Human cilia were once thought merely to be important in respiratory mucociliary 
clearance, with primary ciliary dyskinesia (PCD) the sole manifestation of 
ciliary dysfunction. There are now known to be three types of cilia: primary, 
nodal and motile. Cilia are complex, likely involving more than 1000 gene 
products; in this review, recent advances in PCD genetics, and the potential 
relationships with genes causing other ciliopathies, are discussed. PCD is the 
most important respiratory disease, characterized by upper and lower airway 
infection and inflammation and disorders of laterality. Ciliary gene mutations 
are now known to cause single organ disease, as well as complex syndromes. The 
focus of the review is primarily PCD, in the context of the expanding ciliopathy 
spectrum. The authors consider the clinical situations in which ciliary disease 
should be considered, and the implications for specialist respiratory practice.