Julian L. Allen

Variants of DENND1B Associated with Asthma in Children

BACKGROUND Asthma is a complex disease that has genetic and environmental causes. The genetic factors associated with susceptibility to asthma remain largely unknown. METHODS We carried out a genomewide association study involving children with asthma. The sample included 793 North American children of European ancestry with persistent asthma who required daily inhaled glucocorticoid therapy and 1988 matched controls (the discovery set). We also tested for genomewide association in an independent cohort of 917 persons of European ancestry who had asthma and 1546 matched controls (the replication set). Finally, we tested for an association between 20 single-nucleotide polymorphisms (SNPs) at chromosome 1q31 and asthma in 1667 North American children of African ancestry who had asthma and 2045 ancestrally matched controls. RESULTS In our meta-analysis of all samples from persons of European ancestry, we observed an association, with genomewide significance, between asthma and SNPs at the previously reported locus on 17q21 and an additional eight SNPs at a novel locus on 1q31. The SNP most strongly associated with asthma was rs2786098 (P=8.55x10(-9)). We observed replication of the association of asthma with SNP rs2786098 in the independent series of persons of European ancestry (combined P=9.3x10(-11)). The alternative allele of each of the eight SNPs on chromosome 1q31 was strongly associated with asthma in the children of African ancestry (P=1.6x10(-13) for the comparison across all samples). The 1q31 locus contains the 1q31 locus contains DENND1B, a gene expressed by natural killer cells and dendritic cells. DENND1B protein is predicted to interact with the tumor necrosis factor α receptor [corrected]. CONCLUSIONS We have identified a locus containing DENND1B on chromosome 1q31.3 that is associated with susceptibility to asthma.

Hypoxaemia in sickle cell disease: biomarker modulation and relevance to pathophysiology

BACKGROUND Nocturnal oxyhaemoglobin desaturation might have a role in CNS complications related to sickle cell disease, and rates of painful crises. We attempted to examine the biological relations, and describe the haematological risk factors for oxyhaemoglobin desaturation. METHODS The study population included children with sickle cell disease and controls. Cellular activation was assessed by measurement of soluble vascular cell adhesion molecule 1, P-selectin, L-selectin, and leukotriene B4. Erythrocyte-endothelial adhesion and routine haematological variables were assessed. Oxygen saturation (SaO2) was measured by pulse oximetry while children were awake and asleep. Children with a mean sleeping SaO2 of < or =93% were identified as hypoxaemic. Children were divided into four groups: controls (ten children), HbSC (nine, all normoxic), HbSS normoxic (13), and HbSS hypoxaemic (15). FINDINGS Among haematological variables, sleeping SaO2 correlated only with packed-cell volume (r=0.7; p<0.0001). Inverse relations were noted between sleeping SaO2 and adhesion (-0.45; p<0.01), and markers of white-cell (-0.51; p<0.01), platelet (-0.61; p<0.001), and endothelial activation (-0.46; p<0.01). In the HbSS group who had sleeping hypoxaemia, waking SaO2 measurements showed continuing hypoxaemia, with similar correlation between SaO2 and cell activation markers. INTERPRETATION Our adhesion-related findings suggest a potential mechanism for the increased occurrence of clinical vaso-occlusive crises in individuals with sickle cell disease who have oxyhaemoglobin desaturation. Release of cellular mediators in hypoxaemia, and the relation between anaemia and oxyhaemoglobin desaturation, suggest that risk factors for stroke, including anaemia, might have a role in CNS-vasculopathy through hypoxia-mediated pathways. Further more, hypoxaemia in the older child also occurs during the day; such mild untreated hypoxia could lead to an increased risk of vaso-occlusive episodes.

Airway hyperreactivity in children with sickle cell disease.

