This mutation was identified in a screen of G3 progeny of ENU mutagenized male mice for altered responses to toll-like receptor (TLR) ligands. The mutation is a T to A transversion in the acceptor splice site of intron 4 (TTGCAG --> TAGCAG), at nucleotide position 13346 of the genomic sequence (Genbank accession NC_000084). Three differently spliced transcripts have been observed in the mutant mice, one of which is similar in size to the wild type mRNA. One of the aberrant splicing events skips exon 5 and causes a frame shift. The second abnormal splicing event joins exon 3 to exon 6 in-frame, skipping exons 4 and 5.