S C I E N C E N E W S

In separate tests, the team also found twogenes that carry resistance to tetracycline inColorado drinking water and recycledwastewater. Current methods of treatingdrinking water aren’t getting rid of thegenes, says Pruden.

“I think we need environmental scien-tists and engineers on board, looking at thisproblem,” she says. “Maybe there are sim-ple ways we can modify wastewater-treat-ment plants or simple things farmers cando with their lagoons.”

The team reports its findings in an upcom-ing Environmental Science & Technology.

Pedro J. Alvarez, an environmental engi-neer at Rice University in Houston, callsthe work “very important.” The discoveryof antibiotic-resistance genes in drinkingwater demonstrates the “ubiquitous natureof the problem,” he says.

By viewing antibiotic-resistance genes aspollutants, “we can begin to consider envi-ronmental-engineering solutions,” Alvarezadds. —A. CUNNINGHAM

Problem PaternityOlder men seem more aptto have autistic kids

Children born to fathers who are age 40 orolder have an increased risk of developingautism, a new study suggests.

Autism is marked by poor verbal skills,repetitive behavior patterns, and socialdetachment. It shows a hereditary compo-nent; someone with an autistic sibling has anincreased risk of being autistic. But no sin-gle gene mutation or alteration appears toexplain most cases of the disease. “There areprobably many genes that might contributeto it,” says Abraham Reichenberg, a neuro-psychologist at Mount Sinai School of Med-icine in New York City.

The incidence of autism rose roughly ten-fold in the United States between 1975 and1995. While some of the increase mighthave resulted from greater awareness anddiagnosis of the condition, scientists havesought other explanations. Some havefocused on paternal age, which appears tobe increasing in industrialized countries.

Reichenberg and his colleagues tappedinto a database of Israeli young people, whoare required to register with a draft boardat age 17. Records of more than 300,000

youths revealed that children fathered bymen age 40 or older were nearly six timesas likely to be autistic as those with fathersunder 30. In a separate calculation, theteam found that fathers in their 30s wereno more likely than younger men to haveautistic children. The findings appear inthe September Archives of General Psychi-atry. Previous studies attempting to linkadvanced paternal age to autism risk hadshown mixed results.

Scientists are speculating about howadvanced paternal age might impart autismrisk. The fault could lie in genetic changesthat accumulate in a man’s sperm-produc-ing cells as they regenerate over the years,Reichenberg says. “These are spontaneousmutations in the germ line, and they juststay there,” he says. An older man wouldhave more mutations that might lead toautism to pass on to his children.

Another proposed explanation evokesgene imprinting. Children get two copiesof every gene, one apiece from the motherand father. Some genes arrive from a par-ent with chemical groups—or imprints—that influence whether that copy will beactivated or silenced in the offspring. Stud-ies have linked a loss of imprinting to somediseases, including cancer.

It isn’t known whether paternal age dis-rupts this system of imprinting, but someimprinted genes play a role in brain devel-opment, says behavioral geneticistLawrence Wilkinson of Cardiff Universityin Wales. “Abnormalities in genomicimprinting could lead to abnormal gene[activation] in the brain—perhaps duringcritical stages of development—that couldincrease the risk for autism,” he says.

A third possibility rests on past reports

that parents of some autistic children arethemselves prone to social awkwardness,potentially reflecting autism’s geneticunderpinnings. “We and others wonder if,in families with autism, there might be[others] with problems of social interac-tion, or speech problems, or shyness,” saysRichard Schroer, a geneticist and pediatri-cian at the Florence, S.C., branch of theGreenwood Genetic Center, a nonprofitresearch-and-diagnostic institute. The con-nection found in this study, he says, “mightbe that some men, because of social-inter-action problems, may have taken longer tomarry and to have children.” —N. SEPPA

Size MattersBiosensors behave oddlywhen very small

Physicists have built tiny instruments sen-sitive enough to detect single molecules ofDNA, and the construction of these sen-sors generally follows a simple rule: thesmaller the better. However, this rule mighthave a limit, a new study finds.

Scientists have used microsensors todetect lone viruses, and some researchershave proposed using them to screen for HIVand cancer-indicating proteins (SN:10/13/01, p. 237). The common assump-tion is that even smaller sensors coulddetect such particles more precisely.

Now, a team of researchers at PurdueUniversity in West Lafayette, Ind., has dis-covered that nanosize sensors display dif-ferent properties than larger ones. Thisunusual behavior could keep scientists from

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SCIENCENEWSThis Week

TINY CONCERN Antibodies, depicted in green and blue, bunch up toward the free end of ananosize cantilever instead of coating the sensor evenly. Viruses, shown in red in thisillustration, would therefore collect at that end of a nanosensor and might yield incorrect readings. SE

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