Asthma research: the real action is in children

Maternal and neonatal risk factors of asthma in children: Nationwide population based study

BACKGROUND

Small population group-based cohorts have found that perinatal factors may contribute to the development of asthma in children. We aimed to investigate maternal and neonatal risk factors for the asthma phenotypes using two databases from the Taiwan's Maternal and Child Health Database (TMCHD) and the National Health Insurance Research Database (NHIRD).

METHODS

Perinatal data was obtained from 2004 to 2008 in the TMCHD and linked the NHIRD to obtain relevant medical information regarding maternal and neonatal risk factors of three asthma phenotypes which were identified as transient early asthma, persistent asthma, and late-onset asthma. A multivariate logistic regression analysis was conducted to adjust for covariates.

RESULTS

The percentage of non-asthmatic patients was 77.02% and asthmatic (transient early asthma, late onset asthma, and persistent asthma) patients were 8.96%, 11.64%, and 2.42%, respectively. Maternal risk factors-including Cesarean section, maternal asthma, maternal allergic rhinitis (AR), and premature rupture of membranes-and neonatal risk factors, such as male gender, gestational age 29-37 weeks, ventilator use, antibiotics use, AR, and atopic dermatitis, were associated with the development of these three asthma phenotypes. Twins and a gestational age of 28 weeks or less premature were associated with the development of transient early asthma and persistent asthma, but not late onset asthma. Triplets and above were associated with the development of transient early asthma, but not late onset or persistent asthma.

CONCLUSION

Various asthma phenotypes have different risk factors; therefore, their distinct risk factors should be identified in order to early diagnosis and treatment.

Critical Time Windows for Air Pollution Exposure and Birth Weight in a Multicity Canadian Pregnancy Cohort

BACKGROUND

Maternal prenatal exposure to air pollution has been associated with adverse birth outcomes. However, previous studies focused on a priori time intervals such as trimesters reported inconsistent associations.

OBJECTIVES

We investigated time-varying vulnerability of birth weight to fine particulate matter (PM2.5) and nitrogen dioxide (NO2) using flexible time intervals.

METHODS

We analyzed 1,300 live, full-term births from Maternal-Infant Research on Environmental Chemicals, a Canadian prospective pregnancy cohort spanning 10 cities (2008-2011). Daily PM2.5 and NO2 concentrations were estimated from ground-level monitoring, satellite models, and land-use regression, and assigned to participants from pre-pregnancy through delivery. We developed a flexible two-stage modeling method-using a Bayesian Metropolis-Hastings algorithm and empirical density threshold-to identify time-dependent vulnerability to air pollution without specifying exposure periods a priori. This approach identified critical windows with varying lengths (2-363 days) and critical windows that fell within, or straddled, predetermined time periods (i.e., trimesters). We adjusted the models for detailed infant and maternal covariates.

RESULTS

Critical windows associated with reduced birth weight were identified during mid- to late-pregnancy for both PM2.5 and NO2: -6 g (95% credible interval: -11, -1 g) and -5 g (-10, -0.1 g) per µg/m3 PM2.5 during gestational days 91-139 and 249-272, respectively; and -3 g (-5, -1 g) per ppb NO2 during days 55-145.

DISCUSSION

We used a novel, flexible selection method to identify critical windows when maternal exposures to air pollution were associated with decrements in birth weight. Our results suggest that air pollution impacts on fetal development may not be adequately captured by trimester-based analyses.

Programming of the lung by early-life infection

Many important human diseases, such as asthma, have their developmental origins in early life. Respiratory infections in particular may alter the course of asthma and may either protect against or promote the development of this disease. It is likely that the nature of the effects depends on the type and age of infection and is determined by the impact of infection on the immune and respiratory systems. Immunity in early life is plastic and can be moulded by antigen encounter, which may enhance or reinforce the asthmatic phenotype of early life, or induce protective responses. Chlamydial respiratory infections have specific effects and may increase asthma severity in early life by promoting systemic interleukin 13 responses and causing permanent changes in lung structure. Respiratory viral infections, such as those of respiratory syncytial virus and rhinovirus, promote pro-asthmatic responses in early life that contribute to the induction of asthma. By contrast, probiotics or infection or exposure to certain bacteria, such as Streptococcus pneumoniae, may have protective effects in asthma by increasing the numbers and activity of regulatory T cells. Here, we review the impact of infections on the developmental origins of asthma. Understanding these effects may lead to new therapeutic approaches for asthma that either target deleterious infections or utilize beneficial ones.

