Exon 1, encoding the enzymes signal peptide, was flanked by loxP sites. An FRT-flanked neomycin selection cassette was inserted and removed via Flp-mediated recombination. Exon 1 was deleted via cre-mediated recombination in the germline. Removal of the signal peptide disrupts lysosomal targeting of the enzyme. Mice exhibit reduced ceramidase activity in liver, spleen, thymus, and bone marrow.