Genes & Cells

Rare variants, not common, cause disease
Strike another blow against the idea that common genetic variants cause common diseases like diabetes and heart disease. An analysis of the complete genetic makeup of 29 people shows that common variants usually don’t alter proteins or gene activity, because most common variants are not located within genes or gene-control regions, say researchers led by David B. Goldstein of Duke University Medical Center. Rare genetic variants are more likely to be detrimental and are kept at low frequency by natural selection, the researchers conclude in a paper appearing in the April 8 American Journal of Human Genetics. Common variants that are found in more than 8 to 10 percent of people probably got that way because they don’t have any functional consequences. —Tina Hesman Saey

Caffeine genes
If even the baristas at the local coffeehouse think you drink a lot of java, blame your genes. Caffeine consumption is partially based on genes, but until now it wasn’t clear which genes were responsible. To find out, an international team reanalyzed genetic data from 47,341 Americans of European heritage who participated in five previous unrelated studies. Genetic variants located near the CYP1A2 gene, which makes the main enzyme that breaks down caffeine, and the AHR gene, which a makes a protein that controls CYP1A2 activity, were associated with how many cups of joe people typically drink, the researchers report online April 7 in PLoS Genetics. —Tina Hesman Saey

Making eyes
Eyes make themselves, a study using embryonic stem cells reveals. Researchers had previously thought that eyes got their shape from a combination of the lens, surrounding tissue and internal pressure. Now Japanese researchers report in the April 7 Nature that clumps of embryonic stem cells growing in three-dimensional cultures can spontaneously organize into optic cups — precursors of eyes. The self-assembling cells make both the colored part of the eye and the retina. Making a hole in the structure didn’t cause the eye to lose its shape. Taken together, the results suggest stem cells draw on chemical and other cues to help build an eye from scratch. —Tina Hesman Saey