MBL deficiency, characterized by low MBL levels and/or the low expression genotype (XA/O or O/O) [5, 19], has been associated with a decreased ability of opsonization of microorganisms and an increased susceptibility to infections, mainly in early childhood and in immunocompromised individuals [20–22]. The gene discussed is MBL2; the disease is hyperinsulinemic hypoglycemia, familial, 4.