A novel c.-22T>C mutation in GALK1 promoter is associated with elevated galactokinase phenotype

Mutations in the promoter region of the aldolase B gene that cause hereditary fructose intolerance

Hereditary fructose intolerance (HFI) is a potentially fatal inherited metabolic disease caused by a deficiency of aldolase B activity in the liver and kidney. Over 40 disease-causing mutations are known in the protein-coding region of ALDOB. Mutations upstream of the protein-coding portion of ALDOB are reported here for the first time. DNA sequence analysis of 61 HFI patients revealed single base mutations in the promoter, intronic enhancer, and the first exon, which is entirely untranslated. One mutation, g.-132G>A, is located within the promoter at an evolutionarily conserved nucleotide within a transcription factor-binding site. A second mutation, IVS1+1G>C, is at the donor splice site of the first exon. In vitro electrophoretic mobility shift assays show a decrease in nuclear extract-protein binding at the g.-132G>A mutant site. The promoter mutation results in decreased transcription using luciferase reporter plasmids. Analysis of cDNA from cells transfected with plasmids harboring the IVS1+1G>C mutation results in aberrant splicing leading to complete retention of the first intron (~5 kb). The IVS1+1G>C splicing mutation results in loss of luciferase activity from a reporter plasmid. These novel mutations in ALDOB represent 2% of alleles in American HFI patients, with IVS1+1G>C representing a significantly higher allele frequency (6%) among HFI patients of Hispanic and African-American ethnicity.

Galactose toxicity in animals

In most organisms, productive utilization of galactose requires the highly conserved Leloir pathway of galactose metabolism. Yet, if this metabolic pathway is perturbed due to congenital deficiencies of the three associated enzymes, or an overwhelming presence of galactose, this monosaccharide which is abundantly present in milk and many non-dairy foodstuffs, will become highly toxic to humans and animals. Despite more than four decades of intense research, little is known about the molecular mechanisms of galactose toxicity in human patients and animal models. In this contemporary review, we take a unique approach to present an overview of galactose toxicity resulting from the three known congenital disorders of galactose metabolism and from experimental hypergalactosemia. Additionally, we update the reader about research progress on animal models, as well as advances in clinical management and therapies of these disorders.