Genetic research into dyslexia

Main articles: Medicine:Dyslexia and Medicine:Dyslexia research

The genetic research into dyslexia has its roots in the work of Galaburda and Kemper, 1979,[1] and Galaburda et al. 1985,[2] from the examination of post-autopsy brains of people with dyslexia. When they observed anatomical differences in the language center in a dyslexic brain, they showed microscopic cortical malformations known as ectopias and more rarely vascular micro-malformations, and in some instances these cortical malformations appeared as a microgyrus. These studies and those of Cohen et al. 1989[3] suggested abnormal cortical development which was presumed to occur before or during the sixth month of foetal brain development.[4]

## Overview

High genetic concordance found in twin studies suggest a significant genetic influence on reading ability,[5][6] although the degree depends on the definition of dyslexia.[7] Linkage analysis and genetic association studies (typically quantitative trait locus association studies, which use microarrays to look at single nucleotide polymorphisms of multiple genes at once) have been used to identify candidate genes that may be implicated in dyslexia.[8] Several genes have been linked to dyslexia, including DCDC2[9][10] and KIAA0319[9][11] on chromosome 6,[12][13] DYX1C1 on chromosome 15,[9][12] ROBO1,[14] DYX3,[15] the language-disorder candidate gene CMIP,[16] and several others. However, these genes account for a small proportion of variance in reading disability, often less than 0.5%.[17][18] Additionally, the findings are not always replicated. Therefore, no single gene is definitively implicated in dyslexia. A 2007 review reported that no specific cognitive processes are known to be influenced by the proposed genes.[19]

It is likely that multiple genes, as well as the environment, interact to influence reading ability. The Generalist Genes Hypothesis proposes that many of the same genes are implicated within different aspects of a learning disability as well as between different learning disabilities. Indeed, there also appear to be a large genetic influence on other learning abilities, such as language skills.[20] The Generalist Genes Hypothesis supports the findings that many learning disabilities are comorbid, such as speech sound disorder, language impairment, and reading disability,[21] although this is also influenced by diagnostic overlap.

Many of the genes implicated in dyslexia play a role in general neural development. For example, dyslexia candidate genes DYX1C1, ROBO1 KIAA0319, and DCDC2 appear to be involved in neuronal migration.[10][22][23][24] Animal models are especially useful in determining the function of these genes. For example, Gene knockdown in utero of DYX1C1 disrupts hippocampal development and causes impairments in auditory processing and spatial learning in rodents[25] and mutations in DCDC2 impairs visuo-spatial memory, visual discrimination, and long-term memory in mice.[26] The role of neuronal migration in dyslexia is reviewed in Galaburda (2005).[27]

## Genes and chromosomes associated with dyslexia

A 2007 review reported that no specific cognitive processes are known to be influenced by the proposed susceptibility genes. Some studies have already started to include neurophysiological (e.g., event-related potential) and imaging (e.g., functional MRI) procedures in their phenotype characterisation of patients. Such samples are an important prerequisite for the identification of those processes that are most proximal to the effects of particular genes and their associated biological pathways.[28]

