Analysis of amplified α-spectrin cDNA. (A) Agarose gel of PCR-amplified cDNA products from a control (C), the propositus (P), and both parents (F, M). The expected sized fragment of 429 bp was present in the control, the propositus, and both parents. An additional band, roughly 100 bp shorter, was observed in the propositus and both parents and could correspond to the skipping of exon 20, which is 93 bp long. (B) Nucleotide sequence of the two PCR-amplifed α-spectrin gene cDNA fragments from the propositus. Direct nucleotide sequencing of the upper band (A above) showed the insertion of 12 additional nucleotides (caataaatgcag) upstream of exon 20. Sequencing of the lower band showed the junction between exons 19 and 21, indicating the skipping of exon 20.