Molecular basis ofgalactosemia: Mutations andpolymorphisms in thegeneencoding humangalactose-1-phosphate uridylyltransfer ase

We describe themolecular characterization oftwomutations responsible forgalactosemia, aninherited disorder ofgalatose metabolism thatcauses jaundice, cata- racts, andmental retardation inhumans. Thecoding region of galactose-1-phosphate uridylyltransfer ase (GALT;UDPglu- cose:a-D-galactose-1-phosphate uridylyltransfer ase, EC 2.7.7.12) wasamplified bythepolymerase chain reaction from total cDNAofaclassic galactosemic individual andwaschar- acterized bydirect sequencing oftheproducts. Twomissense mutations wereidentified: (i)replacement ofvaline-44 by methionine and(a)replacement ofmethionine-142 bylysine. Thesemutations ledtoadrastic reduction inGALTactivity whenindividual mutant cDNAswereoverexpressed inamam- malian cell system, although full-length protein issynthesized inthis assay. Thetwogalactosemia mutations account for3of the15galactosemia alleles analyzed. These results suggest that galactosemia iscaused byavariety ofmutations, which might beresponsible fortheobserved clinical heterogeneity ofthis disorder. Wealso present themolecular characterization oftwo GALTpolymorphisms: (i)replacement ofleucine-62 byme- thionine and(ii) replacement ofasparagine-314 byaspartate. Itappears that galactosemia mutations tend tooccur inregions thatarehighly conserved throughout evolution while the polymorphisms change variable residues. Classic galactosemia (McKusick 23040), aninborn error of humangalactose metabolism, iscaused bydeficiency of galactose-1-phosphate uridylyltransfer