Genes and environment in common neonatal lung disease

The Common Haplotype GATGACA in Surfactant-Protein B Gene Is Protective for Respiratory Distress Syndrome in Preterm Neonates

Background

Respiratory distress syndrome (RDS), a disorder of primary surfactant deficiency resulting in pulmonary insufficiency, remains a significant problem for preterm neonates. Associations between genetic variants of surfactant proteins and RDS have been reported, but haplotypes of the surfactant protein B gene (SFTPB) have not been studied. The aim of the study was to prove the hypothesis that certain haplotypes of SFTPB may be protective or risk factors for RDS.

Methods

The study was performed with 149 preterm infants, born <34 weeks of gestation, with 86 infants with mild RDS or without RDS (control group) and 63 infants with severe RDS (patient group). RDS was considered severe if multiple doses of exogenous surfactant and/or mechanical ventilation within the first 72 h of life were needed. The venous blood sample was used for the analysis of gene polymorphisms associated with RDS, genotyping, and haplotype estimation. Multivariate logistic regression analysis and the odds ratio were calculated to detect the contribution of the studied variables to the development of RDS.

Results

A new association of the common single nucleotide polymorphism (SNP) rs2304566 with RDS in premature infants was detected. Analysis of rs2304566 polymorphisms using a logistic regression model showed that there are two significant predictors inversely related to the occurrence of RDS (Apgar score of 5 min, CT and TT genotype in rs2304566 polymorphism). Gestational age, birth weight, and sex have border significance. Moreover, in the patient group, the frequency of the GATGACA haplotype in the SFTPB gene was lower (p = 0.037), and the GATGGCA haplotype was higher (p = 0.059) in comparison with the control group.

Conclusion

The common haplotype GATGACA of the SFTPB gene can be protective against RDS in preterm infants. The trend of a higher frequency of GATGGCA in the SFTPB gene in infants with severe RDS suggests that this haplotype may be a risk factor for RDS susceptibility.

Umbilical cord levels of macrophage migration inhibitory factor in neonatal respiratory distress syndrome

Background/aim

We aimed to evaluate the association of the umbilical cord macrophage migration inhibitory factor (MIF) with the respiratory distress syndrome (RDS) in preterm infants.

Materials and methods

A total of eighty six preterm infants (38 with RDS and 48 without RDS) were involved in the study. ELISA is the technique assaying MIF values.

Results

The mean of the infants’ gestational ages and birth weights were significantly different (P = 0.0001). There were no significant differences in sex, delivery mode or exposure to antenatal steroid among the groups (P > 0.05). Umbilical cord MIF levels of the infants were not correlated with gestational age and birth weight (Spearman’s rho = –0.22 and 0.28 respectively, P > 0.05). There was no statistically significant difference in umbilical cord MIF levels of infants whether or not they were administered antenatal steroid (median:17.88 vs. median:17.60, Mann–Whitney U test, P = 0.42). Cord serum MIF levels were higher (mean, 17.09 ± 5.86 ng/mL) in the RDS group than in the non-RDS group (mean, 14.72 ± 4.18 ng/mL) (P = 0.005).

Conclusion

This study shows that, MIF level is higher in the cord blood of the infants with RDS than of the infants without RDS. This supports that MIF expression begins in prior to the birth of the preterm infants and MIF has enhancing impact on the lung development of premature babies. With future studies, the assessment of the cord MIF levels at the bedside may be beneficial for the diagnosis and treatment of RDS, and taking actions to prevent long-term consequences.

The impact of vitamin D on fetal and neonatal lung maturation. A systematic review

Respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD) are major complications to preterm birth. Hypovitaminosis D is prevalent in pregnancy. We systematically reviewed the evidence of the impact of vitamin D on lung development, surfactant synthesis, RDS, and BPD searching PubMed, Embase, and Cochrane databases with the terms vitamin D AND (surfactant OR lung maturation OR lung development OR respiratory distress syndrome OR fetal lung OR prematurity OR bronchopulmonary dysplasia). Three human studies, ten animal studies, two laboratory studies, and one combined animal and laboratory study were included. Human evidence was sparse, allowing no conclusions. BPD was not associated with vitamin D receptor polymorphism in a fully adjusted analysis. Animal and laboratory studies showed substantial positive effects of vitamin D on the alveolar type II cell, fibroblast proliferation, surfactant synthesis, and alveolarization. These data support the hypothesis of hypovitaminosis D as a frequent, modifiable risk factor of RDS and BPD, which should be tested in randomized controlled trials on pregnant women, those with threatening preterm delivery, or in the preterm neonates. Future experimental and human studies should aim to identify optimal time windows, vitamin D doses, and cut-off levels for 25-hydroxyvitamin D in interventions against RDS, BPD, and later adverse respiratory outcomes.

