GH deficiency occurs rarely in IGSF1 deficiency; however, IGF‐1 is usually in the upper part of normal range in IGSF1 deficient adults and may be associated with acromegaloid features consistent with mild GH excess.7, 9 In our kindred, one individual had GH deficiency and another had insufficient GH concentrations on stimulation testing with normal IGF‐1 and growth velocity. Here, IGF1 is linked to hyperinsulinemic hypoglycemia, familial, 4.