F13B is encoded on the long arm of Chromosome 1q32–32.1 and contains 12 exons encoding for a protein of 641 amino acids reaching 79.7 kDa.6–9 Genetic defects in F13A1 and F13B genes result in congenital FXIII deficiency.10,11. The gene discussed is F13B; the disease is hyperinsulinemic hypoglycemia, familial, 4.