Early origins of chronic obstructive lung diseases across the life course

Chronic obstructive lung diseases, like asthma and chronic obstructive pulmonary disease, have high prevalences and are a major public health concern. Chronic obstructive lung diseases have at least part of their origins in early life. Exposure to an adverse environment during critical periods in early life might lead to permanent developmental adaptations which results in impaired lung growth with smaller airways and lower lung volume, altered immunological responses and related inflammation, and subsequently to increased risks of chronic obstructive lung diseases throughout the life course. Various pathways leading from early life factors to respiratory health outcomes in later life have been studied, including fetal and early infant growth patterns, preterm birth, maternal obesity, diet and smoking, children's diet, allergen exposure and respiratory tract infections, and genetic susceptibility. Data on potential adverse factors in the embryonic and preconception period and respiratory health outcomes are scarce. Also, the underlying mechanisms how specific adverse exposures in the fetal and early postnatal period lead to chronic obstructive lung diseases in later life are not yet fully understood. Current studies suggest that interactions between early environmental exposures and genetic factors such as changes in DNA-methylation and RNA expression patterns may explain the early development of chronic obstructive lung diseases. New well-designed epidemiological studies are needed to identify specific critical periods and to elucidate the mechanisms underlying the development of chronic obstructive lung disease throughout the life course.

Genetic risk factors associated with respiratory distress syndrome

Respiratory distress syndrome (RDS) among preterm infants is typically due to a quantitative deficiency of pulmonary surfactant. Aside from the degree of prematurity, diverse environmental and genetic factors can affect the development of RDS. The variance of the risk of RDS in various races/ethnicities or monozygotic/dizygotic twins has suggested genetic influences on this disorder. So far, several specific mutations in genes encoding surfactant-associated molecules have confirmed this. Specific genetic variants contributing to the regulation of pulmonary development, its structure and function, or the inflammatory response could be candidate risk factors for the development of RDS. This review summarizes the background that suggests the genetic predisposition of RDS, the identified mutations, and candidate genetic polymorphisms of pulmonary surfactant proteins associated with RDS.

Chorioamnionitis and lung injury in preterm newborns

There is a strong evidence that histologic chorioamnionitis is associated with a reduction of incidence and severity of respiratory distress syndrome (RDS). Short-term maturational effects on the lungs of extremely premature infants seem to be, however, accompanied by a greater susceptibility of the lung, eventually contributing to an increased risk of bronchopulmonary dysplasia (BPD). Genetic susceptibility to BPD is an evolving area of research and several studies have directly related the risk of BPD to genomic variants. There is a substantial heterogeneity across the studies in the magnitude of the association between chorioamnionitis and BPD, and whether or not the association is statistically significant. Considerable variation is largely dependent on differences of inclusion and exclusion criteria, as well as on clinical and histopathological definitions. The presence of significant publication bias may exaggerate the magnitude of the association. Controlling for publication bias may conduct to adjusted results that are no longer significant. Recent studies generally seem to confirm the effect of chorioamnionitis on RDS incidence, while no effect on BPD is seen. Recent data suggest susceptibility for subsequent asthma to be increased on long-term followup. Additional research on this field is needed.

Surfactant protein A associated with respiratory distress syndrome in Korean preterm infants: evidence of ethnic difference

BACKGROUND

Insufficiency of the pulmonary surfactant system is the primary cause of respiratory distress syndrome (RDS) in preterm infants. Genetic factors, including specific single-nucleotide polymorphisms in the genetic components of surfactant protein A (SP-A1 and SP-A2), affect protein structure and function, as well as risk of RDS.

OBJECTIVE

We investigated the association between variations in SP-A genotypes and RDS within the genetically homogeneous Korean population.

METHODS

We used TaqMan® real-time polymerase chain reaction technology to assess nine single-nucleotide polymorphisms of SP-A in 261 full-term and 152 preterm infants. Among the preterm infants, 76 infants with RDS were matched with 76 control infants with respect to gestation, use of antenatal steroids and gender.

RESULTS

The SP-A2 1A(0) variant and the homozygous 1A(0)/1A(0) genotype were associated with protection from RDS (OR 0.31, 95% CI 0.13-0.78). In addition, the 1A(1) carrier genotype (containing one copy of the 1A(1) variant) was associated with increased risk of RDS (OR 2.42, 95% CI 1.06-5.52). The significance of these results is that the association of patterns with RDS was opposite to the findings of previous research with Finnish and North American study populations.

