Direct detection of plasminogen exon 7 mutation in patient no. 2 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 BstE II restriction site into the wild-type allele only. Amplified PCR products were digested with BstE II, electrophoresed in a 2.5% agarose gel, and visualized by ethidium bromide staining. The wild-type BstE II-digested PCR fragment has a size of 119 bp; the mutant (uncut) PCR fragment has a size of 141 bp. −, no BstE II added to PCR product; +, BstE II added to PCR product. Lane M, 100-bp ladder; lane 1, healthy control; lane 2, homozygous Turkish girl with ligneous conjunctivitis16; lane 3, patient no. 2. The larger (mutant) allele is found after BstE II-digestion in an unrelated girl with ligneous conjunctivitis (lane 2+, homozygous)16 and in patient no. 2 (lane 3+, heterozygous), but not in the healthy control (lane 1+).