Analyses of 1,236 genotyped primary ciliary dyskinesia individuals identify regional clusters of distinct DNA variants and significant genotype-phenotype correlations.

BACKGROUND: Primary ciliary dyskinesia (PCD) represents a group of rare hereditary disorders characterized by deficient ciliary airway clearance that can be associated with laterality defects. We aimed to describe the underlying gene defects, geographical differences in genotypes and their relationship to diagnostic findings and clinical phenotypes. METHODS: Genetic variants and clinical findings (age, sex, body mass index, laterality defects, FEV1) were collected from 19 countries using the ERN LUNG International PCD Registry. Genetic data were evaluated according to ACMG guidelines. We assessed regional distribution of implicated genes and genetic variants as well as genotype correlations with laterality defects and FEV1. RESULTS: 1236 individuals carried 908 distinct pathogenic DNA variants in 46 PCD genes. We found considerable variation in the distribution of PCD genotypes across countries due to the presence of distinct founder variants. The prevalence of PCD genotypes associated with pathognomonic ultrastructural defects (mean 72%; 47-100%) and laterality defects (mean 42%; 28-69%) varied widely among the countries. The prevalence of laterality defects was significantly lower in PCD individuals without pathognomonic ciliary ultrastructure defects (18%). The PCD cohort had a reduced median FEV1 z-score (-1.66). In the group of individuals with CCNO (-3.26), CCDC39 (-2.49), and CCDC40 (-2.96) variants, FEV1 z-scores were significantly lower, while the group of DNAH11 (-0.83) and ODAD1 (-0.85) variant individuals had significantly milder FEV1 z-score reductions compared to the whole PCD cohort. CONCLUSION: This unprecedented multinational dataset of DNA variants and information on their distribution across countries facilitates interpretation of genetic epidemiology of PCD and provides prediction of diagnostic and phenotypic features such as the course of lung function.

Recurrent wheezing during the first 3 years of life in a birth cohort of moderate-to-late preterm infants.

BACKGROUND: Data addressing short- and long-term respiratory morbidity in moderate-late preterm infants are limited. We aim to determine the incidence of recurrent wheezing and associated risk and protective factors in these infants during the first 3 years of life. METHODS: Prospective, multicenter birth cohort study of infants born at 32+0 to 35+0  weeks' gestation and followed for 3 years to assess the incidence of physician-diagnosed recurrent wheezing. Allergen sensitization and pulmonary function were also studied. We used multivariate mixed-effects models to identify risk factors associated with recurrent wheezing. RESULTS: A total of 977 preterm infants were enrolled. Rates of recurrent wheezing during year (Y)1 and Y2 were similar (19%) but decreased to 13.3% in Y3. Related hospitalizations significantly declined from 6.3% in Y1 to 0.75% in Y3. Independent risk factors for recurrent wheezing during Y2 and Y3 included the following: day care attendance, acetaminophen use during pregnancy, and need for mechanical ventilation. Atopic dermatitis on Y2 and male sex on Y3 were also independently associated with recurrent wheezing. Palivizumab prophylaxis for RSV during the first year of life decreased the risk or recurrent wheezing on Y3. While there were no differences in rates of allergen sensitization, pulmonary function tests (FEV0.5 ) were significantly lower in children who developed recurrent wheezing. CONCLUSIONS: In moderate-to-late premature infants, respiratory symptoms were associated with lung morbidity persisted during the first 3 years of life and were associated with abnormal pulmonary function tests. Only anti-RSV prophylaxis exerted a protective effect in the development of recurrent wheezing.

Risk factors for bronchiolitis, recurrent wheezing, and related hospitalization in preterm infants during the first year of life.

