SLC6A1 and Global developmental delay: Numerous genetics studies have identified pathogenic variants of CACNA1A (Epi, 2016; Luo et al., 2017), CSNK2A1 (Trinh et al., 2017), PPP1CB (Gripp et al., 2016; Ma et al., 2016), PPP2CA (Reijnders et al., 2017), SLC6A1 (Carvill et al., 2015; Halvorsen et al., 2016; Palmer et al., 2016; Yuan et al., 2017), and USP7 (Zarrei et al., 2017) from large cohorts of unrelated patients who presented a wide spectrum of neurological and behavioral phenotypes of global developmental delay, attention deficit disorder, epileptic encephalopathy, macrocephaly, ID or sensory processing disorder.