IGSF1 and hyperinsulinemic hypoglycemia, familial, 4: 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.