Multiple disabilities, depending upon the definition used, may or may not include mental retardation as one disability, while severe disabilities requires mental retardation but does not require an additional disability
Most individuals who have multiple disabilities also fit the criteria for severe disabilities, while not all with severe disabilities have multiple disabilities.
People with severe or multiple disabilities may exhibit a wide range of characteristics, depending on the combination and severity of disabilities, and the person’s age. There are, however, some traits they may share, including:
Limited speech or communication
Difficulty in basic physical mobility
Tendency to forget skills through disuse
Trouble generalizing skills from one situation to another
A need for support in major life activities (e.g., domestic, leisure, community use, vocational).
Autism Spectrum Disorder/Definition for Mental Retardation:
Individuals with several autism spectrum disorders, by definition, have significant developmental delays in communication and social interaction, and may exhibit extensive limitations in many adaptive skills. Thus, their disability may be extensive enough to fit the definition for mental retardation and severe disabilities, though this is not true for all persons identified with autism (e.g., Asperger's syndrome).
A combination of impairments (such as mental retardation-blindness, or mental retardation-physical disabilities) that causes such severe educational problems that the child cannot be accommodated in a special education program solely for one of the impairments. The term does not include deaf-blindness.