These often resolve by around 4–5 years of age with specialist intervention, and so would not meet criteria for DLD. Where such problems continue beyond five years of age, they are usually accompanied by problems in broader language domains and have a poorer prognosis, so a diagnosis of DLD with SSD is then appropriate. Relationship with other neurodevelopmental disorders
DLD often co-occurs with milder neurodevelopmental disorders of unknown origin, such as attention-deficit hyperactivity disorder, developmental dyslexia or developmental coordination disorder. These do not preclude a diagnosis of DLD, but should be noted as co-occurring conditions. Risk factors
It is generally accepted that DLD is strongly influenced by genetic factors. The best evidence comes from the twin study method. Two twins growing up together are exposed to the same home environment, yet may differ radically in their language skills. Such different outcomes are, however, much more common in fraternal (non-identical) twins, who are genetically different. Identical twins share the same genes and tend to be much more similar in language ability. There can be some variation in the severity and persistence of DLD in identical twins, indicating that non-genetic factors affect the course of disorder, but it is unusual to find a child with DLD who has an identical twin with typical language.There was considerable excitement when a large, multigenerational family with a high rate of DLD were found to have a mutation of the FOXP2 gene just in the affected family members.
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 childs 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 as Down syndrome, sensorineural hearing loss, autism spectrum disorder, or intellectual disability.For research and epidemiological purposes, specific cutoffs on language assessments have been used to document the first criterion. Tomblin et al. proposed the EpiSLI criterion, based on five composite scores representing performance in three domains of language (vocabulary, grammar, and narration) and two modalities (comprehension and production). Children scoring in the lowest 10% on two or more composite scores are identified as having language disorder. The second criterion, persistence of language problems, can be difficult to judge in a young child, but longitudinal studies have shown that difficulties are less likely to resolve for children who have poor language comprehension, rather than difficulties confined to expressive language. In addition, children with isolated difficulties in just one of the areas noted under subtypes tend to make better progress than those whose language is impaired in several areas.The third criterion specifies that DLD is used for children whose language disorder is not part of another biomedical condition, such as a genetic syndrome, a sensorineural hearing loss, neurological disease, autism spectrum disorder or intellectual disability – these were termed differentiating conditions by the CATALISE panel.