The low gene frequency of FCN3 + 1637delC and the small sample size of the blood donor cohort preclude significant conclusions regarding the FCN3 + 1637delC gene frequency in MBL deficiency or low producers of ficolin-2 (FCN2 + 6424 homozygotes). The gene discussed is FCN3; the disease is hyperinsulinemic hypoglycemia, familial, 4.