A K19E missense mutation in the plasminogen gene is a common cause of familial hypoplasminogenaemia

Plasminogen missense variants and their involvement in cardiovascular and inflammatory disease

Human plasminogen (PLG), the zymogen of the fibrinolytic protease, plasmin, is a polymorphic protein with two widely distributed codominant alleles, PLG/Asp453 and PLG/Asn453. About 15 other missense or non-synonymous single nucleotide polymorphisms (nsSNPs) of PLG show major, yet different, relative abundances in world populations. Although the existence of these relatively abundant allelic variants is generally acknowledged, they are often overlooked or assumed to be non-pathogenic. In fact, at least half of those major variants are classified as having conflicting pathogenicity, and it is unclear if they contribute to different molecular phenotypes. From those, PLG/K19E and PLG/A601T are examples of two relatively abundant PLG variants that have been associated with PLG deficiencies (PD), but their pathogenic mechanisms are unclear. On the other hand, approximately 50 rare and ultra-rare PLG missense variants have been reported to cause PD as homozygous or compound heterozygous variants, often leading to a debilitating disease known as ligneous conjunctivitis. The true abundance of PD-associated nsSNPs is unknown since they can remain undetected in heterozygous carriers. However, PD variants may also contribute to other diseases. Recently, the ultra-rare autosomal dominant PLG/K311E has been found to be causative of hereditary angioedema (HAE) with normal C1 inhibitor. Two other rare pathogenic PLG missense variants, PLG/R153G and PLG/V709E, appear to affect platelet function and lead to HAE, respectively. Herein, PLG missense variants that are abundant and/or clinically relevant due to association with disease are examined along with their world distribution. Proposed molecular mechanisms are discussed when known or can be reasonably assumed.

Novel homozygous mutation of plasminogen in ligneous conjunctivitis: a case report and literature review

Background:Ligneous conjunctivitis (LC) is a rare disease characterized by the development of a wood-like pseudomembrane on the tarsal conjunctiva secondary to type I plasminogen deficiency. Here we reported on a Chinese patient with LC in a consanguineous family and performed a literature review of all reported mutations for this disease. Methods: A 13-month-old girl diagnosed with LC and her parents were included in this study. Hematoxylin and eosin staining was used to perform histopathology examination. The plasminogen activity was determined by chromogenic assay. Sanger sequencing was performed to screen the mutation site for the disease. In silico analysis was applied to predict the pathogenesis of the identified mutation. In addition, we reviewed the literatures on PLG mutations of LC. Results: Histopathology examination revealed the infiltration of inflammatory cells on membranous lesions. Plasma plasminogen activity was severely decreased in the patient and moderately decreased in her parents (patient: plasminogen activity, 2.50%; father: plasminogen activity, 41.02%; mother: plasminogen activity, 54.07%). Co-segregation analysis indicated that the patient was homozygous for the c.763 G > A (p.Glu255Lys) mutation in plasminogen gene (PLG). Bioinformatics analysis strongly suggested that the mutation was damaging for the disease. The model analysis indicated the mutation might cause abnormal spatial structure and low stability, thus affecting functional activity. A literature review of the LC mutations indicated a strong genetic heterogeneity of the disease. Conclusions: LC exhibited strong genetic heterogeneity, and our study identified a novel homozygous missense mutation of plasminogen (c.763 G > A, p.Glu255Lys) in one Chinese patient with LC.

An international registry of patients with plasminogen deficiency (HISTORY)

Plasminogen deficiency is an ultra-rare multisystem disorder characterized by the development of fibrin-rich pseudomembranes on mucous membranes. Ligneous conjunctivitis, which can result in vision impairment or loss, is the most frequent symptom reported. Affected systems may also include the respiratory tract, oropharynx, female reproductive tract, gingiva, middle ear, renal collecting system, skin and central nervous system. Untreated, plasminogen deficiency may result in significant reduction in quality of life and morbidity with potential life-threatening complications. Non-specific therapies are inadequate and plasminogen concentrates are not commercially available. The current understanding of plasminogen deficiency and management of disease symptoms and its progression are based on case reports/series and two small clinical trials. To date there has never been a comprehensive, international study to examine the natural history or optimal therapeutic intervention; knowledge gaps include identification of contributing factors and triggers of disease manifestations, inability to predict disease course, and insufficient real-world data for use of therapeutics. We have created an international, observational study (HISTORY) in a large cohort of persons with plasminogen deficiency and first-degree family members to address these gaps and to advance knowledge and care. HISTORY will build upon the established relationship between the Indiana Hemophilia and Thrombosis Center and the Fondazione Angelo Bianchi Bonomi, IRCCS Ca' Granda Ospedale Maggiore Policlinico - University of Milan and will utilize a modified version of the Prospective Rare Bleeding Disorders Database (PRO-RBDD). A biorepository containing samples from subjects with plasminogen deficiency will be established. This article describes the rationale behind the study and efforts towards its goals.

