Primary Ciliary Dyskinesia
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- Primary ciliary dyskinesia (PCD) is a rare autosomal recessive disorder of cilia structure, function, and biogenesis leading to neonatal respiratory distress, chronic oto-sino-pulmonary disease, infertility and organ laterality defects:
- PCD was formerly referred to as immotile cilia syndrome, but because cilia in most of these patients are not immotile but stiff, uncoordinated, or ineffective at beating, the name of the disorder was changed.
- When concurrent with situs inversus, chronic rhinosinusitis, and chronic bronchitis leading to bronchiectasis, the disease is referred to as Kartagener syndrome.
- PCD differs from secondary ciliary dyskinesia, which refers to ciliary defects acquired secondary to epithelial injury (i.e., infection, inflammation).
- Cilia are typically found in the sinuses, ears, and lung and on sperm.
- Synonym(s): Kartagener syndrome
1 in 15,000 to 60,000 live births, although this is likely an underestimate as PCD is an underdiagnosed disease
Etiology and Pathophysiology
Most of the deficits seen in PCD can be explained by impaired ciliary function:
- The respiratory manifestations of PCD (chronic otitis media, chronic rhinosinusitis, chronic bronchitis leading to bronchiectasis) reflect the impaired mucociliary clearance due to impaired ciliary motility. The airways become inflamed due to the inability to remove microorganisms and respiratory irritants.
- The neonatal respiratory distress common in PCD reflects the impaired ability of cilia to clear lung fluid during the transition from fetal to neonatal life. ~50% of patients with PCD have laterality defects including situs inversus, totalis, and heterotaxy, which are attributed to the dysfunction of embryologic nodal cilia during development. During embryogenesis, nodal cilia normally beat in a clockwise direction and generate a fluid gradient. In PCD, in contrast to the waveform sliding motion of 9 + 2 cilia, nodal motile 9 + 0 cilia beat with a vertical/rotational motion resulting in a leftward flow of extracellular fluid which is important for cell signaling during the development of normal human left–right asymmetry (1).
- Male infertility is common (~50%) and reflects the impairment in sperm motility. Similarly, infertility and subfertility are common in females and are thought to reflect impaired ciliary motility in the fallopian tubes.
- Reports have linked hydrocephalus to PCD; thought to be related to impaired ciliary function of ependymal cells
- Predominantly an autosomal recessive disease
- In rare cases, autosomal dominant or X-linked recessive inheritance has been described.
- A genetically heterogeneous disorder that can be caused by an inherited defect in a ciliary axonemal, membrane, matrix, or assembly protein
- So far, specific mutations have been identified in 12 genes (DNAI1, DNAH5, DNAH11, DNAAF1, DNAAF2, DNAI2, RSPH9, RSPH4A, NME8, CCDC39, CCDC40, and DNAL1).
Commonly Associated Conditions
- Oral-facial-digital syndrome type I
- Transposition of the great vessels and other cardiovascular abnormalities
- Tracheoesophageal fistula
- Biliary atresia
- Pyloric stenosis
- Severe GERD
- Asplenia or polysplenia
- Midgut volvulus