BACKGROUND: Airway diseases are highly prevalent in infants and cause significant morbidity. We aimed to determine the incidence and risk factors for respiratory morbidity in a Spanish cohort of moderate-to-late preterm (MLP) infants prospectively followed during their first year of life. METHODS: SAREPREM is a multicenter, prospective, longitudinal study. Preterm infants born at 32-35 weeks of gestation with no comorbidities were enrolled within 2 weeks of life and followed at 2-4 weeks, 6, and 12 months of age. Multivariate mixed-models were performed to identify independent risk factors associated with (i) development of bronchiolitis, (ii) recurrent wheezing, or (iii) related hospital admissions. RESULTS: Overall, 977 preterm infants were included, and 766 (78.4%) completed follow-up. Of those, 365 (47.7%) developed bronchiolitis during the first year, 144 (18.8%) recurrent wheezing, and 48 (6.3%) were hospitalized. While low birthweight, day care attendance (DCA) and school-age siblings were significantly and independently associated with both the development of bronchiolitis and recurrent wheezing, lower maternal age increased the risk for bronchiolitis and respiratory-related hospitalizations. Lastly, mechanical ventilation was associated with a higher risk of bronchiolitis and history of asthma in any parent increased the likelihood of developing recurrent wheezing. CONCLUSIONS: In this study, several non-modifiable parameters (family history of asthma, low birthweight, need for mechanical ventilation) and modifiable parameters (young maternal age, DCA, or exposure to school-age siblings) were identified as significant risk factors for the development of bronchiolitis and recurrent wheezing during the first year of life in MLP infants.

Elevated Prostaglandin E2 Synthesis Is Associated with Clinical and Radiological Disease Severity in Cystic Fibrosis.

Background: Previous studies found high but very variable levels of tetranor-PGEM and PGDM (urine metabolites of prostaglandin (PG) E2 and PGD2, respectively) in persons with cystic fibrosis (pwCF). This study aims to assess the role of cyclooxygenase COX-1 and COX-2 genetic polymorphisms in PG production and of PG metabolites as potential markers of symptoms' severity and imaging findings. Methods: A total of 30 healthy subjects and 103 pwCF were included in this study. Clinical and radiological CF severity was evaluated using clinical scoring methods and chest computed tomography (CT), respectively. Urine metabolites were measured using liquid chromatography/tandem mass spectrometry. Variants in the COX-1 gene (PTGS1 639 C>A, PTGS1 762+14delA and COX-2 gene: PTGS2-899G>C (-765G>C) and PTGS2 (8473T>C) were also analyzed. Results: PGE-M and PGD-M urine concentrations were significantly higher in pwCF than in controls. There were also statistically significant differences between clinically mild and moderate disease and severe disease. Patients with bronchiectasis and/or air trapping had higher PGE-M levels than patients without these complications. The four polymorphisms did not associate with clinical severity, air trapping, bronchiectasis, or urinary PG levels. Conclusions: These results suggest that urinary PG level testing can be used as a biomarker of CF severity. COX genetic polymorphisms are not involved in the variability of PG production.

Primary Ciliary Dyskinesia and Retinitis Pigmentosa: Novel RPGR Variant and Possible Modifier Gene.

We report a novel RPGR missense variant co-segregated with a familial X-linked retinitis pigmentosa (XLRP) case. The brothers were hemizygous for this variant, but only the proband presented with primary ciliary dyskinesia (PCD). Thus, we aimed to elucidate the role of the RPGR variant and other modifier genes in the phenotypic variability observed in the family and its impact on motile cilia. The pathogenicity of the variant on the RPGR protein was evaluated by in vitro studies transiently transfecting the mutated RPGR gene, and immunofluorescence analysis on nasal brushing samples. Whole-exome sequencing was conducted to identify potential modifier variants. In vitro studies showed that the mutated RPGR protein could not localise to the cilium and impaired cilium formation. Accordingly, RPGR was abnormally distributed in the siblings' nasal brushing samples. In addition, a missense variant in CEP290 was identified. The concurrent RPGR variant influenced ciliary mislocalisation of the protein. We provide a comprehensive characterisation of motile cilia in this XLRP family, with only the proband presenting PCD symptoms. The variant's pathogenicity was confirmed, although it alone does not explain the respiratory symptoms. Finally, the CEP290 gene may be a potential modifier for respiratory symptoms in patients with RPGR mutations.

Arrangement of residence before hospital discharge for children on home-invasive mechanical ventilation.

