This ENU-induced mutation was isolated in a screen at the University of Pittsburgh. The causitive molecular lesion for the cardiovascular phenotypes is a T to C substitution in the +2 position after coding nucleotide 1137 of the cDNA (c.1137+2T>C, NM_010060) in intron 6 of the gene. This changes the splice donor site from G-GT to G-GC (which is assumed to be less efficient).