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What Causes Primary Ciliary Dyskinesia?

Primary ciliary dyskinesia (PCD) is a rare, inherited disease. "Inherited" means the disease is passed from parents to children through genes. With PCD, this process is very complex. Researchers are still learning how the disease is inherited and which genes are involved.

Generally, a child must inherit faulty genes from both parents to have PCD. These genes affect how cilia grow and function. Cilia are tiny, hair-like structures that line the airways.

The airways include your nose and linked air passages; mouth; larynx (LAR-ingks), or voice box; trachea (TRA-ke-ah), or windpipe; and tubes called bronchial tubes or bronchi, and their branches.

Cilia move mucus (a slimy substance) through your airways and toward your mouth to be coughed or sneezed out of your body. The mucus contains inhaled dust, bacteria, and other small particles.

Faulty genes may cause the cilia to be the wrong size or shape or move in the wrong way. Sometimes the cilia are missing altogether. If the cilia don't work well, bacteria stay in your airways. This can cause breathing problems, infections, and other disorders.

Primary Ciliary Dyskinesia

Figure A shows the location of the lungs, airways, pleura, and diaphragm (a muscle that helps you breathe). The inset image shows a detailed view of the two pleural layers and pleural space. Figure B shows lungs with pleurisy and pneumothorax. The inset image shows a detailed view of an infected lung with thickened and inflamed pleural layers.

Figure A shows the organs that primary ciliary dyskinesia can affect. Figure B shows a cross-section of the trachea (windpipe). Figure C shows a closeup view of normal cilia lining the trachea. The cilia move together in wave-like motions to transport mucus toward the mouth. Figure D shows a closeup view of faulty cilia lining the trachea. The cilia are deformed and do not move together, causing a buildup of mucus.

No single faulty gene causes all cases of PCD. Rather, many genes are associated with the disease.

If a child inherits a faulty gene (or genes) from only one parent, he or she may be a "PCD carrier." Carriers usually have no symptoms of PCD. However, carriers can pass faulty PCD genes on to their children.

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June 1, 2011