Figure 5 Effect of c.4217–1G→T mutation in intron 25 on the apolipoprotein (apo)B pre‐mRNA splicing. The upper panel shows the abridged APOB gene region spanning from the 3′‐end of exon 25 to the 5′‐end of exon 27 and the normal splicing. The mutation in the acceptor splice site of intron 25 (indicated by an asterisk) abolishes the function of this site. The lower panel shows the abnormal splicing due to the activation of a cryptic acceptor splice site located in exon 26 (AG dinucleotide of this site at position c.5395–5396 is boxed). In the mutant mRNA, exon 25 joins a partially deleted exon 26 (devoid of the first 1180 nucleotides; fig 4). Ex, Exon; IVS, intron.