Schematic representation of alternative splicing of the DAF gene in H.A. An alternatively spliced mRNA results from the activation of a cryptic splice site due to a C→A mutation upstream from the normal splice site. This abnormal mRNA lacks the last 26 bp of exon 2, which causes a reading frame shift and creates a stop codon next to the end of the deletion. (▾) base substitution, (—) normal 5′-splice site, (dashed line) cryptic 5′-splice site, (=) mutated 5′-splice site, (*) the truncated exon.