IGF1 and hyperinsulinemic hypoglycemia, familial, 4: In human beings, SNHL occurs in patients with mutations in Igf1 gene (Woods et al., 1996; Bonapace et al., 2003; Walenkamp et al., 2005), primary IGF-1 deficiency (Attias et al., 2012), or low serum IGF-1 levels due to other genetic defects (Barrenas et al., 2000; Johnson et al., 2007), indicating the importance of IGF-1 in hearing.