Primary ciliary dyskinesia syndrome associated with abnormal ciliary orientation in infants

The syndrome of primary ciliary dyskinesia (PCD, also known as Kartagener's syndrome or immotile cilia syndrome) is a spectrum of conditions caused by a failure of mucociliary clearance related to congenital, structural or functional ciliary abnormalities. Clinically it is characterized by onset in the neonatal period of respiratory distress and rhinitis 1, and if untreated, subsequent chronic rhinosinusitis, recurrent respiratory infections and bronchiectasis, and chronic secretory otitis media 2, 3. Half the patients have mirror image organ arrangement 2, 3. Other features described more rarely include oesophageal atresia and severe gastro-oesophageal reflux 4; complex congenital heart disease often with disorders of laterality 4; biliary atresia 5; and hydrocephalus 6, 7. The diagnosis is important, to ensure that aggressive airway clearance and antibiotics are used to prevent the development of bronchiectasis, and that inappropriate ear, nose and throat procedures are avoided 3, 8.

The diagnosis is established firstly, by functional studies, usually a direct measurement of ciliary beat frequency on nasal epithelial cells; and secondly, from ciliary ultrastructure determined by electron microscopy 3. Underlying structural defects include absent inner and/or outer dynein arms 9, 10, tubular defects 11, and radial spoke defects 12. Rarely patients with a typical PCD clinical phenotype have normal or near normal ciliary beat frequency (CBF) and normal ciliaryultrastructure, so the cause of their condition is unexplained. Recently a group of these patients were found to have a disorder of ciliary orientation 13–15, in which the individual cilia have a normal ultrastructure but their orientation with respect to each other was abnormal, leading to poor co-ordination between the beating ciliaand inefficient mucociliary clearance. Although a primary abnormality of ciliary orientation was proposed, since secondary orientation defects may occur due to chronic infection 16, the existence of primary ciliary disorientation has been questioned. Furthermore, the youngest patient in the original reports was aged 10 yrs 15; there are no normal data for younger children, making it impossible to assess the significance of ciliary orientation in the new-born period, at the very time when more than half of patients with PCD first become symptomatic 2.

There are marked developmental changes in the upper airway in children. The sinuses do not reach a mature state until 6 yrs of age, thus in young children by definition chronic sinusitis cannot occur. There is no reason to suppose that ciliary orientation in health or disease is necessarily the same in infants as in adults. Indeed, CBF is known to vary with age 17. The aim ofthis study was: firstly, to describe the normal range ofciliary orientation in children <2 yrs of age; andsecondly to describe two infants with typical PCD associated with normal ciliary ultrastructure but abnormal orientation.

Methods

Results

Ciliary orientation was obtained for eight control infants (3 males), mean age 13.1 months, range 7–23. Details of the underlying diagnoses are given in table 1⇓. Nasal swabs for bacterial culture were all negative. Primary abnormalities of ciliary ultrastructure were not recognized, nor were there any secondary abnormalities (e.g. compound cilia or microtubular disarrangements) seen. A mean of 254 central pairs was examined, range 82–453. The mean ciliary orientation for the eight controls was 14.9 degrees, range of orientation for the individuals 12.9–17.5.

Discussion

This study has defined for the first time the normal range for nasal ciliary orientation in children <2 yrs of age, and described two infants with typical features of primary ciliary dyskinesia with normal ciliary ultrastructure. The mean ciliary orientation obtained in normals was 14.9±0.7 degrees, range of mean orientation for the individuals 12.9–17.5, and the range of orientation considering all fields examined was 6.0–41.7. This was similar to the results obtained in normal adult subjects using the same equipment (12.8±1.5 degrees) 15. Similar results were reported by others 13.

