A de novo heterozygous mutation (c.811C > T, p.R271W) was subsequently detected in the gene encoding POU1FI (PIT1) (11), accounting for his severe GH, TSH, and prolactin deficiencies; however, this could not explain the putative ACTH and gonadotropin deficiencies (8). The gene discussed is PRL; the disease is hyperinsulinemic hypoglycemia, familial, 4.