Progressive restrictive defect with increasing age, obstructive lung disease, and bronchodilator responsiveness have been reported in sickle cell disease (SCD). Because airway hyperreactivity (AHR) can be underestimated when assessed by bronchodilator responsiveness in patients with normal baseline lung function, the aim of this study was to investigate the prevalence of AHR in SCD by cold-air bronchial provocation testing, and to assess whether AHR can be present in symptom-free patients with SCD. Forty patients aged 6 to 19 years (mean, 10.7 years +/- 3.5 SD) performed pulmonary function tests. Eighteen were known to have a history of reactive airway disease (RAD group), and 22 had no known history of RAD (non-RAD group). A control group, aged 6 to 7 years (mean, 10.5 +/- 3.1 years), consisted of 10 siblings of the non-RAD SCD group. There were no significant differences in age and height among the groups. If the forced expiratory volume in 1 second (FEV1) was greater than 70%, cold air challenge (CACh) was performed; if the FEV1 was less than 70%, aerosolized bronchodilator therapy was given. A decrease in FEV1 of more than 10% after CACh or an increase in FEV1 of 12% or greater after bronchodilator inhalation was considered evidence of AHR. In the RAD group, the total lung capacity was 88.9% +/- 14.0% of race-corrected predicted values, the forced vital capacity was 91.2% +/- 12.6%, and FEV1 was 85.3% +/- 16.2%. The mean maximal percent fall in FEV1 after CACh (n = 13) was 18.5% +/- 9.6% and was greater than 10% in 11 of 13 patients. The mean increase in FEV1 after bronchodilator therapy (n = 5) was 11.5% +/- 8.3%, and it was greater than 12% in 4 of 5 patients. In the non-RAD group the baseline total lung capacity was 101.6% +/- 11.7%, forced vital capacity was 95.5% +/- 10.2%, and FEV1 was 93.3% +/- 13.2%. The mean maximal percent fall in FEV1 after CACh (n = 19) was 14.1% +/- 8.8% and was greater than 10% in 13 of 19 patients. The mean increase in FEV1 after bronchodilator therapy (n = 3) was 14.7% +/- 11.3%, and was 12% of greater in 1 of 3 patients. In the control group the baseline total lung capacity was 105.7% +/- 12.1%, forced vital capacity was 96.2% +/- 11.1%, and FEV1 was 92.9% +/- 10.3%. The mean maximal percent fall in FEV1 was 5.0% +/- 2.5%, and was greater than 10% in none of 10 patients. The prevalence of AHR in the control group, the RAD group, and the non-RAD group was zero, 83%, and 64%, respectively (p < 0.0001). The overall prevalence in the SCD group was 73%. We conclude that there is a high prevalence of AHR in children with SCD and that airway hyperreactivity may exist in patients with SCD even in the absence of the clinical symptoms of RAD. AHR may be a significant component of sickle cell lung disease.

ORMDL3 variants associated with asthma susceptibility in North Americans of European ancestry

are the dominant isoforms in human MCs. We have previously shown that T cells could activate MCs by means of heterotypic adhesion. This pattern of activation involves the MAPK5 system and resulted in release of different cytokines. In this study we report that N-Ras is activated downstream of this pathway and is localized to the PM. The question as to which of the 2 GEFs, RasGRP1 or RasGRP4, is principal in MCs is still a matter of debate. Our data support a crucial role for RasGRP1. This work suggests that targeting the Ras pathway might be a possible treatment option for conditions in which MCs interact with T cells, such as sarcoidosis, rheumatoid arthritis, and graft tolerance.

An Official American Thoracic Society Workshop Report: Optimal Lung Function Tests for Monitoring Cystic Fibrosis, Bronchopulmonary Dysplasia, and Recurrent Wheezing in Children Less Than 6 Years of Age

Although pulmonary function testing plays a key role in the diagnosis and management of chronic pulmonary conditions in children under 6 years of age, objective physiologic assessment is limited in the clinical care of infants and children less than 6 years old, due to the challenges of measuring lung function in this age range. Ongoing research in lung function testing in infants, toddlers, and preschoolers has resulted in techniques that show promise as safe, feasible, and potentially clinically useful tests. Official American Thoracic Society workshops were convened in 2009 and 2010 to review six lung function tests based on a comprehensive review of the literature (infant raised-volume rapid thoracic compression and plethysmography, preschool spirometry, specific airway resistance, forced oscillation, the interrupter technique, and multiple-breath washout). In these proceedings, the current state of the art for each of these tests is reviewed as it applies to the clinical management of infants and children under 6 years of age with cystic fibrosis, bronchopulmonary dysplasia, and recurrent wheeze, using a standardized format that allows easy comparison between the measures. Although insufficient evidence exists to recommend incorporation of these tests into the routine diagnostic evaluation and clinical monitoring of infants and young children with cystic fibrosis, bronchopulmonary dysplasia, or recurrent wheeze, they may be valuable tools with which to address specific concerns, such as ongoing symptoms or monitoring response to treatment, and as outcome measures in clinical research studies.

Mechanisms of nocturnal oxyhemoglobin desaturation in children and adolescents with sickle cell disease

Oxyhemoglobin desaturation in patients with sickle cell disease has been proposed as a possible mechanism in the initiaton of vasco‐occlusive pain crises. Nocturnal oxyhemoglobin desaturation (NOD) has been described with a prevalence of up to 40% in children and adolescents with sickle cell disease. The objective of this study was to evaluate the mechanisms of nocturnal oxyhemoglobin desaturation in sickle cell disease and determine the role of obstructive sleep apnea. We performed 16‐channel polysomnograms and pulmonary function testing in 20 patients with sickle cell disease (ages 7–21 years) who had documented desaturation on home oximetry studies.

