Microglia in the pathogenesis of autism spectrum disorders

Proper synaptic pruning is essential for the development of functional neural circuits. Impairments in synaptic pruning disrupt the excitatory versus inhibitory balance (E/I balance) of synapses, which may cause neurodevelopmental disorders such as autism spectrum disorder (ASD). Recent studies have determined molecular mechanisms by which microglia, the brain's resident immune cells, engulf inappropriate and less active synapses. Thus, microglial dysfunction may be involved in the pathogenesis of ASD through attenuated or excess synaptic pruning. In this review, we discuss recent animal and human studies that report an E/I imbalance and the characteristics of microglia in ASD. We will further discuss whether and how synaptic pruning by microglia is involved in the pathogenesis of ASD.