SLC6A1 and Epileptic encephalopathy: Attention-deficit hyperactivity disorder (ADHD)-like clinical characteristics can exist in individuals with ASD and epileptic encephalopathy who have alterations in CHD2 [41], GRIN2A [26], PCDH19 [36, 42], SLC6A1 [29], and STXBP1 [43].