An International Study on Genotype/Phenotype Correlation With Focus on Lung Function in Patients With Primary Ciliary Dyskinesia (PCD)

Background Primary Ciliary Dyskinesia (PCD) is a rare genetic disorder characterized by dysfunction of motile cilia associated with recurrent infections of the airways, laterality defects (Situs inversus totalis in about 50% of cases) and fertility problems. At present, mutations in > 40 genes associated with PCD and mucociliary clearance disorders have been identified, representing most likely two thirds of all human cases. While being involved in the majority of identified PCD genes, our working group has a great expertise in genetic analysis and diagnostic work-up of patients with PCD.

Hallmark symptom of PCD is the chronic purulent lung disease due to the reduced mucociliary clearance. Chronic inflammation and recurrent infections of the airways promote continuous lung damage, bronchiectasis and could finally lead to total lung failure. For other congenital diseases with chronic lung conditions, e.g. cystic fibrosis (CF), an affected lung function with a steady decline is well described and spirometry is widely used to monitor disease progression. For PCD there are only limited data available and studies often comprise small cohorts. In general, available data assume a decline of lung function in PCD patients compared to healthy individuals, but less pronounced than in CF. Altogether, results of the studies remain heterogeneous, in particular concerning the influence of an early diagnosis and a proper treatment on lung function.

Furthermore, despite a significant progression in genetically solved cases there are almost no data on genotype specific lung function in patients with PCD. Recently, there are few studies indicating an association between specific ultrastructural or genetic defects, e.g. patients carrying mutations in the genes MCIDAS (Multicilin), CCNO (Cyclin O), CCDC39 (Coiled-Coil Domain Containing 39) and CCDC40 (Coiled-Coil Domain Containing 40) and a severe clinical course in particular a worse respiratory phenotype. There might be a less severe phenotype in PCD sub-types due to mutations in genes encoding radial spoke components.

Currently a systematic review shows the high variation of spirometric indices in a great PCD cohort. These findings underline the great necessity of detailed characterization of genotype specific phenotypes with focus on important parameters such as lung function to better understand the natural history of distinct PCD-variants with a view to improve individual patient care by tailored treatment activity according to likely disease severity.

Aim of this study are: