ENU induced a T-to-G mutation 13 bases upstream of exon 19. RT-PCR and sequencing analysis showed the inclusion of 29 bases of intronic sequence in the mutant transcript, owing to the use of an alternative the acceptor site. The inclusion of the additional bases should cause a frameshift mutation and multiple premature stop codons. Semi-quantitative RT-PCR analysis showed that the mutant mRNA was less abundant compared to wild-type mRNA. Immunoblot analysis failed to detect protein in brain lysates from homozygous mutants.