Isolation and characterization of the normal canine beta-galactosidase gene and its mutation in a dog model of GM1-gangliosidosis

The acid beta-galactosidase cDNA of Portuguese Water dogs was isolated and sequenced. The entire coding region of the gene consists of 2004 nucleotide s encoding a protein of 668 amino acids. Its encoding sequence indicates ap proximately 86.5% identity at the nucleotide level and about 81% identity a t the amino acid level with the encoding region of the human acid beta-gala ctosidase gene. The deduced amino acid sequence contains a 24-amino-acid pu tative signal sequence, six possible glycosylation sites, and seven cystein e residues. A homozygous recessive mutation, causing canine GM1-gangliosido sis, was identified at nucleotide G(200)--> A in exon 2 resulting in an Arg (60)--> His (mutation R60H) amino acid substitution. The mutation creates a new restriction enzyme site for Pml1. Genotyping 115 dog samples for this acid beta-galactosidase gene alteration readily distinguished affected homo zygous recessives (n=5), heterozygous carriers (n=50) and normal homozygote s (n=60). DNA mutation analysis provided a method more specific than enzyme assay of beta-galactosidase for determination of carriers.