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Nucleotide sugars (NS) are fundamental molecules in life and play a key role in glycosylation reactions and signal conduction. Several pathways are involved in the synthesis of NS. The Leloir pathway, the main pathway for galactose metabolism, is crucial for production of uridine diphosphate (UDP)-glucose and UDP-galactose. The most common metabolic disease affecting this pathway is galactose-1-phosphate uridylyltransferase (GALT) deficiency, that despite a lifelong galactose-restricted diet, often results in chronically debilitating complications. Alterations in the levels of UDP-sugars leading to galactosylation abnormalities have been hypothesized as a key pathogenic factor. However, UDP-sugar levels measured in patient cell lines have shown contradictory results. Other NS that might be affected, differences throughout development, as well as tissue specific profiles have not been investigated. Using recently established UHPLC-MS/MS technology, we studied the complete NS profiles in wildtype and galt knockout zebrafish (Danio rerio). Analyses of UDP-hexoses, UDP-hexosamines, CMP-sialic acids, GDP-fucose, UDP-glucuronic acid, UDP-xylose, CDP-ribitol, and ADP-ribose profiles at four developmental stages and in tissues (brain and gonads) in wildtype zebrafish revealed variation in NS levels throughout development and differences between examined tissues. More specifically, we found higher levels of CMP-N-acetylneuraminic acid, GDP-fucose, UDP-glucuronic acid, and UDP-xylose in brain and of CMP-N-glycolylneuraminic acid in gonads. Analysis of the same NS profiles in galt knockout zebrafish revealed no significant differences from wildtype. Our findings in galt knockout zebrafish, even when challenged with galactose, do not support a role for abnormalities in UDP-glucose or UDP-galactose as a key pathogenic factor in GALT deficiency, under the tested conditions., (© 2020 The Authors. Journal of Inherited Metabolic Disease published by John Wiley & Sons Ltd on behalf of SSIEM.)

Type III galactosemia is a metabolic disorder caused by reduced activity of UDP-galactose-4-epimerase, which participates in galactose metabolism and the generation of various UDP-sugar species. We characterized gale-1 in Caenorhabditis elegans and found that a complete loss-of-function mutation is lethal, as has been hypothesized for humans, whereas a nonlethal partial loss-of-function allele causes a variety of developmental abnormalities, likely resulting from the impairment of the glycosylation process. We also observed that gale-1 mutants are hypersensitive to galactose as well as to infections. Interestingly, we found interactions between gale-1 and the unfolded protein response., (Copyright © 2014 by the Genetics Society of America.)

Classic galactosemia is a genetic disorder that results from profound loss of galactose-1P-uridylyltransferase (GALT). Affected infants experience a rapid escalation of potentially lethal acute symptoms following exposure to milk. Dietary restriction of galactose prevents or resolves the acute sequelae; however, many patients experience profound long-term complications. Despite decades of research, the mechanisms that underlie pathophysiology in classic galactosemia remain unclear. Recently, we developed a Drosophila melanogaster model of classic galactosemia and demonstrated that, like patients, GALT-null Drosophila succumb in development if exposed to galactose but live if maintained on a galactose-restricted diet. Prior models of experimental galactosemia have implicated a possible association between galactose exposure and oxidative stress. Here we describe application of our fly genetic model of galactosemia to the question of whether oxidative stress contributes to the acute galactose sensitivity of GALT-null animals. Our first approach tested the impact of pro- and antioxidant food supplements on the survival of GALT-null and control larvae. We observed a clear pattern: the oxidants paraquat and DMSO each had a negative impact on the survival of mutant but not control animals exposed to galactose, and the antioxidants vitamin C and α-mangostin each had the opposite effect. Biochemical markers also confirmed that galactose and paraquat synergistically increased oxidative stress on all cohorts tested but, interestingly, the mutant animals showed a decreased response relative to controls. Finally, we tested the expression levels of two transcripts responsive to oxidative stress, GSTD6 and GSTE7, in mutant and control larvae exposed to galactose and found that both genes were induced, one by more than 40-fold. Combined, these results implicate oxidative stress and response as contributing factors in the acute galactose sensitivity of GALT-null Drosophila and, by extension, suggest that reactive oxygen species might also contribute to the acute pathophysiology in classic galactosemia.