Children on long-term home mechanical ventilation are a growing population due to clinical and technological advances and the benefit for the child's quality of life. Invasive home ventilation is one of the most complex therapies offered in the home setting, requiring adequate home environment and appropriate equipment and supplies before discharge. The transition from hospital to home represents a vulnerable period that can be facilitated with an established transition plan with multidisciplinary team involvement. Readiness for home care is achieved when the patient is stable and has been transitioned from a critical care ventilator to a home mechanical ventilator. In parallel, comprehensive competency-based training regarding the knowledge and skills needed to help families use the equipment confidently and safely. Before discharge, families should be counseled on an adequate home environment to ensure a safe transition. The residence arrangement may include physical space modifications, verifying electrical installation, or moving to another home. Durable medical equipment and supplies must be ordered, and community healthcare support arranged. Parents should receive practical advice on setting up the equipment at home and on preventive measures to minimize complications related to tracheostomy and ventilator dependence, including regular maintenance and replacement of necessary equipment. Given the overall impact of invasive ventilation on home life, a structured home care action package is essential to alleviate the burdens involved.

Incidence and Prevalence of Children's Diffuse Lung Disease in Spain.

BACKGROUND: Children's diffuse lung disease, also known as children's Interstitial Lung Diseases (chILD), are a heterogeneous group of rare diseases with relevant morbidity and mortality, which diagnosis and classification are very complex. Epidemiological data are scarce. The aim of this study was to analyse incidence and prevalence of chILD in Spain. METHODS: Multicentre observational prospective study in patients from 0 to 18 years of age with chILD to analyse its incidence and prevalence in Spain, based on data reported in 2018 and 2019. RESULTS: A total of 381 cases with chILD were notified from 51 paediatric pulmonology units all over Spain, covering the 91.7% of the paediatric population. The average incidence of chILD was 8.18 (CI 95% 6.28-10.48) new cases/million of children per year. The average prevalence of chILD was 46.53 (CI 95% 41.81-51.62) cases/million of children. The age group with the highest prevalence were children under 1 year of age. Different types of disorders were seen in children 2-18 years of age compared with children 0-2 years of age. Most frequent cases were: primary pulmonary interstitial glycogenosis in neonates (17/65), neuroendocrine cell hyperplasia of infancy in infants from 1 to 12 months (44/144), idiopathic pulmonary haemosiderosis in children from 1 to 5 years old (13/74), hypersensitivity pneumonitis in children from 5 to 10 years old (9/51), and scleroderma in older than 10 years old (8/47). CONCLUSIONS: We found a higher incidence and prevalence of chILD than previously described probably due to greater understanding and increased clinician awareness of these rare diseases.

The disease-specific clinical trial network for primary ciliary dyskinesia: PCD-CTN.

Primary ciliary dyskinesia (PCD) is a rare genetic disorder characterised by impaired mucociliary clearance leading to irreversible lung damage. In contrast to other rare lung diseases like cystic fibrosis (CF), there are only few clinical trials and limited evidence-based treatments. Management is mainly based on expert opinions and treatment is challenging due to a wide range of clinical manifestations and disease severity. To improve clinical and translational research and facilitate development of new treatments, the clinical trial network for PCD (PCD-CTN) was founded in 2020 under the framework of the European Reference Network (ERN)-LUNG PCD Core. Applications from European PCD sites interested in participating in the PCD-CTN were requested. Inclusion criteria consisted of patient numbers, membership of ERN-LUNG PCD Core, use of associated standards of care, experience in PCD and/or CF clinical research, resources to run clinical trials, good clinical practice (GCP) certifications and institutional support. So far, applications from 22 trial sites in 18 European countries have been approved, including >1400 adult and >1600 paediatric individuals with PCD. The PCD-CTN is headed by a coordinating centre and consists of a steering and executive committee, a data safety monitoring board and committees for protocol review, training and standardisation. A strong association with patient organisations and industrial companies are further cornerstones. All participating trial sites agreed on a code of conduct. As CTNs from other diseases have demonstrated successfully, this newly formed PCD-CTN operates to establish evidence-based treatments for this orphan disease and to bring new personalised treatment approaches to patients.

Implementation of a Gene Panel for Genetic Diagnosis of Primary Ciliary Dyskinesia. / Implementación de un panel de genes para el diagnóstico genético de la discinesia ciliar primaria.