Perinatal risk factors for wheezing phenotypes in the first 8 years of life

BACKGROUND

A novel data-driven approach was used to identify wheezing phenotypes in pre-schoolchildren aged 0-8 years, in the Prevention and Incidence of Asthma and Mite Allergy (PIAMA) birth cohort. Five phenotypes were identified: never/infrequent wheeze, transient early wheeze, intermediate onset wheeze, persistent wheeze and late onset wheeze. It is unknown which perinatal risk factors drive development of these phenotypes.

OBJECTIVE

The objective of the study was to assess associations of perinatal factors with wheezing phenotypes and to identify possible targets for prevention.

METHODS

In the PIAMA study (n = 3963), perinatal factors were collected at 3 months, and wheezing was assessed annually until the age of 8 years. Associations between perinatal risk factors and the five wheezing phenotypes were assessed using weighted multinomial logistic regression models. Odds ratios were adjusted for confounding variables and calculated with 'never/infrequent wheeze' as reference category.

RESULTS

Complete data were available for 2728 children. Risk factors for transient early wheeze (n = 455) were male gender, maternal and paternal allergy, low maternal age, high maternal body mass index, short pregnancy duration, smoking during pregnancy, presence of older siblings and day-care attendance. Risk factors for persistent wheeze (n = 83) were male gender, maternal and paternal allergy, and not receiving breastfeeding for at least 12 weeks. Intermediate onset wheeze (n = 98) was associated with a lower birth weight and late onset wheeze (n = 45) with maternal allergy.

CONCLUSION AND CLINICAL RELEVANCE

We identified different risk factors for specific childhood wheezing phenotypes. Some of these are modifiable, such as maternal age and body mass index, smoking, day-care attendance and breastfeeding, and may be important targets for prevention programmes.

Acetaminophen and asthma

Acetaminophen is a widely used medication for the treatment of pain and fever in children and pregnant women. There is substantial epidemiological evidence in adults and children that acetaminophen use is associated with asthma symptoms. There is also a considerable body of evidence that supports a modest but consistent association of acetaminophen use in pregnancy and early infancy with asthma in later childhood. This relationship is robust to adjustment for a large range of potential confounding factors and, in some studies, shows clear evidence of a dose-dependent association but the possibility of confounding by indication has remained a concern. However, the epidemiological evidence is now compelling and there is a clear need to establish causation so that appropriate advice and interventions can be developed for children at risk of asthma. This requires randomised trials of analgesics and antipyretics, including acetaminophen, in a variety of clinical settings.

Imprinted gene expression in fetal growth and development

Experimental studies showed that genomic imprinting is fundamental in fetoplacental development by timely regulating the expression of the imprinted genes to overlook a set of events determining placenta implantation, growth and embryogenesis. We examined the expression profile of 22 imprinted genes which have been linked to pregnancy abnormalities that may ultimately influence childhood development. The study was conducted in a subset of 106 placenta samples, overrepresented with small and large for gestational age cases, from the Rhode Island Child Health Study. We investigated associations between imprinted gene expression and three fetal development parameters: newborn head circumference, birth weight, and size for gestational age. Results from our investigation show that the maternally imprinted/paternally expressed gene ZNF331 inversely associates with each parameter to drive smaller fetal size, while paternally imprinted/maternally expressed gene SLC22A18 directly associates with the newborn head circumference promoting growth. Multidimensional Scaling analysis revealed two clusters within the 22 imprinted genes which are independently associated with fetoplacental development. Our data suggest that cluster 1 genes work by assuring cell growth and tissue development, while cluster 2 genes act by coordinating these processes. Results from this epidemiologic study offer solid support for the key role of imprinting in fetoplacental development.

