Genetics of Communication Disorders

A communication disorder is an inability to understand and/or use speech and language to relate to others. For the majority of communication disorders, we do not understand the cause. We know that many result from hearing impairment, intellectual disabilities, cerebral palsy, mental retardation, and cleft lip and/or cleft palate. Over the past 10 years, there has been considerable progress in human genetics, and the mechanisms by which genetic defects can cause speech, language, hearing, cognitive, and behavioral disorders have been described. The presence of a genetic component of a disease can be difficult to identify. Evidence supporting a genetic component includes familial clustering of cases, increased incidences of consanguineous mating (i.e., mating between closely related individuals), increased prevalence that exists within genetically segregated communities, increased risk that exists for the children or siblings of affected individuals, and concurrence of identical twins with the disorder. When more than one member in a family is affected by the same rare condition, it is tempting to speculate that there is a genetic contribution to the aetiology. Although for a long time the ability to speak was considered instinctive and specific to human beings and innate bases were suggested for language acquisition, only quite recently has the genetic role been taken into consideration in language studies. In the past few decades, language studies and research on the acquisition of a first language have given great importance to the fact that linguistic abilities and their development depend on the existence of innate information. The complex interactions between “nature” and “nurture” have also been underlined; that is the interactions between genes and environment through which the genotype, or the genetic information coded in the DNA of each individual, becomes the phenotype—observable physical and behavioural features. Individual differences in cognitive abilities, primarily verbal, appear to originate at the interface between genetic and environmental aspects, family, school, therapeutic experiences, and so on. On a theoretical basis, finding a genetic influence on individual differences in vocabulary does not contradict the assumption that words are learned. It means that DNA differences between people affect how easily they learn, remember, and use words. On the clinical plane, supposing there is a reciprocal interaction between environment and genes in the constitution of a specific behavioural profile means going beyond a diagnosis based on symptoms, in order to try to identify the aetiology of specific cognitive and behavioural phenotypes.