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. Here, INS is linked to Dravet syndrome.