Individuals carrying an extra copy of the genetic region that’s missing in Williams syndrome — which causes mental retardation and a hyper-friendly personality — have language impairments and other autism-like social difficulties, according to a wave of new research on this duplication syndrome.

The mouse brain has more than 1,300 regions for which the copy from one parent is expressed more often than the one from the other parent, according to two studies published today in Science. These so-called imprinted genes have been proposed to cause some cases of autism, but the researchers say their findings do not support that theory.

Children with fragile X syndrome show abnormal growth in several brain structures during the first few years of life, according to the first study to track how the disease unfolds in the brain during early development.

Several independent groups have found previously unknown risk genes for autism, schizophrenia and mental retardation. The candidate genes have one thing in common: they encode proteins that are needed for the healthy function of synapses, the junctions between neurons.

A decade of research on the biology of autism, combined with a steady rise in diagnoses, has finally piqued the pharmaceutical industry’s interest in developing drugs for the disorder. Preliminary data from one small clinical trial already show positive results, and results from several others are expected early this summer.

Babies born to rhesus monkeys infected with the flu virus during pregnancy have significantly smaller brains than normal, and other brain abnormalities seen in schizophrenia, researchers have found. The study, published last month in Biological Psychiatry, provides the first evidence in non-human primates linking flu infection to a higher risk of schizophrenia.

A study of a rare form of epilepsy found in Amish groups adds heft to the idea that mTOR — a much-studied hub in a massive network of brain cell proteins — is an important biochemical player in autism.

Mice engineered to carry a well-known risk factor for schizophrenia show disruptions in the connections between two brain regions that coordinate memory and learning. And these disruptions directly cause problems with working memory — the ability to actively hold information and to recall that information to make a decision, according to a study published in Nature.

Microglia, brain cells that provide immune protection to neurons, may influence the onset and course of Rett syndrome, according to a study published in the Journal of Neuroscience.

Worms, despite their crude nervous system, can be useful models of the genetic underpinnings of autism, according to unpublished work presented today at a meeting of the Genetics Society of America in Boston.