Comparison of α-dystrobrevin gene structure and isoforms in humans and mice. The central genomic DNA structure and observed transcript isoforms are shown for A) most tetrapods, including humans, and B) mice and rats. In each instance, the partial genomic DNA structure (not to scale) is shown at the top, with the coarse isoforms (numbered as in Peters et al. ) shown below. To the right are shown the fine isoforms generated by alternative splicing of the SBS-encoding region, labelled from 'a' to 'c' according to the SBS content, and '+' or '-' according to whether tiny exon 9 is included. We suggest an extension to the existing nomenclature system, such that, for example, a transcript starting with exon 7b and ending at the polyadenylation site in intron 18, containing exon 11b spliced to exon 14 and including exon 9, would be called 'α-dystrobrevin-5b+'. Red boxes - constitutive coding exons. Orange boxes - alternatively spliced coding regions. White boxes - untranslated regions. Green boxes - encoded SBSs. Black crosses - exons disrupted in murids. Exon numbering according to Ambrose et al. , apart from exons 7b and 11b, which are described first here.