Autism and related neurodevelopmental conditions are clinically diverse and their etiological mechanisms are poorly understood. To inform prognosis and generate intervention opportunities we need a better understanding of causal pathways. In my talk, I will describe how our research has confirmed that fundamental differences in GABA-dependent brain sensory systems and wider brain networks at birth provide a setting for the later emergence of autistic traits in childhood. I will then show how investigating sensory processing in adults can confirm that GABA differences in sensory processing contribute to autism and can be modulated pharmacologically.