Language Development in Genetic Disorders

The study of language in developmental disorders is an important endeavour for several reasons. First, it is essential to identify areas of relative strength and weakness in order to gain a profile of the disorder, so that we may best support and facilitate the development of language and communication skills in these individuals. Second, such research allows us the opportunity to gain an insight into questions about the process of normal language development. For example: to what extent do biological factors influence language development? Does language learning rely on general cognitive processes, or processes that are specific to language? In this chapter, we focus on the process of language development in two contrasting developmental disorders: (i) Williams syndrome and (ii) Down syndrome. This chapter will describe what has been learned about normal language development through the study of these disorders and discuss unresolved issues that still exist in this field. Both Williams syndrome (WS) and Down syndrome (DS) are genetically defined disorders. WS is caused through the deletion of approximately 28 genes from one copy of chromosome 7. The incidence of WS is rare, occurring in approximately 1 in 20,000 live births (Morris et al. 1998). DS is more common by comparison, affecting approximately 14 in 10,000 live births (Roberts et al. 2007) and is the result of three copies (referred to as ‘trisomy’) of chromosome 21 (Tassabehji 2003). In normal individuals, there are only two copies of chromosome 21 – one from each parent. Both disorders result in some degree of learning disability or learning