EXT1 and hereditary multiple exostoses: Similarly, EXT1/EXT2-CDG, commonly known as Multiple Hereditary Exostoses (MHE), results from heterozygous mutations in EXT1 or EXT2, which encode glycosyltransferases essential for heparan sulfate elongation, leading to the formation of bony outgrowths that cause chronic pain and can interfere with normal bone development17.