A G-to-T splice donor site mutation was introduced in the first nucleotide of intron 2 (c.544+1G>T) to mimic the mutation found in some MODY5 (maturity-onset diabetes of the young) patients. RT-PCR experiments confirmed the skipping of exon 2 and also identified transcripts missing the last 32 bp of exon 2 owing to the use of a cryptic splice donor site.