Archive for the 'Causes' Category

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IQ, memory, and reading are hertitable

In a forthcoming report in Behavioral Genetics, Professor M. van Leeuwen of VU University (Amsterdam, NL) and colleagues reported that the vast majority of variation in children’s reading performance is heritable, with most of the variance in reading attributable to IQ and memory. The researchers studied twins and siblings (only some of whom had reading disabilities), and they measured children’s reading rate, how many times they could correctly tap blocks in a sequence that had just been displayed, the number times the children could correctly recall the location of a part of a visual display (a catepillar in different holes in an apple), repetition of sequences of digits, and IQ.

Figure 3 from van Leeuwen et al.

Before folks begin using this study to argue that there is a simple causal relationship between IQ and reading, please remember three things: (a) this research also implicates memory as an explanatory factor; (b) there are likely other factors that affect IQ, memory, and reading; and (c) even if lots of variance is explained by such factors as IQ and memory, the remaining variance is sufficient to allow fairly substantial instructional effects.

This study investigates the genetic relationship among reading performance, IQ, verbal and visuospatial working memory (WM) and short-term memory (STM) in a sample of 112, 9-year-old twin pairs and their older siblings. The relationship between reading performance and the other traits was explained by a common genetic factor for reading performance, IQ, WM and STM and a genetic factor that only influenced reading performance and verbal memory. Genetic variation explained 83% of the variation in reading performance; most of this genetic variance was explained by variation in IQ and memory performance. We hypothesize, based on these results, that children with reading problems possibly can be divided into three groups: (1) children low in IQ and with reading problems; (2) children with average IQ but a STM deficit and with reading problems; (3) children with low IQ and STM deficits; this group may experience more reading problems than the other two.

van Leeuwen, M. van den Berg, S. M., Peper, J. S., Hulshoff Pol, H. E., & Boomsma, D. I. (2009). Genetic covariance structure of reading, intelligence and memory in children. Behavioral Genetics, [forthcoming].

Link to the PubMed abstract I’ve reproduced here.

Davis goes on tour

Ron Davis, whose arguments that dyslexia is something worth having ring hollow and whose claims to have discovered the answer to dyslexia deserve strong challenge, will begin a speaking tour of the US and CA in May. If the lectures are like the public relations materials promoting them and Mr. Davis’ views, they will be heavy on a recounting of his terrific childhood triumphs, when he overcame Autism, taught himself to read, and learned to speak during his late adolescence. He will also provide a first-person account of what it is like to have dyslexia—one is likely to resonate with others’ views—and tout his books, The Gift of Dyslexia and The Gift of Learning, as well as his methods, “Davis Dyslexia Correction®,” “Davis Math Mastery®,” and “Davis Learning Strategies®.”

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Anesthesia and LD


Cumulative percentage of learning disabilities diagnosis by the age at exposure shown separately for those that have zero, one, or multiple anesthetic exposures before age 4 yr. (Fig 1 from Wilder et al., see sources).

Writing in the academic journal Anesthesiology under the title “Early Exposure to Anesthesia and Learning Disabilities in a Population-based Birth Cohort,” Robert T. Wilder, M.D., and colleagues reported that young children’s exposure to anesthesia was associated with a significant risk for development of Learning Disabilities in children having anesthesia two or more times during early childhood. Although the findings are consistent with analog studies showing that anesthetics affect baby animals’ brain development, they do not necessarily indicate that the drugs caused the children’s LD; one or more other factors could have caused both the need for the surgeries and the LD.

The investigators studied the association between anesthetic exposure before age 4 yr and the development of learning disabilities (LD). A single exposure to anesthesia (n = 449) was not associated with an increased risk of LD (hazard ratio = 1.0, 95% confidence interval [CI], 0.79-1.27). However, children receiving two anesthetics (n = 100) or three or more anesthetics (n = 44) were at increased risk for LD (hazard ratio = 1.59, 95% CI, 1.06-2.37, and hazard ratio = 2.60, 95% CI, 1.60-4.24, respectively). The team noted they cannot determine whether anesthesia itself may contribute to LD, or whether the need for anesthesia is a marker for other unidentified factors that contribute to LD.

In the following video, two of the researchers discuss the project and it’s implications.

Link to the Mayo Clinic press release. Free access to the full article. Hear (or read, or both) Joseph Shapiro’s report on the story for US National Public Radio.

Wilder, R. T., Flick, R. P., Sprung, J., Katusic, S. K., Barbaresi, W. J., Mickelson, C., Gleich, S. J., Schroeder, D. R., Weaver, A. L., & Warner, D. O. (2009). Early exposure to anesthesia and learning disabilities in a population-based birth cohort. Anesthesiology, 110, 796-804.

Sigh–new content

Despite getting virtually no recommendations about future content (3 votes!), I’m starting to post some new content. The new content is, in my obviously biased view (else, why would I post it?), pretty important stuff. It’s about research, practice, knowledge, and all that sort of stuff as it connects to Learning Disabilities. In this page, I discuss big-idea concepts that recur in Learning Disabilities. These are the themes that one sees when one reads a diverse array of literature on the topic of LD.

