A targetting constract inseted two loxP sites flanking exons 2 and 3 of Mpz12 gene encoding for the extracellular portion of the protein. Mice are then crossed with cre deleter to remove exons 2 and 3. This allele is a null allele, however RT-PCR on liver RNA confirmed transcript splicing of exon 1 to exon 4 was detectable in the mutant mice (J:267871). The presence of the shortened protein in tisses of has not been tetermined. (J:267880)