In Nature a group of researchers from Denmark and Iceland report the results of their studies of mutation rates of Icelandic parent-child groups. They found that the level of new mutations, called a “de novo mutations,” in their samples when father’s average age was 29.7 was 1.20?X?10?8 per nucleotide per generation, but that number increases by two every year. In round numbers one might estimate that at about 20 years of age a father’s single sperm cell could carry 25 new spontaneous mutations, but at 40 years of age it might carry more than 65.
Continue reading ‘Nature: De novo mutations, autism, and schizophrenia, redux’
In articles published online by Nature, Professors Stephan Sanders and colleagues and Brian J. O’Roak his colleagues reported additional evidence that rare mutations contribute to risk for Autism. By analyzing genetic material from parents who had children with Autism, the researchers were able to focus on differences in specific genes, what changed from one generation to the next. One team, working in the research lab of Professor Matthew State at Yale University, found strikingly unusual matches for a specific mutation at SCN2A. The other team, under the direction of Professor Evan Eichler at the University of Washington, found several candidates (including SCN1A) and a strong (4 to 1) relationship for older fathers.
Continue reading ‘De novo mutations and Autism redux’
New research by Joachim F. Hallmayer and colleagues released on 4 July 2011 raises questions about how strong a role genetic factors play in causing Autism. A large and careful twin study by Professor Hallmayer’s Stanford University team conducted with the support of the US National Institutes of Health (NIH) found that other factors known as the “shared environment” also influence susceptibility to Autism to a greater degree than previous research had indicated.
In genetics research, outcomes such as Autism can be caused by (a) genes, (b) shared environmental factors, (c) non-shared environmental factors, and (d) various interactions among these first three factors. (Technically, there is also “error,” a factor which is included to allow for some slippage is the relationships among these four.) Genes, of course, can be the same or different; in monozygotic or dizygotic twins they are all the same or 50% the same, respectively. The shared environment for monozygotic twins begins in the womb where they share the same placenta. After they are born, monozygotic twins are more likely to have more shared experiences (e.g., they are more likely to be dressed in matching outfits) than dizygotic twins, so they have a slightly greater shared environment than their dizygotic peer. Non-shared environments are the unique experiences people have; for twins, this factor is pretty minor, and it carries little power or weight. But, back to the chase….
In contrast, for example, to a famous study by A. Bailey and colleagues from 1995 that showed a very high heritability for Autism (92% of monozygotic twins were concordant for Autism but only 10% of dizygotic twins were concordant), the present study found that genetic heritability accounted for only 37% of the variance in Autism and shared environment factors accounted for 55% of Autism disorders. The findings hold whether Autism is diagnosed more strictly or more broadly; when Professor Hallmayer’s team examined Autism Spectrum Disorder cases rather than more narrowly defined cases, the percentages went up to 38% genetic and 58% shared environment contributions.
Continue reading ‘Is environment > genetics in cause of Autism?’
Brian Deer, the journalist who has doggedly pursued the story about a link between materials in vaccines and the onset of childhood Autism proposed by Dr. Andrew Wakefield and colleagues in the late 1990s, has published details explaining why he considers the original research establishing that link to have been fraudulent. In the first of a series of articles appearing in the prestigious British Medical Journal, Mr. Deer reports the results of his efforts to locate and interview the originally anonymous parents of the children included in the study by Dr. Wakefield et al.—which was published in the Lancet and then retracted—and it is sure to generate lots of heat, and perhaps a little bit of light.
Continue reading ‘Deer’s fraud case in BMJ’
Over on LD Blog I have a couple of posts about biological studies firming up possible neuropsychological linkages for maternal smoking and disorders such as ADHD. There are brief stories about two studies presented at Neuroscience 2010:
The sugar-makes-kids-hyper hypothesis is still false. Dan Willingham stuck another fork in it. Roasty-toasty. All done. Fizzle.
Now, I’m not advocating a high-fructose, feed-’em-soda-and-sweets diet, to be sure. It’s just that folks need to disabuse themselves of the popular myth that children’s levels of behavioral activity are governed by consumption of sucrose (whether from sugar cane or sugar beet).
Professor Willingham, who pops bubbles with the best of them, lanced this one in his guest post, “The Answer Sheet: How sugar really affects kids.” The evidence is basically the same as what I covered in the mid 1990s under the title “Sugar High?.”
Writing in the American Journal of Psychiatry, John Gilmore and colleages reported that the size and structure of the brains of newborn boys—but not girls—who are at risk for developing schizophrenia differ from those of their peers. Using multiple scanning methods at different times during gestation and infancy, the researchers compared the brains of offspring of mothers who have schizophrenia to the offspring of mothers who do not have schizophrenia; they found that high-risk boys had larger brains and larger lateral ventricles than baby boys whose mothers did not have psychiatric illness.
Because the risk of developing schizophrenia is much greater for close relatives of schizophrenics, the differences between the groups provides a strong indicator of later potential development of disease. Professor Gilmore wondered “Could it be that enlargement is an early marker of a brain that’s going to be different?”
Continue reading ‘Brain features associated with neonatal risk for schizophrenia’