in diseases with a defect in a pathway in which a glycosylation reaction involving a udp - sugar ( or in the case of sialic acid , a cytidine monophosphate ( cmp )- sugar ) are at fault , production of the deficient nucleotide sugar ( pyrimidine - phospho - sugar ) via residual , but inadequate , enzyme activity is augmented by precursor loading , i . e . increasing intracellular uridine triphosphate ( utp ) and the specific sugar or its precursor , to form increased intracellular concentrations of the udp - sugar . extracellular uridine concentrations sufficient to increase intracellular utp and udp sugars are required , and are in the range of & gt ; 30 micromolar steady - state concentration , advantageously & gt ; 50 micromolar while at the same time increasing availability of the specific sugar . sugar availability may be increased by either administration of the specific sugar or a precursor that is efficiently converted to it , or by inhibiting pathways involved in sugar degradation , or both administering a sugar or precursor and blocking degradation pathways . uridine is advantageously administered to patients in the form of an orally bioavailable prodrug such as uridine triacetate ( 2 ′, 3 ′, 5 ′- tri - o - acetyluridine ). an appropriate single dose is in the range of 2 to 10 grams , administered once to four times daily depending on need and response . the specific sugars , examples of which are glucosamine , n - acetylglucosamine , galactose , n - acetylgalactose , mannose , or n - acetylgalactose , precursors of these or other relevant sugars , or inhibitors of their catabolism , are administered in doses sufficient to raise their intracellular concentrations in tissues affected by the specific glycosylation disorder . cdg often affect the development and function of the brain , but also frequently affect peripheral organs as well . a wide variety of symptoms can be caused by glycosylation disorders , including developmental delays ( both cognitive and physical ), seizures , ataxia , hypotonia , seizures , retinal problems , liver abnormalities including fibrosis , impaired hematopoiesis , and structural malformations . definitive diagnosis generally requires identification of a pathogenic mutation in a glycosylation pathway , which provides the requisite information for determining whether uridine loading is likely to be beneficial . cdg have classically been divided into two main groups based on diagnosis using transferrin glycosylation patterns . type i cdg affects the early steps in oligosaccharide synthesis , production of lipid - linked oligosaccharides in the endoplasmic reticulum . type ii glycosylation disorders comprise defects in glycosylation that occur after glycans are added to proteins , and affect subsequent elongation , trimming and processing of the attached glycans . more recently , cdg that do not fit into either of these categories have been identified , affecting non - glycan glycosylation of proteins . see freeze h ( 2013 ) jbc 288 ( 210 ): 6936 - 6945 , and the references cited therein , all of which are incorporated herein by reference . pyrimidine - phospho - sugar precursors are involved in subsets of both type i and type ii cdg , and in glycosylation disorders not falling into either of these categories which will be referred to herein as type iii glycosylation disorders . (“ type i ” cdg and “ type ii ” cdg are art - recognized names for these categories of cdg , whereas the name “ type iii ” cdg is used in this document for convenience .) pgm deficiency ( see below and example 3 ) and gpt deficiency ( see example 4 ) are examples of type ii cdg . gne myopathy ( see below and example 2 ) is primarily a type ii cdg but also extends to type iii cdg . the typical dose for uridine prodrugs in general and uridine triacetate in particular is an amount sufficient to achieve steady state average plasma concentration & gt ; 30 micromolar , but levels as high as about 50 micromolar ( e . g ., from 45 to 55 micromolar ) may be necessary for some difficult patients . appropriate doses of uridine triacetate to achieve steady state plasma uridine & gt ; 30 micromolar are 0 . 5 to 5 grams per square meter of body surface area ( bsa ), advantageously 1 . 5 to 3 grams per square meter of bsa . bsa is determined using standard drug dosing tables or formulas , using body weight , height , sex and age as input variables . doses are administered orally one to four times per day , approximately evenly spaced throughout the 24 hour day . the distinguishing characteristic of cdg that are beneficially treated with a uridine precursor and sugar or sugar precursor are those in which the biochemical lesion comprises a deficiency in production or availability ( including transport deficits reducing pyrimidine nucleotide sugar delivery into the endoplasmic reticulum ) of a pyrimidine nucleotide sugar , or those in which enzyme activity using a pyrimidine nucleotide sugar as a substrate are low , and thereby contributing to disease pathogenesis . glucosamine ( udp - n - acetyl )- 2 - epimerase / n - acetylmannosamine kinase ( gne ) is an enzyme involved in synthesis of sialic acid , a sugar found in many glycoproteins . gne myopathy , or hereditary inclusion body myopathy is caused by a defect in production