4 | NewScientist | 21 August 2010

Autism explosionWHY have the numbers of autism diagnoses increased seven-fold in recent decades? Part of the increase could be down to a trend for later parenthood in the west, yet half of the rise remains a mystery.

A series of US studies by Peter Bearman of Columbia University in New York identified changes in diagnosis as the most important factor. He estimates that a switch from diagnoses of mental retardation to autism accounts for 26 per cent of extra cases seen in California between 1993 and 2005.

But a trend towards having children later in life also plays a part, since older parents are more likely to give birth to a child with autism. Together with increased awareness of the condition, this factor accounts for another 25 per cent of the increase.

Environmental factors are the most likely cause of the remaining 50 per cent, although no definite candidates have been identified, says Tom Insel, director of the National Institute of Mental Health in Rockville, Maryland. “These studies give me the feeling that there must be a true increase in the number of children affected,” Insel says.

Alzheimer’s keyHAVE the benefits of a test for Alzheimer’s been overlooked? A biological “signature” for diagnosing the disease from cerebrospinal fluid may be the key to new treatments.

A study published last week found the protein signature in 90 per cent of 102 people with the disease, 72 per cent of 200 people with mild cognitive impairment and, crucially, 36 per cent of 114 people with no cognitive problems.

Lasting danger for Pakistan’s cropsIN PAKISTAN, the flood waters just keep on coming. While the stationary weather system that produced the extreme rainfall seems to have dissipated, the annual monsoon rains continue to fall. As New Scientist went to press, a new wave of flood water was heading down the Indus river, with the populous southern province of Sindh already suffering the consequences.

With over 1400 people confirmed dead and millions affected, the immediate health consequences have been dire. But the biggest problem may be an escalating food shortage. According to a report issued on 14 August by the United Nations Office for the Coordination of Humanitarian Affairs, 3.2 million hectares of standing crops and

200,000 head of livestock have been lost, along with most food supplies stored in affected homes. These figures will only grow, compounded by the fact that Sindh is one of the country’s main agricultural areas.

The situation can be partly salvaged if the winter wheat crop is planted by September, but that depends on clearing the sediment dumped by the floods. “Pakistan has the largest continuously managed irrigation system in the world,” says James Wescoat of the Massachusetts Institute of Technology. Now the system is almost certainly silted up. Clearing it will be a huge task, especially now that floods and landslides have knocked out many roads.

“It will take a long time until the

infrastructure is up and running,” says economist Reinhard Mechler of the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria.

In the longer term, floods can flush salt out of the soil and deposit better topsoil, says David Wiberg, also at the IIASA, so in theory the country may end up more fertile than before. “But that’s a maybe,” he warns. And Godert van Lynden of ISRIC – World Soil Information in Wageningen, the Netherlands, cautions that the sediment will contain the rubbish and pollution that the water has picked up on its way. “Any positive impacts will probably be more than counterbalanced by other negative effects of the floods,” he says.

“These studies give me the feeling there must be a true increase in the number of children affected”

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