Classical or transferase-deficient galactosaemia is an inherited metabolic disorder caused by mutation in the human Galactose-1-phosphate uridyl transferase (GALT) gene. Of some 170 causative mutations reported, fewer than 10% are observed in more than one geographic region or ethnic group. To better understand the population history of the common GALT mutations, we have established a haplotyping system for the GALT locus incorporating eight single nucleotide polymorphisms and three short tandem repeat markers. We analysed haplotypes associated with the three most frequent GALT gene mutations, Q188R, K285N and Duarte-2 (D2), and estimated their age. Haplotype diversity, in conjunction with measures of genetic diversity and of linkage disequilibrium, indicated that Q188R and K285N are European mutations. The Q188R mutation arose in central Europe within the last 20 000 years, with its observed east-west cline of increasing relative allele frequency possibly being due to population expansion during the re-colonization of Europe by Homo sapiens in the Mesolithic age. K285N was found to be a younger mutation that originated in Eastern Europe and is probably more geographically restricted as it arose after all major European population expansions. The D2 variant was found to be an ancient mutation that originated before the expansion of Homo sapiens out of Africa.

Classic galactosemia is caused by impaired galactose-1-phosphate uridyltransferase (GALT EC 2.7.712). If discovered and treated within the first days of life, the acute problems of hepatocellular damage, sepsis, and death are prevented. However, chronic problems such as ataxia, tremor, dyspraxic speech, and ovarian failure may occur. To determine whether screening newborns before discharge from the nursery for GALT deficiency is feasible and whether acute and chronic signs could be prevented by earlier intervention, we developed a simplified "breath test." We quantitated total body oxidation of C-D-galactose to CO2 in expired air by normal newborns between 2 h and 2 mo of age and compared their results to older children with GALT deficiency. We found no differences in total body galactose oxidation (TBGO) among normal newborns up to 48 h of age, but a 2-fold rise in TBGO developed during their first 2 wk of life. Older children with galactosemia had significantly less oxidative capacity than normal newborns. We conclude that newborn breath testing for total body galactose oxidation is feasible before discharge from nursery. It has potential utility for both preventing acute neonatal toxicity and determining the mechanisms producing long-term complications such as ovarian failure, dyspraxia, ataxia, and tremors.

We developed a new non-derivatization analytical method for the determination of galactose in the diagnosis of galactosemia by high-performance anion-exchange chromatography (HPAEC)-pulsed amperometric detection (PAD). With an anion-exchange column, the analytes were separated efficiently using 3mM NaOH containing 1mM NaOAc, and 200mM NaOH was added for post-column reagent. The limit of detection (S/N=3) and limit of quantification (S/N=10) for galactose were 25ng/mL and 83ng/mL, respectively. Linear dynamic range was from 4.67mg/dL to 53.46mg/dL (r(2)=0.9999). The mean recovery of galactose for intra-, inter-day assays were found to be of satisfactory results (98.14-101.42%).

UDP-glucose pyrophosphorylase (E.C. 2.7.7.9), encoded by ugp, provides UDP-glucose which is critical to the synthesis of glycogen, and also catalyzes the reaction between UTP and galactose-1-phosphate, yielding UDP-galactose. This activity of UDP-gal pyrophosphorylase (UDP-galPP) suggests a role in an alternate pathway for galactose metabolism in patients with deficiency of galactose-1-phosphate uridyltransferase (GALT). We examined the effects of GALT deficiency and dietary galactose on UDP-glucose pyrophosphorylase (UDP-gluPP) and UDP-galactose pyrophosphorylase activity and ugp expression in liver of mice with homozygous deletion of the critical regions of galt. Activity with glucose-1-phosphate as substrate was significantly higher than that with galactose-1-phosphate. In liver from mice with GALT deficiency (G/G), UDP-galPP activity appeared to be lower than that measured in liver from control (N/N) animals. This difference disappeared when the N/N tissue homogenate was dialyzed to remove residual UDP-glucose, confirming that careful elimination of residual GALT activity is necessary, since GALT has 1000-fold greater activity toward galactose-1-phosphate than that of UDP-galPP in liver homogenates. Prior exposure to conventional mouse chow, high galactose chow, and high glucose chow did not alter UDP-glu PP or UDP-galPP activity. Steady state UGP mRNA levels were determined in tissues from normal and G/G animals. UGP expression was highest in liver, and did not differ by genotype or exposure to high galactose chow. UDP-galPP activity may account for unexplained ability to oxidize galactose in animals with no GALT activity, but is insufficient to alter accumulation of galactose metabolites.

