Primary ciliary dyskinesia

The integrity of healthy respiratory epithelium is maintained, at least in part, by trapping inhaled particles and microorganisms in a protective blanket of mucus which is transported towards the oropharynx by the coordinated action of the underlying ciliated cells. Ciliary dyskinesia is a recently recognised condition in which there is profound disturbance of this clearance mechanism because of the ineffective beating of cilia, and results in the stasis of airway mucus. The incidence of this disorder has been estimated at between 1 in 15 000 and 30 000 and it is thought to be inherited as an autosomal recessive. It was first described in three males with Kartagener's syndrome (situs inversus, bronchiectasis, and sinusitis) who were found to have immotile spermatozoa as well as recurrent respiratory infections. ' It was suggested that as sperm tails and respiratory cilia have similar ultrastructure there might be a generalised defect causing immotility of both sperm tails and cilia. The finding of impaired tracheobronchial clearance, a shared abnormality of ciliary and sperm tail ultrastructure, and the observation of absent ciliary motility in bronchial biopsy specimens strongly supported this hypothesis. Cilia and sperm tails both contain nine pairs of protein filaments arranged around a central pair. Attached to each of the nine outer doublets are structures containing adenosine triphosphatase called dynein armswhich are thought to be responsible for normal ciliary beating by sliding on the adjoining inner microtubule of the next pair. It was these dynein arms that were noted to be missing from the cilia and sperm tails of patients with Kartagener's syndrome. The original term describing this condition-immotile cilia syndrome-is, in fact, a misnomer. A limited amount of ciliary activity may occur in patients with Kartagener's syndrome because absolute deficiency of both sets of dynein arms is unusual. When it occurs, however, ciliary movement is abnormal, usually very slow and stiff, and the beating of adjacent ciliated cells is not coordinated. It has been suggested that dextrocardia occurs in this condition because the direction of rotation of the archenteron is random in the absence of ciliary beating on embryonic cells so that there will be only a 50% chance that the dextral spiral (and hence normal cardiac situs) will occur.' The spectrum of primary ciliary dyskinesia also includes patients without dextrocardia but who have an identical structural abnormality of their cilia. Kartagener's syndrome is therefore a subgroup of primary ciliary 704 dyskinesia-with the important implication that only some patients will be recognisable clinically and radiologically on the basis of situs inversus.