Regulation of galactose metabolism: implications for therapy

Positive correlation between galactose-1-phosphate uridyltransferase (GALT) and UDP-galactose-4'-epimerase (GALE) activities

OBJECTIVES

The aim of our study was to determine whether the activities of galactose-1-phosphate uridyltransferase and UDP-galactose-4'-epimerase are correlated, and in what way they may influence one another.

DESIGN AND METHODS

Enzyme activities were measured in red blood cells from 214 individuals.

RESULTS

A statistically significant (p<0.001) positive correlation was observed between GALT and GALE activities.

CONCLUSIONS

Our results suggest that GALT and GALE activities are correlated and that GALE activity has a greater impact on GALT activity than vice versa.

The call from the newborn screening laboratory: frustration in the afternoon

Newborn screening programs in the United States are evolving in concert with technologic advances in analytic chemistry and medicine. Many more disorders are being identified on dried filter paper blood spots without fundamentally altering the basic principles first put forward in the 1960s. Some disorders have been added without researchers knowing if there is a true benefit to early diagnosis and treatment; some disorders currently being detected will merit little or no follow-up in the future. The general principles underlying newborn screening are discussed, as are the individual disorders screened in most programs. The expanding and evolving impact of tandem mass spectrometry on newborn screening is also explored.

Insights into the pathogenesis of galactosemia

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.

Functional analysis of the mouse galactose-1-phosphate uridyl transferase (GALT)promoter

Galactose-1-phosphate uridyltransferase (GALT) is expressed in most tissues, but the near total absence of catalytic activity in humans with the disease galactosemia leads to specific organ dysfunction, the pathophysiology of which remains an enigma. To characterize the transcriptional regulation of the mouse GALT gene, we isolated and sequenced over 3 kb of a 5'-flanking sequence and functionally characterized the region using in vitro transient transfection and in transgenic mice. A minimal promoter of 145 bp was found to function in both HepG2 cells and NS20Y mouse neuroblastoma cells. The minimal promoter contains regions of homology to the corresponding rat and human GALT genes. In transgenic mice expressing a luciferase transgene under control of a 1.9-kb fragment of the mGALT promoter region, reporter activity was found in most tissues, with higher than expected reporter levels in neonatal brain. To determine if high galactose levels in tissues could induce promoter activity, we bred the mGALT:luciferase transgene into a line of mice in which the GALT gene function has been eliminated by homologous recombination. High tissue levels of galactose and metabolites did not induce reporter activity above background. The studies show that GALT transcriptional regulation is complex and not directly induced by substrate levels.

Dietary lactose intake, lactose intolerance, and the risk of epithelial ovarian cancer in southern Ontario (Canada)

A case-control study of dietary factors and cancer of the ovary was conducted during 1989-92 in metropolitan Toronto and surrounding areas of southern Ontario, Canada. Four hundred and fifty women aged 35-79 years, with newly diagnosed, histologically verified, primary epithelial ovarian-cancer were interviewed concerning reproduction and diet. Over the same period, 564 randomly-selected population controls, frequency-matched to the cases within three 15-year age groups, also were interviewed. From information obtained by quantitative diet history, average daily macro- and micronutrient intake values were calculated through use of the United States Department of Agriculture Food Composition Databank, which was extended and modified for Canadian items and recipes. Analysis was performed with continuous, unconditional logistic-regression methods, adjusting for age at interview, number of full-term pregnancies, total duration of oral contraceptive use, and total daily caloric intake. Neither reported history of lactose intolerance, nor average daily consumption of lactose or free galactose, were found to be associated with risk of ovarian cancer. Lactose intake or intolerance did not appear to modify the protective effects of parity and oral contraceptive use. Nevertheless, other studies suggest that ovarian galactose metabolism still may have a relationship with risk of ovarian cancer, though more evidence is needed.

Screening for metabolic disorders. How are we doing?

Routine screening for phenylketonuria and congenital hypothyroidism has become an integral part of pediatric practice in the United States. Screening for several other metabolic disorders is now entering the second or third decade of use. New information is available for the pediatrician for both groups of disorders that will be of help in caring for children in the years to come.

Galactose disorders: an overview

There are three separate disorders of galactose metabolism of clinical importance. Galactokinase deficiency mainly causes cataracts which regress without complications providing a galactose-free diet is started early enough. UDPgalactose-4-epimerase deficiency seems extremely rare. A common feature of the two reported cases is nerve deafness. Galactose-1-phosphate uridyl transferase deficiency poses the greatest problems because of the poor long-term outcome in spite of a galactose-restricted diet, and with no clear indications of how and when the underlying damage occurs. Recent evidence of low erythrocyte and tissue UDPgal levels, associated with ovarian dysfunction, may indicate impaired galactoside synthesis. Administration of uridine corrects the UDPgal depletion and trials in which it is added to the galactose-restricted diet have begun.