According to the National Institute of Child Health and Human Development (NICHHD), autism is a complex biological disorder that generally lasts throughout a person's life. Pervasive development disorders (PDD) generally referred to as autism is a group of disorders that is usually noticeable in toddles by age three. PDD includes Autistic Disorder, Asperser's Syndrome, Child Disintegrative Disorder, Rhett's Disorder, and PPD, Not Otherwise Specified (NOS). Collectively, they are grouped as "autism." Autistic Disorder, Asperger's Syndrome, and PDD-NOS are the most common of all five. Autism Spectrum Disorders is referred to as Pervasive Development Disorders (PDDs) because it starts in children before the age of three and involves delays in the development of many basic skills, such as the ability to socialize with others, communicate both verbal and nonverbal, and to use imagination. Although the condition begins at infant, much earlier than 3 years of age, parents often do not notice a problem until the child is a toddler who is not walking, talking, or developing as well as other children of the same age. Common characteristics shared by people with autism generally include varying degrees of the impairment in the triad of: a) verbal and non-verbal communication, b) social interaction, and c) restricted repetitive and stereotyped patterns of behaviors or interests, such as autistic children may not want their mothers to hold them, while adult with autism may not look at others in the eyes. While there are no known causes of autism, it is generally believed that gene and other factors, such as environmental and biological: .
a) Occurs more in people with certain genetic or chromosomal conditions. It has also been identified as having Down syndrome, fragile X syndrome, tuberous sclerosis, or genetic chromosomal disorder. .
b) Prescription such as valproic acid and thalidomide when taken during pregnancy has been linked with a higher risk of ASDs.