Developmental language disorder (DLD) is a neurodevelopmental disorder that affects language acquisition and use during childhood. Simply put, it can manifest in the following ways:

• Expressive: when it hinders speech production.
• Comprehensive: when it affects language comprehension.
• Mixed: when it impacts both areas.

On the other hand, level 3 autism spectrum disorder (ASD) refers to individuals who require a very high level of support in their daily lives. In these cases, autism itself often involves difficulties in language development, so this characteristic is included as a specifier within the diagnosis.

However, both the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) and the International Classification of Diseases (ICD-11) allow for the diagnosis of a developmental language disorder in addition to autism when language difficulties are more severe than would be expected from autism alone. But if these language impairments are considered characteristic of the autism context, they should only be noted as a specifier in the diagnosis.

Thus, if a child with level 3 autism presents particularly intense or disproportionate language problems—for example, very marked grammatical or phonological errors—, the diagnosis of developmental language disorder can be added alongside that of autism.