The chemical messenger serotonin has long been associated with autism. Serotonin is made in the blood and in the brain. In the brain, it is made by a specialized group of neurons in the brainstem and functions as a neurotransmitter, influencing the activity of neurons in virtually all regions. How abnormal serotonin function contributes to some of the key behaviors that define autism is not clear, but serotonin has been shown to affect the development and function of synapses, the junctions between brain cells. This is consistent with the idea that autism might be a disorder of the synapse.

Autism spectrum disorder is widely regarded as one of the most severe childhood psychiatric conditions. The root causes of this disorder have generally been viewed as either genetic or environmental. The interaction between genetic and environmental factors has not been investigated widely, however, despite the fact that synergistic effects have been found for other neurodevelopmental disorders such as depression.

The deletion of 27 genes in the 16p11.2 chromosomal region is associated with autism spectrum disorders, intellectual disability and obesity. To study the underlying cellular, molecular and anatomical basis of autism, Ricardo Dolmetsch and his colleagues at Stanford University in California have generated a mouse that lacks the same 27 genes on a corresponding chromosome in the mouse genome. Their goal, in collaboration with Jacqueline Crawley’s lab, is to characterize the neuroanatomical, neurophysiological and behavioral features of these mice.

During embryonic development, a ‘protomap’ of the cortex forms in the developing brain region that will become the cerebral cortex. Robert Hevner and his colleagues at Seattle Children’s Research Institute are studying the mechanisms that maintain this patterning of regional identity throughout embryonic development.

Fragile X syndrome is the most common heritable form of intellectual disability and a leading genetic cause of autism. The disorder results from loss of a key regulatory protein known as FMRP, but how the absence of this protein causes the cognitive impairments associated with fragile X syndrome is still unclear. Suzanne Zukin and her colleagues at Albert Einstein College of Medicine in New York, as well as others, have identified hyperactivation of a key cellular signaling pathway — the PI3K-mTOR signaling pathway — as a key feature of the syndrome.

Some overlap between 7q11.23 duplication syndrome and autism spectrum disorder has been reported in a large cohort of children. Individuals with duplication of this region show features commonly found in individuals with autism, such as speech delay.

Choline is an essential nutrient for all animals, including humans. Prenatal and early postnatal supplementation with choline has been shown to enhance long-term cognitive performance, improve motor deficits in a mouse model of Rett syndrome, and reduce the adverse effects of neonatal alcohol exposure in rodents.

Environmental and genetic risk factors are both known to contribute to autism. Theo D. Palmer and his colleagues at Stanford University in California studied how a relatively common genetic risk factor may make developing fetuses more vulnerable to the mother’s immune response to illness or infections during pregnancy.

Autism is commonly seen in people with the genetic disorder tuberous sclerosis complex (TSC). TSC involves two genes, TSC1 and TSC2, encoding the proteins hamartin and tuberin, respectively. TSC proteins regulate an important signaling pathway known as the mTOR pathway, which plays an essential role in interconnectivity and communication between neurons in the brain.

Most research into autism spectrum disorders has focused on genetic, behavioral and neurological aspects of the illness, but people with autism also show striking alterations in immune status.