IGF1 and hyperinsulinemic hypoglycemia, familial, 4: Additional conditions leading to congenital IGF1 deficiency are defects of post-GHR signaling (e.g., STAT5 defects) as well as a number of disorders associated with reduced IGF1 stability or availability, including acid-labile subunit (ALS) mutation and molecular defect of the metalloproteinase pregnancy-associated plasma protein A2 (PAPP-A2) [23,24,25,26,27,28,29,30].