GENETIC STUDIES OF APRAXIA AND SPEECH SOUND DISORDERS

Case Western Reserve University, Cleveland OH

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Abstract

This is a pilot grant to examine the familial and genetic basis of developmental phonology disorders, the most prevalent group of communication disorders in children. The overall goal of this project is to determine if a gene(s) on chromosome 7q31 plays a substantial role in development of phonology disorders in the general population. We will examine ten microsatellite markers encompassing a 5.6 cM region on chromosome 7q31 in 20 families of children with Developmental Apraxia of Speech (DAS) and 20 families of children with developmental phonology disorders identified in a familial study of phonology disorders. A recent study of a single family with DAS in combination with a grammatical deficit found linkage of this phenotype to markers on this 5.6 cM region of chromosome 7q31. This study was the first clear demonstration that susceptibility to speech sound disorders is mediated via genes. We intend to extend these analyses to a more substantive dataset from the general population to determine if the locus on chromosome 7 has a substantial impact in the etiology of developmental phonology disorders. Model-free approaches to genetic linkage analysis based upon juvenile sibling pairs concordant for DAS or developmental phonology disorder will be used to evaluate phenotypic data separately and as a composite. We will use linkage disequilibrium analysis for fine mapping if we obtain evidence for linkage. Family-based association testing methods will be used to evaluate if any of the markers tested are in very close proximity to the gene for apraxia. This application is intended to provide a core for a further, more extensive, acquisition of DAS and developmental phonology disorder phenotype and genotype data. We, ultimately, intend to expand the entire population to include a genome scan and to positionally clone genes for developmental phonology disorders.