## References

1. ↑ "Cytoarchitectonic abnormalities in developmental dyslexia: a case study". Annals of Neurology 6 (2): 94–100. August 1979. doi:10.1002/ana.410060203. PMID 496415.
2. ↑ "Developmental dyslexia: four consecutive patients with cortical anomalies". Annals of Neurology 18 (2): 222–33. August 1985. doi:10.1002/ana.410180210. PMID 4037763.
3. ↑ "Neuropathological abnormalities in developmental dysphasia". Annals of Neurology 25 (6): 567–70. June 1989. doi:10.1002/ana.410250607. PMID 2472772.
4. ↑ Habib M (December 2000). "The neurological basis of developmental dyslexia: an overview and working hypothesis". Brain 123 (Pt 12): 2373–99. doi:10.1093/brain/123.12.2373. PMID 11099442.
5. ↑ Wadsworth, SJ; DeFries JC; Olson RK; Willcutt EG. (December 2007). "Colorado longitudinal twin study of reading disability". Annals of Dyslexia 57 (2): 139–60. doi:10.1007/s11881-007-0009-7. PMID 18060583.
6. ↑ Harlaar, N; Spinath FM; Dale PS; Plomin R (April 2005). "Genetic influences on early word recognition abilities and disabilities: a study of 7-year-old twin". J Child Psychol Psychiatry 46 (4): 373–84. doi:10.1111/j.1469-7610.2004.00358.x. PMID 15819646.
7. ↑ Olson, RK (2002). "Dyslexia: nature and nurture". Dyslexia 8 (3): 143–159. doi:10.1002/dys.228. PMID 12222731.
8. ↑ "Susceptibility loci for distinct components of developmental dyslexia on chromosomes 6 and 15". American Journal of Human Genetics 60 (1): 27–39. January 1997. PMID 8981944.
9. ↑ 9.0 9.1 9.2 Shastry BS (2007). "Developmental dyslexia: an update". J. Hum. Genet. 52 (2): 104–9. doi:10.1007/s10038-006-0088-z. PMID 17111266.
10. ↑ 10.0 10.1 Meng H, Smith SD, Hager K (November 2005). "DCDC2 is associated with reading disability and modulates neuronal development in the brain". Proc. Natl. Acad. Sci. U.S.A. 102 (47): 17053–8. doi:10.1073/pnas.0508591102. PMID 16278297. PMC 1278934. Bibcode: 2005PNAS..10217053M. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=16278297.
11. ↑ "Association of the KIAA0319 dyslexia susceptibility gene with reading skills in the general population". The American Journal of Psychiatry 165 (12): 1576–84. December 2008. doi:10.1176/appi.ajp.2008.07121872. PMID 18829873.
12. ↑ 12.0 12.1 Bishop, DVM (March 2009). "Genes, cognition, and communication: insights from neurodevelopmental disorders". Annals of the New York Academy of Sciences 1156 (1): 1–18. doi:10.1111/j.1749-6632.2009.04419.x. PMID 19338500. Bibcode: 2009NYASA1156....1B.
13. ↑ "Chromosome 6p influences on different dyslexia-related cognitive processes: further confirmation". American Journal of Human Genetics 66 (2): 715–23. February 2000. doi:10.1086/302755. PMID 10677331.
14. ↑ Hannula-Jouppi, Katariina; Nina Kaminen-Ahola; Mikko Taipale; Ranja Eklund; Jaana Nopola-Hemmi; Helena Kääriäinen; Juha Kere (October 2005). "The Axon Guidance Receptor Gene ROBO1 Is a Candidate Gene for Developmental Dyslexia". The Axon Guidance Receptor Gene ROBO1 is a Candidate Gene for Developmental Dyslexia 1 (4): 0467–0474. doi:10.1371/journal.pgen.0010050. PMID 16254601.
15. ↑ Fagerheim, T; Raeymaekers P; Tønnessen FE; Pedersen M; Tranebjaerg L; Lubs HA. (September 1999). "A new gene (DYX3) for dyslexia is located on chromosome 2". J Med Genet 36 (9): 664–9. doi:10.1136/jmg.36.9.664. PMID 10507721.
16. ↑ Scerri, TS; Morris AP; Buckingham LL; Newbury DF; Miller LL; Monaco AP; Bishop DV; Paracchini S. (August 2011). "DCDC2, KIAA0319 and CMIP are associated with reading-related traits". DCDC2, KIAA0319 and CMIP Are Associated with Reading-related Traits 70 (3): 237–45. doi:10.1016/j.biopsych.2011.02.005. PMID 21457949.
17. ↑ Butcher, LM; O S P Davis; I W Craig; R Plomin (June 2008). "Genome-wide quantitative trait locus association scan of general cognitive ability using pooled DNA and 500K single nucleotide polymorphism microarrays". Genes Brain Behav. 7 (4): 435–46. doi:10.1111/j.1601-183X.2007.00368.x. PMID 18067574.
