CD40LG and hyperinsulinemic hypoglycemia, familial, 4: Immunoglobulin-(Ig)A deficiency is the most common PHI, affecting 1 in 200–500 individuals [6], followed by common variable immunodeficiency (CVID) (1 in 25,000–50,000) [7], IgG subclasses deficiency (1 in 500–2000) [8], and IgM deficiency (1 in 100,000–200,000) [9].