NKX2-1 and Intellectual disability: More recently, psychiatric symptoms, as well as cognitive deficiencies that include mental retardation (Gras et al., 2012), learning difficulties (Gras et al., 2012), and memory deficits (Sempere et al., 2013) have been identified in individuals with mutations in NKX2-1, raising the possibility that NKX2-1 may be required for development of the cognitive system.