A loxP site was inserted upstream of exon 5 and an FRT flanked neo cassette and loxP site were inserted downstream of exon 6 via homologous recombination. Recombinase mediated recombination removed exons 5-6 and the neo cassette. qPCR analysis of total RNAs isolated from brain, liver, skeletal muscle and heart tissues confirmed the absence of mRNA transcripts in homozygous mutant mice.