Word: variants
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Dates: during 2000-2009
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...study published on June 16 in the Journal of the American Medical Association (JAMA) now threatens to send researchers back to the drawing board. The meta-analysis of 14 prior studies concludes that the so-called depression gene - a variant of a serotonin-transporter gene called 5-HTTLPR - may not be associated with an elevated risk for depression, as many researchers had believed. "Knowing whether or not you have this gene is irrelevant," says the study's co-author Kathleen Merikangas, a genetic epidemiologist at the National Institute of Mental Health, who adds that future studies of genetic risk factors...
...Meta-analyses can be a steamroller," says Alexandre Todorov, a genetic epidemiologist at Washington University in St. Louis, Mo., whose 2007 peer-reviewed study was included in the JAMA piece. (While Todorov's study found an association between the gene and depression, it was based on a different variant - the long allele as opposed to the short one.) "If you have three studies and two find nothing and the third finds something significant, that does not mean that the third study is not real...
...Beaver's study shows, not all carriers of the defective MAO-A gene join a gang, and not all gang members have the defect. It remains largely unknown how common the low-active gene variant is in the general population, though one 2002 study indicated that genetic factors, including MAO-A, account for as much as 50% of the population variance in risk for antisocial behaviors. Additionally, Beaver's and other studies have found that low levels of the MAO-A enzyme affect only men, despite the fact that the MAO-A gene is located on the X chromosome...
...Males, who have one X chromosome and one Y chromosome, possess only one copy of this gene, while females, who have two X chromosomes, carry two," Beaver says. "Thus, if a male has a variant for the MAO-A gene that is linked to violence, there isn't another copy to counteract it." (See the top 10 scientific discoveries...
...scientists focused on the more than 1,000 genetic samples of families in which at least one son was affected by the disorder, prompted by the results of an earlier study using the same database, which identified a rich autism-related genetic region on chromosome 17 that contained genetic variants more common in boys than in girls. While nearly 40% of the general population has the most common form of CACNA1G, one variant of the gene was more prevalent in autistic boys, researchers found. "There is a strong genetic signal in this region," says Dr. Daniel Geschwind, director of UCLA...