Exostosin-1 is a protein that in humans is encoded by the EXT1 gene. [5]
This gene encodes one of the two endoplasmic reticulum-resident type II transmembrane glycosyltransferase – the other being EXT2 – which are involved in the chain elongation step of heparan sulfate biosynthesis. Mutations in this gene cause the type I form of multiple exostoses. [5]
Hereditary multiple osteochondromas (HMO), also known as hereditary multiple exostoses, is a disorder characterized by the development of multiple benign osteocartilaginous masses (exostoses) in relation to the ends of long bones of the lower limbs such as the femurs and tibias and of the upper limbs such as the humeri and forearm bones. They are also known as osteochondromas. Additional sites of occurrence include on flat bones such as the pelvic bone and scapula. The distribution and number of these exostoses show a wide diversity among affected individuals. Exostoses usually present during childhood. The vast majority of affected individuals become clinically manifest by the time they reach adolescence. A small percentage of affected individuals are at risk for development of malignant transformation namely sarcomas. The incidence of hereditary multiple exostoses is around 1 in 50,000 individuals. Hereditary multiple osteochondromas is the preferred term used by the World Health Organization.
Osteochondromas are the most common benign tumors of the bones. The tumors take the form of cartilage-capped bony projections or outgrowth on the surface of bones exostoses. It is characterized as a type of overgrowth that can occur in any bone where cartilage forms bone. Tumors most commonly affect long bones about the knee and in the forearm. Additionally, flat bones such as the pelvis and scapula may be affected. Hereditary multiple exostoses usually present during childhood. Yet, the vast majority of affected individuals become clinically manifest by the time they reach adolescence. Osteochondromas occur in 3% of the general population and represent 35% of all benign tumors and 8% of all bone tumors. The majority of these tumors are solitary non-hereditary lesions and approximately 15% of osteochondromas occur as hereditary multiple exostoses preferably known as hereditary multiple osteochondromas (HMOs). Osteochondromas do not result from injury and the exact cause remains unknown. Recent research has indicated that multiple osteochondromas is an autosomal dominant inherited disease. Germ line mutations in EXT1 and EXT2 genes located on chromosomes 8 and 11 have been associated with the cause of the disease. The treatment choice for osteochondroma is surgical removal of solitary lesion or partial excision of the outgrowth, when symptoms cause motion limitations or nerve and blood vessel impingements. In hereditary multiple exostoses the indications of surgery are based upon multiple factors that are taken collectively, namely: patient's age, tumor location and number, accompanying symptomatology, esthetic concerns, family history and underlying gene mutation. A variety of surgical procedures have been employed to remedy hereditary multiple exostoses such as osteochondroma excision, bone lengthening, corrective osteotomy and hemiepiphysiodesis. Sometimes a combination of the previous procedures is used. The indicators of surgical success in regard to disease and patient characteristics are greatly disputable. Because most studies of hereditary multiple exostoses are retrospective and of limited sample size with missing data, the best evidence for each of the currently practiced surgical procedures is lacking.
Heparan sulfate (HS) is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins. It is in this form that HS binds to a variety of protein ligands, including Wnt, and regulates a wide range of biological activities, including developmental processes, angiogenesis, blood coagulation, abolishing detachment activity by GrB, and tumour metastasis. HS has also been shown to serve as cellular receptor for a number of viruses, including the respiratory syncytial virus. One study suggests that cellular heparan sulfate has a role in SARS-CoV-2 Infection, particularly when the virus attaches with ACE2.
Arylsulfatase A is an enzyme that breaks down sulfatides, namely cerebroside 3-sulfate into cerebroside and sulfate. In humans, arylsulfatase A is encoded by the ARSA gene.
N-acetylgalactosamine-6-sulfatase is an enzyme that, in humans, is encoded by the GALNS gene.
The human gene SPAST codes for the microtubule-severing protein of the same name, commonly known as spastin.
Syndecan-2 is a protein that in humans is encoded by the SDC2 gene.
Cell division cycle 73, Paf1/RNA polymerase II complex component, homolog , also known as CDC73 and parafibromin, is a protein which in humans is encoded by the CDC73 gene.
In enzymology, a N-acetylglucosaminyl-proteoglycan 4-beta-glucuronosyltransferase is an enzyme that catalyzes the chemical reaction
Protein patched homolog 1 is a protein that is the member of the patched family and in humans is encoded by the PTCH1 gene.
Exostosin glycosyltransferase-2 is a protein that in humans is encoded by the EXT2 gene.
Heat shock protein 75 kDa, mitochondrial is a protein that in humans is encoded by the TRAP1 gene.
Exostosin-like 3 is a protein that in humans is encoded by the EXTL3 gene.
Exostosin-like 1 is a protein that in humans is encoded by the EXTL1 gene.
Heparan sulfate glucosamine 3-O-sulfotransferase 3A1 is an enzyme that in humans is encoded by the HS3ST3A1 gene.
Heparan-α-glucosaminide N-acetyltransferase is an enzyme that in humans is encoded by the HGSNAT gene.
Heparan sulfate 2-O-sulfotransferase 1 is an enzyme that in humans is encoded by the HS2ST1 gene.
Heparan sulfate glucosamine 3-O-sulfotransferase 3B1 is an enzyme that in humans is encoded by the HS3ST3B1 gene. Heparan sulfate biosynthetic enzymes are key components in generating myriad distinct heparan sulfate fine structures that carry out multiple biologic activities. The enzyme encoded by this gene is a member of the heparan sulfate biosynthetic enzyme family. It is a type II integral membrane protein and possesses heparan sulfate glucosaminyl 3-O-sulfotransferase activity ( HS3ST3A1). The Sulfotransferase domain of this enzyme is highly similar to the same domain of heparan sulfate D-glucosaminyl 3-O-sulfotransferase 3A1 and these two enzymes sulfate an identical disaccharide. This gene is widely expressed, with the most abundant expression in liver and placenta.
Exostosin-like 2 is a protein that in humans is encoded by the EXTL2 gene. EXTL2 Glycosyltransferase is required for the biosynthesis of heparan-sulfate and responsible for the alternating addition of beta-1-4-linked glucuronic acid (GlcA) and alpha-1-4-linked N-acetylglucosamine (GlcNAc) units to nascent heparan sulfate chains.
Glucuronosyl-N-acetylglucosaminyl-proteoglycan 4-alpha-N-acetylglucosaminyltransferase is an enzyme with systematic name UDP-N-acetyl-D-glucosamine:beta-D-glucuronosyl-(1->4)-N-acetyl-alpha-D-glucosaminyl-proteoglycan 4-alpha-N-acetylglucosaminyltransferase. This enzyme catalyses the following chemical reaction
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