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PubMed1993

Electron microscopic immunocytochemical evidence for the mechanism of blood-retinal barrier breakdown in galactosemic rats and its association with aldose reductase expression and inhibition.

Blood-retinal barrier (BRB) breakdown occurs in human diabetic retinopathy and can lead to significant loss of vision. The galactosemic rat serves as a model for human diabetic retinopathy and develops many of the same ocular complications, including BRB failure. Aldose reductase (AR), an enzyme in the polyol pathway, has been implicated in several of these complications. Electron microscopic immunocytochemical staining for albumin can be used to visualize extravasated albumin in control and galactosemic rats with and without AR inhibition to reveal the mechanism for galactosemia-related BRB failure without the use of tracer substances, and to determine whether AR activity influences this mechanism. Electron microscopic immunocytochemical labeling of AR can reveal the cellular distribution of AR in normal and galactosemic rat retina and determine whether a correlation exists between BRB breakdown and AR expression in cells that form or influence the BRB. Extravascular albumin is demonstrable as early as 2.5 months in galactosemic rats, which is prior to the presentation of ultrastructural changes. Albumin-positivity is visualized in retinal vascular endothelial (RVE) cell cytoplasm from galactosemic rats both diffusely and within vesicles, but it is not detected in comparably aged normal rat RVE cells or within the tight junctions of the RVE or RPE (the cells that form the BRB) in control or galactosemic rats, suggesting that BRB breakdown in galactosemic rats may be mediated through two mechanisms: a permeation of the RVE cell membrane leading to diffuse cytoplasmic positivity for albumin, and vesicular transport across the RVE. The AR inhibitor, sorbinil, prevents diffuse cytoplasmic staining of RVE cells, but not vesicular staining, implying that RVE membrane permeability may be altered by AR activity, but vesicle formation does not appear to be affected. AR was immunocytochemically demonstrated in some RVE cells from galactosemic rats, but not from controls. In perivascular astrocytes, which may influence the integrity of the inner BRB, AR labeling was augmented in galactosemic rats. Increased AR expression in RVE cells and perivascular astrocytes from galactosemic rats provides additional support for a role for AR in galactosemia-related BRB failure.

Albumins↗
PubMedDate not supplied

Molecular basis of disorders of human galactose metabolism: past, present, and future.

Molecular cloning and characterization of all three human galactose-metabolic genes have led to the identification of a number of mutations which result in three forms of galactosemia which are caused by kinase (GALK), transferase (GALT), or epimerase (GALE) deficiency. We review here recent developments in the molecular characterization of all three disorders of human galactose metabolism. Recent progress in the biochemical and/or structural analyses of the GALT and GALE proteins has complemented human mutational studies. Interestingly, genotype/phenotype correlations have been modest as in some other Mendelian disorders. We discuss possible reasons for this apparent paradox. Finally, we note the panethnic nature of galactosemia and suggest a hypothesis for it.

Galactokinase↗
PubMed1995

Characterization of two stop codon mutations in the galactose-1-phosphate uridyltransferase gene of three male galactosemic patients with severe clinical manifestation.

Classical galactosemia, which is caused by deficiency of galactose-1-phosphate uridyltransferase, is characterized by acute problems of hepatocellular dysfunction, sepsis, cataracts and failure to thrive. Galactose limitation reverses these symptoms immediately; however, the long-term complications, such as mental retardation and ovarian failures are major problems in most of these patients. In order to investigate the molecular basis for phenotype variation in galactosemia, we have screened the most common mutation in the GALT gene, Q188R. We have further examined those patients who are heterozygous for Q188R or negative for this mutation by SSCP analysis and direct sequencing. In three male patients, we have identified, for the first time, two stop-codon mutations in the GALT gene, G212X (exon 7) and E340X (exon 10). Two patients of 8 and 28 years of age, respectively, who are compound heterozygotes for Q188R and G212X, have severe mental retardation and their general clinical condition is more severe than that of patients with missense mutations. The third patient, who is 8 years of age and who is homozygous for E340X, the N314D polymorphism and a silent substitution L218L, presents with a relatively normal physical and mental condition to date.