Galactosemia is an inherited metabolic disorder due to a defect in one of the three enzymes required to fully metabolize the galactose in glucose: the galactose 1-phosphate uridyltransferase. Because this enzyme is present in the normal foetal liver since the tenth week of gestation, its defect cause congenital abnormality due to galactose accumulation, when the mother had taken milk during the pregnancy. It is mainly a liver pathology whereas the foetal cataract is rare. This latter is usually considered as the sole ophthalmic consequence of this disorder but exceptional ocular haemorrhages have also been described. We report the case of a neonate with galactosemia free from foetal cataract but presenting an unilateral vitreous haemorrhage. Retinal anomalies seen after vitrectomy are probably the source of the vitreous blood favoured by the coagulopathy associated with the neonatal disease. The causes of infant vitreous haemorrhages are often debated and their complications, especially severe amblyopia, require vitrectomy within the month following their discovery. In galactosemia, vitreous haemorrhage can be prevented by an early diagnosis and an appropriate treatment of the liver pathology.

Classic galactosemia is an autosomal recessive disorder that is caused by activity deficiency of the UDP-galactose uridyl transferase (GALT). The clinical spectrum of classic galactosemia differs according to the type and number of mutations in the GALT gene. Short-term clinical symptoms such as jaundice, hepatomegaly, splenomegaly and E. coli sepsis are typically associated with classic galactosemia. These symptoms are often severe but quickly ameliorate with dietary restriction of galactose. However, long-term symptoms such as mental retardation and primary ovarian failure do not resolve irrespective of dietary intervention or the period of initial dietary intervention. There seem to be an association between deficient galactosylation of cerebrosides and classic galactosemia. Galactocerebrosides and glucocerebrosides are the primary products of the enzyme UDP-galactose:cerebroside galactosyl transferase (CGT). There has been an observation of deficient galactosylation coupled with over glucosylation in the brain tissue specimens sampled from deceased classic galactosemia patients. The plausible mechanism with which the association between GALT and CGT had not been explained before. Yet, UDP-galactose serves as the product of GALT as well as a substrate for CGT. In classic galactosemia, there is a consistent deficiency in cerebroside galactosylation. We postulate that the molecular link between defective GALT enzyme, which result in classic galactosemia; and the cerebroside galactosyl transferase, which is responsible for galactosylation of cerebrosides is dependent on the cellular concentrations of UDP-galactose. We further hypothesize that a threshold concentration of UDP-galactose exist below which the integrity of cerebroside galactosylation suffers.

In humans, the absence of galactose-1-phosphate uridyltransferase (GALT) leads to significant neonatal morbidity and mortality which are dependent on galactose ingestion, as well as long-term complications of primary ovarian failure and cognitive dysfunction, which are diet independent. The creation of a knockout mouse model for GALT deficiency was aimed at providing an organism in which metabolic challenges and gene manipulation could address the enigmatic pathophysiologic questions raised by humans with galactosemia. Instead, the mouse represents a biochemical phenotype without evidence of clinical morbidity. The similarities and differences between mice and humans with galactosemia are explored from metabolite, enzyme, and process points of view. The mouse both produces and oxidizes galactose in a manner similar to humans. It differs in brain accumulation of galactitol. Future directions for exploration of this enigmatic condition are discussed.

In order to assess the pathways by which galactose is metabolized by galactose-1-phosphate uridyltransferase (GALT) deficient cells, lymphoblasts from 10 galactosemic patients with defined genotypes (six Q188R homozygotes, two S153L homozygotes, and two with homozygous deletions) were incubated with 1mM 1- or 2-13C galactose for 2.5 and 5 h. The 13C-labeled metabolites were identified and quantified using nuclear magnetic resonance and the results were compared to that obtained with cells from eight normal individuals. Cells from galactosemic patients formed two to three times the galactose-1-phosphate (Gal-1P) in normal cells, no difference being observed between the various genotypes. Galactitol formation was not significantly different from normal cells. No labeled galactonate was detected. Cells with the Q188R and S135L mutations formed both labeled uridine diphosphogalactose (UDPgal) and uridine diphosphoglucose (UDPglu), but to a lesser extent than normals, whereas cells with the GALT deletion did not. The pattern of 13C enrichment of the ribose carbons of adenosine monophosphate upon incubation of the normal cells with 1-13C galactose paralleled that found for incubations with 1-13C glucose, which is consistent with galactose disposition through the Leloir pathway to glucose and its subsequent metabolism to ribose. Cells with the GALT deletion formed no detectable labeled ribose, whereas cells from a patient homozygous for Q188R mutation formed labeled ribose in a pattern similar to normal albeit with lower enrichment. The results suggest that there is residual GALT activity and function of the Leloir pathway in the presence of the Q188R as well as S135L mutation.

