DOCK8 deficiency is a rare autosomal recessive combined immunodeficiency caused by pathogenic variants in DOCK8 (Engelhardt et al. 2009; Zhang et al. 2009), a gene encoding a guanine nucleotide exchange factor expressed in B and T lymphocytes and hematopoietic tissues including the placenta, kidney, lung and pancreas (Ruusala and Aspenström 2004). The gene discussed is DOCK8; the disease is hyperinsulinemic hypoglycemia, familial, 4.