Effect of an extra chromosome

The French geneticist, Jerome Lejeune, discovered more than 50 years ago that Down syndrome is caused by the presence of an extra copy of chromosome 21.

But, to this day, it has remained a mystery why that results in impaired physical and cognitive development. Now, researchers at the Sanford-Burnham Medical Research Institute think they have found a clue.

The scientists, who were investigating Alzheimer’s disease, found that mice that lacked a protein known as SNX27 had many of the same learning and memory defects as mice with Down syndrome. Looking at the brains of people with the syndrome, the researchers discovered that they too lacked SNX27.

While chromosome 21 is not directly involved in SNX27 production, it does encode a regulator ‘miR-155’ that inhibits production. According to the study published in the journal Nature Medicine, levels of ‘miR-155’ in the brains of people with Down syndrome corelate almost exactly with the decrease in SNX27.

“In the brain, SNX27 keeps certain receptors on the cell surface — receptors that are necessary for neurons to fire properly,” the study’s senior author, Huaxi Xu, said in a statement released by the institute. “So in Down syndrome, we believe lack of SNX27 is at least partly to blame for developmental and cognitive defects.”

To test their findings, Xu’s team introduced more SNX27 to mice with Down syndrome. As they expected, the mice showed immediate improvements in cognitive function and behaviour. Now the researchers are investigating molecules that might increase production of SNX27 in the human brain.

Douglas Quenqua

Not just aping around Researchers have found that monkeys can co-operate to solve a problem, demonstrating that coordination among groups does not necessarily require language. The scientists, who report their findings in the journal, Current Biology, had a group of vervet monkeys play a game called the forbidden circle.

A single low-ranking female was trained to open a container holding a large amount of food but only when dominant monkeys in the group stayed outside an imaginary circle. For anyone to get any treats, they all had to coordinate their activity and show restraint. It took 30 trials, but after learning the rules, all the monkeys followed them.

“Think of a human situation where a school teacher has a movie in mind if the class is quiet for an hour,” said Ronald Noe, a behavioural ecologist at the University of Strasbourg in France. “That is really hard for kids to understand, if one is noisy, the film is not shown.” Yet, trial after trial, the monkeys patiently waited for one another to understand the game. “They didn’t react with aggression, Noe said. “Everyone was keen on opening the box as fast as possible.”

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