NALCN and X-linked intellectual disability: We detected de novo variants in five recently published genes (Table 1, Additional file 3: Table S2): ZBTB20 associated with Primrose syndrome [39] (MIM 259050); NR2F1 causing the Bosch-Boonstra-Schaaf optic atrophy syndrome [40] (MIM 615722); DDX3X associated with X-linked intellectual disability [41] (MIM 300958); CACNA1A implicated in non-fluctuating ataxia [42]; and NALCN associated with congenital contractures of the limbs and face, hypotonia, and developmental delay [43] (MIM 616266).