This mutation was identified in an ENU mutagenesis screen. It constitutes a T-to-G transversion in intron 12 that results in altered mRNA splicing. Homozygous mutant mice express two processed transcripts, the normal, wild-type mRNA and a second lacking exon 12 and having a premature stop codon in exon 13. T cells of mutant mice express reduced levels of SLP76/LCP2.