Exons 7 and 8 were replaced with a neomycin selection cassette. The absence of protein expression was confirmed by western blot analysis on liver extracts using antibody to the C-terminal part of the protein. Subsequent studies showed that an N-terminal portion of the protein containing the UBL domain was still present, possibly the product of a splice variant of the gene not affected by the mutation, or because of incomplete nonsense-mediated mRNA decay (NMD).