The first patient with a deficiency in factor V was identified in 1943, while the initial mutation responsible for factor V deficiency was discovered over 50 years later.[7] Mutations in the F5 gene encompass missense mutations, premature termination mutations (including small deletions, small insertions, and nonsense mutations), as well as splicing and frameshift mutations.[8] Most nonsense mutations in the F5 gene are predominantly located within the factor V B domain, whereas missense mutations primarily occur in the A and C domains. The gene discussed is F5; the disease is hyperinsulinemic hypoglycemia, familial, 4.