Early-life chlamydial lung infection enhances allergic airways disease through age-dependent differences in immunopathology

BACKGROUND

Asthma typically originates in early-life, and the impact of infection during immunologic maturation is a critical factor in disease pathogenesis. The progression of aberrant T(H)2 cell responses and disease development has been attributed to a lack of infections. However, exposure to specific pathogens such as Chlamydia may alter immunologic programming and predispose to asthma.

OBJECTIVE

To investigate the effects of chlamydial infection at different ages on allergic airways disease in later life.

METHODS

Neonatal, infant, or adult BALB/c mice were infected and 6 weeks later were sensitized and subsequently challenged with ovalbumin. Hallmark features of allergic airways disease were compared with uninfected allergic and nonallergic controls.

RESULTS

Early-life (neonatal and infant) but not adult chlamydial infection enhanced the development of hallmark features of asthma in ovalbumin-induced allergic airways disease. Notably early-life infection increased mucus-secreting cell numbers, IL-13 expression, and airway hyperresponsiveness. Neonatal infection attenuated eosinophil influx and ovalbumin-specific T(H)2 cytokine release and numbers of activated myeloid dendritic cells (DCs) in lymph nodes. By contrast, infant infection augmented features of allergic inflammation with increased airway eosinophils, T(H)2 cytokine, and DC responses. Both neonatal and infant infection increased systemic DC-induced IL-13 release from CD4(+) T cells. The timing of infection had significant effects on lung structure because neonatal but not infant or adult infection induced increases in alveolar diameter.

CONCLUSION

Early-life respiratory chlamydial infections modulate immune responses, alter lung function and structure, and enhance the severity of allergic airways disease in later life.

Airway remodelling in children: when does it start?

PURPOSE OF REVIEW

The review characterizes airway remodelling in childhood asthma and describes how early in life it is possible to detect, and possibly cure, the cellular and biochemical changes that characterize this event. This topic is timely and relevant since a variety of clinical and epidemiologic studies strongly suggest that in asthma, remodelling may start very early in life and that current prevention and treatment measures, including early avoidance measures and pharmaceutical interventions, are relatively ineffective in preventing the development of irreversible airway changes or in reverting them, once established.

RECENT FINDINGS

Recent findings show that structural changes characterizing remodelling, such as subepithelial basement membrane thickening, epithelial cell disruption, protease/antiprotease imbalance and neoangiogenesis, are detectable in children with asthma and even in children with respiratory symptoms or with atopy, before a clear clinical diagnosis of bronchial asthma is made.

SUMMARY

Identification of the early structural changes that may precede the development of asthma and of factors leading to permanent loss of lung function appear central to future asthma management.

Early detection of lung disease in preschool children with cystic fibrosis

PURPOSE OF REVIEW

Babies with cystic fibrosis are born with essentially normal lungs but rapidly develop inflammation and infection. Evaluation is generally based on history and physical examination until school age, when children become able to perform spirometry. In these 'silent years', however, unrecognized lung damage can occur. Recently, techniques to improve the evaluation of preschool children have been developed, and an assessment of where they fit into clinical and research practice is now needed. This is particularly urgent to select groups of children for new, phenotype-specific therapies, and monitor their effects.

RECENT FINDINGS

The techniques in which there have been major recent advances include physiologic methods, particularly indices of gas mixing; imaging techniques, especially high-resolution computed tomographic scanning; and bronchoscopic studies. The clinical roles of these techniques need to be explored, as do comparisons between techniques.

SUMMARY

The preschool years need no longer be silent. Some simple techniques such as spirometry can be performed in much younger children than conventionally believed to be practical. Others currently require sophisticated apparatus (lung clearance index) or carry potential risks (radiation, high-resolution computed tomographic scanning). We need good long-term, prospective comparisons of these techniques, with measurement of inflammatory markers. We also need to know which are sufficiently reproducible, and indicative of prognosis, for use as endpoints in clinical trials.