People with autism spectrum disorders have more mutations in their DNA than do their unaffected siblings. The emerging picture is that the genetics of autism is very complex: Dozens or perhaps even hundreds of different mutations may contribute to the disease in each person with autism.

A hallmark symptom of autism spectrum disorders is impairment in social interactions, yet little is known about the neural mechanisms underlying this deficit. In contrast to autism, Williams-Beuren syndrome involves enhanced sociability. The syndrome affects many systems, including the motor, sensory, language, cognitive, emotional and social systems. It is caused by a chromosomal microdeletion. Most individuals with the disorder have relatively preserved language skills in conjunction with high sociability, which are quite opposite from the salient features of autism.

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.

In recent years, autism heritability has been the focus of intense research, and a number of autism susceptibility genes and loci have been identified. This progress has allowed researchers to generate mouse models that carry relevant mutations, providing a biological system for dissecting the circuit, cellular and molecular mechanisms underlying autism-associated changes in brain development.

Vikaas Sohal and his colleagues set out to test the hypothesis that excessive entry of calcium into neurons within the medial prefrontal cortex (mPFC) impairs social behavior and contributes to additional aspects of autism. The researchers learned that the excessive entry of calcium does not affect all neurons in the mPFC equally. Rather, neurons in the mPFC can be divided into different subpopulations, and the excessive entry of calcium has a profound effect on one of these subpopulations.

Large-scale population studies are valuable for elucidating gene-environment interactions that contribute to the risk of autism. Young Shin Kim and her colleagues at Yale University are assembling a large-scale collection of autism-related data from a group of children in South Korea who show a variety of symptoms across the autism spectrum.

Many children with autism have unusually high numbers of synapses, or connections between neurons, particularly in the cortex, which may result from overgrowth and a disruption of neuronal pruning during childhood. Pruning and reshaping of neurons pares down the number of synapses in the brain while eliminating inappropriate synapses that lead to over-connectivity between brain regions, and possibly inappropriate learning, behavior and seizures. David Sulzer and his colleagues at Columbia University hypothesize that autism-associated mutations in the tuberous sclerosis gene, TSC, can cause over-connectivity when the target of TSC, the mTOR pathway, interferes with normal neuronal pruning.