Tim's parents brought him to a psychological clinic when he was 5 years old. The clinician's

assessment shows that he currently meets diagnostic criteria for severe mental retardation and
autism.

However, Tim's parents report that he was a "normal little boy" until 6 months ago.
Then, over a period of a few weeks, many aspects of his behavior deteriorated very rapidly.
Which of the following diagnosis best fits this description of Tim's symptoms:
a. Autism
b. Asperger's disorder
c. Rett's syndrome
d. Childhood disintegrative disorder
e. Childhood-onset schizophrenia

D