PGK1 and Mungan syndrome: Since human mutations in RAD21 and PGK1 are characterized by significant disorders affecting numerous organ systems—Cornelia de Lange syndrome 4 (Deardorff et al., 2012), Mungan syndrome (Bonora et al., 2015), and phosphoglycerate kinase 1 deficiency (Fermo et al., 2012)—extraordinary effort would need to be made to generate specific drug molecules against RAD21L1 and PGK2.