Primary ciliary dyskinesia due to CCNO mutations-A genotype-phenotype correlation contribution.

Primary ciliary dyskinesia (PCD) is genetically and clinically heterogeneous. CCNO mutations are associated with chronic destructive lung disease and were first described in 2014. Early reports suggest that CCNO is mutated more frequently than expected, however, these are considered rare. We report on three eleven-year-old children with PCD due to CCNO mutations. All children presented early-onset respiratory symptoms, no cardiac or situs anomalies and moderate to severe clinical courses. Patients 1 and 3 were admitted to a neonatal intensive care unit due to respiratory distress. Patients 1 and 2 had atelectasis and lobar collapse, for which lobectomy was performed for patient 1. Patient 3 also presented otitis media with effusion with conductive hearing loss, requiring tympanostomy tube insertion twice. Diagnosis of PCD for all three required repeated nasal brushings, delaying diagnostic confirmation. Microscopy analysis revealed severely decreased numbers of cilia, but normal ultrastructure and uncoordinated beat pattern in the residual cilia. Surprisingly, the prevalence of pathogenic CCNO variants in our centre is higher than expected (three out of sixteen patients). Pathogenic variants in PCD-causing genes lead to specific ultrastructural defects, and there is a suggestion for genotype-phenotype association. However, there are little longitudinal data evaluating the impact of specific defects on disease progression, but a recent study showed a worse lung disease and poorer nutritional status. Concluding, this report underlies the importance of patient-oriented diagnosis and management in highly experienced PCD centres.