Sequencing studies reveal that this allele comprises the insertion of an extra cytosine residue into splicer acceptor 2, an 18 bp alternatively spliced exon. This exon is missing in transcripts encoded by this allele. The extra C residue is thought to either reduce use of the associated splice acceptor site or result in a frameshift mutation that creates a 19 bp rather than the expected 18 bp exon. (J:21366)