In adults, circulating IGF-1 deficiency is associated with cognitive dysfunction (Deijen et al., 1996; Lijffijt et al., 2003; van Dam, 2005; Koltowska-Haggstrom et al., 2006) that can be reversed by increasing circulating IGF-1 levels (Sartorio et al., 1995; Deijen et al., 1998; Golgeli et al., 2004; Oertel et al., 2004; Arwert et al., 2006). Here, IGF1 is linked to hyperinsulinemic hypoglycemia, familial, 4.