Adult↗
PubMed1994

On the molecular nature of the Duarte variant of galactose-1-phosphate uridyl transferase (GALT).

Galactosemia is an inborn error of galactose metabolism secondary to deficiency of galactose-1-phosphate uridyl transferase (GALT). GALT is a polymorphic enzyme and Duarte (D) is the most common enzyme variant. This variant is characterized by faster electrophoretic mobility and reduced activity. Duarte/galactosemia compound heterozygotes (D/G) are commonly identified in galactosemia newborn screening programs. However, these patients do not generally require treatment. By using a "candidate mutation" approach to define the molecular basis of the Duarte variant of GALT, a close association between the previously reported N314D polymorphism and the Duarte variant of GALT was found. We suggest that N314D encodes the D variant of GALT and that molecular testing for N314D might be useful to confirm a biochemical diagnosis of Duarte variant of GALT.

Alleles↗
PubMed1977

Variants of galactose-1-phosphate uridyl transferase in the Greek populations.

The frequency of variants of galactose-1-phosphate uridyl transferase was determined among the nine Greek populations by studying a sample of 1570 unselected individuals. Average frequency of normal allele GALT=0.942, galactosemia gen GALTG=0.0021 and the Duarte variant gene GALTD=0.0548 were observed. Frequency of galactosemia heterozygotes among Greeks was similar to that in other Caucasian populations, but the frequency of the Duarte variant was considerably higher. With the exception of two populations, one with low (Epirus) and one with high (Thrace) frequencies, the polymorphism of the Duarte variant displays very similar frequencies in the various Greek population groups.

Adult↗
PubMed1995

Leguminosae in the diet: the raffinose-stachyose question.

Adhering to a galactose-free diet by strictly avoiding dairy products and known hidden sources of galac-tose does not completely normalize galactose-1-phosphate (gal-1-P) in erythrocytes from patients with galactosemia. Major neurological complications, even in the best treated patients, are threatening a good clinical outcome and dictate a continuous search for leaks in the dietary regimen. Raffinose and stachyose, present in important amounts in various vegetables, contain alpha-1,4 linked galactose which is cleaved only by bacterial alpha-galactosidases, presumably in the lower part of the gut. In order to test the hypothesis whether galactose released from raffinose and stachyose could be a source of absorbed galactose and a cause of elevated gal-1-P six patients with galactosemia (aged 6-24 years), underwent a raffinose- and stachyose-poor dietary regimen for 2 weeks. Before, after, and during the test period, the daily intake of stachyose and raffinose as well of protein, carbohydrate, fat and minerals was calculated from food protocols obtained from the patients. Plasma galactose and erythrocyte gal-1-P were measured at the end of the three test phases. Stachyose and raffinose intake was reduced to 5%-10% during the experimental diet, which was well tolerated, except for constipation in some patients. In five of the six patients gal-1-P in erythrocytes was somewhat lower (statistically not significant) during the test phase than during regular diet while plasma galactose remained unchanged. Galactose released from raffinose and stachyose may be absorbed and contribute to elevated gal-1-P values in erythrocytes of galactosemic patients.

Adult↗
PubMed1977

Starch gel electrophoresis for galactose-1-phosphate uridylyl-transferase applied to dried filter paper blood specimens.

Starch gel electrophoresis of galactose-1-phosphate uridylyl transferase has been adapted for use on dried filter paper blood specimens submitted for the purposes of routine newborn screening for galactosemia and other inborn errors of metabolism. Selected for study were those specimens with reduced transferase activity, as determined by the Beutler enzyme spot screening test. Clinically benign low activity enzyme variants were readily identified, thus reducing significantly the number of requested additional blood specimens. Transferase-deficient specimens with potential clinical significance had too little activity for transferase visualization and thus could be separated from the benign variants. This technique would facilitate routine newborn screening for galactosemia.

Carrier State↗
PubMed1987

Agarose gel isoelectrofocusing of UDP-galactose pyrophosphorylase and galactose-1-phosphate uridyltransferase. Developmental aspect of UDP-galactose pyrophosphorylase.

