Plasminogen is a circulating zymogen that is converted to the active enzyme plasmin. The main function of plasmin is the degradation of the insoluble fibrin blood clots that have been generated at a site of vascular injury. In addition, plasmin acts as a proteolytic factor in a variety of other processes including embryonic development, tissue remodeling, angiogenesis, inflammation, tumor cell invasion, and metastasis.
Inherited PLG deficiency can be divided into two types: true PLG deficiency (type I, or hypoplasminogenemia) and dysplasminogenemia (type II). Additionally, it has been shown that homozygous or compound-heterozygous type I PLG deficiency is a major cause of a rare inflammatory disease affecting mainly mucous membranes in different body sites. The most common clinical manifestation is ligneous conjunctivitis. Other, less common manifestations are ligneous gingivitis, otitis media, ligneous bronchitis and pneumonia, involvement of the gastrointestinal or female genital tract, juvenile colloid milium of the skin, and congenital occlusive hydrocephalus.