Introduction: Siblings with primary ciliary dyskinesia (PCD) share similar genetic and environmental factors. In cystic fibrosis, siblings express variability in disease severity, but data in PCD is scarce. The aim of this study was to compare disease manifestations among siblings with PCD.

Methods: Clinical, microbiology and pulmonary function results were analyzed in a retrospective study for children followed with a confirmed PCD diagnosis at The Hospital for Sick Children (Ontario, Canada) between 2000-2022. Continuous variables were compared by using Mann?Whitney test.

Results: 15 siblings pairs were included. The median (IQR) age of diagnosis was 10.5 (1.2-13) in the older sibling (OS) and 3 years (0.3-10) for the younger sibling (YS) group with a median age difference of 3 years (1-7). Symptom presence was similar between the YS and OS groups for early onset chronic cough (80% vs 73%), nasal congestion (93% vs 87%), unexplained neonatal respiratory distress (53% vs 40%), and organ laterality defect (53% vs 53%). When comparing outcomes at the last clinic visit at similar age (YS-17.6 years, OS-17.5 years): there was no difference in mean body mass index (20.8 vs 21.2 kg/m²) and in the lifetime cumulative prevalence of airway infection with methicillin-susceptible Staphylococcus aureus, Haemophilus influenzae and Pseudomonas aeruginosa. The median FEV1 precent predicted was 79% (63-86) in the YS compared to 78% in the OS (51-88), p=0.57.

Conclusion: No significant difference in clinical outcomes was found between siblings with PCD, although some variability was found in individual cases.