INTRODUCTION: Primary ciliary dyskinesia (PCD) is characterized by an alteration in the ciliary structure causing difficulty in the clearance of respiratory secretions. Diagnosis is complex and based on a combination of techniques. The objective of this study was to design a gene panel including all known causative genes, and to corroborate their diagnostic utility in a cohort of Spanish patients. METHODS: This was a multicenter cross-sectional study of patients with a high suspicion of PCD, according to European Respiratory Society criteria, designed around a gene panel for massive sequencing using SeqCap EZ capture technology that included 44 genes associated with PCD. RESULTS: We included 79 patients, 53 of whom had a diagnosis of confirmed or highly probable PCD. The sensitivity of the gene panel was 81.1%, with a specificity of 100%. Candidate variants were found in some of the genes of the panel in 43 patients with PCD, 51.2% (22/43) of whom were homozygotes and 48.8% (21/43) compound heterozygotes. The most common causative genes were DNAH5 and CCDC39. We found 52 different variants, 36 of which were not previously described in the literature. CONCLUSIONS: The design and implementation of a tailored gene panel produces a high yield in the genetic diagnosis of PCD. This panel provides a better understanding of the causative factors involved in these patients and lays down the groundwork for future therapeutic approaches.

Immunofluorescence Analysis as a Diagnostic Tool in a Spanish Cohort of Patients with Suspected Primary Ciliary Dyskinesia.

Primary ciliary dyskinesia (PCD) is an autosomal recessive rare disease caused by an alteration of ciliary structure. Immunofluorescence, consisting in the detection of the presence and distribution of cilia proteins in human respiratory cells by fluorescence, has been recently proposed as a technique to improve understanding of disease-causing genes and diagnosis rate in PCD. The objective of this study is to determine the accuracy of a panel of four fluorescently labeled antibodies (DNAH5, DNALI1, GAS8 and RSPH4A or RSPH9) as a PCD diagnostic tool in the absence of transmission electron microscopy analysis. The panel was tested in nasal brushing samples of 74 patients with clinical suspicion of PCD. Sixty-eight (91.9%) patients were evaluable for all tested antibodies. Thirty-three cases (44.6%) presented an absence or mislocation of protein in the ciliary axoneme (15 absent and 3 proximal distribution of DNAH5 in the ciliary axoneme, 3 absent DNAH5 and DNALI1, 7 absent DNALI1 and cytoplasmatic localization of GAS8, 1 absent GAS8, 3 absent RSPH9 and 1 absent RSPH4A). Fifteen patients had confirmed or highly likely PCD but normal immunofluorescence results (68.8% sensitivity and 100% specificity). In conclusion, immunofluorescence analysis is a quick, available, low-cost and reliable diagnostic test for PCD, although it cannot be used as a standalone test.

[50 years of the Neonatal Screening Program in Catalonia.] / 50 años del Programa de Cribado Neonatal en Cataluña.

The Catalonian Newborn Screening Program (CNSP) began in 1969, in Barcelona. It was promoted by Dr. Juan Sabater Tobella and supported by Barcelona Provincial Council and Juan March Foundation. That is how the Institute of Clinical Biochemistry was born, whose aims were diagnosis, research and teaching, along with the spirit of contributing to the prevention of mental retardation. The CNSP began with the detection of phenylketonuria (PKU), and, in 1982, the Program was expanded with the inclusion of congenital hypothyroidism detection. Towards 1990, the Program covered almost 100% of all newborns (NB) in Catalonia. In 1999, the CNSP was expanded with the incorporation of cystic fibrosis. It took fourteen years, until 2013, to make the largest expansion so far, with the incorporation of 19 metabolic diseases to the screening panel. The detection of sickle cell disease began in 2015 and in 2017 the detection of severe combined immunodeficiency was included. Currently, the CNSP includes 24 diseases in its main panel. Since 1969, 2,787,807 NBs have been screened, of whom 1,724 have been diagnosed with any of these diseases, and 252 of other disorders by differential diagnosis with those included in the main panel. The global prevalence is 1: 1,617 NBs affected by any of the diseases included in the CNSP and 1: 1,140 NBs if incidental findings diagnosed through the CNSP are included.

