ABSTRACT

M ost contemporary views of language development assume that the capacity forlanguage development in humans is, at least in part, dependent upon neural sys-tems that are genetically influenced (Elman et al., 1996; Pinker, 1994). Although speculation regarding the genetic basis of language has a long history, we are only now beginning to find direct evidence of gene(s) that may affect systems necessary for language acquisition and are therefore important to language disorder. This chapter emphasizes the status of research aimed at identifying genes resulting in children with specific language impairment (SLI), because this research allows us to identify genes that may influence the systems that are most specific to language. After discussing this work, I summarize more briefly our knowledge about the genetics of developmental disorders of autism and dyslexia.

The literature on the genetics of developmental language disorder requires a basic familiarity with genetics and some of the terms used to characterize genetic features of DLD (developmental language disorder). Thus, I begin by reviewing some basic concepts and terms in genetics that are relevant to our understanding of the literature in this area. Within the nucleus of each of our cells are structures called chromosomes, consisting of deoxyribonucleic acid (DNA) along with additional proteins. DNA is composed of complementary pairs of four bases (adenine, guanine, cytosine, and thymine). These bases pair up systematically adenine (A) with thymine (T) and guanine (G) with cytosine (C) to form a linear sequence along a sugar phosphate backbone (2′-deoxyribose) forming each chromosome (Figure 10.1). Human cells contain 23 pairs of chromosomes including 2 sex chromosomes (X, Y). The chromosomes are numbered based roughly on their size from 1 (the largest) to 22 (one of the smallest). Each chromosome contains a central hub-like structure called the centromere and extending from the centromere are two arms referred to as the p and q arms, respectively. Each arm ends at a structure called the telomere (Figure 10.2). Each member of the chromosome pair contains genetic information from one parent. The pair of chromosomes contains the individual’s genomic information (genotype) for that chromosome. Genomic information on one chromosome is referred to as a haplotype. The location of genetic sequences on chromosomes is referenced to the chromosome number, the arm of the chromosome along with a numbered region based on bands revealed through staining and numbered from the centromere to the telomere. Thus, region 2q11 refers to a region close to the centromere on the q (shorter) arm of chromosome 2.