Novel plasminogen gene mutations in Turkish patients with type I plasminogen deficiency

The plasminogen (Plg) protein is the inactive proenzyme form of plasmin that dissolves fibrin thrombi by a process called fibrinolysis. It has been shown that homozygous or compound-heterozygous deficiency of this protein is a major cause of a rare inflammatory disease affecting mainly mucous membranes found in different body sites. In this study, five individual Turkish patients and nine Turkish families with type 1 Plg deficiency were investigated for PLG gene mutations. All of the coding regions of the PLG gene mutations were screened for mutations using denaturing high-pressure liquid chromatography (DHPLC). Samples showing a different DHPLC profile were subjected to DNA sequencing analysis. Here, we described five novel mutations namely, Cys49Ter, +1 IVS6 G>A, Gly218Val, Tyr283Cys, and Gly703Asp. Previously identified five nonsynonymous (Lys38Glu, Glu180Lys, Gly420Asp, Asp453Asn, Pro763Ser), five synonymous (330 C>T, 582 C>T, 771 T>C, 1083 A>G, 2286 T>G), and a 3' untranslated region (3' UTR) mutation (c.*45 A>G) were also reported in this present study. In this study, we have identified a total of eight mutations, five of which are novel. The mutations/polymorphisms identified in eight of the patients do not explain the disease phenotype. These cases probably carry other pathological mutations (homozygous or compound heterozygous) that cannot be detected by DHPLC.

The Unravelling of the Genetic Architecture of Plasminogen Deficiency and its Relation to Thrombotic Disease

Although plasminogen is a key protein in fibrinolysis and several mutations in the plasminogen gene (PLG) have been identified that result in plasminogen deficiency, there are conflicting reports to associate it with the risk of thrombosis. Our aim was to unravel the genetic architecture of PLG in families with plasminogen deficiency and its relationship with spontaneous thrombotic events in these families. A total of 13 individuals from 4 families were recruited. Their genetic risk profile of thromboembolism was characterized using the Thrombo inCode kit. Only one family presented genetic risk of thromboembolism (homozygous carrier of F12 rs1801020 and F13A1 rs5985). The whole PLG was tested using Next Generation Sequencing (NGS) and 5 putative pathogenic mutations were found (after in silico predictions) and associated with plasminogen deficiency. Although we can not find genetic risk factors of thrombosis in 3 of 4 families, even the mutations associated with plasminogen deficiency do not cosegregated with thrombosis, we can not exclude plasminogen deficiency as a susceptibility risk factor for thrombosis, since thrombosis is a multifactorial and complex disease where unknown genetic risk factors, in addition to plasminogen deficiency, within these families may explain the thrombotic tendency.

Ligneous membranitis in Scottish Terriers is associated with a single nucleotide polymorphism in the plasminogen (PLG) gene

Ligneous membranitis (LM) is a rare chronic inflammatory condition of the mucous membranes associated with plasminogen (encoded by PLG) deficiency in affected humans and dogs. In human, the condition is genetic in nature with numerous mutations and polymorphisms in PLG identified in affected individuals and related family members. The condition is uncommonly reported in dogs and, to date, no genetic studies have been performed. We identified related Scottish Terriers (littermates) with severe LM and unaffected relatives (sire, dam and a sibling from a previous litter). Plasma plasminogen activity was below normal in one affected dog but within normal reference intervals for the other. Sequencing of PLG from the affected dogs revealed a homozygous A>T single nucleotide polymorphism in an intron donor site (c.1256+2T>A). The related, unaffected dogs displayed heterozygous alleles at this position (c.1256+2T/A), whereas no mutation was detected in unaffected, non‐related control dogs. This is the first report to identify gene polymorphisms associated with LM in dogs.

Comprehensive genetic analysis of complement and coagulation genes in atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy caused by uncontrolled activation of the alternative pathway of complement at the cell surface level that leads to microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney failure. In approximately one half of affected patients, pathogenic loss-of-function variants in regulators of complement or gain-of-function variants in effectors of complement are identified, clearly implicating complement in aHUS. However, there are strong lines of evidence supporting the presence of additional genetic contributions to this disease. To identify novel aHUS-associated genes, we completed a comprehensive screen of the complement and coagulation pathways in 36 patients with sporadic aHUS using targeted genomic enrichment and massively parallel sequencing. After variant calling, quality control, and hard filtering, we identified 84 reported or novel nonsynonymous variants, 22 of which have been previously associated with disease. Using computational prediction methods, 20 of the remaining 62 variants were predicted to be deleterious. Consistent with published data, nearly one half of these 42 variants (19; 45%) were found in genes implicated in the pathogenesis of aHUS. Several genes in the coagulation pathway were also identified as important in the pathogenesis of aHUS. PLG, in particular, carried more pathogenic variants than any other coagulation gene, including three known plasminogen deficiency mutations and a predicted pathogenic variant. These data suggest that mutation screening in patients with aHUS should be broadened to include genes in the coagulation pathway.

