“…Following our report in 2012 of RTTN mutations in individuals with intellectual disability and cerebral polymicrogyria, additional subjects have been described with a different clinical presentation, including other brain malformations (primary microcephaly), growth defects and congenital anomalies (Kheradmand Kia et al , 2012; Shamseldin et al , 2015; Grandone et al , 2016; Rump et al , 2016; Vora et al , 2017; Cavallin et al , 2018; Chartier et al , 2018; Stouffs et al , 2018; Wambach et al , 2018). The phenotypic spectrum that emerges after reviewing all clinical reports with bi-allelic RTTN variants has been summarized in Table 1 and shows that the most common, although not obligate, features are severe intellectual disability, lack of speech and primary microcephaly.…”