The only previous studies of ciliary orientation were in adults 13–16. The normal range described might not be relevant to infants. It is known that the development of the paranasal sinuses takes place after infancy. It is possible that the cumulative effects over time of recurrent viral colds and other infections suffered by even normal adults might in some way affect ciliary orientation. Furthermore, one could hypothesize that the developing epithelium might function less efficiently than mature adult epithelium; for example, ciliary beat frequency varies with age 17. For all these reasons ciliary orientation might not be the same throughout life. The study could be criticized because of the relatively small number of normals studied, the use of anaesthetized infants rather than absolutely normal controls, and the absence of viral studies in the control infants. Although the numbers are small, the confidence intervals are very narrow, and it is not believed that the use of a larger number would substantially have altered the conclusions. Furthermore, orientation was found to be similar to that found in adults, implying a uniform normal range across all ages. Nasal brushings in the control group were performed during a general anaesthetic because the procedure causes discomfort and it was felt to be more ethical to take every opportunity to minimize any distress to the parent and child. It is unlikely that a brief period of anaesthesia could influence ciliary orientation (the studies were performed immediately after induction of anaesthesia). Although a normal CBF would have added weight to the contention that these were truly normal infants, measurement was not attempted in the samples obtained, in the present study, for a number of reasons. Firstly, normal ranges for CBF have already been established in this group 17. Secondly, anaesthetic agents may reduce CBF 18. Thirdly, orientation studies ideally require a large sample of epithelium, and the authors were keen to maximize their chances of obtaining a good sample. Finally, a normal CBF cannot by itself exclude a ciliary problem 3. Attempts to minimize the chances of inadvertently studying an infant with unsuspected PCD by excluding those with any significant respiratory history and those with any disorder of laterality were made 4.

The congenital cardiac lesions in the study group have not to the best of the authors' knowledge been associated with PCD, nor did these infants have any other feature suggestive of the diagnosis. Nasal nitric oxide has also been proposed as a diagnostic test for PCD 19, 20, but both the subjects and controls were too young for measurements, with the technology then available to the authors, to be made. Ideally polymerase chain reaction for viral detection would have been performed, but this was not available. All the normal controls were evaluated for viral infection by the anaesthetist, who would have deferred the procedure had the child been unwell. Taking all this into consideration, the authors felt it was a reasonable study design.

A further possible control group would have been infants with chronic infective or allergic rhinitis. It is probable that at least some of these infants would have exhibited secondary disorientation. Such infants would however, have been unlikely to be permitted to undergo anaesthesia for elective surgery. There is no question that it would be unwise to diagnose PCD on disorientation alone 3 without carefully considering the clinical picture, which is of paramount importance in this condition. Of particular note, neonatal onset of symptoms is very typical of PCD 2, 3, but virtually unheard of in infective or allergic rhinitis.

Abnormal ciliary orientation in the study by Rayner et al. 16 was correlated with delayed mucociliary clearance, presumably due to inefficient ciliary beating. Whether abnormal ciliary orientation alone could lead to PCD syndrome is still not certain. The possibility that the PCD syndrome in the two infants described in this paper was secondary to an ultrastructural defect too subtle to be detected cannot be excluded. Cilia contain >200 different proteins 21, but only a relatively few abnormal structural patterns have been described using electron microscopy. It seems likely that some subtle structural defects have yet to be described, possibly because the changes are outside the resolving power of the electron microscope, and these changes could influence orientation which is known to be abnormal in cases with an ultrastructural abnormality 13. In favour of this possibility is that static and dyskinetic cilia were observed in both the cases reported here, but not in the adult series reported by Rayner et al. 15. However, the differences may merely have been due to secondary infection in the paediatric cases.

To conclude, the present study has described two infants with the clinical features of primary ciliary dyskinesia, but with no structural abnormality in the individual cilia. The orientation of cilia with respect to each other was abnormal, presumably resulting in inefficient mucociliary clearance and possibly leading to the clinical disease. The authors were able to make this diagnosis by describing for the first time the normal range of ciliary orientation in infancy. The description of abnormal ciliary orientation in infants lends further weight to the view that this is a real clinical entity, and that measurement of ciliary orientation should be part of the assessment of ciliary structure and function in cases of possible primary ciliary dyskinesia, in particular when the ultrastructure of individual cilia appear to be normal.