Autism and mental retardation are both developmental, mental disorders, but autism is a broader term and can coexist with other mental disorders. People who are said to have autism (Autism spectrum disorder) show signs of low to poor social skills, have repetitive behavior, and have challenges in non-verbal communication and speaking.
Their symptoms usually appear at a very early age and are said to be caused by a mixture of genetics and environmental factors. Some people who have autism can recover from it but may need intense therapy and attention, but until now, there is no known cure for autism. Mental Retardation, on the other hand, is a person who has difficulty or cannot fully function in areas such as communication, work, motor skills, self-care, etc. They normally have very low IQs and need someone to take care of them for the rest of their life.