Von Willebrand factor deficiency was also ruled out on the basis of Von Willebrand factor antigen and Ristocetin cofactor activities which resulted within normal range (Von Willebrand factor antigen was 90%, with a normal reference range between 57 and 147%; Ristocetin cofactor was 120% with a normal reference range of 51–147% considering our patient's specific age group). This evidence concerns the gene VWF and hyperinsulinemic hypoglycemia, familial, 4.