We previously identified a missense mutation at amino acid 135 of human galactose 1-phosphate uridyltransferase (hGALT) in which a leucine (TTG) was substituted for a serine (TCG), S135L. This mutation was common in black patients with galactosemia and homozygotes (S135L/S135L) had no GALT activity or protein in their erythrocytes or lymphoblasts. However, there was residual GALT activity and protein in their leukocytes, and they had near normal total body [13C]galactose oxidation to 13CO2 in breath. To evaluate the biochemical mechanism(s) producing these effects, we overexpressed hGALT proteins with site-directed mutations in this nonconserved amino acid in a GALT-minus Escherichia coli. Enzyme activities detected in bacterial lysates overexpressing either S135 (wild type), A135, C135, H135, L135, S132-H135, T135, or Y135 were 100, 4.7, 3.0, 4.0, 2.7, 0.7, 35.4, and 1.4%, respectively. Only the threonine substitution (S135T) had significant enzyme activity in these lysates. There was also decreased abundance of all mutant proteins in the lysates exposed to bacterial proteolysis during preparation and analysis. This added the variable of bio-instability to analysis of enzyme activities in lysates. To further characterize the catalytic role of serine at amino acid 135 and to differentiate bio-instability from impaired catalysis by the leucine substitution, we purified wild-type and L135-hGALT proteins to homogeneity and analyzed identical amounts of enzyme protein. We found that the apparent Vmax of the purified L135-hGALT protein was significantly reduced from 80 +/- 5.9 to 5.8 +/- 1.8 micromol glucose 1-phosphate released/min/mg hGALT protein with no increase in KM for galactose 1-phosphate for the second displacement. The first displacement reaction, although three orders of magnitude slower, was similar between the wild type and L135-hGALT. We conclude that a hydroxyl group on amino acid 135 is required for the catalysis of uridyl transfer from UDP-glucose to UDP-galactose in the presence of galactose 1-phosphate, and plays a role in the bio-stability of hGALT., (Copyright 2001 Academic Press.)

The ability of mice deficient in galactose-1-phosphate uridyltransferase (GALT) to metabolize galactose was determined in animals weaned to a mouse chow diet for a 4-wk period. When given [14C]galactose intraperitoneally, these animals slowly oxidized the sugar, excreting only 5.5% of the dose as 14CO2 in 4 h, whereas normal animals excreted 39.9%. These results mimic those seen in human galactosemic patients given isotopic galactose. When given 10 micromol of [1-13C]galactose, normal animals excrete small amounts of labeled galactose and galactonate but no galactitol in urine whereas GALT-deficient mice excrete significant amounts of all of these as labeled compounds in urine. When challenged with galactose, only about 20% of the dose is excreted in urine, and even on the chow diet, significant amounts of galactose, galactonate, and galactitol are excreted in urine. These compounds are also found to be present in liver, kidney, and brain, except that galactonate is not found in brain. Galactose-1-phosphate accumulates in red blood cells to levels found in humans exposed to large amounts of galactose, and galactose-1-phosphate is found in increased amounts in liver, kidney, and brain of GALT-deficient animals. There was no difference in the hepatic concentration of uridine diphosphate galactose and uridine diphosphate glucose between normal and GALT-deficient mice. The explanation for the presence of galactose and its conversion products in tissues and urine of affected mice appears to be related to the presence of approximately 1.75% of galactose-containing carbohydrates in the chow, which becomes bioavailable to mice. Despite the presence of galactose and its metabolites in tissues and urine and impaired ability to oxidize the sugar, the GALT-deficient animals are indistinguishable from normal animals and do not exhibit the phenotype of humans with GALT-deficiency galactosemia.

