From GeneReviews
SLC6A1-related neurodevelopmental disorder (SLC6A1-NDD) is characterized by mild-to-severe developmental delay and/or intellectual disability, hypotonia, epilepsy, movement disorders (e.g., tremor, stereotypies, ataxia), and neurobehavioral and/or psychiatric manifestations (e.g., autism spectrum disorder, attention-deficit/hyperactivity disorder, aggression, anxiety, and/or sleep disturbances). Language skills, particularly expressive language, are often more significantly affected than motor development. Developmental regression has been reported. Gastrointestinal manifestations (e.g., constipation, diarrhea) are also common.