Probing Question: What accounts for the recent rise in cases of autism?

Dustin Hoffman's memorable portrayal of an autistic savant in the 1988 movie Rain Man brought unprecedented public attention to the much misunderstood condition of autism. Hoffman's character, Raymond Babbitt, is terrified of communicating with other people, stammers when he speaks, and doesn't understand money, yet can perform complex mathematical calculations in his head and recite obscure baseball statistics from memory.

Autism is a neurological disorder that is typically diagnosed within the first three years of life, when affected children fail to meet normal developmental milestones, particularly in areas of language and socialization. The word autism derives from the Greek word "autos," or "self," and refers to the often withdrawn and self-focused perspective people with the disorder appear to have. Four times more likely to occur in boys than in girls, autism is considered an incurable condition with an unknown cause.

James Collins

drawing of two orange people touching feet and hands with black in the background

Though autism encompasses a wide range of symptoms with varying severity, autistic people generally share a difficulty connecting emotionally to others, communicating verbally, and interpreting non-verbal communication, such as facial expressions and gestures. Like the character in Rain Man, those with autism often find any change in routine very disturbing and are prone to repetitive movements, such as rocking or spinning. However, unlike Dustin Hoffman's character, high I.Q. savants (with extraordinary memories and computing abilities) are extremely rare. The majority of autistic people have some degree of mental retardation.

Public interest in autism is on the rise, as new diagnoses have skyrocketed. (One well-known longitudinal study in Minnesota schoolchildren concluded that the incidence of autism rose from 5.5 cases per 100,000 children from 1980 to 1983, to 44.9 cases from 1995 to 1997.) Estimates vary, but today as many as one in 166 children are diagnosed with autism or related disorders, and about one in 500 to 1,000 people live with the disability.

The spike in diagnoses has many seeking answers. A Penn State conference on the subject in August 2005 drew over 2,000 attendees. One question on the minds of parents and professionals is "What has caused this sharp increase?"

Some controversial studies have claimed that overexposure to mercury in the form of thimerosal, a preservative used in children's immunizations, is a likely culprit. During the 1990s, the Centers for Disease Control expanded the number of thimerosal-containing vaccines on the infant immunization schedule. According to some anti-thimerosal activists, some vaccinated children may have been exposed to 125 times the federal limit for mercury exposure.

Another intriguing line of inquiry concerns "mirror neurons," which Italian researchers recently discovered in the brains of chimpanzees. Their hypothesis is that these specialized neurons enable us to understand the actions and emotions of others by replicating their states in our own brains. This neurological "aping" bypasses conceptual reasoning as a means of comprehension and relies instead on an internal, experiential knowledge of others. If, as some believe, the mirror neuron system is impaired in autistic individuals, it might explain their characteristic inability to identify and empathize with others.

"Studies of twins have indicated a strong genetic predisposition to the disability," says Pamela Wolfe, associate professor of special education at Penn State. "If one twin has autism, the other is highly likely to have it as well. But I think it's caused by a combination of genetic predisposition and environmental factors." Wolfe attributes the apparent increase in cases to a broadening of diagnostic criteria, which occurred in the late 1980s. "We've seen significant improvements in diagnosis techniques over the last few years,"she says. "Previous autistic tendencies that might have gone undiagnosed now may fall under that heading." Autism spectrum disorders, as they're known in the profession, have grown to include mild forms like Asperger's Syndrome as well as partial diagnoses like PDD-NOS, which stands for "pervasive developmental disorder, not otherwise specified."

Earlier diagnoses also contribute to the trend. Rebecca Landa, the director of the Center for Autism and Related Disorders, recently completed an early detection study for siblings of autistic children, with the goal of diagnosing and treating children well before their third birthdays. "Landa's studies have helped professionals understand the effects of autism in younger and younger subjects," Wolfe notes. "This heightened awareness refines our diagnostic abilities and enables us to pinpoint the disorder more readily." Still, Wolfe suggests that more long-term studies, which are difficult to conduct, are needed to determine the root causes of autism. "Diagnoses are quite complex and difficult, and mental retardation often accompanies autism. Parents focus on the 'autism' label, because it's preferable to the stigma of having a retarded child, one who is simply developmentally delayed."

Wolfe currently teaches in Penn State's award-winning training program for professionals involved in autism diagnosis. This program, attended by school counselors, therapists, and speech-language pathologists among others, emphasizes applied behavioral analysis to diagnose and treat early childhood illness, and prepares participants for a national certification examination in the subject.

Parents seeking more information about autism and related disorders may want to consult the Autism Encyclopedia, co-authored by Wolfe and Penn State professor emeritus John Neisworth, which defines terms and provides explanations of many aspects of this complex condition.

Pamela S. Wolfe, Ph.D., is associate professor of special education. She can be reached at

Last Updated September 26, 2005