of proteins that play a role in neonatal physiology may contribute to individual susceptibility to both ARF and its risk factors. Our review summarizes the data collected to date. Studies have shown that the risk of preterm neonates for ARF is directly associated with a combination of high tumor necrosis factor-alpha producer and low interleukin-6 producer genotypes, as well as with low heat shock protein 72 producer genotype. Premature birth is itself the most important risk factor for a number of complications, including ARF, and recent studies have also shown an association between several maternal and fetal cytokine genetic polymorphisms and increased inflammatory response in preterm neonates. These polymorphisms could also be associated with increased risk for disorders such as sepsis and necrotizing enterocolitis, which lead to renal hypoperfusion and ARF. Genetic polymorphisms of the renin-angiotensin-aldosterone system have not been shown to directly influence risk for ARF. They may, however, be associated with patent ductus arteriosus, poor postnatal adaptation, and heart failure, which are all prevalent risk factors for ARF.