Summary

Specific language impairment (SLI) is a familial disorder, with which children have difficulty in learning a language but show no other cognitive deficits. Twin studies have suggested a very strong genetic factor to SLI. The purpose of this proposal is to seek out a gene or a genomic region involved in SLI by using positional cloning methods. In this epoch, when Human Genome Project is almost finished, individual investigators will be able to identify disease genes. This proposal requires psycholingual knowledge to characterization of children with SLI in combination with knowledge of molecular epidemiology for genetic analysis. I have studied linguistics as well as natural sciences when I was an undergraduate student. So, this proposal agrees with such interdisciplinary background of mine. I have learned various techniques of biology during my Ph.D. training; however, I have had no chance to study genetics. Since this proposal is considerably different from my previous research in this point, it will help me to develop as a scientist. The achievement of this proposal would contain various kinds of significance: a biological insight into language acquisition, a useful tool (genotyping method) for psychologists studying SLI, a clinical and educational clue for children with SLI, and so on.


Research Plan

Subject and Specific Aims

Among all creatures on the earth, only human (Homo sapience) can use language. Language acquisition is very important for humans to communicate each other; however, it has not been investigated biologically how humans acquire language(s). Through this proposed research, I try to identify the gene involved in a familial language impairment, specific language impairment, to approach language acquisition by the viewpoint of biology. Specific language impairment (SLI) is diagnosed as a marked impairment in the development of expressive and/or receptive language that is not associated with mental retardation, autism, hearing impairment or neurological disorder (1-3). It has been known that children with SLI are more likely than other children to have parents and siblings with a history of language learning problems. Large-scale twin studies have suggested a strong genetic factor in SLI (1, 4). There is much greater concordance for SLI in genetically identical (monozygotic) twins than in nonidentical (dizygotic) twins (70% versus 46%) (4). Recent studies (5, 6) clearly showed that the phenotype of SLI at two-year-old children is much heritable and individual differences in language ability and environmental factor are much less important for SLI. Therefore, SLI is one of the most analyzable hereditary diseases connected with the higher nervous activity of human. The specific aims of this proposal are to: (i) Assess the cheek swab samples, collected by Prof. Wexler and his colleagues, so as to perform linkage analysis most efficiently; (ii) Extract and purify genomic DNA from the cheek swabs; (iii) Undertake a genome-wide search for linkage using with 400 microsatellite markers; (iv) Define the region(s) using higher-density markers and pursue positional cloning. The ultimate goal of this project is to identify the responsible gene(s) for SLI. Prof. Wexler and his colleagues are already pursuing this DNA analysis; I would like to join them and attempt to discover the best techniques for solving this problem.


Strategy

I plan to perform a genome-wide search using two complementary approaches. One approach is to analyze large multigenerational families with many affected members showing a simple Mendelian inheritance of the trait. The second one is to study (large numbers of) small nuclear families with multiple sibs with SLI. This sib-pair analysis does not require prior specification of parameters such as mode of transmission, penetrance, or phenocopy rate (7). These approaches are being pursued by Prof. Wexler and his colleagues, but I would like to think about adding new techniques to theirs. Unlike other hereditary diseases, the known phenotypes of SLI are observed on only 2-8-year-old children (6). Therefore it is very hard to distinguish whether blood relatives of children with SLI, such as parents, grandparents, etc., are (were) affected with SLI. Prof. Wexler and his colleagues are currently testing parents of children with SLI, and he informs me that it is likely that their techniques will be able to pick out SLI in adults, although these results are not yet published. So it is quite possible that we at least have data from parents available (as well as sibs, of course). First, I assess the recruited samples based on a hierarchical priority scheme including extent of family history and volume of impairment. If large multigenerational affected families are identified in which adult members are reliably guessed as SLI, I will focus on the families for linkage analysis. In the event that no appropriate multigenerational family, I will undertake a sib-pair analysis using allele-sharing methods to identify chromosomal regions which are likely to contain genes influencing the trait. I will initially genotype about 50 sib pairs at 400 highly polymorphic microsatellite markers spaced at 10-cM intervals throughout the human genome using an automated fluorescence based genotyping system (PRISM Linkage Mapping Set Ver. 2, Applied Biosystems). Over the next phase of the project, I hope to define critical region(s) suggested by the initial linkage scan. This effort will employ the linkage disequilibrium strategy. The linkage disequilibrium analysis should narrow the region of interest to 100-1000 kb using higher-density markers for microsatellites or single nucleotide polymorphisms (SNPs). At the final stage, I will screen mutation(s) in positional candidate genes, which lie in the defined region of the genome. It would be considerably easier to guess the candidate genes after the interest region is narrowed, because we will have a complete human genome map before long.


