Expressive language disorder

In 1990, it was reported that the several generations of the KE family had developmental verbal dyspraxia and orofacial praxis that were inherited in a typical autosomal dominant pattern.[10] Further analysis traced this inheritance pattern back to mutations in the FOXP2 genes.[11][12] These studies have allowed scientists to begin to investigate how changes to one gene can alter human communication.

FOXP2 is the first gene that has been identified that is specifically linked to speech and language production. Mutant alleles of the normal FOXP2 gene have been found to be the cause of severe speech impairments.[11]

Neuroimaging techniques, such as structural and functional MRI, found no significant differences between individuals with SLI and normal controls. However, more subtle and sophisticated techniques, such as voxel-based morphometry studies have allowed researchers to identify bilateral abnormalities in neural volume in areas of the brain associated with motor functions, such as the caudate nucleus, in the affected members of the KE family when compared to the unaffected family members. This volume reduction showed a high correlation between reduced volume and tests of oral praxis, supporting the idea that odd development of the caudate nucleus is related to the problems in motor control observed in the KE family.[11]

Due to the vague nature of the diagnosis of expressive language disorder, there is little specific scientific research that we can currently locate. A larger body of research exists around neuroscientific studies with children diagnosed with a specific language impairment (SLI). fMRI studies have shown that children with SLI have a significantly smaller left hemispheric pars triangularis (Broca's area) and asymmetry of dominance of language structures, as opposed to the more typical left hemisphere dominance.[13] Scientists are beginning to elucidate differences in activation patterns in children with SLIs using neuroimaging techniques to capture brain activity while performing different cognitive tasks. A major observation is lack of left hemisphere lateralization in major language structures such as the inferior frontal gyrus-opercularis, inferior frontal gyrus-triangularis, supramarginal gyrus and superior temporal gyrus. The same study reported hypoactivation and hyper activation of other brain regions - the supramarginal junction and anterior insula, respectively.[14] Other in-depth imaging studies report finding previously undiagnosed lesions in the brains of children with well-characterized developmental language development.[15] Together, these findings strongly suggest that language impairments are the result of an underlying neurological defect in an area of the brain related to language.

Studies looking at long-term outcomes for individuals with specific language impairments such as expressive language disorder track these individuals from childhood to adulthood. As Whitehouse and his colleagues [16] suggest, "When childhood language problems persist into adulthood, they can have far reaching consequences in terms of academic, social and vocational outcomes." These researchers found that children diagnosed with an SLI would have persistent problems with language and are more likely to pursue vocational training rather than university, thereby avoiding professions requiring high levels of literacy. A lower socioeconomic status was also noted by adults who were diagnosed with an SLI as a child. Whitehouse [16] also reported that these adults had more difficulties in establishing friendships, most likely due to a decreased ability to express themselves socially.