Language disorders are associated with aspects of home environment, and it is often assumed that this is a causal link, with poor language stimulation leading to weak language skills. Twin studies, however, show that two children in the same home environment can have very different language outcomes, suggesting we should consider other explanations for the link. Children with DLD often grow up into adults who have relatively low educational attainments, and their children may share a genetic risk for language disorder. One non-genetic factor that is known to have a specific impact on language development is being a younger sibling in a large family. Associated factors It has long been noted that males are more affected by DLD than females, with a sex ratio of affected males-to-females around 3 or 4:1. However, the sex difference is much less striking in epidemiological samples, suggesting that similar problems may exist in females but are less likely to be detected. The reason for the sex difference is not well understood. Poor motor skills are commonly found in children with DLD. Standardized measures of motor ability confirm that children with DLD exhibit deficits in fine and gross motor skill, both simple and complex. These difficulties also extend to speech-motor ability, particularly with the control of their articulatory movements. Children with DLD have difficulty with motor sequence learning and may show deficits in other procedural motor processes as well. Brain scans do not usually reveal any obvious abnormalities in children with DLD, although quantitative comparisons have found differences in brain size or relative proportions of white or grey matter in specific regions. In some cases, unusual brain gyri are found. To date, no consistent 'neural signature' for DLD has been found, although some studies have noted evidence for involvement of subcortical systems. Differences in the brains of children with DLD versus typically developing children are subtle and may overlap with atypical patterns seen in other neurodevelopmental disorders. Diagnosis DLD is defined purely in behavioural terms: there is no biological test. There are three points that need to be met for a diagnosis of DLD: The child has language difficulties that create obstacles to communication or learning in everyday life, The child's language problems are unlikely to resolve by five years of age, and The problems are not associated with a known biomedical condition such as brain injury, neurodegenerative conditions, genetic conditions or chromosome disorders such