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.
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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.
Here we use the terms developmental dyslexia and specific reading disability interchangeably, referring to a developmental condition of difficulty mastering mental processing and representing of written print.
None of the selection measures were used in the linkage analyses so the linkage results were not to be biased.
This is probably an overly conservative solution. Bayes factors should not particularly change much when the prior is spread over the candidate regions, since the prior and posterior probabilities in each bin would increase proportionately. We have considered this possibility in a number of tests and obtained results similar to those presented here. We did not, however, undertake a comprehensive exploration of this issue.
The analyses are presented for τ = 2, although multiple τ(s) were considered.
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Grigorenko, E.L., Naples, A., Chang, J. et al. Back to Africa: Tracing Dyslexia Genes in East Africa. Read Writ 20, 27–49 (2007). https://doi.org/10.1007/s11145-006-9017-y
- Candidate genes
- Linkage analyses
- Regional mapping