INSR and Rabson-Mendenhall syndrome: 2009), phenotypic variability has been shown to occur. Both novel mutations described here lie in the extracellular region and contain the insulin-binding region and a cysteine-rich domain, presenting severe type of DS. In contrast, Ahmad et al. (2013) reported a c.659C>T substitution in exon 3, which is in the same domain of the INSR, presenting a mild phenotype of AN with normal fasting and postprandial blood glucose levels. The same mutation was reported by Carrera et al. (1993) to cause Rabson–Mendenhall syndrome.