CONCLUSIONS

We have identified associations between specific variants of the SP-A genes and RDS risk in the Korean preterm study population. Our data strongly support SP-A as a candidate gene for susceptibility to RDS, and reveal the dissimilarity of the associated risk/protective genetic variants between different ethnic study populations.

Fetal and infant origins of asthma

Previous studies have suggested that asthma, like other common diseases, has at least part of its origin early in life. Low birth weight has been shown to be associated with increased risks of asthma, chronic obstructive airway disease, and impaired lung function in adults, and increased risks of respiratory symptoms in early childhood. The developmental plasticity hypothesis suggests that the associations between low birth weight and diseases in later life are explained by adaptation mechanisms in fetal life and infancy in response to various adverse exposures. Various pathways leading from adverse fetal and infant exposures to growth adaptations and respiratory health outcomes have been studied, including fetal and early infant growth patterns, maternal smoking and diet, children's diet, respiratory tract infections and acetaminophen use, and genetic susceptibility. Still, the specific adverse exposures in fetal and early postnatal life leading to respiratory disease in adult life are not yet fully understood. Current studies suggest that both environmental and genetic factors in various periods of life, and their epigenetic mechanisms may underlie the complex associations of low birth weight with respiratory disease in later life. New well-designed epidemiological studies are needed to identify the specific underlying mechanisms. This review is focused on specific adverse fetal and infant growth patterns and exposures, genetic susceptibility, possible respiratory adaptations and perspectives for new studies.

Perinatal inflammation and lung injury

Bronchopulmonary dysplasia (BPD) remains the major morbidity of extreme preterm birth. The incidence of BPD has remained stable despite recent efforts to reduce postnatal exposures to volutrauma and hyperoxia. This review will focus on recent clinical and experimental insights that provide support for the concept that the 'new BPD' is the result of inflammation-mediated injury and altered lung development during a window of vulnerability in genetically susceptible infants that is modified by maternal and postnatal exposures.

IL-18R1 and IL-18RAP SNPs may be associated with bronchopulmonary dysplasia in African-American infants

INTRODUCTION

The genetic contribution to the development of bronchopulmonary dysplasia (BPD) in prematurely born infants is substantial, but information related to the specific genes involved is lacking.

RESULTS

Genotype analysis revealed, after multiple comparisons correction, two significant single-nucleotide polymorphism (SNPs), rs3771150 (IL-18RAP) and rs3771171 (IL-18R1), in African Americans (AAs) with BPD (vs. AAs without BPD; q < 0.05). No associations with Caucasian (CA) BPD, AA or CA respiratory distress syndrome (RDS), or prematurity in either AAs or CAs were identified with these SNPs. Respective frequencies were 0.098 and 0.093 in infants without BPD and 0.38 for each SNP in infants with BPD. In the replication set (82 cases; 102 controls), the P values were 0.012 for rs3771150 and 0.07 for rs3771171. Combining P values using Fisher's method, overall P values were 8.31 × 10(-7) for rs3771150 and 6.33 × 10(-6) for rs3771171.

DISCUSSION

We conclude that IL-18RAP and IL-18R1 SNPs identify AA infants at risk for BPD. These genes may contribute to AA BPD pathogenesis via inflammatory-mediated processes and require further study.

METHODS

We conducted a case-control SNP association study of candidate genes (n = 601) or 6,324 SNPs in 1,091 prematurely born infants with gestational age <35 weeks, with or without neonatal lung disease including BPD. BPD was defined as a need for oxygen at 28 days.

A polymorphism in the macrophage migration inhibitory factor promoter is associated with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common adverse outcome of prematurity, causing severe morbidity and mortality. The cytokine macrophage migration inhibitory factor (MIF) has been recently shown to favor murine fetal lung development. In this prospective study, we evaluate the expression of MIF in the lung and in the serum of preterm infants (n = 50) and investigate whether the -173 G/C MIF promoter polymorphism is associated with the risk of BPD (n = 103). MIF was highly expressed in lung tissue from preterm infants. Serum MIF levels were measured by ELISA at d 1 after birth. MIF levels were increased [median (interquartile range), 71.01 (44.9-162.3) ng/mL], particularly in those infants with RDS [110.4 (59.4-239.2) ng/mL] compared with healthy adults [2.4 (1.2-5.0) ng/mL], (p < 0.001). The MIF -173*C allele, which predisposes to higher MIF production, was associated with a lower incidence of BPD (OR, 0.2; 95% CI, 0.04-0.93), independently from mechanical ventilation and oxygen exposure (p = 0.03). In conclusion, these data show that MIF expression is increased in lung and serum of preterm infants and suggest that the high producing MIF -173*C allele may be a protective factor for BPD.

