Pedigrees of 4 families of patients with pregnancy-onset hereditary TTP (USS). The siblings of patients 21 and 32 (sisters), who share the same ADAMTS13 genotype, including 2 heterozygous mutations (p.Glu812X and p.Arg1060Trp) and 3 SNPs (p.Arg7Trp, p.Gln448Glu, and p.Ala1033Thr), included 1 miscarriage at 6 months of gestation and 1 unaffected sister. Both parents have a partial ADAMTS13 functional deficiency (ADAMTS13 activity: 25%) and each of them transmitted 1 mutation. Patient 5 has a twin sister who also has a severe ADAMTS13 functional deficiency related to the same ADAMTS13 genotype, including 3 heterozygous mutations (p.Ala95Pro, p.Ala631Val, and p.Arg1060Trp) and 2 polymorphisms (p.Arg7Trp and p.Ala1033Thr). Until now, the twin sister experienced neither pregnancy nor TTP boot. The father has a partial ADAMTS13 functional deficiency (45%) and he transmitted 2 mutations (p.Ala95Pro and p.Ala631Val, likely located on the same allele). The mother also has a partial ADAMTS13 functional deficiency (30%) and she transmitted the third mutation (p.Arg1060Trp). In family of patient 22, both siblings share the same ADAMTS13 phenotype and genotype (2 heterozygous mutations, c.825-10_843del29 and p.Cys758Arg, and 1 homozygous polymorphism, p.Gln448Glu) despite variable clinical expression (childhood-onset TTP in the brother). Both parents exhibit a normal ADAMTS13 activity and each of them transmitted 1 mutation (c.825-10_843del29 for the father and p.Cys758Arg for the mother) and the p.Gln448Glu polymorphism. The brother of patient 8 exhibits an ADAMTS13 activity lower than 10% and a clinical history of recurrent adulthood-onset TTP. His DNA was not available (NA) for genotypic analysis. Neither parent was available for familial inquiry.