When you look for a cause of your disease, it is important to bear in mind that in 90 % of all cases of pulmonary alveolar proteinosis (PAP) there is no known cause.
When you are diagnosed with PAP, your doctor will probably be able to tell you which kind of PAP you have. It will be one of the three different forms:
The three forms are distinguished by the cause of the disease and the different mechanisms in the body that cause symptoms. Common to them all is the build-up of a grainy substance, consisting of waste material from lung surfactant, in your lungs. This causes symptoms like shortness of breath and cough.
The most common form of PAP is called acquired or autoimmune PAP. Approx. 90 % of all the people with PAP has this type of the disease.
Patients suffering from this form have antibodies in the blood and the lungs to a protein called Granulocyte Macrophage Colony-Stimulating Factor (GM-CSF); these antibodies inactivate the protein so that it cannot function properly. It is not known why some people develop antibodies to their own GM-CSF. This is why doctors sometimes refer to it as idiopathic PAP as idiopathic means ‘with no known cause’.
The GM-CSF protein in necessary for the immune cells called alveolar macrophages to mature and be activated to digest waste material from a substance called lung surfactant. The macrophages are the dustmen or garbage collectors of the body and they have a very important task of keeping the air sacs (alveoli) in the lungs clean of inhaled particles and waste material.
However, when GM-CSF is inactivated by antibodies and not able to send signals making the macrophages mature and active, grainy waste material builds up gradually in the lungs and eventually fills the alveoli causing the patient to feel breathless.
Secondary PAP is the second most common form of PAP and accounts for approx. 10 % of all PAP patients. Unlike autoimmune PAP it is possible to identify a specific cause of the disease when you have secondary PAP.
The cause of secondary PAP may be:
Congenital PAP is a very rare form of PAP. It is usually diagnosed among infants and young children as it is linked to gene defects. The defects may occur in genes for surfactant proteins or for the receptor transferring GM-CSF signals to the cells.