Forty-six reported total IgG below normal limits (BLN); 23 reported one or more IgG subclass deficiencies (IgG1: 9; IgG2: 13; IgG3: 7; IgG4: 14); 5 reported an inadequate response to pneumococcal vaccine with total IgG and IgG subclasses within normal limits (indicating Specific Antibody Deficiency); and 27 reported IgA BLN, although only 9 reported Selective IgA deficiency without concurrent deficiencies of IgG. Here, IGHG3 is linked to hyperinsulinemic hypoglycemia, familial, 4.