Preterm birth and respiratory disease in later life

Chronic respiratory diseases are a common complication of preterm birth, particularly among very immature infants or those suffering from bronchopulmonary dysplasia. Major progress in the treatment of preterm newborns has changed the pattern of late respiratory complications. The major respiratory problem in infancy and early childhood is respiratory exacerbations caused by infections (particularly viral ones), which need hospitalization. The symptoms become mild in school-age children; however, a group of children still present with chronic airway obstruction defined by recurrent episodes of wheezing and decreased lung function tests (decreased forced expiratory volume). For some preterm infants, particularly those with bronchopulmonary dysplasia, obstructive lung disease persists into adulthood. They are very likely to develop chronic obstructive pulmonary disease or similar disease later in life. In these patients, a program of lung function monitoring and pulmonary prophylaxis by means of elimination of specific risk factors in adulthood is advisable.

Lack of association between FXIII-Val34Leu, FVII-323 del/ins, and transforming growth factor beta1 (915G/T) gene polymorphisms and bronchopulmonary dysplasia: a single-center study

Bronchopulmonary dysplasia (BPD) is a multifactorial disease of preterm infants that is characterized by airway injury, inflammation, and parenchymal remodeling. Extravascular fibrin deposits in septae and alveoli due to the altered fibrin turnover are the pathological hallmarks of BPD that strongly indicates the importance of the imbalance in the competing activities of coagulation and fibrinolysis. Activation of the coagulation cascade leads to intraalveolar fibrin deposition in many inflammatory pulmonary disorders. Increased fibrin formation or decreased fibrinolysis may cause extravascular fibrin deposition. We evaluated the association between FXIII-Val34Leu, FVII-323 del/ins, and transforming growth factor beta1 (TGF-beta(1)) (915G/T) gene polymorphisms in patients with BPD. The study group consisted of 98 preterm infants with BPD. Ninety-four of the 192 preterm neonates were without BPD and sampled for the control group. Restriction fragment size analyses were performed by examining digested PCR products for FXIII-Val34Leu, FVII-323 del/ins, and TGF-beta(1) (915G/C) genotypes. No significant associations were found between FXIII-Val34Leu, FVII-323 del/ins, TGF-beta(1) (915G/C) gene polymorphisms and BPD phenotype in our population. Further studies with other genes are required for the identification of molecular predisposing factors for BPD that may help in the development of new treatments and hence might allow for targeting of this treatment to a "high-risk" subgroup, reducing unnecessary exposure to potentially harmful therapies.

The 'new' bronchopulmonary dysplasia: challenges and commentary

Lung development is orchestrated by highly integrated morphogenic programs of interrelated patterns of gene and protein expression. Injury to the developing lung in the canalicular and saccular phases of lung development alters subsequent alveolar and vascular development resulting in simplified alveolar structures, dysmorphic capillary configuration, variable interstitial cellularity and fibroproliferation that are characteristic of the 'new' bronchopulmonary dysplasia (BPD). Fetal and neonatal infection, abnormal stretch of the developing airways and alveoli, altered expression of surfactant proteins (or genetically altered proteins), polymorphisms of genes encoding for vascular endothelial growth factors, and reactive oxygen species result in imparied gas exchange in the developing lung. However, the 'new' BPD represents only one form of neonatal chronic lung disease and the consistent use of both the physiologic definition and severity scale would provide greater accuracy in determining the impact of the disease currently defined by its treatment. Our present labelling of the clinical state of oxygen supplementation and/or ventilatory support at 36 weeks' postmenstrual age and the histopathologic severity of alveolar arrest and vascular 'simplification' may not always be predictive of the degree of altered lung development and thus longer-term pulmonary function evaluations are needed to determine the impact of this disorder in specific infants. The proposed role of novel molecular therapies, and the combined effects of currently established therapies, as well as exogenous surfactant and inhaled nitric oxide or repetitive surfactant dosing, on the severity and incidence of new BPD hold considerable promise for reducing the long-term pulmonary morbidity among infants delivered prematurely.

Pitfalls, problems, and progress in bronchopulmonary dysplasia

Bronchopulmonary dysplasia is a chronic lung disease associated with premature birth and characterized by early lung injury. In this review we discuss some pitfalls, problems, and progress in this condition over the last decade, focusing mainly on the last 5 years, limited to studies in human neonates. Changes in the definition, pathogenesis, genetic susceptibility, and recent biomarkers associated with bronchopulmonary dysplasia will be discussed. Progress in current management strategies, along with novel approaches/therapies, will be critically appraised. Finally, recent data on long-term pulmonary and neurodevelopmental outcomes of infants with bronchopulmonary dysplasia will be summarized.