Identification of the Tyr16Cys mutation in the twins.

The family pedigree is presented on the left side with the corresponding plasma FVIII activity for each member. Sequence chromatogram from twin II.1 is shown on the right side with the relevant wild-type and mutant partial sequences of the F8gene noted under the chromatogram. The arrow points to the double peaks of A and G at the second nucleotide position of codon 16, demonstrating a nucleotide transition in the heterozygous state.