Primary ciliary dyskinesia

Primary ciliary dyskinesia is a genetic disorder that affects the motile cilia, those tiny hairs that cover the surface of certain cells and that move. In this disease they are poorly formed and work poorly, and the result is chronic oto-sino-pulmonary disease, that is, disease of the ears, sinuses and lungs.

To understand why, you have to look at how the airway is normally cleaned. Each cell of the respiratory epithelium, the layer that lines it on the inside, carries hundreds of cilia, and the cleaning depends on all of them beating in coordination, like oars keeping time together. When that beating is abnormal, what fails is mucociliary clearance, that is, the sweeping of mucus outward. Cilia that beat out of rhythm do not sweep: they only move.

And there is a consequence that seems to belong to another topic but is the same one. Ciliary motion is also what orients the internal organs while the embryo is forming. That is why nearly half of the people with this disorder have situs abnormalities, meaning organs positioned differently from usual.