Expert Q+A: Is There a Link Between Vaccines and Autism?

Autism Spectrum Disorder (ASD) is really a collection of several disorders that have three abnormal areas in common: social skills, communication skills, and repetitive or obsessive traits. There's a broad range from mildly to severely affected. Specialists use the terms ASD and Pervasive Developmental Disorders (PDD) interchangeably. And, to get even more confusing, Asperger's syndrome, and "pervasive developmental disorder, not otherwise specified" (PDD-NOS) are other categories that fall under the ASD heading. Here is a brief explanation of each:

• Autism Spectrum Disorder (ASD) or Pervasive Developmental Disorder (PDD): These terms describe the entire group of conditions that include autism, Asperger's Syndrome, and PDD-NOS:

• Autism: These children are the most severely impaired. They have little or no social and communication skills and have repetitive, obsessive behaviors.

• Asperger's Syndrome: These children have normal intelligence and language development but have trouble reading social cues and making conversation. Asperger's kids often obsess about certain interests.

• PDD-NOS (Pervasive Developmental Disorder-Not Otherwise Specified) is the default diagnosis for a child who has problems with social and communication skills, but does not fit into either of the above categories.

Autism affects one in 150 children. It is four times more common in males, and seems to run in families.