Figure 2. Parent-child segregation of 12q23.2 region in monozygotic twin sisters discordant for HELLP.

3 informative SNPs located within the HELLP region with linkage were analyzed for parent-child segregation in discordant, monozygotic twin sisters. Only 1 sister (patient 1) developed the HELLP syndrome during pregnancy. The other sister (patient 3) had 2 normal pregnancies. The minor alleles (red) were homozygous in the child born of affected patient 1 (patient A). In contrast, homozygosity for the major alleles (green) was seen in the children born of normal patient 3 (patients B and C). This pattern supports the presence of a placental susceptibility gene for the HELLP syndrome, in which the fetal genotype expressed in the placenta determines the maternal phenotype.