Direct detection of plasminogen exon 7 mutation in family 1 by amplification mutagenesis. A part of plasminogen exon 7 containing the mutation (G → A at position 780) was amplified by PCR as described in Materials and Methods. The first primer has a single sequence mismatch that results in the introduction of an artificial BstEII restriction site into the wild-type allele only. Amplified PCR products were digested with BstEII, electrophoresed in a 2.5% agarose gel, and visualized by ethidium bromide staining. The wild-type BstEII-digested PCR fragment has a size of 119 bp, the mutant (uncut) PCR fragment has a size of 141 bp. −, No BstEII added to PCR product; +, BstEII added to PCR product. Lane M, 100-bp ladder; lane 1, patient 1; lane 2, mother of patient 1; lane 3, father of patient 1; lane 4, sister of patient 1; lane 5, healthy control. The larger (mutant) allele is found after BstEII-digestion in patient 1 (lane 1+), both parents (lanes 2+ and 3+, heterozygotes) and the sister (lane 4+, heterozygote), but not in the healthy control (lane 5+).