What is (are) Primary Ciliary Dyskinesia ? 

Primary ciliary (SIL-e-ar-e) dyskinesia (dis-kih-NE-ze-ah), or PCD, is a rare disease that affects tiny, hair-like structures that line the airways. These structures are called cilia (SIL-e-ah).
                
Cilia move together in wave-like motions. They carry mucus (a slimy substance) toward the mouth to be coughed or sneezed out of the body. The mucus contains inhaled dust, bacteria, and other small particles.
                
If the cilia don't work well, bacteria stay in your airways. This can cause breathing problems, infections, and other disorders. PCD mainly affects the sinuses, ears, and lungs. Some people who have PCD have breathing problems from the moment of birth.
                
Sperm cells have structures that are like cilia. In men who have PCD, these structures also may not work well. This can cause fertility problems. "Fertility" refers to the ability to have children.
                
Fertility problems also occur in some women who have PCD. These problems likely are due to faulty cilia in the fallopian tubes. (The fallopian tubes carry eggs from the ovaries to the uterus.)
                
Overview
                
PCD is an 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. 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.
                
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.
                
The symptoms and severity of PCD vary from person to person. If you or your child has the disease, you may have serious sinus, ear, and/or lung infections. If the disease is mild, it may not show up until the teen or adult years.
                
The symptoms and severity of PCD also vary over time. Sometimes you may have few symptoms. Other times, your symptoms may become more severe.
                
Some people who have PCD have a condition called situs inversus (SI-tus in-VER-sus). This is a condition in which the internal organs (for example, the heart, stomach, spleen, liver, and gallbladder) are in opposite positions from where they normally are.
                
A correct and early diagnosis of PCD is very important. It will allow you or your child to get the proper treatment to keep your airways and lungs as healthy as possible. An early diagnosis and proper treatment also can prevent or delay lung damage.
                
Outlook
                
Many people who have PCD have normal lifespans. However, about 25 percent of people who have the disease may develop respiratory failure, a life-threatening condition. A small number of people who have PCD need lung transplants.
                
Scientists continue to study the faulty genes that cause PCD. Further studies of the disease will likely lead to earlier diagnoses, better treatments, and improved outcomes.