PAM stands for pulmonary alveolar microlithiasis, which is a rare lung disease. It is where small stones accumulate in the alveolar air sacs in the lungs and therefore makes it increasingly difficult to breathe. The cause has been found to be due to a DNA mutation which results in the loss of a cellular pump which would normally remove excess phosphate from the air sacs. As a result there is a build-up of calcium and phosphate which leads to the formation of microliths or stones. These cause chronic inflammation, lung tissue damage and scarring and respiratory failure and patients require a continuous oxygen supply of a high oxygen concentration in order for patients to be able to get enough oxygen into their bodies to function.
New research has identified biomarkers, which may hold the key to being able to treat this rare and debilitating disease. It seems that the condition causes elevations of certain proteins (cytokines and surfactant) in the blood. By monitoring these levels doctors will be able to follow disease progression and treatment response in patients.
Another finding was that the stones dissolve in EDTA which is used currently as a treatment for heavy metal poisoning. If the lungs can be washed in a solution containing EDTA then the stones could be dissolved and reduce the burden being placed on the air spaces and relieve respiratory symptoms. As long as there are no toxic side-effects then this could become a new therapy for patients with PAM.
As the stones are caused by excess phosphate it has been surmised that a low phosphate diet may be able to prevent the formation of the stones, however a phosphate-restricted diet brings with it other medical problems such as rickets. Another possible idea is to restore the function of the pump in the cells by inserting a phosphate pump gene into the DNA of the cells using viral vectors.
“This study demonstrates how discovering the causes of these rare lung diseases not only can inform us how the lung normally functions, but can also lead us to potential therapeutic interventions for these rare and often lethal lung diseases,” says James Kiley, PhD, Director of the Division of Lung Diseases at NHLBI.
Rare disease research can reveal insights into the fundamental biology of the lung and this study for PAM has revealed a potential role for phosphate in the regulation of surfactant balance in the lung and have attracted the interest of cystic fibrosis scientists who may be able to use the findings to help treat CF.