ADAMTS13 mutation in the patient with congenital TTP. DNA sequence chromatograms corresponding to ADAMTS13 exon 15 are shown here for PCR-amplified genomic DNA from a healthy control (A), the patient (B), the patient's mother (C), and the patient's father (D). The patient DNA exhibits a homozygous 2-nucleotide (TT) deletion at the end of exon 15 (corresponding to position 1783-1784 of the ADAMTS13 cDNA), resulting in a frameshift after His594, followed by a predicted 18–amino acid extension and premature termination. The DNA chromatograms from both parents demonstrate superimposed normal and deletion allele sequences, indicating that they are heterozygous for this mutation.