Pulmonary alveolar proteinosis (PAP) is a rare lung disease, which affects approx. 7 in a million people. So despite the fact that you have a very rare disease, you are not the only one.
PAP is characterised by the build-up of grainy material in the air sacs (alveoli) in your lungs. The grainy material consists of proteins and lipids from lung surfactant – an important substance that coats the inside of the air sacs to prevent your lungs from collapsing. The air sacs need to be inflated for your lungs to work properly to absorb the oxygen that you breathe and transfer it to the blood circulation.
Your body continuously produces new active surfactant and in healthy lungs the old, inactivated surfactant is digested by immune cells called alveolar macrophages. They are the dustmen or garbage collectors of the body and they have a very important task of keeping the alveoli clean from inhaled particles and inactive surfactant material.
In PAP lungs, however, the macrophages fail to clean the air sacs. Consequently, the old surfactant material builds up gradually in your lungs and eventually fills the alveoli causing you to feel breathless.
Scientific research shows that the macrophages need to be stimulated by a protein called Granulocyte Macrophage Colony-Stimulating Factor (GM-CSF) in order to function. This GM-CSF protein works as a growth factor that helps the macrophages to mature and activates them so that they can digest the waste surfactant material properly.
But in PAP lungs the GM-CSF protein is either inactivated or defective, rendering the alveolar macrophages unable to get rid of the material they ingest and eventually not able to take up more of the waste material.
When your air sacs are filled with lung surfactant it will become a barrier between the air that you breathe and the blood vessels in the lungs that need to take up oxygen from the air. You may experience shortness of breath and reduced physical capacity due to the lack of oxygen, as well as coughing. In severe cases respiratory failure can occur although it is very rare. As a PAP patient you are also at higher risk of acquiring infections because GM-CSF is also an important component in the immune defence to infections.
There are three different types of PAP:
The most common form of PAP is called acquired or autoimmune PAP. Approx. 90 % of all PAP patients have this form of PAP. Patients suffering from this form have antibodies in the blood and the lungs to their own GM-CSF protein. The 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’.
Secondary PAP is the second most common form of PAP and accounts for approx. 10 % of all PAP patients. You can get this form of PAP from inhaling toxic substances such as mineral and metal dust. In some cases the disease is caused by an underlying disease such as HIV or certain types of bone marrow cancer.
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. Congenital PAP may be caused by mutations that cause defect in the surfactant proteins, or in the receptor that transfers the GM-CSF signal to the cells.
PAP usually develops slowly and remains unnoticed until you have accumulated enough surfactant for it to cause symptoms. Over time the disease may progress in several ways:
However, according to doctors most patients experience persistent symptoms that require medical treatment.