Study relies on twins and their parents to understand height-IQ connection

Aug. 27, 2013 — The fact that taller people also tend to be slightly smarter is due in roughly equal parts to two phenomena — the same genes affect both traits and taller people are more likely than average to mate with smarter people and vice versa — according to a study led by the University of Colorado Boulder.The study did not find that environmental factors contributed to the connection between being taller and being smarter, both traits that people tend to find attractive.The modest correlation between height and IQ has been documented in multiple studies stretching back to the 1970s. But the reasons for the relationship between the two traits has not been well understood.The technique developed by the researchers at CU-Boulder to tease out those reasons may open the door for scientists to better understand why other sexually selected traits — characteristics that individuals find desirable in mates — tend to be linked. People who are attractive because of one trait tend to have other attractive traits as well.”Not just in humans but also in animals, you see that traits that are sexually attractive tend to be correlated,” said Matthew Keller, assistant professor of psychology and neuroscience at CU-Boulder and lead author of the study appearing in the journal PLOS Genetics. “So if you have animals that are high on one sexually selected trait they are often high on other ones, too. And the question has always been, ‘What’s the cause of that?’ And it has always been very difficult to tease apart the two potential genetic reasons that those could be related.”The key to the technique developed by Keller, also a fellow at CU-Boulder’s Institute for Behavioral Genetics, and his colleagues is using data collected about fraternal twins, identical twins and, importantly, their parents.It has been common in the past to use information about identical twins and fraternal twins to determine whether a particular trait is inherited, caused by environmental factors or affected by some combination of both. This kind of twin study assumes that each twin grows up with the same environmental factors as his or her sibling.If a trait that’s present in one twin is just as often present in the other — regardless of whether the twins are fraternal or identical — then the trait is likely caused by environmental conditions. On the other hand, if a trait is generally found in both identical twins but only in one of a set of fraternal twins, it’s likely that the trait is inherited, since identical twins have the same genetic material but fraternal twins do not.Similar studies also can be done for linked traits, such as height and IQ. But while scientists could determine that a pair of traits is passed down genetically, they could not further resolve whether inherited traits were linked due to the same genes influencing both traits, called “pleiotropy,” or because people who have those traits are more likely to mate with each other, known as “assortative mating.”The new CU-Boulder study solves this problem by including the parents of twins in its analysis. While this has occasionally been done in the past for single traits, information on parents has not previously been used to shed light on why two traits are genetically correlated. …

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Marijuana use in adolescence may cause permanent brain abnormalities, mouse study suggests

July 24, 2013 — Regular marijuana use in adolescence, but not adulthood, may permanently impair brain function and cognition, and may increase the risk of developing serious psychiatric disorders such as schizophrenia, according to a recent study from the University of Maryland School of Medicine. Researchers hope that the study, published in Neuropsychopharmacology — a publication of the journal Nature — will help to shed light on the potential long-term effects of marijuana use, particularly as lawmakers in Maryland and elsewhere contemplate legalizing the drug.”Over the past 20 years, there has been a major controversy about the long-term effects of marijuana, with some evidence that use in adolescence could be damaging,” says the study’s senior author Asaf Keller, Ph.D., Professor of Anatomy and Neurobiology at the University of Maryland School of Medicine. “Previous research has shown that children who started using marijuana before the age of 16 are at greater risk of permanent cognitive deficits, and have a significantly higher incidence of psychiatric disorders such as schizophrenia. There likely is a genetic susceptibility, and then you add marijuana during adolescence and it becomes the trigger.””Adolescence is the critical period during which marijuana use can be damaging,” says the study’s lead author, Sylvina Mullins Raver, a Ph.D. candidate in the Program in Neuroscience in the Department of Anatomy and Neurobiology at the University of Maryland School of Medicine. “We wanted to identify the biological underpinnings and determine whether there is a real, permanent health risk to marijuana use.”The scientists — including co-author Sarah Paige Haughwout, a research technician in Dr. Keller’s laboratory — began by examining cortical oscillations in mice. Cortical oscillations are patterns of the activity of neurons in the brain and are believed to underlie the brain’s various functions. These oscillations are very abnormal in schizophrenia and in other psychiatric disorders. The scientists exposed young mice to very low doses of the active ingredient in marijuana for 20 days, and then allowed them to return to their siblings and develop normally.”In the adult mice exposed to marijuana ingredients in adolescence, we found that cortical oscillations were grossly altered, and they exhibited impaired cognitive abilities,” says Ms. …

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