Back to Africa: Tracing Dyslexia Genes in East Africa
- 167 Downloads
A sample of Swahili-speaking probands with reading difficulties was identified from a large representative sample of 1,500 school children in the rural areas of Tanzania. Families of these probands (n = 88) were invited to participate in the study. The proband and his/her siblings received a battery of reading-related tasks and performance on these tasks was recorded and treated as phenotypic data. Molecular-genetic analyses were carried out with 47 highly polymorphic markers spanning three previously identified regions of interest harboring susceptibility loci for reading difficulties: 2p, 6p, and 15q (DYX1–DYX3). The analyses revealed the involvement of these regions in the development of reading difficulties in Swahili. The linkage signals are especially pronounced for time (compared with error) indicators of reading difficulties. These findings are easily interpretable because in transparent languages such as Swahili deficits in reading are more related to the rate/speed of reading and reading-related processes than to the number of errors made. In short, the study incrementally advances the field by adding an understudied language and an understudied population to the variety of languages and populations in the field of molecular-genetic studies of reading difficulties.
KeywordsCandidate genes Dyslexia Linkage analyses Regional mapping Swahili
Unable to display preview. Download preview PDF.
This research was supported primarily by the Partnership for Child Development, with headquarters at Imperial College, London, United Kingdom. The PCD in turn received major support from the James S. McDonnell Foundation. This work also received partial support from a grant under the Javits Act Program (Grant No. R206R00001), administered by the Institute for Educational Sciences, U.S. Department of Education, and from a grant P01 HD 21887, administered by the U.S. National Institutes of Health.
We express our gratitude to our many Tanzanian colleagues who assisted us in data collection and processing. Moreover, the project would never have been completed without the support of the Tanzanian Ministries of Education and Health and local authorities in Bagamoyo. We also express our gratitude to Dr. Linda Jarvin for her assistance with transporting the samples and to Ms. Robyn Rissman for her editorial aid. Finally, our special thanks are due to the children and their families who participated in this research.
- Amberber, M., Collins, P. (Eds.). (2002). Language universals and variation. Praeger, Westport, CTGoogle Scholar
- Barr C., (2005). Linkage studies of reading disabilities and ADHD in the chromosome 6p and 15q regions. SSSR Annual Meeting: Pre-conference, Toronto, CAGoogle Scholar
- Brady S. A., (1997). Ability to encode phonological representations: An underlying difficulty of poor readers. In: Blachman B. A., (Eds) Foundations of reading acquisition and dyslexia: Implications for early intervention. Lawrence Erlbaum Associates, Publishers, Mahwah, NJ, pp. 21–47Google Scholar
- Chapman N. H., Igo R. P., Thomson J. B., Matsushita M., Brkanac Z., Holzman T., et al. (2004). Linkage analyses of four regions previously implicated in dyslexia: Confirmation of a locus on chromosome 15q American Journal of Medical Genetics (Neuropsychiatric Genetics) 131B:67–75CrossRefGoogle Scholar
- Chiu Y. F., Chuang L. M., Hsiao C. F., Hung Y. J., Lin M. W., Chen Y. T., et al. (2005). An autosomal genome-wide scan for loci linked to pre-diabetic phenotypes in nondiabetic Chinese subjects from the Stanford Asia-Pacific Program of Hypertension and Insulin Resistance Family Study Diabetes 54:1200–1206Google Scholar
- Denckla, M. A., & Rudel, R. G. (1976). Naming of object drawing by dyslexia and other learning disabled children. Brain and Language, 3, 1–16Google Scholar
- Fabian J., (1986). Language and colonial power. University of California Press, BerkleyGoogle Scholar
- Fagerheim T., Raeymaekers P., Tønnessen F. E., Pedersen M., Tranebjærg L., Lubs H. A., (1999). A new gene (DYX3) for dyslexia is located on chromosome 2 Journal of Medical Genetics 36:664–669Google Scholar
- Francks C., Paracchini S., Smith S. D., Richardson A. J., Scerri T. S., Cardon L. R., et al. (2004). A 77-kilobase region on chromosome 6p22.2 is associated with dyslexia in families from the United Kingdom and from the United States American Journal of Human Genetics 75:1046–1058CrossRefGoogle Scholar
- Gathercole S. E., Willis G. S., Baddeley A. D., Emslie H., (1994). The childrenȁ9s test of non-word repetition: A test of phonological memory Memory 2:103–127Google Scholar
- Goulandris, N. (Ed.). (2003). Dyslexia in different languages: A cross-linguistic comparison. Whurr Publishers, LondonGoogle Scholar
- Grigorenko E. L., (2005b). If John were Ivan: Would he fail in reading? In: Joshi R. M., Aaron P. G., (Eds) Handbook of orthography and literacy. Lawrence Erlbaum Associates, Mahwah, NJ, pp. 303–320Google Scholar
- Grigorenko E. L., Ngorosho D., Romano C., Turechek L., Yrigollen C., (2004). Two failed attempts to replicate the association between DD and DYX1C1/EKN1 Behavior Genetics 34:642–643Google Scholar
- Grigorenko E. L., Wood F. B., Meyer M. S., Hart L. A., Speed W. C., Shuster A., et al. (1997). Susceptibility loci for distinct components of developmental dyslexia on chromosomes 6 and 15 American Journal of Human Genetics 60:27–39Google Scholar
- Heath S. C., (1997). Markov Chain Monte Carlo segregation and linkage analysis for oligogenic models American Journal of Human Genetics 61:748–760Google Scholar
- Heine, B., Nurse, D. (Eds.). (2000). African languages: An introduction. Cambridge University Press, New YorkGoogle Scholar
- Hombert J.-M., Hyman L. M., (1999). Bantu historical linguistics. CSLI Publications, Washington, DCGoogle Scholar
- Neuman R. J., Yuan B., Gerhard D. S., Liu K.-Y., Yue P., Duan S., et al. (2002). Replication of linkage of familial hypobetalipoproteinemia to chromosome 3p in six kindreds Journal of Lipid Research 43:407–415Google Scholar
- Paracchini S., (2005). Functional analysis of the risk haplotype for dyslexia on chromosome 6p22. SSSR Annual Meeting: Pre-conference, Toronto, CAGoogle Scholar
- Partnership for Child Development (2002). Heavy schistosomiasis associated with poor short-term memory and slower reaction times in Tanzanian school children. Tropical Medicine & International Health, 7, 104–117Google Scholar
- Raskind W. H., Igo R. P. J., Chapman N. H., Berninger V. W., Thomson J. B., Matsushita M., et al. (2005). A genome scan in multigenerational families with dyslexia: Identification of a novel locus on chromosome 2q that contributes to phonological decoding efficiency Molecular Psychiatry 10:699–711CrossRefGoogle Scholar
- Rosner J., (1999). Test of auditory analysis skills. Academic Therapy Publications, Novato, CAGoogle Scholar
- Taipale M., Kaminen N., Nopola-Hemmi J., Haltia T., Myllyluoma B., Lyytinen H., et al. (2003). A candidate gene for developmental dyslexia encodes a nuclear tetratricopeptide repeat domain protein dynamically regulated in brain Proceedings of the National Academy of Sciences of the United States of America 100:11553–11558CrossRefGoogle Scholar