The uridine diphosphogalactose pyrophosphorylase activity has been determined in human adult and fetal tissues as well as blood of various ages by measurement of UDP-galactose production from gal-1-p and UTP. The highest activity was found from adult liver in which the specific activity was about 5% of the gal-1-p uridyltransferase activity. In general adult tissues had a somewhat higher activity than the corresponding fetal tissues except erythrocytes in which fetuses had a 5-10 times higher activity than adults. From normal blood the pyrophosphorylase activity in erythrocytes decreased with age, but in the case of galactosemia the decrease with age was not distinct. According to agarose gel isoelectrofocusing studies, at least two isozyme forms for UDP-galactose pyrophosphorylase exist with the activity bands between pH 6.0-6.15. The patterns of AGIF bands of pyrophosphorylase varied according to the age of the samples, suggesting the development of the isozyme forms of pyrophosphorylase to be age-dependent. Uridyltransferase, on the other hand, resolved into multiple bands between pH 5.1-5.6 on agarose gels and the patterns varied according to the variants but not to the age. Significance of the decrease in the pyrophosphorylase activity in erythrocytes with age as well as of the difference in AGIF bands between normal and the galactosemic were discussed with regard to the pathology of classical galactosemia.

Adolescent↗
PubMed1977

Biochemical expression of the galactosemic defect in lymphocytes and the effects on glycoprotein synthesis.

Incorporation of radioactive galactose, fucose, mannose, glucosamine, and N-acetylmannosamine into acid-precipitable glycoproteins of purified peripheral blood lymphocytes froom three patients with congenital galactosemia, their healthy parents, and control subjects have been measured. In the galactosemic lymphocytes, the incorporation of galactose into acid-precipitable glycoproteins was less than 7% of values obtained with controls and the presumed heterozygotes. The incorporation of other sugars into the glycoprotein fraction did not differ significantly from normal. Attempts to demonstrate a deficiency in cell-surface galactose groups proved negative. Galactosemic lymphocytes responded well to galactose-binding mitogens and were fully sensitive to a galactose-binding toxic lectin. We conclude that a defect in the galactose-1-phosphate uridyl transferase pathway to uridine diphosphate-galactose does not affect appreciably normal carbohydrate chain assembly in galactosemic lymphocytes. However, we cannot rule out minor changes which might account for the decreased responsiveness to serotonin in an experimental animal model of galactosemia. The approaches used in this paper may be useful in detecting other inborn errors of carbohydrate metabolism.

Adolescent↗
PubMedDate not supplied

Galactose and cataract.

Galactosemia is a disorder caused by a deficiency of any one of three possible enzymes involved in the metabolism of galactose: galactokinase, transferase or epimerase. Any single deficient enzyme can result in cataract through the accumulation of galactitol in the lens. The ophthalmologist may play an important role in this disease, since early recognition of cataract development followed by the initiation of a galactose-free diet may lead to clearing of lenticular opacities. The clinical and laboratory findings that distinguish the three enzyme deficiency disorders of galactosemia are discussed. The biochemical genetics of each enzyme also are reviewed, along with the recent evidence linking heterozygous galactokinase deficiency and presenile cataract.

Animals↗
PubMed2005

Urinary galactitol and galactonate quantified by isotope-dilution gas chromatography-mass spectrometry.

