SLC6A1 encodes GAT-1, a gamma-aminobutyric acid (GABA) transporter in the brain. We describe 28 individuals recruited through Simons Searchlight with heterozygous pathogenic or likely pathogenic SLC6A1 variants to better understand the associated neurobehavioral phenotype. Individuals all have some combination of developmental delay, intellectual disability, speech delay, language disorder, seizures, autism, hypotonia, and/or movement/coordination disorders. We provide detailed behavioral profiles and seizure data and expand the number of reported SLC6A1 variants. (By Dr. Ashley Kahen, https://jmg.bmj.com/content/early/2021/05/18/jmedgenet-2021-107694 )