Figure 2. Twin/Sibling Pairwise Concordance in FASD outcomes and prenatal/postnatal risks.

Monozygotic twins, dizygotic twins, full siblings and half siblings share 100%, 50%, 50% and 25% of their genome respectively as depicted by the first set of bars. If fetal genetics is modifying the teratogenic impact of PAE, the pattern of pairwise concordance reflected in the bars for each FASD outcome will more closely resemble the pattern of bars for Genome Shared than the patterns of bars reflecting pairwise concordance in Alcohol Rank, other Prenatal Risks or Postnatal Risks. The bar patterns across all FASD outcomes are far more reflective of the pattern of bars for Genome Shared than the pattern of bars for Alcohol Rank, Prenatal Risk Rank or Postnatal Risk Rank. Although the bar pattern for Postnatal Risk Rank resembles the bar pattern for Face Rank, discordance in postnatal risk factors cannot be contributing to discordance in Face Rank because only prenatal factors can impact facial morphology. Since the FAS facial phenotype, as defined by the 4-Digit Code, is so specific to (caused only by) PAE, the most compelling evidence supporting the role genetics plays in modifying the teratogenic impact of PAE is illustrated in how highly correlated the bar patterns are between Genome Shared and Face Rank and how poorly correlated the bar patterns are between Face Rank and Alcohol Rank (especially between monozygotic and dizygotic twins with virtually identical PAE).