Patient fibroblasts displayed severely impaired processing of p100 into p52 (p.H142R/p.P190L, p.G167R, and p.Y580C) and defective RelB translocation to the nucleus and DNA binding (p.H142R/p.P190L and p.G167R), together with low levels of VCAM1 upregulation upon Lt stimulation (p.Y580C), as observed in fibroblasts from patients with AR NIK deficiency (32). The gene discussed is RELB; the disease is hyperinsulinemic hypoglycemia, familial, 4.