Based on the study in 77 causative MED12 variants, Plassche and Brouwer (2021) declared that the three clinically named syndromes, FGS1, LS, and XLOS, were attributed to only eight out of 77 variants, which means a high heterogeneity of phenotype of MED12 deficiency. The gene discussed is MED12; the disease is hyperinsulinemic hypoglycemia, familial, 4.