El Programa de Cribado Neonatal de Cataluña (PCNC) se inició en el año 1969, en Barcelona, impulsado por el Dr. Juan Sabater Tobella y apoyado por la Diputación de Barcelona y la Fundación Juan March. Así nació el Instituto de Bioquímica Clínica para acometer funciones asistenciales, de investigación y docencia, con el espíritu de contribuir a la prevención del retraso mental. El PCNC se inició con la detección de la fenilcetonuria (PKU) y en el año 1982 se amplió con la detección del hipotiroidismo congénito. Hacia el año 1990 la cobertura territorial llegó casi al 100% de todos los recién nacidos en Cataluña. En 1999 se amplió el PCNC con la incorporación de la fibrosis quística y tras catorce años, en 2013, se realizó la ampliación más numerosa hasta ahora, con la incorporación de la detección de 19 enfermedades metabólicas hereditarias. En el año 2015 comenzó la detección de la enfermedad de células falciformes y en el 2017 la detección de la inmunodeficiencia combinada grave. Actualmente, el PCNC incluye la detección de 24 enfermedades. Desde su inicio en el año 1969, se han cribado 2.787.807 recién nacidos, de los cuales 1.724 han sido diagnosticados de alguna de las 24 enfermedades que componen nuestro panel principal y 252 por diagnóstico diferencial de las primeras. En total la prevalencia global es de 1:1.617 RN afectos de alguna de las enfermedades incluidas en el PCNC y de 1:1.140 RN si se incluyen los hallazgos incidentales encontrados.

Isolated pulmonary interstitial glycogenosis associated with alveolar growth abnormalities: A long-term follow-up study.

INTRODUCTION: Pulmonary interstitial glycogenosis (PIG) is a rare infant interstitial lung disease characterized by an increase in the number of interstitial mesenchymal cells, presenting as enhanced cytoplasmic glycogen, and is considered to represent the expression of an underlying lung development disorder. METHODS: This study describes the clinical, radiological, and functional characteristics and long-term outcomes (median 12 years) of nine infants diagnosed with isolated PIG associated with alveolar simplification in the absence of other diseases. RESULTS: All patients presented with tachypnea. Additionally, seven patients had breathing difficulties and hypoxemia. Abnormalities in chest-computerized tomography (CT) with a pattern of ground-glass opacity, septal thickening, and air trapping were observed in all individuals, with images suggesting abnormal alveolar growth (parenchymal bands and architectural distortion). All lung biopsies showed alveolar simplification associated with an increased number of interstitial cells, which appeared as accumulated cytoplasmic glycogen. In the follow-up, all patients were asymptomatic. The respiratory function test was normal in only two patients. Five children showed an obstructive pattern, and two children showed a restrictive pattern. Chest-CT, performed after an average of 6.5 years since the initial investigation, revealed a partial improvement of the ground-glass opacity pattern; however, relevant alterations persisted. CONCLUSION: Although the patients with PIG in the absence of other associated pathologies had a good clinical outcome, significant radiographic alterations and sequelae in lung function were still observed after a median follow-up of 12 years, suggesting that PIG is a marker of some other persistent abnormalities in lung growth, which have effects beyond the symptomatic period.

Validation of Global Lung Function Initiative and All Ages Reference Equations for Forced Spirometry in Healthy Spanish Preschoolers. / Validación de las ecuaciones propuestas por la Iniciativa Global de Función Pulmonar (GLI) y las de Todas las Edades para espirometría forzada en preescolares sanos españoles.

INTRODUCTION: Recent publication of multi-ethnic spirometry reference equations for subjects aged from 3-95 years aim to avoid age-related discontinuities and provide a worldwide standard for interpreting spirometric test results. OBJECTIVES: To assess the agreement of the Global Lung Function Initiative (GLI-2012) and All ages (FEV0.5) reference equations with the Spanish preschool lung function data. To verify the appropriateness of these reference values for clinical use in Spanish preschool children. METHODS: Spirometric measurements were obtained from children aged 3 to 6 years attending 10 randomly selected schools in Barcelona (Spain). Stanojevic's quality control criteria were applied. Z-scores were calculated for the spirometry outcomes based on the GLI equations. If the z-score (mean) of each parameter was close to 0, with a maximum variance of ± 0.5 from the mean and a standard deviation of 1, the GLI-2012 equations would be applicable in our population. RESULTS: Of 543 children recruited, 405 (74.6%) were 'healthy', and of these, 380 were Caucasians. Of these 380, 81.6% (169 females, 141 males) performed technically acceptable and reproducible maneuvers to assess FEVt, and 69.5% achieved a clear end-expiratory plateau. Z-scores for FVC, FEV1, FEV1/FVC, FEV0.75, FEV0.75/FVC, FEV0.5, FEF75 and FEF25-75 all fell within ± 0.5, except for FEV1/FVC (0.53 z-scores). CONCLUSIONS: GLI equations are appropriate for Spanish preschool children. These data provide further evidence to support widespread application of the GLI reference equations.

