Abstract: The present disclosure a system and methods for early diagnosis of neurodevelopmental or neurobehavioral diseases, such as autism spectrum disorders (“ASD”). In one aspect, a method for determining a risk for a neonatal patient to develop as ASD is provided. The method includes coupling a sensor assembly comprising plurality of electroencephalogram (“EEG”) sensors to a neonatal patient, and acquiring, using the sensor assembly, EEG data during a sleep state of the neonatal patient. The method also includes analyzing the EEG data to determine neural signatures indicative of a brain activity of the neonatal patient during the sleep state, and generating, based on the neural signatures, a composite representing a neurofunctional profile of the neonatal patient. The method further includes determining a risk for the neonatal patient to develop an autism spectrum disorder (“ASD”) by comparing the composite to a reference, and generating a report indicating the risk.