Exon 2 was disrupted by a neomycin selection cassette inserted by homologous recombination. While transcript was undetected by Northern blot analysis of most tissues, truncated transcript was detected in homozygous mutant testes. Hydrolysis of 4-methylumbelliferyl-Beta-D-acetylglucosamine (MUG) and 4-MUG-6-sulfate (MUGS) were both reduced to 1.5% in homozygous mutant mice. Analysis of the aberrant 1.8 kb transcript showed that it did not contain a neo sequence and indicated that it was non-functional.