Alternate pathways of galactose metabolism were explored in erythrocytes from normal subjects and patients with galactose-1-phosphate uridylyltransferase (GALT) deficiency incubated with galactose. Micromolar quantities of galactonate accumulated in both normal and mutant cells linearly with time up to 5 hours and with concentrations of galactose up to 25 mmol/L. Galactitol also was found at levels less than one third of the galactonate level, while galactose-1-phosphate concentrations comparable to those of galactonate were found in galactosemic cells. Concomitant with the formation of these galactose metabolites, the erythrocyte redox potential based on measurement of lactate and pyruvate increased fourfold in both cell types. This was due to a 60% to 72% decrease in pyruvate and a 24% to 26% increase in lactate. The oxidation of galactose to galactonate, which is known to generate NADH, is the most likely explanation for the increase in the redox state. The aldose reductase inhibitor (ARI), Tolrestat (Wyeth Ayerst Research, Princeton, NJ), at 70 micromol/L inhibited the formation of both galactonate and galactitol in both cell types without affecting galactose-1-phosphate, and eliminated the increase in the redox potential as indicated by restoration of pyruvate and lactate levels to the levels obtained before exposure of the cells to galactose. A functioning galactonate pathway is a route of galactose disposal in patients with GALT deficiency, but by altering the cellular redox potential, it may also contribute to galactose toxicity.

The glycosylation of serum transferrin from galactosemic patients with a deficiency of galactose-1-phosphate uridyl transferase (EC 2. 7.7 12) is abnormal but becomes normal after treatment with a galactose-free diet. To understand the structural and biochemical basis of the abnormal glycosylation, transferrin was purified from the serum of untreated and treated galactosemic patients and normal controls and the N-linked glycans analyzed by HPLC. The glycans from normal transferrin consisted predominantly (86%) of the disialylated biantennary complex type. The glycans from untreated galactosemic patients were more heterogeneous and contained four major truncated glycans in addition to a smaller amount (13%) of the disialylated biantennary complex type. The truncated glycans were deficient in galactose and sialic acid and their structures were consistent with a decrease in galactosyltransferase activity in hepatocytes, the probable cells of origin of the transferrin. This is postulated to be due to direct inhibition of the galactosyltransferase activity by the accumulated galactose-1-phosphate or to an effect on the formation of UDP-galactose, the donor substrate in the reaction. After treatment the proportion of the truncated glycans decreased and the proportion of the disialylated biantennary complex type increased, returning almost but never completely to normal, even after prolonged treatment in some cases. There was no clear relationship between the length of treatment and the normalization of glycosylation and the level of galactose-1-phosphate in red blood cells, the usual parameter for monitoring the treatment of galactosemics. It is suggested that the persistence of abnormally glycosylated proteins may contribute to the long-term complications in galactosemia.

Galactose-1-phosphate uridyl transferase (GALT) deficiency causes classical galactosemia in humans. Mice deficient in this enzyme were created by gene targeting. GALT-deficient mice develop biochemical features similar to those seen in humans with GALT deficiency, but fail to develop the pattern of acute toxicity seen in newborns with classical galactosemia. This study suggests that alternative routes of galactose metabolism are important in the pathogenesis of galactosemia.

Whole-blood galactose-1-phosphate uridyl transferase (Gal-PUT) (EC 2.7.7.12) activity was absent in a newborn boy with galactosaemic symptoms. The symptoms disappeared on a galactose free diet. In the next pregnancy prenatal diagnosis was performed. Gal-PUT activity was measured by isotope technique and Gal-PUT genotype was determined by gel electrophoresis. The mother was shown to be heterozygous Duarte/heterozygous Los Angeles, the father heterozygous Duarte/heterozygous galactosaemia. The fetus had the same genotype as the father. A normal girl without galactosaemic symptoms was born. Reinvestigation of the index case showed that he was also heterozygous Duarte/heterozygous galactosaemia. It is concluded that the activity of Gal-PUT should always be measured by isotope technique to prove the diagnosis of heteditary galactosaemia. Furthermore, Gal-PUT-genotyping in families with rare alleles is essential for safe prenatal diagnosis.

