Cilia-related diseases

Abstract

There are at least eight categories of cilia in the human body and malfunctioning of any one or several of them will have different consequences for the patient. A genetic error of the respiratory cilia (9 + 2) is the cause of the airways disease named immotile-cilia syndrome (or PCD), whereas defective ependymal cilia (9 + 2) carries an increased risk of hydrocephalus. When the so-called nodal cilia (9 + 0) of the early embryo are malfunctioning, there is a random determination of asymmetry of the heart and visceral organs ('a 50% risk of situs inversus'). Some genes are responsible for the synthesis, transport, and assembly of the cilia, and mutations in these genes may lead to progressive degeneration of ciliary structures, such as the connecting cilium (9 + 0) of the photoreceptor cells-this is the cause of retinitis pigmentosa. Ciliary malfunctions due to genetic errors tend to be systemic and life-long, whereas acquired diseases are local and may be temporary only.

Figure 1

Diagram of a ciliary axoneme, ie the central structure of a cilium or of a sperm flagellum. The diameter of the axoneme is about 0.2 µm. Reprinted from Thorax, vol 53, BA Afzelius, Immotile cilia syndrome: past, present, and prospects for the future, pp 894–897, Copyright (1998), with permission from the British Medical Association

Figure 2

Computer averages of cross‐sectioned axonemes from a healthy man (A) and a man who suffers from the immotile‐cilia syndrome (B). The complete lack of dynein arms in axonemes from the man with the disease is striking. Reprinted from Tissue Cell, vol 27, BA Afzelius, R Dallai, S Lanzavecchia, PL Bellon, Flagellar structure in normal human spermatozoa and in spermatozoa that lack dynein arms, pp 241–247, Copyright (1995), with permission from Elsevier