Normally, cilia beat 7 to 22 times per second, and any impairment can result in poor mucociliary clearance, with subsequent upper and lower respiratory infection.

Cilia also are involved in other biological processes (such as nitric oxide production), currently the subject of dozens of research efforts.

[1] The main consequence of impaired ciliary function is reduced or absent mucus clearance from the lungs, and susceptibility to chronic recurrent respiratory infections, including sinusitis, bronchitis, pneumonia, and otitis media.

[9] Many affected individuals experience hearing loss and show symptoms of otitis media which demonstrates variable responsiveness to the insertion of myringotomy tubes or grommets.

Treatment with various chest physiotherapy techniques has been observed to reduce the incidence of lung infection and to slow the progression of bronchiectasis dramatically.

Aggressive measures to enhance clearance of mucus, prevent respiratory infections, and treat bacterial superinfections have been observed to slow lung-disease progression.

[16] This has been shown to generate a net leftward flow in mouse and chick embryos, and sweeps the protein to the left, triggering normal asymmetrical development.

[17] However, in some individuals with PCD, mutations thought to be in the gene coding for the key structural protein left-right dynein (lrd)[4] result in monocilia which do not rotate.

There is therefore no flow generated in the node, Shh moves at random within it, and 50% of those affected develop situs inversus, which can occur with or without dextrocardia, where the laterality of the internal organs is the mirror-image of normal.

[5] These include nasal nitric oxide levels as a screening test, light microscopy of biopsies for ciliary beat pattern and frequency and electron microscopic examination of dynein arms, as the definite diagnosis method.

[10][36] The recent body of published data from respected clinicians in (the United Kingdom, Europe, North America, Canada and Israel) indicate that PCD morbidity and mortality appear to have been under-estimated by the medical community.

[28][25][39][40][41] While prospective outcome data is limited due to the early-stage patient registries, there is a growing body of evidence[25][39][40][41][42] that dispels any "myth that PCD is a mild disease.

[7] Future promising avenues for functional replacement of cilia involve antisense, gene editing via CRISPR-Cas9 and mRNA therapies.