We correlated the clinical symptoms of transferase-deficient galactosemia with the plasma galactose and erythrocyte galactose-1-phosphate concentrations in six galactosemic patients during dietary treatment, in a child before treatment, and in 12 individuals with below-normal erythrocyte hexose-1-phosphate uridylyltransferase activity. All the treated patients were asymptomatic. Normal galactose and either normal or above-normal galactose-1-phosphate concentrations were found. Three of these patients were clinically normal as newborns while ingesting galactose-containing foods and may resemble the asymptomatic Negro galactosemic. The clinical symptoms of galactosemia were observed in the untreated patient, who showed markedly above-normal concentrations of galactose and galactose-1-phosphate, protein and reducing substances in the urine, above-normal bilirubin and alkaline phosphatase in the plasma, with normal values for glucose, aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyltransferase. Clinical improvement in this patient paralleled the decline in erythrocyte galactose-1-phosphate. The individuals with below-normal hexose-1-phosphate uridylyltransferase activity (range 7--17 U/g of hemoglobin) had normal galactose and galactose-1-phosphate concentrations and were asymptomatic.

Clinical and biochemical diagnostic studies concerned 17 cases of galactosemia coming from 15 not consauguineous families. Galactosemia was diagnosed between 1-st day and 11-th month of life. Tentative diagnosis based on clinical picture was made in 12 infants, others were detected through family history of galactosemia and/or biochemical newborn screening carried out at the National Research Institute of Mother and Child since 1969. Clinical symptoms of galactosemia occurred in most patients in the first week of life. They were the following (tab. II): hepatomegaly (in 94%), jaundice (81%), splenomegaly (79%), vomitus (62%) and diarrhoea in 56% of patients. Cataract was found in 6 infants (38%). Biochemical diagnosis was based on the results of enzymatic estimation of galactose-1-phosphate uridyl transferase activity in blood, galactose-1-phosphate in red blood cells and galactose in blood and urine. No activity of galactose-1-phosphate uridyl transferase was found in all patients, and the concentration of galactose-1-phosphate was higher than 25 mg/100 ml of red blood cells. High galactose level was observed in blood and urine in all patients with typical clinical course of galactosemia. In 2 patients however without clinical symptoms of the disease only trace amounts of galactose was detected in blood and urine. All these patients were treated with galactose free diet.

The clinical, biochemical and anatomical studies of one case of galactosemia with cow's milk intolerance in a one month old infant are reported. Diagnosis was ascertained measuring the enzyme (Gal-1-P-Uridyl-transferase) deficiency with the methods of Anderson, Kalckar and Isselbacher. Overload and enzymatic studies were also carried out in relatives. The interest of this association of galactosemia with cow's milk intolerance, and its clinical and therapeutic implications are pointed out in the discussion.

This paper is a review of inborn errors in galactose metabolism with special attention being paid to practical aspects of this problem. The authors presented the history of experimental research on galactose metabolism in human body, patomechanisms of biochemical abnormalities and clinical course of the disease as well as the review of genetic papers regarding polymarphism of galactose-1-phosphate uridyl transferase, galactosemic variants in human population and the possibilities of early diagnosis and treatment of galactosemia.

14C galactose incorporation into the TCA-precipitable material of cultures of fibroblasts deficient in galactokinase (GALK-) was nil. In cultures of fibroblasts deficient in uridyltransferase (GALT-), it was 30 to 75% of control incorporation. In cocultures of GALK and GALT-deficient fibroblasts, 14C incorporation was restored to near-normal levels. This restoration produced in the presence of close cellular contacts was not increased by polyethyleneglycol somatic hybridization. Our results indicate that metabolic cooperation occurred involving the transfer of galactose 1-phosphate from the GALT-deficient to the GALK-deficient cells via intercellular connections.

The authors define the main stages of the biochemical study of hereditary abnormalities of galactose metabolism. They review laboratory examinations for detection, enzyme examinations which provide the diagnostic proof, further examinations which permit one to follow the course and efficacy of a galactose-free diet, the demonstration of genetic variants, the technics of antenatal diagnosis and routine neonatal detection.

Five galactosemic and 5 normal children received an oral load of galactose under standardized conditions. The maximal blood galactose level after 1.5 hours was 12.6 +/- 2.0 (S.D.) mmol/l in individuals with a deficiency of uridylyl transferase (EC2.7.7.12) as compared to 5.8 +/- 1.2 (S.D.) mmol/l in the controls. The concentration of serum urate in galactosemics increased to 155% of the fasting level (P less than 0.005); no rise was detectable in the controls. The elimination of urate with the urine was augmented by the same amount in both groups. Our studies provide evidence for an increased catabolism of hepatic nucleotides. This may lead to a deficiency of nucleotides which is proposed as a cause of galactosemic liver injury.