BACKGROUND: Measurements of urine galactitol have been used to monitor the adequacy of diet therapy in the treatment of galactosemia. We have devised a gas chromatographic mass spectrometry (GC/MS) isotope-dilution method for the simultaneous quantification of urine galactitol and another alternate pathway product, galactonate. METHODS: We prepared trimethylsilyl (TMS) derivatives and used D-[UL-13C]galactitol and D-[UL-13C]galactonate as the internal standard for GC/MS. Results obtained with this method were compared with those determined by the established GC method for galactitol and the NMR method for galactonate. Thirty-three normal urine specimens were analyzed by the isotope dilution technique for galactitol and galactonate. Results of galactitol in 6 of these urine specimens along with 18 from classic galactosemics and 19 variant galactosemics were compared with the established GC method. Results for galactonate in 15 urine specimens from galactosemics were compared to the established NMR technique. RESULTS: The method was linear up to 200 nmol with lower limits of detection of 1.1 nmol (1.75 mmol/mol creatinine) (Cr) and 0.8 nmol (1.28 mmol/mol Cr) for galactitol and galactonate, respectively. Intra- and Interassay imprecision ranged from 2.1-6.7% for galactitol and 3.5-8.0% for galactonate. The excretion of both metabolites was age dependent in both normal and galactosemics. In 12 normal urines from subjects under 1 year, values for galactitol ranged from 8-107 mmol/mol Cr, and in 7 over age 6, ranged from 2-5 mmol/mol Cr. Under 1 year, the range for galactonate was non-detectable to 231 and in the over 6 years group non-detectable to 25 mmol/mol Cr. In galactosemics under 1 year, the value for galactitol ranged from 397-743 and for galactonate 92-132 mmol/mol Cr while in nine patients over age 6 the range was 125-274 mmol/mol Cr for galactitol and 17-46 mmol/mol Cr for galactonate. CONCLUSIONS: The GC/MS method enables the simultaneous determination of urine galactitol and galactonate and is precise and useful over the wide range of concentrations needed to assess the galactose burden in patients with galactosemia.

Adolescent↗
PubMed1989

Galactose-1-phosphate uridyl transferase activity associated with age at menopause and reproductive history.

Reproductive history was obtained and the activity and electrophoretic pattern of the blood enzyme galactose-1-phosphate uridyl transferase (transferase) was measured in 104 adult Caucasian women, less than 70 years of age, sampled from the general population. Fifteen women were identified as carriers for the Duarte (GtD) or galactosemia (gt) variants of transferase--genes associated with reduced transferase activity compared with normal (Gt+). The mean age at menopause for 8 women with a natural menopause who were GtD/Gt+ or gt/Gt+ was 44.8, significantly younger (P = 0.007) than the mean age of 49.2 reported by 31 naturally postmenopausal subjects with Gt+/Gt+ genotypes and normal transferase activity. Compared with the latter group, women who were Duarte or galactosemia carriers were 13.7 times more likely to have a menopause before age 48 (with 95% confidence limits of 2.0 to 95.5). Six of 13 (46%) married women who were GtD/Gt+ or gt/Gt+ reported more than 2 years' trying to achieve a pregnancy, compared with 11 of 74 (15%) with normal genotypes and activity (P = 0.02). The authors conclude that genetic deficiency of transferase may be associated with infertility and early menopause.

Adult↗
PubMed1994

Correlation of cognitive, neurologic, and ovarian outcome with the Q188R mutation of the galactose-1-phosphate uridyltransferase gene.

This study was conducted to determine whether there is a genotype/phenotype correlation between aspects of cognitive, neurologic, and ovarian outcome in patients with galactosemia and the Q188R mutation of the galactose-1-phosphate uridyltransferase gene. The results showed that the Q188R mutation was found in 72% of alleles: 38 patients were homozygous and 21 were heterozygous for Q188R; eight patients did not have the mutation. The mean Broad Cognitive score for the group homozygous for Q188R was 75 (SD = 16), which was not statistically different from the outcome for the heterozygous group (mean score, 67; SD = 25) or the negative group (mean score, 88; SD = 21). Tremor, ataxia, and dysmetria were found in 12 subjects, and there was no association with Q188R status. Similarly, there was no association of this mutation with the development of primary amenorrhea (8 subjects) versus secondary amenorrhea (found in 14 women). Our findings suggests that the variability of outcome for patients with classic galactosemia cannot be explained by Q188R status alone, at least with regard to cognitive functioning, presence of neurologic symptoms, and timing of the onset of ovarian failure.

Adolescent↗
PubMed1999

Urine screening of five-day-old newborns: metabolic profiling of neonatal galactosuria.

