In addition, the probands in family F and H, displayed a peculiar EEG pattern characterized by diffuse spike-and wave discharges with posterior predominance, an EEG feature previously reported in a proportion of individuals by Johannesen et al. (2018), possibly suggesting this EEG feature as a possible EEG biomarker for SLC6A1-NDD. This evidence concerns the gene SLC6A1 and Neurodevelopmental delay.