Previous investigations found that a subset of children with autism spectrum disorder (ASD) in California possessed plasma autoantibodies that reacted intensely with brain interneurons or other neural profiles. Moreover, for several cohorts of American women, maternal autoantibody reactivity to specific fetal brain proteins was highly specific to mothers of children with ASD. We sought to determine whether children and their mothers from a regionally specific cohort from the Basque Country of Spain demonstrated similar reactivity. Some children’s plasma reacted to interneurons, beaded axons or other neural profiles with no difference in the occurrence of these antibodies in children with or without ASD. Findings on the maternal antibodies confirmed previous research; plasma reactivity to fetal brain a combination of proteins at 37 and 73 kDa or 39 and 73 kDa was found exclusively in mothers of children with ASD.