SLC6A1 and Epileptic encephalopathy: In contrast to GRIN2A-related disorders, epileptic encephalopathies associated with mutations in CDKL5 (encoding cyclin-dependent kinase-like 5), SCN1A (encoding sodium voltage-gated channel alpha subunit 1), and SLC6A1 (encoding GABA transporter 1, which enables GABA re-uptake from the synaptic cleft) have a high co-occurrence of ASD features.