The causes of social dysfunction in autism, a core symptom of the disorder, remain unknown. Many genetic abnormalities seem to be involved in the disorder. Because behavioral problems are mediated by malfunctions in neural circuits, it is likely that diverse genetic defects converge to cause similar functional abnormalities at the neural circuit level. Therefore, understanding the neural circuit malfunctions may hold the key to understanding social dysfunction in autism.

Similar to the well-known critical period in development for language acquisition, there is likely to be a critical window during childhood for acquiring normal social behavior. An important goal in autism research is to identify this critical period, and possibly to manipulate the length of the window or reopen it in adulthood to help with the acquisition and maintenance of appropriate social behaviors.

The diagnosis of autism spectrum disorders is currently based on behavioral observations. As a result, many children with autism are not diagnosed until after their third birthday. This delay in diagnosis can be detrimental, as earlier interventions can significantly improve cognition, adaptive behavior and symptoms.

Few robust biomarkers have been identified for autism, and there are no medications that treat the social deficits associated with the disorder. Progress has been impeded in part by the challenge of obtaining relevant tissue samples from people with autism and matched controls.

Disruption in the number and function of brain synapses — the connections between neurons — is a central feature in the development of autism and associated cognitive disabilities. Although our understanding of how brain development differs in autism is not complete, an early overgrowth of neurons and synapses, as well as a failure to prune inappropriate synapses, has been observed in the brains of children with autism and in autism mouse models. At the molecular level, overproduction of key synaptic proteins may contribute to the atypical neural and synaptic growth in autism.

Rett syndrome involves a number of developmental deficits similar to those observed in autism, including dysregulated motor movements, communication skills and cognitive processes. Rett syndrome is caused by mutations in a single gene, MeCP2, allowing researchers to study the disorder in mice that carry the mutations.

Autism is a deeply complex and poorly understood developmental brain disorder. Defined genetic disorders that cause autism may be instructive for unraveling the cellular and developmental changes that underlie the disorder.

Significant progress has been made in recent years in identifying genetic factors contributing to autism. Although the genes identified have diverse biological functions, many of them are important for controlling the structure and function of the connection points between brain cells, called synapses. Alterations in synapse function affect the ability of brain cells to communicate with each other, and can lead to imbalanced or inappropriate activity in brain networks.

The core set of behavioral symptoms that define autism spectrum disorders can arise from a wide array of genetic and environmental causes. This many-to-one correspondence between genetic causes and behavioral phenotypes suggests that understanding and eventually treating autism may depend on identifying common intermediate biomarkers  at the level of neural circuits or biochemical pathways.