of sialic acid , a precursor for synthesis of sialoglycoconjugates . exogenous sialic acid ( or sialic acid prodrugs or precursors such as mannosamine or n - acetylmannosamine ) is being tested as a treatment , bypassing the enzymatic defect . the agents and methods of this disclosure augments the efficacy of exogenous sialic acid by increasing intracellular pyrimidine nucleotides , including cytidine triphosphate ( ctp ), which is derived from uridine triphosphate ( utp ). increased intracellular ctp improves the efficiency of conversion of exogenous sialic acid to cmp - sialic acid , the nucleotide sugar used for transfer of sialic acid onto growing oligosaccharides . appropriate doses of sialic acid or n - acetylmannosamine for treatment of gne myopathy are 3 to 10 grams per day , depending on the severity of the molecular lesion and the size of the patient . phosphoglucomutase - 1 ( pgm - 1 ) deficiency is a cdg involving insufficient production of galactose , with multisystem symptoms that may include growth delay , malformations like cleft palate , hypoglycemia , and liver and heart dysfunction . supplementary galactose at doses of 0 . 5 to 1 g / kg per day is used for treatment , with partial resolution of some symptoms . uridine triacetate administered concurrently with galactose augments the therapeutic efficacy of galactose in this disease . several known cdg feature defects in n - glycan synthesis and processing . type ii cdg are often associated with developmental delays , hypotonia , seizures , and organ dysfunction . for these type ii cdg including cpt deficiency , n - acetylglucosamine is a potential treatment , given in doses up to 200 mg / kg / day . in these patients , uridine triacetate is co - administered with n - acetylglucosamine to enhance its efficacy in restoring n - glycan synthesis and processing . in other glycosylation disorders in which the production , utilization , transport or availability of a pyrimidine nucleotide sugar contributes to disease pathogenesis , uridine triacetate is administered to enhance the efficacy of the particular monosaccharide deemed appropriate for that specific cdg , and the monosaccharide is administered in daily doses that are considered appropriate for it as monotherapy . the subject that can be treated in accordance with this invention is any animal , whether vertebrate or invertebrate , but is preferably a mammalian subject including a human subject . the invention will be better understood by reference to the following examples , which illustrate but do not limit the invention described herein . a patient displaying developmental delays is diagnosed with a congenital disorder of glycosylation by detection of a mutation affecting glycosylation by reducing availability of a uridine - diphospho sugar , corroborated by biochemical measurements in cells from the patient . the patient is treated with oral uridine triacetate at a dose of 2 grams per square meter of body surface area , administered three times per day . the patient responds to treatment , displaying biochemical measures of improved protein glycosylation and concurrent improvements in clinical condition . a patient displaying progressive distal muscle weakness , with vacuoles and filamentous inclusions in a muscle biopsy , is diagnosed with gne myopathy by testing for mutations in gne , which result in impaired synthesis of endogenous sialic acid . the patient is treated with oral n - acetylmannosamine at a dose of 3 to 10 grams per day . the patient is also treated with uridine triacetate a dosage of 2 grams per square meter of body surface area administered twice per day . the uridine triacetate improves the clinical response beyond that achieved with n - acetylmannosamine alone . a patient with multisystem disease consistent with phosphoglucomutase deficiency receives a definitive diagnosis via detection of impaired transferring glycosylation and a mutation in pgm - 1 . the patient is treated with 1 gram / kg of d - galactose per day , and with uridine triacetate a dosage of 2 grams per square meter of body surface area administered twice per day the uridine triacetate improves the clinical response beyond that achieved with d - galactose alone . a patient displaying severe hypotonia , medically intractable seizures , developmental delay andmicrocephaly is diagnosed with a deficiency of activity of the enzyme gpt , a type ii cdg , by detection of a mutation in its encoding gene dpagt - 1 . (“ gpt ” is the enzyme dolichol phosphate n - acetyl - glucosamine - 1 phosphate transferase ; “ dpagt - 1 ” is the gene that encodes gpt .) the patient is treated with n - acetylglucosamine at a dose of 200 mg / kg per day . the patient is also treated with uridine triacetate a dosage of 2 grams per square meter of body surface area administered twice per day . the uridine triacetate improves the clinical response beyond that achieved with n - acetylglucosamine alone .
uridine triacetate or other uridine prodrugs are used to treat genetic glycosylation disorders by administering them in an amount sufficient to raise plasma uridine in the to a level greater than 30 micromolar . they can be administered alone or in combination with a sugar whose transfer is defective in the glycosylation disorder being treated .