Keck School of Medicine of USC Apr 14 2026 The USC research team that recently identified the hormone-encoding gene GDF15 as a key driver of pregnancy sickness has identified 9 additional genes linked to its most severe form, hyperemesis gravidarum (HG). Six of these genes had not been previously linked to the condition.  HG, which affects about 2% of women, causes nausea and vomiting so severe that eating can become extremely difficult. The condition was long misunderstood and often dismissed