[Pulmonary hypoplasia: An analysis of cases over a 20-year period]. / Hipoplasia pulmonar: análisis de la casuística durante 20 años.

INTRODUCTION: Pulmonary hypoplasia is the most frequent congenital anomaly associated with perinatal mortality. MATERIAL AND METHODS: A retrospective and descriptive review was conducted on cases of patients diagnosed with pulmonary hypoplasia between 1995 and 2014 in a tertiary university hospital. An analysis was made of the prenatal imaging, clinical manifestations, post-natal diagnostic tests, treatment and management, long-term follow up, and survival data. RESULTS: A total of 60 cases were identified, all of them with prenatal imaging. Sixteen patients required foetal surgery. Congenital diaphragmatic hernia was the most frequent diagnosis. Main clinical presentation was respiratory distress with severe hypoxemia and high requirements of mechanical ventilation. Mortality rate was 47% within first 60 days of life, and 75% for the first day of life. Pneumonia and recurrent bronchitis episodes were observed during follow-up. They had a lung function obstructive pattern, and their quality of life and exercise tolerance was good. CONCLUSIONS: High neonatal mortality and significant long-term morbidity associated with pulmonary hypoplasia requires an early diagnosis and a specialised multidisciplinary team management.

Use of inhaled iloprost in children with pulmonary hypertension.

Pulmonary hypertension (PH) in children is a serious disorder, for which the major goal of treatment is to prevent progressive vascular remodeling, and improve clinical status and survival. Iloprost is approved for the treatment of PH in adults; however, few studies have evaluated its effects in children. The objective of this study is to analyze the long-term effects of inhaled iloprost treatment in children with PH. A retrospective study was conducted in patients treated with iloprost between 2000 and 2012. Patients with left-right cardiac shunt and persistent PH of the newborn were excluded. The cohort comprised 22 patients (15 females) with a median age of 2.6 years. Twelve patients had pulmonary arterial hypertension including idiopathic (n = 6), hereditary (n = 2) and associated (congenital heart disease [n = 3], and schistosomiasis [n = 1]). One patient had pulmonary veno-occlusive disease, six patients had PH secondary to lung disease and three had multifactorial PH. Median mean pulmonary arterial pressure was 55 mmHg and median pulmonary vascular resistance was 15.5 Wood units. Good tolerability was observed, with the exception of one case of recurring abdominal pain. PH resolved in two patients, with functional capacity improvement in 10 patients and stabilization in three patients. The clinical condition of six patients deteriorated; two died, and two received lung transplants. In conclusion, the results of this uncontrolled study showed that iloprost was effective and well tolerated in children. However, further research is needed to support this study, as PH is a serious condition that can require organ transplantation or result in death.

[Bronchial hyperresponsiveness to methacholine in children under 4 years with recurrent bronchitis]. / Hiperrespuesta bronquial a la metacolina en niños menores de 4 años con bronquitis de repetición.

OBJECTIVE: To evaluate bronchial hyperresponsiveness in children under 4 years of age with recurrent wheezing bronchitis, and to determine if its presence or absence can predict the subsequent progression to a transient or persistent wheezing bronchitis phenotype. POPULATION AND METHODS: A bronchial challenge test was performed with methacholine using a modified tidal volume method, without sedation in a group of patients from 8 to 47 months of age with recurrent wheezing bronchitis and a control group of healthy children. A decrease in oxygen saturation of ≥ 5% or an increase in respiration rate of >50% [PCwheeze (PCw)] was considered a positive response. The patients were subsequently clinically followed up to assess their progress. RESULTS: A total of 63 patients and 16 controls were studied (mean age 23.9 vs. 25.2 months). The PCw was lower than the control group (≤ 4 mg/ml) in 43 (68%) children from the bronchitis group (P<0.001). No significant adverse effects were observed on performing the test. After a mean follow up of 28.5 months, completed in 49 of the patients, no differences were seen between the presence of bronchial hyperresponsiveness at the beginning of the study and the subsequent progression to transient, infrequent and frequent wheezing (P=0.63). CONCLUSIONS: A high percentage of children under 4 years of age affected by wheezing bronchitis had a bronchial hyperresponse. The subsequent progression to transient or persistent wheezing bronchitis phenotype is not associated with bronchial hyperresponsiveness.