MBL deficiency is the prime example of a related controversial condition, originally described as an immunodeficiency with susceptibility to pyogenic infections, albeit with low clinical penetrance [100], only to later have this status revoked due to the high frequency of asymptomatic MBL-deficient individuals [101,102,103]. The gene discussed is MBL2; the disease is hyperinsulinemic hypoglycemia, familial, 4.