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    EXT2 Gene

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    Submitted by: Vivi Li
    (This entry belongs to Entry Collection "MedlinePlus ")

    Definition

    exostosin glycosyltransferase 2

    1. Normal Function

    The EXT2 gene provides instructions for producing a protein called exostosin-2. This protein is found in a cell structure called the Golgi apparatus, which modifies newly produced enzymes and other proteins. In the Golgi apparatus, exostosin-2 attaches (binds) to another protein, exostosin-1, to form a complex that modifies a protein called heparan sulfate so it can be used in the body. Heparan sulfate is involved in regulating a variety of body processes including the formation of blood vessels (angiogenesis) and blood clotting. It also has a role in the spread (metastasis) of cancer cells.

    2. Health Conditions Related to Genetic Changes

    2.1 Hereditary Multiple Osteochondromas

    About 220 mutations in the EXT2 gene have been identified in people with hereditary multiple osteochondromas type 2, a condition in which people develop multiple benign (noncancerous) bone tumors called osteochondromas. Most of these mutations prevent any functional exostosin-2 protein from being made, and are called "loss-of-function" mutations. The loss of exostosin-2 protein function prevents it from forming a complex with the exostosin-1 protein and modifying heparan sulfate. It is unclear how this impairment leads to the development of multiple osteochondromas.

    2.2 Potocki-Shaffer Syndrome

    A genetic change resulting in the deletion of the EXT2 gene causes a condition called Potocki-Shaffer syndrome. People with this condition have multiple osteochondromas (described above) and enlarged openings in two bones that make up much of the top and sides of the skull (enlarged parietal foramina). Other signs and symptoms seen in some people with Potocki-Shaffer syndrome include intellectual disability, developmental delay, distinctive facial features, vision problems, and defects in the heart, kidneys, and urinary tract.

    Potocki-Shaffer syndrome (sometimes referred to as proximal 11p deletion syndrome) is caused by a deletion of genetic material from the short (p) arm of chromosome 11. In people with this condition, a loss of the EXT2 gene within this region is responsible for multiple osteochondromas. The deletion likely leads to a reduction of exostosin-2 protein and the inability to process heparan sulfate correctly. Although heparan sulfate is involved in many body processes, it is unclear how the lack of this protein causes multiple osteochondromas. The loss of additional genes in the deleted region likely contributes to the other features of Potocki-Shaffer syndrome. Specifically, loss of the ALX4 gene results in enlarged parietal foramina, and deletion of the PHF21A gene causes intellectual disability and distinctive facial features.

    2.3 Other Disorders

    At least two mutations in the EXT2 gene have been found in a family with seizures-scoliosis-macrocephaly syndrome. In individuals with this condition, seizures typically begin in early childhood. Affected individuals also have an abnormal curvature of the spine (scoliosis), an unusually large head (macrocephaly), intellectual disability, and weak muscle tone (hypotonia). The EXT2 gene mutations associated with seizures-scoliosis-macrocephaly syndrome change single protein building blocks (amino acids) in the exostosin-2 protein. These changes reduce the amount of functional exostosin-2 protein, which likely disrupts normal modification of heparan sulfate. It is unclear how this disruption leads to the varied signs and symptoms of the condition. Individuals with seizures-scoliosis-macrocephaly syndrome do not appear to develop osteochondromas (described above).

    3. Other Names for This Gene

    • exostoses (multiple) 2

    • exostosin 2

    • EXT2_HUMAN

    • Glucuronosyl-N-acetylglucosaminyl-proteoglycan 4-alpha-N- acetylglucosaminyltransferase

    • N-acetylglucosaminyl-proteoglycan 4-beta-glucuronosyltransferase

    • SOTV

    The entry is from https://medlineplus.gov/genetics/gene/ext2

    References

    1. Clement ND, Porter DE. Hereditary multiple exostoses: anatomical distribution and burden of exostoses is dependent upon genotype and gender. Scott Med J. 2014 Feb;59(1):35-44. doi: 10.1177/0036933013518150.
    2. Farhan SM, Wang J, Robinson JF, Prasad AN, Rupar CA, Siu VM; FORGE CanadaConsortium, Hegele RA. Old gene, new phenotype: mutations in heparan sulfatesynthesis enzyme, EXT2 leads to seizure and developmental disorder, no exostoses.J Med Genet. 2015 Oct;52(10):666-75. doi: 10.1136/jmedgenet-2015-103279.
    3. Jochmann K, Bachvarova V, Vortkamp A. Heparan sulfate as a regulator ofendochondral ossification and osteochondroma development. Matrix Biol. 2014Feb;34:55-63. doi: 10.1016/j.matbio.2013.11.003.
    4. Labonne JD, Vogt J, Reali L, Kong IK, Layman LC, Kim HG. A microdeletionencompassing PHF21A in an individual with global developmental delay andcraniofacial anomalies. Am J Med Genet A. 2015 Dec;167A(12):3011-8. doi:10.1002/ajmg.a.37344.
    5. Lonie L, Porter DE, Fraser M, Cole T, Wise C, Yates L, Wakeling E, Blair E,Morava E, Monaco AP, Ragoussis J. Determination of the mutation spectrum of theEXT1/EXT2 genes in British Caucasian patients with multiple osteochondromas, and exclusion of six candidate genes in EXT negative cases. Hum Mutat. 2006Nov;27(11):1160.
    6. McCormick C, Duncan G, Goutsos KT, Tufaro F. The putative tumor suppressorsEXT1 and EXT2 form a stable complex that accumulates in the Golgi apparatus andcatalyzes the synthesis of heparan sulfate. Proc Natl Acad Sci U S A. 2000 Jan18;97(2):668-73.
    7. Musso N, Caronia FP, Castorina S, Lo Monte AI, Barresi V, Condorelli DF.Somatic loss of an EXT2 gene mutation during malignant progression in a patientwith hereditary multiple osteochondromas. Cancer Genet. 2015 Mar;208(3):62-7.doi: 10.1016/j.cancergen.2015.01.002.
    8. Romeike BF, Wuyts W. Proximal chromosome 11p contiguous gene deletion syndromephenotype: case report and review of the literature. Clin Neuropathol. 2007Jan-Feb;26(1):1-11. Review.
    9. Tian C, Yan R, Wen S, Li X, Li T, Cai Z, Li X, Du H, Chen H. A splice mutationand mRNA decay of EXT2 provoke hereditary multiple exostoses. PLoS One. 2014 Apr 11;9(4):e94848. doi: 10.1371/journal.pone.0094848.
    10. Wakui K, Gregato G, Ballif BC, Glotzbach CD, Bailey KA, Kuo PL, Sue WC,Sheffield LJ, Irons M, Gomez EG, Hecht JT, Potocki L, Shaffer LG. Construction ofa natural panel of 11p11.2 deletions and further delineation of the criticalregion involved in Potocki-Shaffer syndrome. Eur J Hum Genet. 2005May;13(5):528-40.
    11. Wuyts W, Waeber G, Meinecke P, Schüler H, Goecke TO, Van Hul W, Bartsch O.Proximal 11p deletion syndrome (P11pDS): additional evaluation of the clinicaland molecular aspects. Eur J Hum Genet. 2004 May;12(5):400-6. Review.
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