SfaNI restriction of the normal wild-type 854-bp fragment (WT) and the 2 patient fragments of 724 bp (A2) and 852 bp (A1). The cDNAs were amplified by PCR with the primers TRN-2s and NTR-4as (Table 1). The SfaNI digestion of the wild type gives 3 fragments of 228, 114, and 512 bp in the wild type; 3 fragments of 228, 114, and 382 bp in the patient's A2 allele; and 5 fragments of 151, 77, 55, 57, and 512 bp in the patient's A1 allele. The size reduction from 512 to 382 of the third A2 digestion fragment is due to the lack of the 130 bp corresponding to the partial skipping of exon 6. The 5 digestion fragments of the A1 allele are due to the creation of 2 new SfaNI restriction sites, one in the 228 fragment that is split in 2 fragments of 151 and 77 bp and one in the 112 fragment that is split into 2 fragments of 55 and 57 bp.