Glutamic acid codon 506 (487 in mature peptide) (GAA) in exon 12 was changed to lysine (AAA) (p.E506K) and a neomycin resistance gene cassette was inserted downstream of last exon 13. The mutation is the equivalent of the human p.E504K mutation, prevalent in East Asians, associated with metabolic disorders and increased sensitivity to pain. Isoelectric focusing gel electrophoresis and Western blot confirmed the expression of the mutant protein. Protein levels and enzymatic activity in heterozygous mice are reduced.