Beliefs and Barriers to Follow-up After an Emergency Department Asthma Visit: A Randomized Trial

BACKGROUND: Studies in urban emergency departments (EDs) have found poor quality of chronic asthma care and identified beliefs and barriers associated with low rates of follow-up with a primary care provider (PCP). OBJECTIVES: To develop an ED-based intervention including asthma symptom screening, a video addressing beliefs and a mailed reminder; and measure the effect on PCP follow-up and asthma-related outcomes. METHODS: This randomized, controlled trial enrolled children aged 1 to 18 years who were discharged after asthma treatment in an urban pediatric ED. Control subjects received instructions to follow-up with a PCP within 3 to 5 days. In addition, intervention subjects (1) received a letter to take to their PCP if they screened positive for persistent asthma symptoms, (2) viewed a video featuring families and providers discussing the importance of asthma control, and (3) received a mailed reminder to follow-up with a PCP. All subjects were contacted by telephone 1, 3, and 6 months after the ED visit, and follow-up was confirmed by PCP record review. Asthma-related quality of life (AQoL), symptoms, and beliefs about asthma care were assessed by using validated surveys. RESULTS: A total of 433 subjects were randomly assigned, and baseline measures were similar between study groups. After the intervention and before ED discharge, intervention subjects were more likely to endorse beliefs about the benefits of follow-up than controls. However, rates of PCP follow-up during the month after the ED visit (44.5%) were similar to control subjects (43.8%) as were AQoL, medication use, and ED visits. CONCLUSIONS: An ED-based intervention influenced beliefs but did not increase PCP follow-up or asthma-related outcomes.

Measurement of hemoglobin saturation by oxygen in children and adolescents with sickle cell disease

Pulse oximetry is a noninvasive method of measuring oxyhemoglobin saturation. The validity of pulse oximetry in sickle cell disease (SCD) has been questioned. We evaluated pulse oximetry, arterial blood gas analysis, and co‐oximetry in patients with SCD, and we assessed the effect of dyshemoglobin and altered blood‐oxygen affinity on their accuracy. Sixteen patients with SCD aged 7–21 years had arterial and venous blood drawn and transcutaneous pulse oximetry performed. Oxyhemoglobin dissociation curves were plotted from the venous blood of 15 patients.

Effects of Inspiratory Resistive Loading on Chest Wall Motion and Ventilation: Differences between Preterm and Full-Term Infants

The ability to maintain effective tidal volume and minute ventilation during resistive loaded breathing depends on both adequate central neural respiratory output response and respiratory system mechanical properties such as respiratory muscle strength and chest wall stability. We hypothesized that chest wall instability limits the ability of the preterm (PT) infant to respond to inspiratory resistive loading (IRL) compared with full-term (FT) infants. To test this hypothesis, we subjected eight FT and 10 PT infants to IRL with loads of 1.3, 2, and 6 times intrinsic lung resistance and measured steady state tidal volume (VT), minute ventilation (VE), and chest wall motion. Thoracoabdominal asynchrony was measured by respiratory inductive plethysmography and quantitated by measuring the phase angle, θ between rib cage and abdominal motion (0° = synchronous motion, 180° = paradoxic motion). At baseline, VT/kg (mL/kg, mean ± SEM) was similar between PT (7.0 ± 0.7) and FT (7.5 ± 0.5) infants. VE/kg (mL/min/kg) was greater in PT (545 ± 50) than in FT (385 ± 33) infants (p <0.05) as a result of increased respiratory frequency in the former. PT infants demonstrated significantly greater chest wall asynchrony (θ = 38 ± 9°) than FT infants (θ = 9 ± 3°) (p < 0.01). With the highest resistive loads, VT decreased significantly in the PT but not the FT infants. Furthermore, during IRL, VE decreased to 417 ± 50 mL/min/kg (p < 0.05) and θ increased to 56 ± 7 (p < 0.05) in the PT infants, whereas no significant change in either value was observed in the FT group. We conclude that IRL breathing significantly decreases VT and VE in PT infants. Chest wall instability in the PT group, as reflected by the increased asynchrony between rib cage and abdomen, contributes to the relative inability of PT infants to maintain ventilation during inspiratory resistive loaded breathing.

Development and validation of an instrument to measure asthma symptom control in children

Background. Few instruments exist to measure control of asthma symptoms in children. A brief instrument administered at healthcare visits could provide a more consistent approach to symptom recognition for patients and providers. Objective. To develop a Pediatric Asthma Control Tool to measure asthma symptom control at pediatric healthcare visits and evaluate the instrument compared to expert assessment and an asthma-related quality-of-life (QOL) measure. Design/method. A preliminary 14-item instrument was generated through a process of literature review, meetings of institutional experts, and focus groups of parents and providers. The preliminary survey measured asthma control over the past 3 months in 2 domains: frequency of asthma flares and presence of symptoms when the child was at their best. Persistent symptoms were categorized according to published national asthma guidelines (NAEPP). The instrument and an asthma-related QOL measure were administered in the waiting room before a specialist visit for asthma. After the visit the specialist independently assessed asthma control in both domains on a 7-point Likert scale. Internal consistency and assessments of criterion and construct validity were calculated using standard statistics. Results. A total of 200 subjects ranging from 1 to 18 years of age and their caregivers were enrolled; 60% were male. During the prior 3 months, 19% had an emergency visit and 24% described persistent asthma symptoms. After item review the instrument was shortened to five items each for frequency of flares and symptoms at best. Internal consistency was high for each of these domains (Cronbach s alpha = 0.81/0.83, respectively). Correlation of each domain was good when compared to expert assessment (r = 0.54/0.59) and QOL (r = 0.61/0.77). Conclusions. Responses to a 10-item instrument to measure control of asthma symptoms in children at a healthcare visit demonstrated internal consistency and criterion and construct validity.