The last three codons in exon 10 comprising the C-terminal PDZ-ligand motif were replaced with alanine codons via homologous recombination. A floxed neo cassette was also inserted and subsequently removed by Cre mediated recombination in the ES cells. Western blot analysis indicated that protein levels were reduced by about 35% and 15% in the brains of homozygous and heterozygous mice, respectively.