18. ↑ Meaburn, EL; N Harlaar; I W Craig; L C Schalkwyk; R Plomin (2008). "Quantitative trait locus association scan of early reading disability and ability using pooled DNA and 100K SNP microarrays in a sample of 5760 children". Molecular Psychiatry 13 (7): 729–740. doi:10.1038/sj.mp.4002063. PMID 17684495.
19. ↑ "Genetics of dyslexia: the evolving landscape". Journal of Medical Genetics 44 (5): 289–97. May 2007. doi:10.1136/jmg.2006.046516. PMID 17307837.
20. ↑ Stromswold, Karin (December 2001). "The Heritability of Language: A Review and Metaanalysis of Twin, Adoption, and Linkage Studies.". Language 77 (4): 647–723. doi:10.1353/lan.2001.0247.
21. ↑ Pennington BF, Bishop DVM (2009). "Relations Among Speech, Language, and Reading Disorders". Annual Review of Psychology 60: 283–306. doi:10.1146/annurev.psych.60.110707.163548. PMID 18652545. ,
22. ↑ Kid, T; Brose K; Mitchell KJ; Fetter RD; Tessier-Lavigne M (1998). "Roundabout controls axon crossing of the CNS midline and defines a novel subfamily of evolutionarily conserved guidance receptors". Cell 92 (2): 205–215. doi:10.1016/S0092-8674(00)80915-0. PMID 9458045.
23. ↑ Wang, Y; Paramasivam M; Thomas A; Bai J; Kaminen-Ahola N; Kere J; Voskuil J; Rosen GD et al. (2006). "DYX1C1 functions in neuronal migration in developing neocortex". Neuroscience 143 (2): 515–22. doi:10.1016/j.neuroscience.2006.08.022. PMID 16989952.
24. ↑ "The chromosome 6p22 haplotype associated with dyslexia reduces the expression of KIAA0319, a novel gene involved in neuronal migration". Hum. Mol. Genet. 15 (10): 1659–66. 2006. doi:10.1093/hmg/ddl089. PMID 16600991.
25. ↑ Threlkeld, SW; McClure MM; Bai J; Wang Y; LoTurco JJ; Rosen GD; Fitch RH. (March 2007). "Developmental disruptions and behavioral impairments in rats following in utero RNAi of Dyx1c1". Brain Res Bull 71 (5): 508–14. doi:10.1016/j.brainresbull.2006.11.005. PMID 17259020.
26. ↑ Gabel, LA; Marin I; LoTurco JJ; Che A; Murphy C; Manglani M; Kass S (November 2011). "Mutation of the dyslexia-associated gene Dcdc2 impairs LTM and visuo-spatial performance in mice". Genes Brain Behav. 10 (8): 868–75. doi:10.1111/j.1601-183X.2011.00727.x. PMID 21883923.
27. ↑ Galaburda, Albert (2005). "Dyslexia—A molecular disorder of neuronal migration". Annals of Dyslexia 55 (2): 151–165. doi:10.1007/s11881-005-0009-4. PMID 17849191.
28. ↑ "Genetics of dyslexia: the evolving landscape". Journal of Medical Genetics 44 (5): 289–97. May 2007. doi:10.1136/jmg.2006.046516. PMID 17307837.

* v
* t
* e

Dyslexia and related specific developmental disorders (F80–F83, 315)

General
conditions|

| Speech and
language
impairment,
communication
disorder|

* Expressive language disorder
* Infantile speech
* Landau–Kleffner syndrome
* Language disorder
* Lisp
* Mixed receptive-expressive language disorder
* Specific language impairment
* Speech and language impairment
* Speech disorder
* Speech error
* Speech sound disorder
* Stammering
* Tip of the tongue

|

Scholastic skills,
learning disorder|

* Developmental dyslexia
* Dyscalculia
* Dysgraphia (Disorder of written expression)

Motor function|

* Developmental coordination disorder
* Developmental verbal dyspraxia also known as Childhood apraxia of speech

Other|

* Auditory processing disorder
* Sensory processing disorder

Related
topics|

* Dyslexia research
* Irlen filters
* Learning Ally
* Learning problems in childhood cancer
* Literacy
* Management of dyslexia
* Multisensory integration
* Neuropsychology
* Reading acquisition
* Spelling
* Writing system

Lists|

* Dyslexia in fiction
* Languages by Writing System
* People with dyslexia

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