Significance and Interdisciplinary Nature

The notable feature of this project is to pioneer the new way to study human language biologically. So, the results achieved by this project would have not only biological but also linguistic, psychological, and educational significance. The gene identified as the SLI susceptibility gene (or the set of genes) by the project will provide the first biological insight into the mechanism of language acquisition at a molecular level. And I will also be able to seek out the homolog in other animals to answer interesting questions: Do they have the homolog (ortholog)? If so, what does the gene product function in these animals? This relation to other animals is not a question that Prof. Wexler and his colleagues (or other researchers in the genetics of language, to my knowledge) are pursuing, so it would add a new question to the field.
The gene or the chromosomal region associated with SLI allows us to genotype from newborn babies to adults. This will be a useful tool for psychologists and linguists, for example, to study the relationship between mother tongue acquisition and foreign language acquisition. In addition, the results of this project will be a very important advance in clinical and educational issues, since the prevalence of SLI is estimated about 7% of schoolchildren (4).


My Contribution, Training Potential, etc.

I have mastered several of the latest techniques of molecular biology and cell biology in the current laboratory. In this proposal, I bring these biological techniques to the field of linguistics. This research plan has been made by myself after consultation with Professor Wexler, and hearing about the sib-pair analyses and others that he and his collaborators are carrying out and how it would be good to search the entire genome, if possible. Although I am planning to conduct established linkage analysis, I have designed the most effective strategy considering the charcteristics of SLI. HFSPO says in the guideline for application that projects involving only large-scale, systematic genome mapping or sequencing are not eligible to receive HFSP funding. Indeed, my proposal involves genome mapping. But, I expect that this proposal is eligible from the following points: o As I have emphasized above, to study SLI is a highly interdisciplinary research, which HFSPO promotes strongly. o Now we have almost all the human genome sequence and a variety of high-performance insturments have been developed. So, genome mapping can be accomplished by a smaller-scale project (8) and it becomes more and more important for each investigator to deal with large quantities of data and information properly.


References

  1. Bishop, D. V. M., et al. (1995) Genetic basis for specific language impairment: evidence from a twin study. Dev. Med. Child. Neurol. 37, 56-71.
  2. Rice, M. L. (Ed.) (1996) Toward a genetics of language. Mahwah, NJ: Lawrence Erlbaum.
  3. Leonard, L. B. (1998) Children with specific language impairment. Cambridge, MA: MIT Press.
  4. Tomblin, J. B. (1996) Genetic and environmental contributions to the risk for specific language impairment. In M. L. Rice (Ed.), Toward a genetics of language. Mahwah, NJ: Lawrence Erlbaum.
  5. Dale, P. S., et al. (1998) Genetic influence on language delay in two-year-old children. Nat. Neurosci. 1, 324-328.
  6. Rice, M. L., et al. (1998) Family histories of children with SLI who show extended optimal infinitives. J. Speech Lang. Hear. Res. 41, 419-432.
  7. Lander, E. S. and Schork, N. J. (1994) Genetic dissection of complex traits. Science 265, 2037-2048.
  8. Hattori, M., et al. (2000). The DNA sequence of human chromosome 21. The chromosome 21 mapping and sequencing consortium. Nature 405, 311-319.