title: Molecular basis of galactosemia: mutations and polymorphisms in the gene encoding human galactose-1-phosphate uridylyltransferase.
abstract: We describe the molecular characterization of two mutations responsible for galactosemia, an inherited disorder of galatose metabolism that causes jaundice, cataracts, and mental retardation in humans. The coding region of galactose-1-phosphate uridylyltransferase (GALT; UDPglucose:alpha-D-galactose-1-phosphate uridylyltransferase, EC 2.7.7.12) was amplified by the polymerase chain reaction from total cDNA of a classic galactosemic individual and was characterized by direct sequencing of the products. Two missense mutations were identified: (i) replacement of valine-44 by methionine and (ii) replacement of methionine-142 by lysine. These mutations led to a drastic reduction in GALT activity when individual mutant cDNAs were overexpressed in a mammalian cell system, although full-length protein is synthesized in this assay. The two galactosemia mutations account for 3 of the 15 galactosemia alleles analyzed. These results suggest that galactosemia is caused by a variety of mutations, which might be responsible for the observed clinical heterogeneity of this disorder. We also present the molecular characterization of two GALT polymorphisms: (i) replacement of leucine-62 by methionine and (ii) replacement of asparagine-314 by aspartate. It appears that galactosemia mutations tend to occur in regions that are highly conserved throughout evolution while the polymorphisms change variable residues.
authors.affiliation: Howard Hughes Medical Institute, Department of Cell Biology, Houston, TX.
authors.forename: J K
authors.initials: JK
authors.lastname: Reichardt
authors.forename: S L
authors.initials: SL
authors.lastname: Woo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D005693:Galactosemias / Q000201:enzymology / Q000235:genetics*; D005796:Genes; D014644:Genetic Variation; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D015345:Oligonucleotide Probes; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D014162:Transfection; D005694:UTP-Hexose-1-Phosphate Uridylyltransferase / Q000235:genetics* / Q000378:metabolism
chemical_list: D015345:Oligonucleotide Probes; D004247:DNA; D005694:UTP-Hexose-1-Phosphate Uridylyltransferase