Plasminogen deficiency

Plasminogen deficiency has emerged as a well-recognized disorder in which reduced levels of plasminogen lead to the development of pseudo membranes on mucosal surfaces, with subsequent end-organ damage of the affected tissue. Ligneous conjunctivitis is the most recognizable, well-documented, and common presentation of the clinical syndromes associated with plasminogen deficiency, although numerous other organs have been reported to be affected. Interestingly, while plasminogen deficiency was initially believed to be related to development of venous thromboembolic disease, more recent data suggest that decreased plasminogen levels may not, in and of themselves, increase the risk of thrombosis. Two types of plasminogen deficiency have been described in the literature. Type I represents a quantitative deficiency and type II a qualitative deficiency. It appears that hypoplasminogenaemia (type I deficiency) is the type most associated with pseudomembrane disease. A variety of genetic mutations has been identified recently and is reported to lead to these disorders. These defects have been identified in diverse populations, with no specific ethnic predilection. However, this disorder may have increased prevalence in areas and communities where consanguinity is more common. Despite the fact that the characteristic lesions are now better recognized and plasminogen levels are accurately and easily measured, adequate treatment of the clinical manifestations of this disorder is lacking. For ligneous conjunctivitis, a plasminogen concentrate formulated into an ophthalmologic preparation has been found to be an effective local therapy. Unfortunately, no plasminogen concentrate is currently available commercially for either systemic or local therapy.

Plasminogen deficiency

Plasminogen (plg) deficiency has been classified as (i) hypoplasminogenemia or 'true' type I plg deficiency, and (ii) dysplasminogenemia, also called type II plg deficiency. Both forms, severe hypoplasminogenemia and dysplasminogenemia, are not causally linked to venous thrombosis. Dysplasminogenemia does not lead to a specific clinical manifestation and probably represents only a polymorphic variation in the general population, mainly in Asian countries. Severe hypoplasminogenemia is associated with compromised extracellular fibrin clearance during wound healing, leading to pseudomembraneous (ligneous) lesions on affected mucous membranes (eye, middle ear, mouth, pharynx, duodenum, upper and lower respiratory tract and female genital tract). Ligneous conjunctivitis is by far the most common clinical manifestation. More than 12% of patients with severe hypoplasminogenemia exhibit congenital occlusive hydrocephalus. In milder cases of ligneous conjunctivitis, topical application of plg-containing eye drops, fresh frozen plasma, heparin, corticosteroids or certain immunosuppressive agents (such as azathioprine) may be more or less effective. Oral treatment with sex hormones was successful in two female patients with ligneous conjunctivitis. In severe cases with possibly life-threatening multi-organ involvement, true therapeutic options are not available at present. The plg-knockout mouse is a useful tool to study the many different properties of plg in a variety of settings, such as wound healing, tissue repair and tissue remodeling, virulence and invasiveness of certain bacteria in the human host, tumor growth and dissemination, as well as arteriosclerosis.

Ligneous conjunctivitis: a clinicopathological, immunohistochemical, and genetic study including the treatment of two sisters with multiorgan involvement

Ligneous conjunctivitis (LC) is a rare disease characterized by wood-like pseudomembranes developing on the ocular and extraocular mucosae secondary to plasminogen (PLG) deficiency. In this paper, we report two cases of LC in two sisters of 57 and 62 years of age that presented with recurrent, bilateral pseudomembranes on conjunctiva and a history of consanguinity and deafness. Pseudomembranes showed superficial and/or subepithelial deposits of eosinophilic amorphous hyaline, amyloid-like material with a variable proportion of granulation tissue, and inflammatory cells. The eosinophilic deposits were negative for Congo red stain, immunoreactive for fibrinogen, and consistently negative for amyloid A component, transthyretin, beta(2)-microglobulin, albumin, fibronectin, collagen type IV, vimentin, and cytokeratins. Among inflammatory cells, a percentage of positivity of roughly 60% for lymphocytes T (CD3+) and 40% for lymphocytes B (CD8+), with a relation of cytotoxic/helper (CD8/4) T cells of 3:2, was found. In one case, nasal polyps and recurrent gastric peptic ulcer were also characterized by the same subepithelial hyaline deposits. A novel homozygous point mutation c.1856 C>T was found in exon 15 of the PLG gene in both patients. Amniotic membrane transplantation was done in one case with promising results.

Molecular characterization of an Italian patient with plasminogen deficiency and ligneous conjunctivitis

Plasminogen deficiency is a rare disease characterized by ligneous conjunctivitis and infections. We observed a 3-year-old Italian boy presenting ligneous conjunctivitis and low plasma levels of plasminogen. Twenty-three different mutations on the PLG gene have been reported to date, but mutation analysis had been troublesome for the presence of highly homologous genes. The aim of the study was to identify the underlying mutation avoiding coamplification of unwanted genetic materials using a long polymerase chain reaction strategy, instead of the previously reported subcloning methods. By this simple strategy the complete sequence analysis of PLG gene was performed, and a previously reported missense homozygous mutation (K19E) was identified.