CD40L deficiency is associated with low IgG and IgA with normal/elevated IgM and normal B cell numbers, as well as increased susceptibility to PJP and recurrent bacterial infections, among other features (França et al., 2019; Levy et al., 1997; Notarangelo et al., 2006). Here, CD40LG is linked to hyperinsulinemic hypoglycemia, familial, 4.