A 1,758 bp deletion encompasses part of intron 8 and most of exon 9. Deletion of the intron 8-exon 9 splice acceptor site leads to the transcription of the undeleted portion of intron 8. A stop codon in the undeleted portion of intron 8 results in the substitution of the last 33 amino acids of the full length allele with 13 amino acids translated from intron 8 sequence. A histidine residue is thus lost that is critical for catalytic activity.