Primary ciliary dyskinesia (ORPHA:244)
A rare, genetically heterogeneous, primarily respiratory disorder characterized by chronic upper and lower respiratory tract disease. Approximately half of the patients have an organ laterality defect (situs inversus totalis or situs ambiguus/heterotaxy).
Epidemiology
Primary ciliary dyskinesia (PCD) has an estimated incidence of 1/15,000-1/30,000 live births, but this is probably underestimation. Prevalence is difficult to determine.
Clinical description
Affected patients develop signs of PCD at birth or within the first few months of life. However, owing to the diagnostic challenges, some cases of PCD are not diagnosed until the adulthood. Most full-term neonates have respiratory distress with tachypnea (infant acute respiratory distress syndrome) and usually require supplemental oxygen for days, some for weeks. The usual findings in infants and children are daily rhinitis, and daily year-round wet cough occurring soon after birth, with associated recurrent or chronic bacterial infections of the lower airways. Chronic otitis media is common, sometimes with temporary or permanent hearing loss and impaired speech development. Most patients have recurrent sinus infections. Bronchiectasis develops in an age-dependent manner, and is nearly universal in adults. Pectus excavatum and scoliosis have been reported rarely (5-10%), as well as digital clubbing. Almost all males with PCD are infertile, due to dysmotility of spermatozoa, although a few have normal sperm motility. Reduced fertility or a history of ectopic pregnancies has been reported in affected women. Situs inversus totalis, a mirror-image reversal of all visceral organs, is found in 40-50% of individuals and is known as the Kartagener type. Heterotaxy (discordance of right and left patterns of normally asymmetric structures) is present in at least 12%, and a subset of those have structural congenital heart disease. A very rare association of X-linked PCD with either retinitis pigmentosa or intellectual deficiency has been reported.
Etiology
Pulmonary disease in PCD is related to defects in lung defense mechanisms due to abnormal ciliary structure and function with impaired mucociliary clearance. Mutations in around 46 different genes throughout the genome have been found to be causative. Some of these include DNAH5, CCDC39, DNAI1, CCDC40, DNAH11, ZMYND10, CCDC103, CCDC151 and ARMC4. A third of currently recognized patients do not have mutations in these genes.
Diagnostic methods
Diagnosis is based on the characteristic clinical signs. Methods include molecular genetic testing identifying biallelic pathogenic variants (or hemizygous in males for X-linked genes, or mono-allelic for autosomal dominant trait) in one of the causative genes, as well as transmission electron microscopy identifying specific ciliary ultrastructural defects in biopsy samples. Other supportive tests include measurement of nasal nitric oxide in upper airways (in patients aged of 5 years or more) that tends to be low in PCD, after cystic fibrosis link has been ruled out, high-speed videomicroscopy to assess cilia waveform and beat frequency, immunofluorescent staining to study ciliary structure, and mucociliary clearance analysis to assess impairment.
Differential diagnosis
The main differential diagnoses are cystic fibrosis, immunodeficiency syndromes and gastroesophageal reflux. Additionally, PCD has been noted in patients with Cri du chat syndrome due to the common locus on chromosome 5p. Segmental deletion of chromosome 5p in Cri du chat syndrome usually includes PCD-associated gene DNAH5 and the pathogenic variant in the remaining allele of DNAH5 renders it to PCD.
Antenatal diagnosis
If disease-causing mutations are known in a family, prenatal diagnosis can be performed using molecular analysis.
Genetic counseling
PCD is usually inherited in an autosomal recessive manner. Some cases with autosomal dominant and X-linked trait have been observed. Genetic counseling should be provided to affected families.
Management and treatment
Regular clinical visits to monitor disease status are key. Aggressive treatment is recommended to improve mucus clearance. Antibiotic therapy is required and routine immunization is advised. Sinus disease can be treated with nasal steroids and nasal lavage. Polyps may require surgical treatment. Audiological assessment, hearing aids, and communication assistance should be offered where necessary. Patients with end-stage lung disease are candidates for lung transplantation.
Prognosis
The prognosis depends on timely diagnosis and appropriate treatment. Life expectancy is likely somewhat shortened, although quantitative estimates are not currently available.

                            Last update: 
                            November 2019


                            - Expert reviewer(s): 
                            Pr Michael KNOWLES  - Pr Maimoona ZARIWALA