Tag Archive for 'genetics'

Testing genetic causes of dyslexia

Although at least four genes have been identified as possible markers for dyslexia, scientists have encountered considerable difficulty in coming to consensus about identifying a culprit as a contributing cause for the perplexing reading disorder. As noted previously here on LD Blog, DCDC2 (1 November 2005) and DYX1C1 (1 August 2008; 19 November 2009), among others, have been cited as possible loci for disruptions. But problems emerge when seeking to connect studies that point toward these candidate genes and studies showing the individuals with the problems. The associations between genes and problems appear in some language populations, but perhaps not in others, making one wonder about the clarity of the relationships.

Seeking a means of examining the relationships at a more abstract level, a group of European researchers collected data from a sample of individuals with dyslexia that represented people from eight different countries (Austria, France, Germany, The Netherlands, Switzerland, Finland, Hungary, and the United Kingdom). Using this diverse language sample, they reasoned, would allow them to search the the connections between genes and dyslexia at a more abstract level than when testing with a sample of people speaking just one or two languages.
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More on smoking and neuropsych disorders

New research shows that using nicotine during pregnancy affects genes involved in myelination and, consequently may help explain why the children of mothers who smoke during pregnancy are more likely to develop such psychiatric disorders as attention deficit hyperactivity disorder, depression, autism, and even drug abuse. In a paper presented at Neuroscience 2010, the annual meeting of the Society for Neuroscience, Professor Ming Li, Ph.D., of the University of Virginia (Charlottesville, VA, US) reported that when rats were given nicotine during pregnancy, their offspring manifested changes in myelin genes for the limbic system, especially the prefrontal cortex, a brain region important for decision-making.

“Our research shows that gestational treatment with nicotine significantly modifies myelin gene expression in specific brain regions that are involved in behavioral processes,” according to Professor Li, leader of the study. “Myelin deficits have been observed in adults with various psychiatric disorders. Our findings suggest that abnormal myelination may contribute to the psychiatric disorders associated with maternal smoking.”
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More on IQ and reading disabilities

Deficits in reading performance may differ in etiology depending on the IQ of the individuals who have the deficits. According to an article in Behavior Genetics, Professor Sally Wadsworth and colleagues confirmed previous research showing that there is a stronger genetic element in the reading deficits of children with higher IQs (mean = 108.97 ± 6.71) than those with lower IQ (mean = 82.85 ± 6.40). The heritability for the former group is 0.75 ± 0.12, but for the latter it is 0.50 ± 0.10.
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The gene DYX1C1 and reading and spelling

Paul Bates and colleagues have reported new findings about the gene DYX1C1, which has been a focal point for research on genetic contributions to dyslexia for at least six years. Writing for the journal Molecular Psychiatry, the research team revealed that their examination of the relationship between DYX1C1 and variations in reading ability points at certain variations in genes and reading ability. Specific differences in individual nucleotides (single nucleotide polymorphisms, or SNPs), different from those reported previously, appear to be associated with ability and disability in reading and spelling.

The status of DYX1C1 (C15q21.3) as a susceptibility gene for dyslexia is unclear. We report the association of this gene with reading and spelling ability in a sample of adolescent twins and their siblings. Family-based association analyses were carried out on 13 single-nucleotide polymorphisms (SNPs) in DYX1C1, typed in 790 families with up to 5 offspring and tested on 6 validated measures of lexical processing (irregular word) and grapheme–phoneme decoding (pseudo-word) reading- and spelling-based measures of dyslexia, as well as a short-term memory measure. Significant association was observed at the misssense mutation rs17819126 for all reading measures and for spelling of lexical processing words, and at rs3743204 for both irregular and nonword reading. Verbal short-term memory was associated with rs685935. Support for association was not found at rs3743205 and rs61761345 as previously reported by Taipale et al., but these SNPs had very low (0.002 for rs3743205) minor allele frequencies in this sample. These results suggest that DYX1C1 influences reading and spelling ability with additional effects on short-term information storage or rehearsal. Missense mutation rs17819126 is a potential functional basis for the association of DYX1C1 with dyslexia.

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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.

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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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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Preschool language factors affecting reading achievement

Although perceptual explanations for reading problems were common in the early discussions of Learning Disabilities, educators now mostly agree that the language factors have far greater influence on reading problems. A recent study by Nicole Halaar and colleagues underscores this idea and, especially importantly, points to the importance of early childhood language development in later reading competence. In fact, although genetic factors play a role in later reading competence, environmental exert substantial influence.

Of course, given the extensive work on them over the past 20 years, educators understand the importance of phonemic awareness and decoding in reading. But these factors do not completely explain the variation in outcomes for children learning to read. The contributions of semantic and syntactic factors must be included to move closer to explaining why children differ in their reading outcomes, especially when the outcome of concern is facility in comprehending what one has read.
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ADHD in families

Dr. M. Romanos and colleagues examined the genetic make-up of several families and found that there are common elements that appear to be associated with ADHD. Although these findings point toward a genetic contribution to ADHD, it is important to note the caveat implied by the final sentence of the abstract: So many factors contribute to ADHD, that these results should not be construed as identifying the precise cause of the disorder. In the full article, the authors are circumspect about this: “The identification [in this study] of several novel linkage regions as well as replication of previously reported loci provides further evidence for the highly heterogeneous genetic etiology of ADHD.”

Genome-wide linkage analysis of ADHD using high-density SNP arrays: Novel loci at 5q13.1 and 14q12

M Romanos, C. Freitag, C. Jacob, D. W Craig, A. Dempfle, T. T. Nguyen, R. Halperin, S. Walitza, T. J Renner, C. Seitz, J. Romanos, H. Palmason, A. Reif, M. Heine, C. Windemuth-Kieselbach, C. Vogler, J. Sigmund, A. Warnke, H. Schäfer, J. Meyer, D. A. Stephan, & K. P. Lesch

Molecular Psychiatry (2008) 13, 522–530; doi:10.1038/mp.2008.12; published online 26 February 2008

Abstract

Previous genome-wide linkage studies applied the affected sib-pair design; one investigated extended pedigrees of a. genetic isolate. Here, results of a. genome-wide high-density linkage scan of attention-deficit/hyperactivity disorder (ADHD) using an array-based genotyping of approx ~50 K. single nucleotide polymorphism (SNPs) markers are presented. We investigated eight extended pedigrees of German origin that were non-related, not part of a. genetic isolate and ascertained on the basis of clinical referral. Two parametric analyses maximizing LOD scores (MOD) and a. non-parametric analysis for both a. broad and a. narrow phenotype approach were conducted. Novel linkage loci across all families were detected at 2q35, 5q13.1, 6q22-23 and 14q12, within individual families at 18q11.2-12.3. Further linkage regions at 7q21.11, 9q22 and 16q24.1 in all families, and at 1q25.1, 1q25.3, 9q31.1-33.1, 9q33, 12p13.33, 15q11.2-13.3 and 16p12.3-12.2 in individual families replicate previous findings. High-resolution linkage mapping points to several novel candidate genes characterized by dense expression in the brain and potential impact on disorder-relevant synaptic transmission. Our study provides further evidence for common gene effects throughout different populations despite the complex multifactorial etiology of ADHD.