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Dyslexia’sDNA ClueGene takes stage in learning disorder

For the first time, scientists have identifieda gene that appears to influence the devel-opment of at least some cases of dyslexia.

This learning disorder is characterizedby difficulties in perceiving sounds withinwords, spelling and reading problems, andtroubles with written and oral expression.It’s estimated that dyslexia affects at least1 in 25 people. Although scientists areinvestigating dyslexia’s suspected neuralroots (SN: 5/24/03, p. 324), the condition’scauses remain unknown.

If confirmed in further studies, the newgenetic finding represents a major stepforward for dyslexia researchers. Untilnow, investigators have only been able tolink dyslexia to alterations along stretchesof DNA containing tens or hundreds ofgenes. The most prominent of thesegenetic segments are located on chromo-somes 6 and 15.

A team led by geneticist Juha Kere of theKarolinska Institute in Huddinge, Sweden,narrowed the search to a gene called DYXC1on chromosome 15. Two disruptions ofthis gene substantially raise the odds ofdeveloping dyslexia, the scientists report inan upcoming Proceedings of the NationalAcademy of Sciences.

“Certainly, there are other genes involvedin dyslexia,” Kere says. Even so, he adds, “ourresearch may [eventually] help doctors todiagnose dyslexia more accurately.”

He and his colleagues first determinedthat a break had occurred at a specific loca-tion on the DYXC1 gene in the three dyslexicmembers of a Finnish family—the fatherand two daughters—as well as in a son with-out the condition. Molecular analyses indi-cated that the genetic break prevented theproduction of the protein encoded by theDYXC1 gene.

The researchers then probed the samegene in 109 children and adults diagnosedwith dyslexia and in 195 others who had no

learning disorder. The previously observedDYXC1 break appeared in nearly 9 percentof those with dyslexia, compared with fewerthan 3 percent of the comparison group.

Another DYXC1 disruption, which yieldsan altered version of the gene’s protein,occurred in about 12 percent of the dyslexicgroup, compared with roughly 5 percent ofthe others.

Evidence of the gene’s activity appears inthe brain, the scientists say. Their analysesof preserved human brains indicate thatonly certain brain cells respond to theDYXC1 protein. The neural function of theprotein remains unknown, Kere says.

The DYXC1 protein’s molecular makeupin people differs to a surprising extent fromthat of corresponding proteins in chim-panzees and other apes, Kere notes. “Thisgene may reveal important evolutionarydifferences in how our brains and those ofother primates work,” he says.

Geneticist Shelley D. Smith of the Uni-versity of Nebraska Medical Center inOmaha calls the new report “a really neatfinding.” The challenge is to confirm theresults in larger samples of people withdyslexia and then determine how the geneand its protein work, Smith says.

Her team is looking for genetic alterationson chromosome 6 that influence dyslexia.

Further work needs to establishwhether the DYXC1 gene influences otherdevelopmental disorders, such as speechproblems and attention-deficit hyperac-tivity disorder, adds psychologist andgeneticist Elena L. Grigorenko of YaleUniversity, in a comment slated to appearwith the new report. Still, Grigorenkodubs Kere’s study “an exciting beginningof a new stage of research into geneticpathways of dyslexia.” —B. BOWER

Long Ride WestMany western sedimentscame from Appalachians

North America may once have hosted acontinent-crossing river system as grand astoday’s Amazon, two new studies suggest.That notion is bolstered by the discoverythat material in several thick layers of sand-stone in the western United States origi-nated in the Appalachians.

About 190 million years ago, what is nowsouthwestern Utah was covered with sanddunes. The so-called Navajo Sandstone oftoday is the preserved remnant of dunesthat covered as many as 660,000 squarekilometers, an area almost the size ofTexas. In some Utah locations, that rockformation is up to 750 meters thick.

Scientists have long debated where allthat sand came from, says Peter W. Rein-ers, a geochemist at Yale University. In an

effort to end the debate, he and his col-leagues used two radioactive dating tech-niques on small mineral grains called zir-cons that they harvested from thesandstone. First, the researchers zapped azircon with a laser and chemically parsedthe vapor to estimate when the mineralcrystallized. Then, they analyzed what wasleft of the mineral grain to determine whenin the past the zircon had cooled below180°C, the temperature at which a zirconstarts trapping the helium being producedby the radioactive decay of other atoms.Rocks cool below that temperature as theyapproach Earth’s surface during episodesof mountain growth.

The researchers found that about two-thirds of the zircons they analyzed hadcooled between 400 million and 250 mil-lion years ago. Of that fraction, most hadoriginally crystallized between 1.2 billionand 950 million years ago. Those periodscorrespond with the uplift of the Appalachi-ans and the formation of the rocks fromwhich they grew. Because no other large-scale mountain growth took place on thecontinent during that time, it’s a safe betthat most of those zircons came from theAppalachians, Reiners asserts. He and hiscolleagues report their findings in the Sep-tember Geology.

If this conclusion is correct, theAppalachian zircons took a long, circuitousroute to reach Utah. After eroding fromexposed rocks, the zircons—and presum-ably many of the sandstone’s other mineralgrains—were carried to a region north and

SCIENCENEWSThis Week

CHANGES IN LONGITUDE Many zircons insome of southern Utah’s sandstone (cliffs inbackground) eroded from the Appalachians ofeastern North America.

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