MBL2 and hyperinsulinemic hypoglycemia, familial, 4: The important functions of MBL in immune defense led to the following implicit assumption: “High serum MBL (sMBL) levels provide protection and low levels risk to the diseases.” This assumption was initially documented in 1989, when the defect in opsonization because of MBL deficiency (i.e., low sMBL levels) was recognized as the reason of frequent inexplicable infections in children [42].