I recommend it. What’s more, you won’t have to find this post each time you want to refer to the page; it will always be directly accessible under the “special content” link in the top navigation bar.

More genetics and dyslexia

Professor Silvia Paracchini and colleagues have correlated the levels of one of the genes associated with chromosome 6p22, KIAA0319, with reading performance among the general population.

Association of the KIAA0319 Dyslexia Susceptibility Gene With Reading Skills in the General Population

Silvia Paracchini, D.Phil., Colin D. Steer, M.Sc., Lyn-Louise Buckingham, B.Sc., Andrew P. Morris, Ph.D., Susan Ring, Ph.D., Thomas Scerri, D.Phil., John Stein, F.R.C.P., Marcus E. Pembrey, M.D., Jiannis Ragoussis, Ph.D., Jean Golding, Ph.D., and Anthony P. Monaco, Ph.D.

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Irlen Kool-Aid consumed again

Yet another reporter has covered the benefits of providing colored lenses or overlays for improving reading performance. Based on subjective reports from a child and her father, Morgan Bond of television station KPVI in Pocatello (ID, US) described Irlen’s Syndrome as the cause and blue-tinted glasses as the solution to Noel Chapman’s reading problems.
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Relaxing to learn?

An anonymous post on the Hattiesburg (MS, US) American caught my attention. The poster applauded a facility called the “Dynamic Dyslexia Design School.” This is the school about which Liz Ditz posted a note a couple of months ago. The school is accredited by the International Multisensory Structured Language Education Council, which is probably a good thing. However, that didn’t prevent it’s director from providing a not-too-thoughtful explanation for reading problems:

The education is delivered in a way the dyslexic students can understand, said director Cena Holifield.

“They don’t feel the stress of everyone around them being able to do something they can’t. When they feel safe and secure, the pathways to the brain open and makes it easier to learn,” she said.

I’d hazard an alternative explanation: If the students seem more relaxed, it’s likely the result of succeeding, not the other way around.

Link to the full statement. Link to the school’s Web site. Link to Liz’s earlier post. More about the International Multisensory Structured Language Education Council.

How genes may affect dyslexia

Writing in the Journal of the Federation of American Societies for Experimental Biology under the title “The Complex of TFII-I, PARP1, and SFPQ Proteins Regulates the DYX1C1 Gene Implicated in Neuronal Migration and Dyslexia,” Isabel Tapia-Páez and colleagues revealed that they have discovered a group of proteins that apparently act together to control the transcription of DNA (deoxyribonucleic acid that forms genetic material) code into RNA (ribonucleic acid which controls synthesis of proteins) code. Although the gene DYX1C1 has been implicated in only a small proportion of cases of dyslexia, it is important in general because the finding moves researchers closer to understanding how genes can influence behavior as complex as reading.
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Hey, teacher, my child can’t read

Dean Geyer, who is a parent of a child who had difficulty learning to read, has launched a blog entitled “Hey, Teacher, My Child Can’t Read.” His daughter’s experience is, in part, a success story; after five years of special education in Delaware (US), he reports that she is on the honor roll and no longer eligible for special education.

In his entries, Mr. Geyer frequently refers to “auditory processing disorder.” Although I am very glad to learn that Mr. Geyer’s daughter is succeeding, I am wary of attributing much to the diagnosis of auditory processing disorder. I’ve been hearing about this disorder for most of my career, but I have as yet not found a satisfactorily rigorous or substantiated account of it.

If someone could point me to a definitive resource on this disorder, we could examine it systematically. I fear, however, that a close examination of the resource will reveal that it is simply hypothesizing some hidden process that can’t be precisely tested and is pretty readily reduced to not having learned some pretty specific skills.

Here are some of the questions one should ask:

  1. How does one distinguish a child with auditory processing disorder from another child who doesn’t have the disorder?
  2. How trustworthy (psychometrically sound) are any instruments used in making the diagnosis of auditory processing disorder?
  3. What specific tasks would a child with auditory processing disorder fail? If the child was taught how to pass those tasks, would she still have auditory processing disorder?

By the way, I think there’s a similar case to be made for “non-verbal learning disability.”

Regardless of the outcomes of an investigation of auditory processing disorder, it’s still quite wonderful to know that Mr. Geyer’s daughter is succeeding. I encourage readers to jump over to Hey, Teacher, My Child Can’t Read and read his posts. I’m adding his site to LD Blog’s blog roll.

Update: It seems this domain name is no longer being maintained. More when I can get in touch with Mr. Geyer. 11 September 2009.

RC > WR

A team of researchers who study reading and neuropsychology has reported results from a study that show what parts of the brain are involved in sentence comprehension other than those used for recognizing the words in the sentences. In a study entitled “Functional MRI of Sentence Comprehension in Children with Dyslexia: Beyond Word Recognition” that will appear soon in Cerebral Cortex, S. L. Rimrodt and colleagues (including Ken Pugh and Laurie Cutting, whom I know) compared the fMRI data from groups of children with and without dyslexia on tasks involving word reading and sentence comprehension. They found that the children with dyslexia had disproportional activation of areas of the brain usually employed in processing linguistic information, attending, and selecting responses.
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