Primary ciliary dyskinesia pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Hafsa Ghaffar, M.B.B.S[2]
Overview
In many people with primary ciliary dyskinesia, the cause of the disease is unknown, but the main factor contributing to the pathogenesis is mutations in the proteins forming the cilia which result in the formation of abnormal or immotile cilia. Clearly, cilia have many important functions within the body, defects in these cell structures cause a variety of signs and symptoms.
Pathophysiology
Physiology
Cilia are responsible for normal clearance of the respiratory system by organized back and forth motion. It also helps in the left-right axis during embryonal development. Pseudostratified columnar epithelium lines the large airways and contiguous structures, including the Paranasal sinuses, middle ears, and posterior nose. Additionally, brain and fallopian tubes are also lined with ciliated columnar epithelium. In addition, the spermatozoa flagella have a core structure that is similar to cilia. The developed ciliated cell has up to 200 cilia. Each cilium has an arrangement of longitudinal microtubules arranged as 9 doublets formed in an outer circle around a central pair.[1]
Pathogenesis
Expression of the NODAL gene in the right arm of the cilia results in congenital abnormalities like situs inverses as compared to mutations in the left arm which ends in PCD without situs inverses. In the respiratory tract, cilia move back and forth in a coordinated to clear mucus. This movement of mucus helps to eliminate fluid, bacteria, and particles from the lungs. Most babies with primary ciliary dyskinesia experience breathing problems at birth, suggesting that the cilia play an important role in clearing fetal fluid from the lungs. Affected individuals develop recurrent respiratory tract infections. Decreased functioning cilia results in chronic infections like bronchiectasis, otitis media with effusion, chronic rhino-sinusitis, and infertility.Sub fertility or infertility in male PCD patients is caused by sperm dysmotility as the sperm tail is architecturally is analogous to respiratory cilia and powered by dynein motors additionally, due to dyskinetic cilia in their oviducts females with PCD also experience fertility problems. Abnormal ciliary movement of brain ependymal cilia causes hydrocephalus in small animals with PCD. However, patients with PCD may demonstrate mild fetal ventriculomegaly on prenatal ultrasound scans, hydrocephalus is extremely uncommon in humans, except in those with ciliary aplasia.[2][3][4]
Genetics
Primary ciliary dyskinesia has an autosomal recessive inheritance. Mutations in DNAI1 and DNAH5 result in Primary Ciliary Dyskinesia.[5]
Associated Conditions
Conditions associated with primary ciliary dyskinesia include:
- Bronchiectasis
- Situs inversus totalis/Kartagener syndrome
- Heterotaxy syndrome or situs ambiguous
- Otitis media
- Infertility
- Hydrocephalus
Gross Pathology
There are no gross features characteristic of primary ciliary dyskinesia.
Microscopic Pathology
Histopathological analysis under an electron microscope may show defects in the dynein arms which could be in inner, outer, or both arms. Irrespective of the location it leads to defective cilia which are unable to maintain normal beat and frequency in variety of epithelial surfaces such as respiratory tract, fallopian tubes, sinuses and development of embryonal axis.
References
- ↑ "Primary Ciliary Dyskinesia: Background, Pathophysiology, Epidemiology".
- ↑ McComb P, Langley L, Villalon M, et al. The oviductal cilia and Kartagener’s syndrome. Fertil Steril 1986; 46: 412–416.PubMedGoogle Scholar
- ↑ Ibañez-Tallon I, Gorokhova S, Heintz N. Loss of function of axonemal dynein Mdnah5 causes primary ciliary dyskinesia and hydrocephalus. Hum Mol Genet 2002; 11: 715–721.Abstract/FREE Full TextGoogle Scholar
- ↑ Wessels MW, den Hollander NS, Willems PJ. Mild fetal cerebral ventriculomegaly as a prenatal sonographic marker for Kartagener syndrome. Prenat Diagn 2003; 23: 239–242.CrossRefPubMedGoogle Scholar
- ↑ "Primary Ciliary Dyskinesia: Background, Pathophysiology, Epidemiology".