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Cynthia Bulik of the University of North Carolina School of Medicine.

In the latest issue of the Archives of General Psychiatry, Bulik and colleagues studied records from 30,000 Swedish twins, some with anorexia, and found that identical twins, who share identical genes, were more likely to share an eating problem compared with fraternal twins, who share half their genes, the same as non-twin siblings.

In this large sample, scientists figured out that genes were responsible for 56 percent of the cases of the potentially life-threatening condition.

People with anorexia - about 10 out of every 1,000 women and 29 in every 1,000 men - have symptoms that include self-starving and an obsessional belief that they are fat.

Bulik and others are trying to identify genetic risk factors so that they can better solve this puzzling eating behavior.

“We have gone through far too much time blaming parents,” said Bulik, who used a 30,000-person twin registry from Sweden to identify the strong genetic contribution.

“People need to understand that they are fighting their biology” and not just a psychological need to be thin.

Once genes are identified, the hope is that scientists can develop drugs that work directly on these target genes.

In another study published in the same journal, a team of investigators at McLea...

The lactase mutation, which enables the digestion of milk to continue into adulthood, appeared in approximately 90 percent of Europeans.

“Presumably,” Pritchard said, “a few thousand years from now, if selection pressure remains the same, everyone will have [the selected mutation].” Classifying all the genes by their biological functions, the researchers listed the top 16 categories that had the strongest signals, including olfaction (the sense of smell), reproduction-related processes and carbohydrate metabolism, which includes the lactase gene.

Other processes that show signals of selection include genes related to metabolism of foreign compounds, brain development and morphology.

For example, the researchers found five genes involved in skin pigmentation that show evidence of positive selection in Europeans.

“Only one of these five signals was known before,” Pritchard said.

The authors also found signals of reproductive selection and sexual competition in all three populations.

“Many of the signals, ho...

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