Today is the last day of discussing the autism diagnosis before moving on to how to cope with a diagnosis. Criteria C states that the disturbance can not be better accounted for by Rett's Disorder or Childhood Disintegrative Disorder.
Rett's Disorder is normal growth and development followed by a slowing of development. It primarily involves the inability to use motor functions. It is a neurodevelopmental disorder primarily affecting girls and does mimic autism in its early stages.
Childhood Disintegrative Disorder also mimics autism. For the first two years the child develops normally and then rapidly loses previously acquired skills. By age ten the child will be socially impaired, have repetitive behaviors, and have a delay in communication.
Once all these criteria have been met, see Criteria A and Criteria B, then the doctor can make a final diagnosis. Once a final diagnosis is made a parent(s) can begin to research and learn about the diagnosed disorder, cope with the emotional effects of a diagnosis, and begin implementing resources to develop a care plan for their child.