Connexin Genotypes in Cystic Fibrosis

Study Overview
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Brief Summary
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Background: There is wide variety in lung disease phenotype for the delta F508 (homozygous) genotype. A leukocyte driven inflammation is most important for the pathogenesis of pulmonary disease in CF. Blood cytokines correlate negatively with pulmonary function in delta F508 homozygous patients. Gap junction proteins might be of importance for the influx of blood cells into the lung and may influence the course of pulmonary inflammation. A primary analysis (Horn et al. 2020) has shown that GJA4 variants (rs41266431) are linked to more severe disease in CF. This is very similar to variants of MBL. Aims: To assess the relationship between gap junction proteins alpha 1 (GJA1/Connexin 43) and alpha 4 (GJA4/connexin 37) genotypes and clinical disease phenotype. Moreover are GJA4 variants in terms of clinical phenotype independent of MBL variants. Methods:Patients homozygous for delta F508 get recruited from the CF centres of Bonn, Frankfurt and Amsterdam. Sequence analysis is performed for connexin 43 and 37 and MBL genotypes. Clinical disease is assessed longitudinally over 3 years by pulmonary function tests (FEV1 (forced expiratory volume in one second), FVC (=(forced vital capacity), FEF75 % (Forced expiratory flow at 75% of the pulmonary volume) pred), BMI (percentiles), P. aeruginosa colonization, diabetes mellitus and survival to end-stage CF lung disease (death or lung transplantation).

Detailed Description
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Progressive pulmonary destruction is the major cause of morbidity and mortality in human subjects with cystic fibrosis. Many studies could not find an association between delta F 508 and severity of pulmonary disease . The most important factor in CF lung disease is an inflammation driven by leukocytes and cytokines. The investigators have provided evidence in former studies that cytokines (Interleukin-8 (IL-8), tumour necrosis factor (TNF) alpha, Lipopolysaccahride binding protein (LBP), transforming growth factor (TGF) ß)measured in blood correlate negatively with lung function in delta 508 homozygous patients. The question arises, what other factors influence recruitment of proinflammatory leukocytes from blood capillaries into the lung . Connexins are a family of transmembrane proteins, which oligomerize into hexameric structures to form a hemichannel (connexon) and ultimately pair with a partner hemichannel in an adjacent cell to form gap junction intercellular communication channels (GJIC) . There is evidence of expression of connexin 37 (=gap junction protein A4 (GJA4)) on macrophages in humans. Moreover there is evidence of expression of connexin 37 on vascular endothelia in humans . Connexin 37 is expressed on human neutrophils . Pulmonary disease in CF is dominated by a leukocyte driven inflammation. GAP junction proteins might be of importance for the influx of blood cells into the lung. In this regard, the hypothesis was that Cx37 or Cx43 genotypes have an impact on clinical disease phenotype in CF patients homozygous for delta F508. The first analysis (Horn et al 2020) has shown a clinical phenotype linked to the GJA4 genotype is very similar to MBL variants. In this regard the question arises whether there is a link between the MBL variant alleles and the GJA4 variants. Moreover some TGFbeta genotypes are linked to certain pulmonary phenotypes. So we are looking for interactions between Cx37 and TGFbeta genotypes and their impact on the clinical phenotype as well.

Official Title
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Impact of Connexin 37, Connexin 43 on Clinical Disease Phenotype in Delta F508 Homozygous Patients With Cystic Fibrosis (CF) (CF-Modifier)

Conditions
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Cystic Fibrosis, Inflammation

Intervention / Treatment
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* Diagnostic Test: Genotyping
* Diagnostic Test: Lung function
* Diagnostic Test: Microbiology
* Diagnostic Test: Blood sample
* Diagnostic Test: Induced Sputum


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Homozygosity for delta F 508 Exclusion Criteria: treatment with systemic steroids 14 days preceding this trial, participation in another study within the past 30 days, treatment with Orkambi or status after lung transplantation (for assessment of all parameters except survival).

Ages Eligible for Study
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Minimum Age: 6 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Diagnostic
Intervention Model: Single Group Assignment
Interventional Model Description: Evaluation of clinical parameters by genotype
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Other: Connexin genotype<br>Genotyping | Diagnostic Test: Genotyping<br>* Genotyping for single nucleotide polymorphisms for Connexin 37&43, Mannose binding lectin (MBL) and transforming growth factor beta (TGF beta) genotypes<br>Diagnostic Test: Lung function<br>* Spirometry,<br>Diagnostic Test: Microbiology<br>* Bacterial culture from Sputum or swab<br>Diagnostic Test: Blood sample<br>* Interleukin-8 assay (via chemiluminescence) blood cell count<br>Diagnostic Test: Induced Sputum<br>* Interleukin-8 assay (via chemiluminescence) blood cell count<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Survival to end stage lung disease | End stage lung disease: Death or lung transplantation | through study completion, on average 27 years | 
| Lung function parameter: FEV1 | Best FEV1 value in % predicted of the year according to German registry according to Global lung initiative (GLI) | 3 years | 
| Lung function parameters: FVC | Best FVC value in % predicted of the year according to German registry according to Global lung initiative (GLI) | 3 years | 
| Lung function parameters: FEF75 | Best FEF75 value in % predicted of the year according to German registry according to Global lung initiative (GLI) | 3 years | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Interleukin-8 in blood | single spot value (cross-sectional) | through study completion, an average of 3 year | 
| Interleukin-8 in sputum | single spot value (cross-sectional) | through study completion, an average of 3 year | 
| White blood cell count | Leukocytes (single spot value (cross-sectional)) | through study completion, an average of 3 year | 
| Inflammatory markers in sputum | Leukocyte count in sputum (single spot value (cross-sectional)) | through study completion, an average of 3 year | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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connexin 37+43, MBL, TGF beta, Lung function, Interleukin 8