We determined urinary galactose and 4-hydroxyphenyllactic acid (4HPLA) in 4338 of 5-day-old newborns using a newly developed GC-MS screening method. Fifty-two infants were chemically diagnosed as having transient galactosuria based upon elevated urinary galactose levels (4.78-30.53 mg/mg creatinine, control 1.10 +/- 0.89 mg/mg creatinine). These infants did not excrete galactitol or galactonic acid into the urine, which is typical of hereditary galactosemia. Nearly 40% of the transient galactosuria was associated with immature infants (low birth weight or borne before 37 gestational weeks). Immature hepatic function is one explanation for neonatal transient galactosuria, but heterozygotes or the carriers of galactose degradation enzyme deficiencies were also suspected in some of the newborns, judging from the comparisons of urinary galactose and 4HPLA excretion between neonates and patients with galactosemia.

Galactose↗
PubMed1992

The human galactose-1-phosphate uridyltransferase gene.

Classical galactosemia is an inborn error of metabolism caused by a deficiency of galactose-1-phosphate uridyltransferase (GALT). Standard treatment with dietary galactose restriction will reverse the potentially lethal symptoms of the disease that are manifest in the newborn period. However, the long-term prognosis for these patients is variable. As a first step toward investigating the molecular basis for phenotypic variation in galactosemia, we have cloned and sequenced the entire gene for human galactose-1-phosphate uridyltransferase. This gene is organized into 11 exons spanning 4 kb. In exons 6, 9, and a portion of 10, there is a high degree of amino acid sequence conservation among Escherichia coli, yeast, mouse, and human. We have identified a number of nucleotide changes in the GALT genes of galactosemic patients that alter conserved amino acids. The most common of these is an A to G transition at nucleotide position 1470, converting a glutamine to an arginine at amino acid codon position 188 (Q188R).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed2004

Pregnancy and delivery after stimulation with rFSH of a galatosemia patient suffering hypergonadotropic hypogonadism: case report.

PURPOSE: To determine if hypergonadotropic hypogonadism related to galactosemia could be linked to anomaly of the circulating FSH. A 26-year-old woman, suffering GALT (Galactoso-1-phosphate uridyltransferase) had a premature ovarian failure with amenorrhea since the age of 19. The circulating level for FSH was 83 and 34 mU/mL for LH. METHODS: After treatment with a hormonal substitution cycle including estradiol and progesterone, the patient underwent stimulations with recombinant FSH. The first cycle, one 16-mm diameter follicle and the second cycle one follicle of 17.5 mm of diameter were obtained at the time of ovulation induction. RESULTS: The patient conceived and delivered a female baby weighting 3.38 kg after the second stimulation protocol. CONCLUSIONS: The impact of galactosemia on the ovary seems rather related to the absence of recognition of circulating FSH by its receptor and not to a toxic alteration of the ovary by itself as it is currently reported. The rFSH treatment following hormonal substitution cycles allows to overcome infertility problems.

Adult↗
PubMed2001

Relationship between genotype, activity, and galactose sensitivity in yeast expressing patient alleles of human galactose-1-phosphate uridylyltransferase.

Impairment of the human enzyme galactose-1-phosphate uridylyltransferase (GALT) results in the potentially lethal disorder galactosemia; the biochemical basis of pathophysiology in galactosemia remains unknown. We have applied a yeast expression system for human GALT to test the hypothesis that genotype will correlate with GALT activity measured in vitro and with metabolite levels and galactose sensitivity measured in vivo. In particular, we have determined the relative degree of functional impairment associated with each of 16 patient-derived hGALT alleles; activities ranged from null to essentially normal. Next, we utilized strains expressing these alleles to demonstrate a clear inverse relationship between GALT activity and galactose sensitivity. Finally, we monitored accumulation of galactose-1-P, UDP-gal, and UDP-glc in yeast expressing a subset of these alleles. As reported for humans, yeast deficient in GALT, but not their wild type counterparts, demonstrated elevated levels of galactose 1-phosphate and diminished UDP-gal upon exposure to galactose. These results present the first clear evidence in a genetically and biochemically amenable model system of a relationship between GALT genotype, enzyme activity, sensitivity to galactose, and aberrant metabolite accumulation. As such, these data lay a foundation for future studies into the underlying mechanism(s) of galactose sensitivity in yeast and perhaps other eukaryotes, including humans.

Alleles↗