It is classified into two types: quantitative deficiency (CRM-), with concordant reductions in FXI:Ag and FXI:C, and qualitative deficiency (CRM+), with normal or slightly reduced FXI:Ag but significantly decreased FXI:C due to dysfunctional circulating FXI. This evidence concerns the gene F11 and hyperinsulinemic hypoglycemia, familial, 4.